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Master’s thesisPhysical Geography and Quaternary Geology, 60 Credits

Department of Physical Geography

The Vegetational and Environmental Development of Lina Mire, Gotland from

6900-400 BC

Nichola Strandberg

NKA 1882017

Preface

This Master’s thesis is Nichola Strandberg’s degree project in Physical Geography and Quaternary Geology at the Department of Physical Geography, Stockholm University. The

Master’s thesis comprises 60 credits (two terms of full-time studies).

Supervisor has been Martina Hättestrand at the Department of Physical Geography,

Stockholm University. Examiner has been Stefan Wastegård at the Department of Physical

Geography, Stockholm University.

The author is responsible for the contents of this thesis.

Stockholm, 26 June 2017

Steffen Holzkämper

Director of studies

The Vegetational and Environmental Development of Lina Mire, Gotland from 6900-400 BC

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Abstract

Lina Mire, Gotland, is an area of archaeological significance and has a complex history of

shoreline displacement. Archaeologists suspect that Lina Mire was once part of an important

inland water system which connected the Littorina Sea with central Gotland. This study

investigates vegetational and palaeoenvironmental changes of the Lina Mire area between

6900 – 400 BC (8850 – 2350 cal years BP) in order to better understand how the area has

developed and how humans have impacted the vegetation. Pollen analysis, C/N ratios,

organic matter and carbon content measurements were conducted. The chronology was based

on 14

C AMS dating of terrestrial macrofossils and bulk sediments. A transgression of the

Littorina Sea at about 6550 BC (8500 cal years BP) inundated the Lina Mire basin, which

was a lake at the time. The onset of cultivation was indicated by the presence of Hordeum

(Barley or Wild Barley) during the Late Neolithic, 2630 BC (4580 cal years BP). Hordeum

continued to grow during the Bronze Age when Cereals appeared at about 970 BC (2920 cal

years BP). During the onset of cultivation during the Late Neolithic, the Lina Mire basin was

a bay of the Littorina Sea. The Lina Mire basin remained connected with the Littorina Sea

until isostatic uplift caused it to become isolated at about 1870 BC (3820 cal years BP). The

lake overgrew and became a mire about 820 BC (2770 cal years BP).

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Table of Contents

Abstract ...................................................................................................................................... 1

Introduction ................................................................................................................................ 5

Aims ....................................................................................................................................... 6

Background ................................................................................................................................ 7

Pollen and charcoal as anthropogenic indicators ................................................................... 7

The Baltic Sea Stages ............................................................................................................. 8

Previous Research on the Vegetational Development of Gotland ....................................... 10

The Climate History of Gotland ........................................................................................... 11

Holocene Plant Migrations and Declines ............................................................................. 12

The Archaeology of Gotland ................................................................................................ 13

The Mesolithic 12,000 – 4000 BC (13,950 – 5950 cal years BP) .................................... 13

The Neolithic 4000 – 1700 BC (5950 – 3650 cal years BP) ............................................ 14

The Bronze Age 1700 – 500 BC (3650 – 2450 cal years BP) .......................................... 15

Site Description .................................................................................................................... 17

Methods.................................................................................................................................... 18

Field Methods ....................................................................................................................... 18

Laboratory Methods ............................................................................................................. 19

Radiocarbon Dating .......................................................................................................... 19

Organic Matter and Carbon Content ................................................................................ 21

Carbon-to-Nitrogen Ratios ............................................................................................... 22

Pollen and Charcoal .......................................................................................................... 22

Results and Interpretations ....................................................................................................... 24

The Mire Stratigraphy .......................................................................................................... 24

Chronology ........................................................................................................................... 27

Organic Matter and Carbon Content .................................................................................... 28

Carbon-to-Nitrogen Ratios ................................................................................................... 29

Pollen and Charcoal Particle Concentrations and Accumulation Rates ............................... 29

Pollen .................................................................................................................................... 30

Pollen Zone One ............................................................................................................... 32

Pollen Zone Two .............................................................................................................. 32

Pollen Zone Three ............................................................................................................ 32

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Pollen Zone Four .............................................................................................................. 33

Discussion ................................................................................................................................ 34

Chronology ........................................................................................................................... 34

Quaternary Geology and Mire Stratigraphy ......................................................................... 36

Pollen .................................................................................................................................... 40

Pollen Zone One ............................................................................................................... 42

Pollen Zone Two .............................................................................................................. 43

Pollen Zone Three ............................................................................................................ 44

Pollen Zone Four .............................................................................................................. 45

Pollen and Charcoal Taphonomy ............................................................................................. 48

Conclusions .............................................................................................................................. 51

The Baltic Sea Stages and Development of the Lina Mire Basin ........................................ 51

Vegetational Development around Lina Mire ...................................................................... 52

Acknowledgements .................................................................................................................. 52

References ................................................................................................................................ 54

Appendix .................................................................................................................................. 64


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Introduction

Since the beginning of the Neolithic period, around 7000 years ago, humans have been

influencing vegetation cover in North Western Europe. Pollen records reflect how farming,

including clearance of woodland and the introduction of new species, changed the landscape

(Lowe and Walker, 2014). Palynology can therefore be used to identify human activities and

periods of abandonment (Brun, 2011).

Behre (1981) proposed a method which relies on the identification of some indicator taxa

such as crop and weed taxa, which are associated with arable farming and ruderal taxa. These

are associated with disturbed land. Behre based his understanding of prehistoric taxa on

modern equivalents. The approach by Behre takes into account traditional farming techniques

described by Oberdorfer (1970) and Ellenberg (1979) among others. In order to create a

precise reconstruction there must be knowledge about the ecosystems associated with human

activities such as cultivated and ruderal environments, grazing land and meadows.

Palynology has been used to investigate when the earliest agriculture can be traced to in

Europe as shown, for example, in Behre (2007; 2008) and Tinner et al., (2007). The use of

indicator taxa for inferring prehistoric human impacts have been adapted to suit countries in

northern Europe, such as Sweden (Berglund and Ralska-Jasiewiczowa, 1986), Norway

(Vorren, 1986) and Finland (Hicks, 1988).

Agriculture was first introduced in Scandinavia about 3950 cal years BP (Gron et al., 2015).

The introduction of agriculture had huge implications for prehistoric humans. Large

Mesolithic settlements were usually near to the coast and were only occupied seasonally.

However, the introduction of agriculture meant that people relocated inland and founded

farming settlements (Gron et al., 2015).

Identifying pre-agrarian and early-agrarian human impacts is more complex than identifying

the onset of agriculture itself. This is partly due to the fact that climate, edaphic and other

ecological factors impacted the woodlands more than humans during the first half of the

Holocene (Behre, 1988 and Hicks, 1992). However, humans as early as the Stone Age used

the woodland resources to collect wood for fires and to build dwellings. The action of

opening up woodland and producing waste meant that the conditions became more

favourable for nitrophilous and light demanding herbs (Behre, 1981 and Berglund, 1985).

People have been living on Gotland, the largest island in the Baltic Sea, for about 9000 years

(Martinsson-Wallin and Wallin, 2010). The lifestyles of these people have been influenced by

changes in culture brought about by the arrival of new groups of people and by changes in the

natural landscape.

Lina Mire, one of the largest mires on Gotland (Fig. 1), was the area of the first settlements

on the island. This area has undergone extensive shore displacement which has created an

ever-changing landscape. During the Mesolithic and Early Neolithic Lina Mire had a narrow

connection with the sea and was a lagoon. Today, the mire is 5 kilometres distance away

from the shoreline. This change in natural landscape has affected the human relationship with

land use based on economic, social, emotional and cognitive aspects. Many important

archaeological sites from different periods have been discovered around the mire, especially

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on the northern and western side. This area is thus of particular importance from an

archaeological perspective.

This study is part of a larger research effort which began in 2009 and was initiated by Helene

Martinsson-Wallin from the Department of Archaeology and Ancient History at Gotland

University. This research effort which later became a project ‘In the footsteps of Tjelvar’

aimed to explore cultural and environmental changes which have occurred on Gotland since

the pioneer phase of the Mesolithic until the early medieval phase. The project name was

derived from the fact that this area of Gotland has the largest concentration of stone ship

settings. This includes Tjelvar’s grave; a well-known legendary figure who was thought to

have founded Gotland (Nihlén, 1928).

A holistic approach to understand the changes surrounding Lina Mire over the past 8000

years was needed and during 2011-2012 the project expanded and became multidisciplinary

with archaeology, social geography, ecology and environmental elements.

In 2013 Gotland University merged with Uppsala University to become Campus Gotland.

Later collaboration on the project began with the Department of Physical Geography at

Stockholm University. Within this collaboration, sediment cores were retrieved from Lina

Mire in spring 2014 and an initial diatom analysis was performed (Martinsson-Wallin, 2017).

In 2016, as part of an internship, further pollen and diatom analyses were carried out on the

cores which were retrieved in 2013 and Yrla Hanström, Uppsala University, wrote her

undergraduate thesis on a study of macrofossils from the core. In August 2016 further cores

were retrieved from Lina Mire with the aim of more detailed pollen and diatom analyses

being carried out.

Preliminary investigations indicated that the shore displacement maps from SGU (Sveriges

geologiska undersökning/Geological Survey of Sweden) were at odds with dating of

archaeological findings in the area. In order to understand the archaeology of the Lina Mire

area better, a more detailed understanding of the shore displacement and landscape

development would be required. The project ‘In the footsteps of Tjelvar’ aims to conduct a

detailed investigation of the mire, including dating, through analyses of sediment cores which

will allow for a digital landscape reconstruction. The project also aims to review and

incorporate archaeological data from previous excavations and engage with the local

community and societies to provide information for local residents and tourists through

interactive communication.

The cores retrieved during August 2016 were used to investigate shore displacement. This

was carried out by Aleftin Barliaev, Master’s student at Stockholm University, through

diatom analysis. Field work, organic matter and carbon content measurements and carbon

dating have been carried out in collaboration with Aleftin Barliaev.

Aims

The present study aims to, using the sediment cores collected in August 2016, investigate

vegetational and landscape evolution through pollen and stratigraphic analyses. Given that

the area surrounding Lina Mire is archaeologically and culturally important, focus is placed

on understanding human impacts and when they become evident.


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The main objectives of this study were to:

1. Investigate the stratigraphy of the mire and what different stratigraphic units

represent. This was done to understand how the mire developed, how it may have

been utilised in the past and to understand the depositional environment for pollen.

2. Identify and discuss vegetational changes based on the pollen record.

3. Detect what, if any, human impacts can be inferred and when they occurred.

Background

Pollen and charcoal as anthropogenic indicators

When the samples have been taken from stratified sediments or accumulations pollen analysis

will show the mixture of fossil pollen; this is the pollen assemblage. Once several depths or

horizons have been analysed it is possible to compare the pollen assemblages. The changes in

the pollen record indicate vegetational change. The pollen data can be displayed in a pollen

diagram; one approach is to show pollen data as a percentage diagram. This is where each

taxon is displayed as a percentage of the total pollen sum. However, the interpretation of the

pollen diagram is not straightforward. To understand the pollen diagram there must be

knowledge of pollen preservation, production and dispersal (Lowe and Walker, 2014).

Iversen (1941; 1949) was the first to see the value of pollen diagrams for understanding

human induced vegetation changes and was also the first to identify which pollen taxa were

related to human activity (Behre, 1981). The problem for archaeologists was to identify

where pastoral and arable farming occurred in different cultures and time periods. This

approach to solving this problem relies on identifying the taxa which are indicators of human

occupation and farming (Behre, 1981).

Naturally, the best indicators of prehistoric human activities are cultivated crops. Some

examples of taxa that may have been cultivated are Cerealia-type, Linum usitatissimum and

Cannabis (Behre, 1981). For most for most of Europe cultivation started around the time of

the beginning of the Neolithic 4000 BC (5950 cal years BP) (Lahtinen and Rowley-Conwy,

2013). However, there are also pollen species, other than cultivated species, which can

indicate human activities. These are known as ruderal taxa. Plantago lanceolata is an

important ruderal taxon which indicates undisturbed grassland and therefore ley farming

(Burrichter, 1969). Plantago lanceolata also colonises abandoned land and is therefore an

indicator of fallow land (Behre, 1981). It is important to note that nowadays in Europe there

are sharp divisions between land areas which are devoted to different uses. However,

prehistoric cultures had a more mixed approach to land use. Rotational farming systems with

fallow years were more common (Vuorela, 1976).

Plants can also be grouped into plant communities which can be useful indicators for land

use. For example, Juniperus, Urtica and Rumex observed together with a peak in charcoal

may indicate human activity. Another example of a plant community is Artemisia,

Chenopodiaceae and Plantago, which together with prior knowledge about the site may

indicate shoreline vegetation (Miller and Robertson, 1981).

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Charcoal fragments in sediments can be used to indicate fire history. Optical counting of

charcoal fragments is a relatively easy and well used method of quantifying charcoal

abundance (Clark, 1982). Changes in the fire history are related to climate changes and

human activities. Charcoal from plant material often appears elongated, black, opaque and

angular (Clark, 1982).Charcoal fragments can be microscopic and counted at the same time

as pollen using a microscope or larger (>100 µm) and separated during wet sieving (Mooney

and Tinner, 2011). Counting charcoal with pollen has been popular since the research carried

out by Iversen (1941) and the method probably shows fires of all scales from local to regional

(Clark, 1988a).

The Baltic Sea Stages

As the Fennoscandian Ice Sheet grew and then melted, the weight of the ice deformed the

Earth’s crust. The Earth’s crust then began to rebound after deglaciation, which is known as

isostatic adjustment (Lowe and Walker, 2014). Eustasy is the fluctuation of water volume in

the oceans and can be affected by melting ice sheets (Lowe and Walker, 2014). The retreating

Fennoscandian Ice Sheet, eustatic sea level rise and isostatic uplift created the Baltic Sea

stages. The associated changes in relative sea level impacted where settlements were located

and even influenced the diet of pre-historic humans.

The Baltic has undergone different phases since the deglaciation of the Baltic basin which

began 15,000-17,000 cal years BP and ended 11,000-10,000 cal years BP (Björck, 2008).

Stroeven et al., (2016) put the general deglaciation of the Gotland area at around 15,000-

14,000 cal years BP. According to Svensson (1989), the deglaciation at Oskarshamn which

is to the SW of Gotland on the Swedish mainland is dated to 14,500 cal years BP (12300 14

C

years BP) which is in agreement with Stroeven et al., (2016). Hughes et al., (2016) indicated

that the ice margin over Gotland retreated at around 14,000 cal years BP.

The melting of the Scandinavian Ice Sheet created an interglacial environment. The gradual

melting of the ice sheet also led to differential glacio-isostatic uplift in the basin of 9 mm/yr

to -1mm/yr; (Ekman, 1996). During the deglaciation of Fennoscandia there were also

variations of the sill locations and depths and widths of the thresholds separating the Baltic

basin and the marine waters of Kattegat-Skagerrak. A combination of isostatic uplift and sill

location caused salinity and water exchange variations in the Baltic basin (Björck, 2008).

Four main stages of the Baltic Sea, during and following the final deglaciation, have been

identified. Following the rapid deglaciation of the southern Baltic basin a proglacial lake, the

Baltic Ice Lake, was formed. Glaciolacustrine sediments were deposited as varves as the ice

sheet retreated northwards (Björck, 2008). As the ice retreated a final drainage of the Baltic

Ice Lake occurred at Mt. Billingen at 11,620 ± 100 cal years BP (Stroeven et al., 2015).

When the Baltic Ice Lake was drained the Yoldia Sea phase began and lasted for about 900

years (Björck, 2008).

The Ancylus Lake was the freshwater Baltic Sea stage which followed the Yoldia Sea and the

Ancylus transgression was formed due to uplift of the outlets which became shallower. Some

outlets were even raised above sea level. The two which remained functioning during this

stage where the Göta Älv (today Göta Älv river) and the Otteid/Steinselva (today east of


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Idefjorden on the Swedish- Norwegian border). Shallowing of the outlets resulted in sea level

rise south of the isobases (south of the outlets) which led to a transgression. The Ancylus

Lake transgressions started at about 10,700 cal years BP and lasted for about 500 years.

Examples of this transgression are drowned pine forests that can be seen in Skåne, and raised

Ancylus beaches on Gotland, Latvia and Estonia. A forced regression, which is caused by a

fall in relative sea level, occurred about 10,200 cal years BP and it is assumed that the

Ancylus Lake found a new outflow between the islands of Zealand and Funen in modern day

Denmark (Björck, 2008).

According to Berglund et al., (2005) the transition between the Ancylus Lake and Littorina

Sea occurred 9800–8500 cal BP, although the first traces of marine influence have been seen

about 9000 cal years BP in the Southern Baltic basin. It is thought that at this time the

Öresund strait was inundated by seawater from the global transgression (Björck, 2008) and

that eustatic sea level outpaced glacio-isostatic uplift. Saline water entered the basin and the

southern Baltic basin experienced several transgressions during the first 2500-3000 years of

the Littorina Sea stage (Björck, 2008). The Littorina transgression is actually the term given

for a number of transgressions (Berglund et al., 2005). The Littorina Sea phase is not well

defined on Gotland.

However, a short regression has also been noted during the Littorina Sea, at about 8100 cal

years BP. This was indicated by coastal sediments in Blekinge, Sweden. This marine

regression has been correlated with a cold phase at 8200 cal years BP. The cold event was

probably caused by a disturbance in the climatic regime in the North Atlantic (Berglund et

al., 2005).

The general development of the Littorina transgression is known but many details remain

unknown (Björck et al., 2008) such as accurate timing and the chronological order in which

the straits were flooded (Rößler et al., 2011). Most of the separate Littorina transgressions

were caused by the sudden melting of the Antarctic Ice Sheet and ice shelves (Björck, 2008).

Whereas the steady rising of the Littorina Sea up until around 6000 cal years BP was due to

the gradual melting of the North American Ice Sheet, during this time the final remnants of

the Labrador Ice Sheet melted (Björck, 2008).

There are also inconsistencies, for example, several transgressions have been seen in Sweden

and Denmark (e.g. Berglund et al., 2005; Christensen and Nielsen, 2008; Wohlfarth et al.,

2008) however, in Finland evidence for only one uniform transgression has been seen

(Eronen, 1974; Miettinen et al., 2007). Similarly, only one main transgression has been seen

in Estonia (Raukas et al., 1995a, Saarse et al., 2009a). At Vääna lagoon, Estonia the Littorina

transgression began about 8300 cal years BP and continued until c.7000 cal years BP. Once

again, only one transgression was seen (Saarse et al., 2009a). On Saaremaa Island, Estonia,

the Littorina Sea transgression began about 8300–8200 cal years BP and lasted up to about

7300 cal years BP (Saarse et al., 2009c). The Littorina transgression altered the coastline; it

created sea arms, lagoons, small islands, suitable for dwelling (Saarse et al., 2009c). These

discrepancies are difficult to interpret but one reason for the difference could be differential

isostasy (Yu, 2003).

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The transgressive trend ended around 6000 cal years BP, although some minor transgressions

possibly occurred up to 5000 cal years BP. Uplift rates around the Baltic basin were different,

but eustatic sea level stopped rising. In Sweden, across from the north coast of Lithuania land

uplift continued resulting in a regression whereas the transgression continued in the most

southern parts of the Baltic Sea basin (Björck, 2008).

Previous Research on the Vegetational Development of Gotland

There has been much archaeological research done on Gotland and there have also been a

few notable studies relating to geology and pollen stratigraphy on the island. Sernander

(1894) was the first to research vegetational development on Gotland and presented his

findings in a table. Munthe et al., (1925) published a study about Gotland’s geology in 1925.

They described the geological layers and varves which were created during the period of the

retreat of the inland ice; the Baltic Ice Lake, the Ancylus Lake, the Littorina Sea. In 1927,

Thomasson described diatoms from the Lina Mire (Thomasson, 1927). In 1927 von Post

made a pollen diagram from Stora Karlsö (Fig. 1) (von Post, 1927). This pollen diagram was

later recalculated and redrawn by Königsson (1983) for a digitalisation project. Lundqvist

(1928) described clayey gyttja taken from Lina Mire which contained marine diatoms and

molluscs and interpreted this as a Littorina Sea deposit. In 1939, Sernander wrote a book

entitled “Lina Myr”, which gave an account of the plant-ecologically of the mire, ditching,

drainage, and nature conservation views (Sernander, 1939).

Pettersson (1958) presented two pollen diagrams from Mobjärgssmyr, Linde and Rövät,

Hejnum, Gotland (Fig. 1). Påhlsson (1977) produced two pollen diagrams from Broträsk,

Lojsta central Gotland (Fig. 1), combined the diagrams cover a period from the Allerød to the

Sub-atlantic chronostratigraphic divisions. No radiocarbon dating was done and the dating

was based on correlations with other studies. Österholm (1989) later compared these pollen

diagrams with knowledge of the archaeology on Gotland.

A pollen diagram from Lina Mire has been described by Svensson (1989). The main aim of

this study was to investigate shore displacement. Pollen analysis was used for a means of

correlation between sites on Gotland. The most recent accumulations, the upper 2.2m of the

stratigraphy, were not analysed in Svensson’s study. Beach ridges were used to indicate the

Littorina Sea and Ancylus Lake shorelines. In 1992, Eriksson published pollen diagrams from

Stora Karlsö (Eriksson, 1992).


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Figure 1. The location of Lina Mire and other notable archaeological and research locations.

The Climate History of Gotland

Blytt-Sernander created a climatic scheme based on data from Scandinavian peat bogs (Lowe

& Walker, 2014). Climate episodes were identified for Northern Europe which were the Pre-

Boreal, Boreal, Atlantic, Sub-Atlantic, Sub-Boreal. This is the Blytt-Sernander climate

scheme (Blytt, 1876 and Sernander, 1908) the scheme was linked to regional pollen zones.

However, it became apparent that the relationship between the climate scheme and regional

pollen zones was not straightforward and the scheme mostly fell out of use (Lowe and

Walker, 2014). Since the scheme was widely used in previous pollen studies, for example,

Svensson, 1989, it can be used here for comparisons.

There are both internal and external factors which have affected climate change in the Baltic

basin, variations in solar radiation, changes in the amount of greenhouse gasses in the

atmosphere, variations in aerosols caused by volcanic activity, albedo changes and circulation

changes caused by salinity variations (Borzenkova et al., 2015). Climate changes throughout

the Holocene impacted vegetation around the Baltic basin, hydrology and human migration.

A recent study by Borzenkova et al., (2015) combined proxy archives to summarise climate

for the Baltic basin for the last 12,000 years. This was based on isotopes, insect remnants and

continental lake level records. Three distinct climate zones were identified, the first, 11,000–

8000 cal year BP was a cold period related to deglaciation. The second climate period

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identified was a warm period 8000–4500 cal year BP. The climate was stable and summer air

temperatures were 1.0–3.5 °C warmer than present day. The third climate period was for the

last 5000–4500 years where the general trend was for decreasing temperatures and increased

instability.

One notable feature of the Early Holocene is the 8.2 ka cold event which lasted 160.5 ± 5.5

years (Thomas et al., 2007). It is thought that air temperatures fell 3 ± 1.1 °C (Thomas et al.,

2007). Cooling occurred throughout the Baltic region (Borzenkova et al., 2015). Pollen data

from both Estonia and in the southern Fennoscandian Peninsula confirms this climate decline

and estimated a decrease of 1˚C. This was indicated by a drop in thermophilus taxa Corylus

and Ulmus (Seppä et al., 2007). It is commonly thought that the cause of the 8.2 ka event was

melt water from continental ice sheets changed the circulation of the North Atlantic Ocean

(Borzenkova et al., 2015).

The Holocene Thermal Maximum occurred between 7500 and 5500 cal year BP.

Temperatures were 0.8 to 1.5 °C warmer than the present day (Borzenkova et al., 2015).

Seppä and Birks (2001) described a decrease in Pinus pollen and fern spores in northern

Finland relating to the temperature increase. In central Sweden thermophilus taxa such as

Tilia and Quercus expanded after 7000 cal year BP (Borzenkova et al., 2015). The same

trend was seen in Estonia between 7000 and 5000 cal year BP (Saarse and Veski, 2001).

There is evidence for Late Holocene cooling around the Baltic region for the last 4500 years.

The cooling is thought to be due to decreased insolation during summers (Borzenkova et al.,

2015). One general trend is for thermophilus taxa such as Corylus to decline. For the last

1500-2000 years climate has been cooler and wetter across Fennoscandia (Esper et al., 2012).

Seppä et al., (2009) described climate variability for the last 5000 years for Northern Europe.

It is thought that there was a cold period 3800-3000 cal years BP and a warm period around

2000 cal years BP (Seppä et al., 2009). These climate variations were associated with

humidity changes, with colder climate linked to more humid conditions Seppä et al., (2009).

Holocene Plant Migrations and Declines

The range of where plants are able to grow changes with varying glacial and interglacial

cycles (Bennett, 1997). Plant migrations can be traced from the last glacial maximum to the

present in pollen diagrams (for example Seppä, 2009). Early pioneers of the pollen diagram

understood that values for certain taxa can be crowded out by the arrival of new taxa (von

Post, 1916). It is therefore beneficial to understand migration patterns of plants as the arrival

of new taxa can appear as a decrease in other taxa even if there was no real decrease in the

plant population (Seppä, 2009).

Pettersson (1958) noted that on Gotland that Ulmus and Corylus migrated during the Boreal

period. According to Svensson (1989), who produced several pollen diagrams around

Gotland including Lina Mire, early-Holocene vegetation was characterised by the migrations

of tree species. Corylus expanded about 10,960 cal years BP (9600 14

C BP) and Alnus

expanded about 10,050 cal years BP (890014

C BP). At around the same time Quercus and

Ulmus appeared, although they expanded more slowly. Tilia and Fraxinus followed the


13

expansion of Quercus and Ulmus. During the Atlantic period 8900- 5730 cal years BP (8000-

500014

C BP) Tilia, Fraxinus, Ulmus and Quercus became important tree species.

According to Seppä (2009) Picea abies, which is now one of the most common trees in

Eurasia, spread in a western direction when it migrated to Fennoscandia. The migration

spread through eastern Finland around 6500 cal years BP, Eastern Sweden around 2700 cal

years BP and reached Southern Norway by about 1000 cal years BP. However, Parducci et

al., (2012) found that conifer trees survived in Scandinavia through the last glaciation in ice

free areas and after the deglaciation may have spread from the west. Österholm (1989) said

that Picea established itself on Gotland during the Boreal period.

One major feature of pollen diagrams in north-western Europe of the Holocene has been the

Ulmus decline. According to Skog and Regnell (1995) the cause of the Ulmus decline has

been attributed to many factors including, climate change, human activity, deterioration of

soil and disease (for example Birks, 1986). A study at Ageröds Mosse, in the very south of

Sweden, dates the Ulmus decline occurred about 3770 BC (5720 cal years BP) and persisted

for a few decades around this time. This decline is shown as a drop in percentage in Ulmus

pollen from 7% to 2% (Nilsson, 1964). According to Österholm (1989) the onset of the Sub-

Boreal is usually indicated in a decrease in Ulmus pollen. Ulmus was rare in the pollen record

and therefore the decline was not very dramatic. A second small decrease in Ulmus was dated

to 3200 BC (5150 cal years BP).

Another feature of pollen diagrams is a decline in Tilia. Today Tilia is rare in forests in

Sweden; however, it was once more common in Southern Sweden and across Northern

Europe. One reason for the Tilia decline was thought to be colder and wetter climate

conditions during the Bronze Age. According to Hultberg (2015), Tilia was abundant in

Southern Sweden around 6000 cal years BP during the Holocene thermal maximum. Tilia

then declined around 4000 cal years BP probably due to the climate deterioration that

occurred around that time. Hultberg (2015) also linked Tilia decline with an increase in cereal

pollen during the Bronze Age, probably related to agricultural management.

The Archaeology of Gotland

The Mesolithic 12,000 – 4000 BC (13,950 – 5950 cal years BP)

Gotland was first populated about 9400 years ago by hunter-gatherers (Martinsson-Wallin et

al., 2011). Human skeletal remains and artefacts have been found on Stora Karlsö in the

mouth of Stora Förvar cave (Lindqvist and Possnert, 1999). This find indicates subsistence

based on seal hunting and fishing. It is uncertain if the first Mesolithic people who settled on

Gotland are the ancestors of Gotlanders (Österholm, 1989). According to Martinsson-Wallin

et al. (2011) it is more likely that people arrived at different times and from different places,

such as Scandinavia and the Baltic countries. The transition from Mesolithic hunter-gatherers

to the domestication of animals and farming remains unclear (Martinsson-Wallin et al.,

2011).

Late Mesolithic stone axes have been found on Gotland, especially on the western side of the

island (Martinsson-Wallin and Wallin, 2010). These stone axes have been interpreted as

Nichola Strandberg

14

being linked to large scale forest clearance on Gotland, which is reflected in pollen diagrams

done by Påhlsson (1977) from central Gotland the island (Österholm, 1989).

During the Mesolithic and early Neolithic, Lina Mire would have been a lake or lagoon

connected to the sea via narrow straits (Wallin, 2010). A settlement from the early Mesolithic

at Svalings (RAÄ Gothem 202:1), was later submerged owing to the Littorina transgression

(Seving, 1986). Flint fragments and Grey Seal bones found beneath gyttja are thought to be

deposited during the Littorina Sea (Welinder, 1975). During the late Mesolithic and the Early

Neolithic many axe settlements existed in the area (Wallin, 2010). Amongst these was an

early Neolithic Funnel Beaker settlement at Ardags, Ekby (RAÄ Ekeby 47:1) a few

kilometres west of Gothem (Österholm, 1989; Lund, 1996).

The Neolithic 4000 – 1700 BC (5950 – 3650 cal years BP)

The Early Neolithic 4000 – 3300 BC (5950 – 5250 cal years BP)

By the Neolithic, the land surface of Gotland had increased. Isostatic uplift, which was

greater in the north than the south would have, by this time, created land which would have

been ideal for pasture and farming land (Martinsson-Wallin et al., 2011). About ten sites with

funnel beaker pottery, from the Early Neolithic, have been found on Gotland. These were

mainly situated on the western side of the island where it is thought that the soils were ideal

for farming or pasture. Neolithic cultures, such as the megalith graves, were probably brought

to the island by new groups which arrived during the Neolithic. Ceramics, with the imprints

of wheat grains, have been found on Gotland which date from the Early Neolithic. The

Funnel beaker culture has been found at Gräne (Martinsson-Wallin et al., 2011) so it is

probable that wheat was being cultivated on the island at this time.

Lina Mire has a rich archaeological history. A late Mesolithic to early Neolithic axe

settlement (RAÄ Vallstena 156:1) has been found close to Lina Mire (Nihlén, 1927;

Lithberg, 1914) (Fig. 2). Early Neolithic carbon residue from a cooking pit have been dated

to 3575- 3535 BC (Martinsson-Wallin, 2014). According to Wallin (2010) Gothem, an area

just a few kilometres to the east was highly resource productive during the Neolithic and

Bronze Age.

The Middle Neolithic 3300 – 2300BC (5250 – 4250 cal years BP) and the Late Neolithic

2300 to 1700 BC (4250 – 3650BP)

During the middle Neolithic the salinity of the Littorina Sea increased and seal hunting and

fishing resurged in popularity (Martinsson-Wallin and Wallin, 2010). A study of graves at

Ajvide in Eksta Socken (Fig. 1), on the south west coast of Gotland, indicates that subsistence

was mainly based on seal hunting and fishing during the late middle Neolithic. Some sheep,

goat, cattle and pig remains from this time (Martinsson-Wallin et al., 2011) indicate there

was also some dependence on terrestrially sourced food. However, no traces of crops have

been found from this period (Palmgren and Martinsson-Wallin, 2015). An increase in

archaeological remains during the middle Neolithic indicates that the islands population

increased during this time (Palmgren and Martinsson-Wallin, 2015). A burial and a


15

settlement (RAÄ Gothem 120:1) from the Pitted Ware culture, of the middle Neolithic, was

discovered at Västerbjers, Gothem (Sundberg, 2008) (Fig. 3).

During the late Neolithic it is thought that people developed control over land resources and

domesticated animals (Martinsson-Wallin et al., 2011). A late Neolithic death house, a

building built upon graves, has also been discovered in the vicinity of Nygårdsrum (RAÄ

Vallstena 73:1) (Hallström, 1971).

The Bronze Age 1700 – 500 BC (3650 – 2450 cal years BP)

During the Neolithic to Bronze Age transition, metal was introduced. Copper appears in

graves during the late Neolithic (Martinsson-Wallin et al., 2011). Land use changed during

the Bronze Age and both arable and pastoral agriculture was intensified. Later, during the

pre-Roman Iron Age (5th

to 4th

century BC) fencing systems created private farming areas

(Lindquist, 1974).

One of the most notable archaeological features in the area is Gothemshammar (Fig. 2)

which is located on a peninsula close to the entrance of the Lina Mire basin and east of the

river Gothem (Wallin, 2010). There a 500 m wall of unknown age is located (RAÄ Gothem

131:4) (Fig. 3). Dating of the domestic materials found during excavations date the stone wall

enclosure at a date of about 900 – 700 BC. It has been suggested that the wall ended at sea

level which would indicate that sea level was 10m above the present day sea level. The wall,

as well as the other archaeological sites, shows the importance of the Line Mire area for the

inhabitants of Gotland and possible visiting traders.

Nichola Strandberg

16

Figure 2. Archaeological sites around Lina Mire. A/ Majsterrojr (RAÄ Gothem 111:1). B and C/ Gothemshammar (RAÄ

Gothem 131:4). D/ Tjelvar’s grave (RAÄ Boge 28:1).

There is a large complex of stone arrangements and a cairn known as the “Majsterrojr” (RAÄ

Gothem 111:1) (Fig. 2). This indicates early Bronze Age activity in the area 3 kilometres

inland from the Gothemshammar. Bronze Age activities are further indicated by the amount

of stone ships in the area, especially to the north of Lina Mire (Wallin, 2010). There is a stone

ship a few hundred meters north of the “Majsterrojr” (RAÄ Gothem 134:1).

There are around 380 stone ship settings on Gotland and they are usually located close to the

shoreline (Wehlin, 2010). Approximately 70 of these have been excavated to some degree. It

is thought that these stone ships date to about 1100 – 500 BC. These stones ships are thought

to be graves (Wehlin, 2010). Stone ship settings can be found along the Ancylus Lake and

Littorina Sea shorelines Hansson (1927). Tjelvar´s Grave (RAÄ Boge 28:1) is also a stone

ship setting (see Fig. 2 and Fig. 3 for location).

According to Wehlin (2010) around 15% of the stone ships on Gotland occur around Lina

Mire. Ohlsson (1984) stated that there may have been a historical route which boats could

have used leading inland in a north-east direction. The opening of this water way would have


17

begun at Vitviken (Fig. 3), a bay just north east of Lina Mire, and then led inland to where

Lina Mire is today.

Figure 3. The Ancylus Lake and Littorina Sea shorelines were drawn after Svensson (1989). The contour lines and

elevation were based on modern day values from SGU. Archaeological sites of importance around Lina Mire are shown;

the archaeological data was downloaded from Riksantikvarieämbetet.

Site Description

Lina Mire (57.570°N 18.643°E) is one of the largest mires on Gotland at 8.5 km2 and located

21 kilometres south-east of Visby (Fig. 1). To the west of the mire is marl and further to the

west till (Fig. 4). To the east of the mire, limestone bedrock is exposed. The whole of Gotland

has surface bedrock which is Silurian (Hede, 1925a). The bedrock geology of the area is

Halla Formation limestone (Laufeld, 1974).

According to the previous investigations of Lina Mire (Svensson, 1989) there were

approximately 4 meters of peat and gyttja, below which was a sand layer and at least 2.5

meters of clay. Lina Mire is downstream from Holm Mire; both of these mires drain into the

north-east via the Gothem River. The Gothem River was straightened during the drainage of

the mire in the 1940’s. Before the drainage of the mire, the mire surface was measured at 13.1

m a.s.l in the southern part of the mire (Generalstabs kartan) and 10.6 m a.s.l in the northern

part. The elevation of the Lina Mire from 2009 or later is about 9 m a.s.l, (Fig. 4) meaning

that the mire surface elevation has sunk about 1.6 m since the drainage of the mire during a

period of six to seven decades. The maximum elevation of Gotland is around 89 m a.s.l at

Lojsta Hed.

Nichola Strandberg

18

Lina Mire is below the highest limit of the Littorina Sea which implies that the whole mire

was submerged during the Littorina Sea phase (Lundqvist, 1928). The shorelines of the

Littorina Sea and the Ancylus Lake, drawn after Svensson (1989), were based on beach

ridges (Fig. 3).

Figure 4. Quaternary sediments and accumulations. The coring locations from 2016 are included and are shown in red.

Coring location 7 was the master core, there were also 15 parallel cores taken from a 2x2m grid around the master core

but these are not shown here. This map is based on data from Quaternary deposit maps downloaded from SGU (2017)

and archaeological data downloaded from Riksantikvarieämbetet (2017).

Methods

Field Methods

The field work was carried out between the 2nd

and 5th

of August 2016. Coring was carried

out in three transects in order to investigate the stratigraphy of the mire. For this study a

master core was required; this master core should be a representative example of the

stratigraphy of the mire. This was interpreted as being the location with all stratigraphic units

present and with the thickest accumulations of fen peat and gyttja. A Russian peat corer that

was 1 m in length and had a diameter of 4.5 cm were used to retrieve the cores for the

transects and the master core.

All of the coring locations were retrieved from the fen peat surface, except one which was

retrieved from the marl surface (Fig. 4). The modern day river and ditches are shown and the

outlet of the mire is towards the north-east. The elevation in the area ranges between 60 m

a.s.l in the north-west and 9 m a.s.l on the mire surface (Fig. 3). The mire has its outlet

towards the north-east (Fig. 3).


19

Extra material was required in order to search for material to date. Thus, fifteen parallel cores

were retrieved in a 2 x 2 m grid around the master core. A Russian peat corer which was 70

cm long and 7 cm in diameter was used to retrieve this extra material. The cores were

wrapped, labelled and brought back to the cold room at the Department of Physical

Geography at Stockholm University. The stratigraphy of the master core was investigated in

the field and a more detailed description was made in the laboratory. The description was

based on analysis of the material under a stereo microscope x25 magnification in petri dishes,

using Munsell colour charts and based on loss on ignition.

Laboratory Methods

Dating of macrofossils, loss on ignition and XRF (X-ray fluorescence) were carried out in co-

operation with Aleftin Barliaev. The XRF results are not presented in this study. Pollen

analysis and preparation for C/N ratios were undertaken independently. The top 40 cm of the

master core and the parallel cores was not subsampled for loss on ignition, pollen or

radiocarbon dating as ploughing had mixed the top 40 cm of fen peat. The parallel cores were

correlated to the stratigraphy of the master core.

Radiocarbon Dating

The fifteen parallel cores were collected in August 2016 whereafter they were stored in a cold

room. The subsampling for macrofossils to use for the radiocarbon dating began later in

August 2016. In the laboratory the fourteen parallel cores were visually correlated by aligning

accumulation boundaries and colour bands. Only fourteen of the extra cores were used as one

of the cores was required for other analyses.

Eleven depths were dated using AMS (Accelerator Mass Spectrometry) radiocarbon dating,

in order to establish a chronology and to study possible changes in accumulation rate. Eight

dates were based on terrestrial macrofossils. Finding terrestrial macrofossils to date was not

possible in all parts of the stratigraphy. As not many macrofossils were found in the Littorina

Sea gyttja, five bulk samples from this part of the stratigraphy were radiocarbon dated (Tab.

1). One bulk sample was dated at the same depth as a terrestrial macrofossil sample (201 cm

depth), so that the reservoir age could be calculated and deducted from the other bulk

samples.

Nichola Strandberg

20

Table 1. Dating materials from fourteen correlated cores which were taken from a 2x2m grid surrounding the master

core.

Laboratory

number

Depth

(cm)

Terrestrial

Macro-

fossil

Stratigraphy Sample material

Ua-54489 41 X Fen peat 2 Carex seeds and 25 Cladium

mariscus

Ua-54979 52 X Fen peat 1 Betula and 7 Cladium

mariscus seeds

Ua-54322 97 X Gyttja 2 Betula seeds

Ua-54782 121 Gyttja Gyttja bulk sample



Ua-54415 201 X Gyttja 4.5 Betula seeds



Ua-55698 276 X Gyttja 3.5 Betula seeds

Ua-54319 309 X Calcareous

gyttja 9 Betula seeds





Over four weeks, 45 subsamples of 2 cm3 were taken at different levels of the parallel cores.

All of the parallel cores were correlated with the master core and then subsampled. The

subsamples from each depth were put in plastic beakers with 10% KOH and left overnight

with the purpose of dissolving fulvic and humic acids (Mauquoy et al., 2010). The material

from the beakers was then sieved through a sieve with a 250 μm mesh size, to remove small

particles. The retrieved macrofossil material was thereafter stored in water for ease of

handling. Portions of the material were put in a petri dish whereafter the macrofossils were

analysed under a stereo microscope at x25 magnification. Identification of seeds was made

using images in literature from Birks (2007). Soft tweezers were used to extract seeds which

were later stored in distilled water in plastic containers.

Initially it was deemed preferable to date terrestrial macrofossils rather than bulk sediments.

Bulk sediment samples contain a reservoir age caused by the older carbon which exists in

marine water (Hedenström and Possnert, 2001). The oceans absorb atmospheric 14

CO2 which

dissolves to H214

CO3. Slow circulation in the oceans means that ages appear older. This

marine 14

C is incorporated into marine macrofossils (Siegenthaler et al., 1980). However,

bulk samples were used for carbon dating because of a scarcity of terrestrial macrofossils.

Of the bulk samples which were subsampled from the gyttja, a 1 cm thick slice was taken

from one of the cores. Only the soluble fraction of the bulk sediments was dated as this

contains pure organic material. By the time sampling for bulk sediments began, much of the

material was already used during subsampling for macrofossils. For this reason, cores from

different holes were required for bulk sediment sampling. Correlation of the gyttja was


21

difficult as there were no stratigraphic boundaries for 228 cm of the cores length. The clearest

way to correlate these cores was through dark sulphide laminations, but these were not

always clearly visible.

Since the extra cores for dating were retrieved in 70 cm long sections radiocarbon dates Ua-

54782 and Ua-54783 were from the same single core. Radiocarbon dates Ua-54784, which

was used to calculate the reservoir age, and Ua-54785 were from another core. Radiocarbon

date Ua-54786, was from another separate core.

All of the bulk samples, which were assumed to be deposited in a brackish environment, had

a reservoir age deducted from them before they were calibrated. The reservoir age was

calculated based on a comparison between two dates at the same depth, Ua-54415 which was

based on 4.5 Betula seeds and Ua-54784 from bulk sediment. The 4.5 Betula seeds were

found in different cores from different holes. Since much of the material from the paralel

cores was destroyed during subsampling the bulk date was also taken from a different core

from a different hole. The difference between 14

C age Ua-54784 and Ua-54415, 6018 ± 32

and 5567 ± 51 respectively was 451 years. The reservoir age was deducted from all of the

bulk sediment 14

C ages before calibration. Calibration and the age depth model were carried

out in and Clam 2.2 and R Workspace using IntCal13. The reservoir age was subtracted from

the bulk sediment 14

C ages prior to calibration. Radiocarbon date Ua-54784 was then omitted

from the age-depth model. The ages from the Blytt- Sernander climatic scheme were also

calibrated in order to directly compare previous studies (for example Svensson, 1989) with

the chronology in this study.

Organic Matter and Carbon Content

Loss on ignition (LOI) was carried out as a measure of organic matter content which is a

proxy for organic carbon (Heiri et al., 2001). LOI can provide information about the

depositional environment such as for example the biological productivity of lakes (Lowe and

Walker, 1997). LOI at 950˚C can be used to estimate carbonate content (Heiri et al., 2001).

Subsamples of about 1 cm3 were cut from the cores and placed into crucibles and dried in an

oven at 110˚C overnight. Dried samples were weighed into pre-weighed crucibles and burnt

at 550˚C in a furnace for 4 hours. The samples were stored in a desiccator and then

reweighed. The same samples were then burnt at 950˚C, left to cool in the desiccator and

reweighed. Loss on ignition for 550˚C and 950˚C was calculated as a percentage.

Since LOI values were very low at some depths in the clay (below 340 cm depth) a different

measure for organic matter content was also used. For these samples carbon content was

measured rather than organic matter. The samples were dried for 2h at 100˚C and then ground

into a powder using a pestle and mortar. Dried samples were stored in desiccators to avoid

the samples taking on moisture and between 150 mg and 200 mg of sample was weighed into

porcelain boats. Samples were combusted in an Eltra CS-500 Carbon Sulfur determinator

where pressurised oxygen passes through a combustion chamber. The names and weights of

the samples were programmed into the display of the Eltra CS-500 Carbon Sulfur

determinator. Each sample was combusted at 550˚C and 950˚C where a new sample was used

for the second combustion at 950˚C. The CO2 generated was then measured by an infrared

Nichola Strandberg

22

detector (Delteus and Kristiansson, 2000). Both the organic carbon and matter contents were

measurement was recorded as percentage dry weight.

Carbon-to-Nitrogen Ratios

The ratio of carbon-to-nitrogen is useful for indicating to source of organic matter (Rice and

Hanson, 1984).Variations in the carbon-to-nitrogen ratio occur because algae are enriched in

nitrogen and depleted in carbon compared with vascular plants (Tyson, 1995). C/N ratios of

<8 typically indicate marine sediments (Bordovskiy, 1965). According to García-Alix et al.,

(2012) a C/N ratio of <10 indicates aquatic organic matter. A C/N ratio of 10–20 values

indicates a mix of terrestrial and aquatic organic matter inputs and a C/N ratio of >20

signifies that terrestrial organic matter was predominant (Jones et al., 2013). Mackie et al.,

(2005) have said that C/N ratios are a reliable proxy for changes in salinity and therefore

relative sea level in isolation basins.

Forty subsamples spaced 7 cm apart at around 1 cm3 volumes were subsampled and placed

into glass beakers. The subsamples were retrieved from the master core. No subsamples were

taken from the fen peat as it is already known that this was a terrestrial deposit. No

subsamples were analysed for the clay as it can be assumed this formed in deep water.

However, the source of organic matter in the calcareous gyttja and gyttja was less obvious.

The samples were then treated with 10% HCl and stirred in order to break up calcium

carbonates. The samples were then dried overnight at 50ºC in an oven and were then ground

into a powder in a pestle and mortar. A microbalance was used to weigh 100μgC-1mgC into

LUDI SWISS φ9.0 mm height 10mm tin foil capsules and sealed with tweezers. The samples

were stored in a plastic container with labelled separators. The C/N ratio measurement

samples were sent to the Atmosphere and Ocean Research Institute, Tokyo University and

processed there using a CHNS analyser. The error of the C/N ratio1 σ ranged between ±41

and ± 1.19.

Pollen and Charcoal

Pollen and Charcoal Preparation

Subsamples of approximately 4 g were taken from the core and weighed. Three to six tablets

of Lycopodium were dissolved with 10% HCl and added to the samples (Lycopodium batch

number 938934 and the average spore amount 10679). The Lycopodium spores were added in

order to compare the amount of indigenous pollen and spores to Lycopodium and to calculate

the amount of pollen per gram. The optimal ratio between the amount of added Lycopodium

spores as indigenous pollen is 1:1 (Regal and Cushing, 1979). However, knowing how many

Lycopodium spores to add to achieve a ratio is difficult. This was also complicated by the

varying amounts of indigenous pollen in the stratigraphy, for example fewer pollen in peat

than in gyttja. After the first batch of pollen samples was counted it became evident that three

Lycopodium tablets were insufficient so more were added.

The pollen was prepared according to Berglund and Ralkska- Jasiewiczowa (2003). Chemical

treatments were performed under a fume hood. To break up calcium carbonates the samples

were mixed with 10% HCl and heated in water a water bath at 100˚C. In order to remove the


23

HCl from the samples they were centrifuged at 4000 rpm for 5 minutes. The HCl was then

decanted away and the samples were rinsed with distilled water once. The process of

centrifuging a decanting before new chemicals were added was repeated after every step

which followed during the pollen preparation.

To remove fine organic fragments and humic acids the samples were treated with 10% NaOH

for 5 minutes in a warm water bath at 100˚C. The samples were then rinsed with water, two

to three times, until the water was clear. To remove minerals and to disperse the samples, 5%

Na4P2O7 was added. Thereafter the samples were heated for 15 minutes in a 100˚C water

bath. After this the samples were rinsed with water once. The samples were then treated with

40% HF for 7-9 days. After the HF treatment the HF was poured off and 10% HCl was

added. The samples were heated in a water bath for 2-5 minutes and rinsed once again with

water. Three batches of twelve samples were prepared in total and 29 samples were counted.

To further reduce non pollen organic material, acetolysis was done. To dehydrate the samples

glacial acetic acid (CH3COOH) was added. The sample was then centrifuged and decanted.

Then the acetolysis solution, consisting of nine parts of acetic anhydride (CH3CO)2O and one

part 95% H2SO4, was added and heated for 8-10min in a water bath at 100˚C. Further

CH3COOH was added to the samples, centrifuged and decanted. Then 10% NaOH was

added. The samples were washed twice with distilled water. The obtained pollen samples

were stored in 1:1 parts with distilled water and glycerine. The microscope slides were

mounted with glycerine and the cover slips were sealed with nail varnish.

Identification of Pollen Grains

A light microscope was then used to count samples; 400X magnification was used for

scanning and 1000X for identification with immersion oil. Pollen types were identified using

literature by Beug, (2004) and Moore et al., (1991). Pollen grains were identified to genus or

species level. Pollen reference slides from Stockholm University were used to aid

identification. A phase contrast microscope was used to aid identification and to discern

surface texture. The target count for each depth was 300 grains. Owing to time restrictions

this target was not met on all of the depths.

A microscope was then used to count samples. Magnification 400X was used for

identification of pollen grains, spores and charcoal. The magnification was increased to

1000X for the identification of problematic pollen grains in order to see the surface structure

with more clarity. Pollen types were identified using Fægri and Iversen (1989), Beug, (2004)

and Moore et al., (1991). Pollen grains were identified to genus or species level. Since there

was a limited amount of pollen on each slide and time restrictions this target was not met on

all of the depths. For example a slide from the peat from a depth of 50 cm only yielded 55

pollen grains despite 5 separate slides being counted.

Charcoal particles were counted and identified in the pollen slides as opaque, black and

angular fragments larger than 25 μm. The charcoal particles were counted across 11 evenly

spaced transects on each slide (Wang et al., 1999).

Nichola Strandberg

24

Diagram Construction, Calculations and Statistical Analysis

Pollen diagrams were created in Tilia 2.0.41. CONISS, a cluster analysis technique which is

included in Tilia, was used (Grimm, 1987). CONISS allows for different pollen assemblages

which have similar pollen percentage data to be grouped together into zones. Only taxa with

over 5% in abundance were included in the CONISS calculations. The CONISS output

diagram was used to interpret the pollen data into different pollen assemblage zones;

however, owing to the importance of some indicator taxa such as Hordeum-type and

Plantago lanceolata zonation was also partly based on the occurrence of these taxa.

The calculation of total pollen and charcoal concentration in each sample was calculated

using the following equation:

𝐶𝑡 = ((𝑇𝑐𝐿𝑐) × 𝐿𝑠

𝑊𝑡𝑠)

Where Ct is the concentration of pollen or charcoal, 𝑇𝑐

𝐿𝑐 is the ratio of taxa counts to

Lycopodium counts, Ls is the total number of Lycopodium grains added to the sample and

𝑊𝑡𝑠 is the sample weight.

Results and Interpretations

The Mire Stratigraphy

Three transects were investigated across the mire and the vertical red lines represent the

maximum depth which the corer reached (Fig. 5). The stratigraphy is generally similar all

over the mire; the lowermost unit was a bluish clay. In one location in the southernmost

transect a reddish clay was found to be underlying the blueish clay.

A layer of sand overlays the clay, which indicates a high energy event. This probably means

that some sediment in the stratigraphy is missing and could have been eroded during a higher

energy event. Part of bluish clay was probably eroded, meaning there was a hiatus in the

stratigraphic record. Above the sand there is a layer of calcareous gyttja which was up to 70

cm thick.

Superimposed onto the calcareous gyttja was gyttja, which was generally the thickest

sediment unit, around 2 m thick. Above the gyttja was a second layer of calcareous gyttja.

This unit can also be interpreted as being formed in a freshwater lake. Here the term

freshwater lake refers to a lake formed in the basin of Lina Mire, disconnected from the

Baltic basin, rather than a lake freshwater stage of the Baltic basin such as the Ancylus Lake.

It can be noted that the first occurrence of calcareous gyttja, i.e. the lower calcareous gyttja

was usually thicker and more extensive than the upper calcareous gyttja (Fig. 5). Peat

overlaid the upper calcareous gyttja, indicating that the freshwater lake infilled and became a

bog.

The uppermost part of the fen peat was later disturbed after the 1940’s by cultivation. Mixing

of the soil by ploughing was evident in the field and these upper parts of the sediment

sequence were not used for laboratory analysis. This means that the most recent period, from

approximately 400 BC (2350 cal years BP) until present, could not be analysed.


25

-

Figure 5. Cross sections of Lina Mire based on transects with vertical red lines indicating the coring depth achieved.

A description of the master core (coring location 7) and some interpretations based on the

stratigraphy is provided (Tab. 2). Coring location 7 was selected as the master core, as it was

deemed to be representative of the mire stratigraphy, and close to the access road through the

Nichola Strandberg

26

mire. The parallel cores which were retrieved for extra material for dating were correlated to

the master core stratigraphy in table 2. Some images of the cores retrieved at coring location

7 can be seen below (Fig. 6). Images B and C show how the cores were correlated using

stratigraphic boundaries and dark sulphide colourings.

Table 2. Description and interpretation of the stratigraphy within the master core (coring location 7).

Depths

(cm) Accumulation type Munsell colour chart code Interpretation

40-57 Fen Peat 25Y 2/0 Fen mire

57-79 Calcareous gyttja Laminated 6/2 with laminations of 3/2 Freshwater lake

79-307 Gyttja 3/2 with some darker bands of Littorina Sea

307-

339 Calcareous gyttja Variations between 7/2 and 5/2 Freshwater lake

339-

348 Fine sand 5GY 4/1

Relatively high

energy event

348-

352 Clay

56/ 5/1 1a with sulphide precipitations

380 Ancylus Lake

352-

354 Coarse sand 5GY 4/1

Relatively high

energy event

354-

400 Clay

56/ 5/1 1a with sulphide laminations

380 Ancylus Lake

Figure 6. Images of core segments retrieved from Lina Mire in 2016. A/ Upper part of the stratigraphy, with fen peat and

the upper calcareous gyttja. / B/ Gyttja with coloured bands which were used for correlation of the parallel core segments.

C/ Lower part of the stratigraphy with the lower calcareous gyttja and bluish clay.


27

Chronology

All the AMS radiocarbon dates are shown in the appendix. Carbon-14 dates, in calibrated

years before present (1950) and AD/ BC ages, are provided. The dates reported in this study

which are based on interpolations have been rounded up or down to the nearest 10. Prior to

calibration the bulk sediment radiocarbon dates had a reservoir age of 451 years subtracted

from them. All radiocarbon dates have been calibrated using Clam 2.2 with R version 3.2.2.

A basic linear regression between neighbouring levels and the IntCal13.14C curve for the

northern hemisphere terrestrial dates were used (Reimer et al., 2013). Dates are reported with

95% probability. The radiocarbon dates had errors of ±28-60 years.

The transparent orange boxes in the age-depth model indicate dates from bulk sediments

which have been corrected with a reservoir age of 451 years (Fig. 7). The calibrated AMS

dates were between 400 BC (2350 cal years BP) for the youngest sediments and 7030 BC

(8980 cal years BP) for the oldest. Sample number Ua54786 which was based on a bulk

sample has been excluded from this model as an outlier as it appeared to be too young.

Radiocarbon date Ua-54320 appeared to be older than the date below it in the stratigraphy

therefore radiocarbon date Ua-54320 was removed as an outlier as it appeared to be older

than the date (Ua-54321) above it in the stratigraphy.

Nichola Strandberg

28

Figure 7. Age-depth model Clam 2.2 and R Workspace IntCal 13.14C atmospheric curve for the Northern hemisphere

(Reimer et al., 2013). The red points indicate outliers and the orange boxes indicate bulk dates which have had the

reservoir age subtracted to them prior to calibration.

Organic Matter and Carbon Content

Loss on ignition at 550˚C and 950˚C is shown for the master core (Fig. 8). The clay and sand,

which was measured using the Carbon and Sulphur determinator, had relatively low loss on

ignition (0.15% and 1.42% at 550˚c and 950˚C respectively) indicating low organic carbon

content. The calcareous gyttja, which was burned in an oven along with the other samples,

from 307 to 338 cm had relatively low organic matter (LOI of 6.8% at 550˚C) and relatively

high calcium carbonate content (LOI of 28.29% at 950˚C) probably due to the occurrence of

shells and perhaps owing to some recycled material from the limestone bedrock. The gyttja

from 307 to 79 had stable LOI values however the organic matter content is lowest in the


29

lower parts and increases upwards until around 270 cm depth, were values become more

stable. The average LOI for the gyttja was 26.58% at 550˚C and 3.46% at 950˚C. The upper

calcareous gyttja between 79 and 57 cm had a LOI of 21.38% at 550˚C and 30.95% at 950˚C.

The organic matter content of the upper calcareous gyttja was higher than for the lower

calcareous gyttja. The organic matter content of the peat was relatively high (LOI of 84.32%)

and the calcium carbonate content was relatively low (LOI of 2.33%).

Figure 8. Loss on ignition at 550˚C and 950˚C. Note that organic carbon and carbonate measurements from samples

below 340 cm were calculated based on carbon and sulphur determination rather than oven burning. C/N ratios, pollen

and charcoal particle concentrations for the wet weight and accumulation rates. The red dashed lines indicate the main

stratigraphic boundaries, interpolated ages for the stratigraphic boundaries have been included.

Carbon-to-Nitrogen Ratios

The C/N ratio was relatively high for the lower calcareous gyttja (C/N ratio between 17-11)

indicating mixed sources of organic matter. The C/N ratio was highest for the lower

calcareous gyttja prior to the first isolation of the basin. The ratio started to shift towards

lower values (C/N ratio of 9) after the transition to gyttja, thought to be formed during the

Littorina Sea. This indicated that there was more aquatic organic material; however, the ratio

did not fall below 8, which would indicate predominance of marine organic matter. After the

initial shift to lower C/N ratios in the gyttja the ratio shifted to a higher value of 12 and then

again to a lower value of 9 a total of three times. These three shifts to lower values at 208,

173 and 117 cm depth in the stratigraphy may indicate increases in aquatic influence. The

C/N ratio increased again to 25 with the boundary of the gyttja and upper calcareous gyttja

deposits but then decreased again to 11 indicating a shift from terrigenous organic matter in

the lake to a mixed source of organic matter.

Pollen and Charcoal Particle Concentrations and Accumulation Rates

Concentrations of pollen and charcoal particles per gram were calculated (Fig. 8). The peat

had the lowest pollen concentrations (average 100 000 pollen/g) whereas the gyttja had the

Nichola Strandberg

30

highest concentration of pollen (500 000 pollen/ g). Charcoal concentrations are similar in

pattern to pollen concentration except for a peak at around 190 cm depth.

Sediment and peat accumulation rates are shown on the right hand side of the diagram in

cm/yr. These accumulation rates are based on interpolated dates from the age-depth model.

Accumulation rates were highest in the peat and gyttja. The upper calcareous gyttja seems to

have had relatively low accumulation rates.

Pollen

A pollen percentage diagram for Lina Mire is shown (Fig. 9). All cf. species or taxa, meaning

those which could not be identified with certainty or any pollen with very low abundance

(less than 1%), were excluded from the diagram. Varia means those pollen grains which

could not be identified.


31

Figure 9. Pollen percentage diagram for Lina Mire.

Nichola Strandberg

32

Pollen Zone One

Pollen zone one is between 330 cm and 260 cm depth, which corresponded to calcareous

gyttja and Littorina Sea gyttja in the stratigraphy. According to the age-depth model the age

of this zone spans a time period of about 1410 years between about 6900 and 5490BC (8850

– 7440 cal years BP) during the Mesolithic period. Arboreal taxa specifically Corylus, Pinus

and Betula were predominant. Corylus peaked at 290 cm at 28.1% of the pollen sum and

Betula peaked at 310 cm at 22.4% of the pollen sum. This was at the expense of Pinus which

fell from 45% of the pollen sum at the onset of zone one to 28% by the middle. By the end of

zone one Pinus seems to have recovered. There were low amounts of QM

(Quercetum mixtum, Quercus, Tilia and Ulmus) taxa and some Equisetum. At 270 cm depth

Polypodiaceae pollen first appeared in the pollen record at 7.9% of the pollen sum. There

was very little charcoal and therefore no indication of increased burning. No Pediastrum

were found despite the calcareous gyttja indicating a freshwater lake environment.

Pollen Zone Two

Pollen zone two is between 260 cm and 190 cm and corresponds to gyttja in the stratigraphy,

with ages spanning around 1230 years between about 5490-4260 (7440-6210 cal years BP)

also during the Mesolithic period. The main difference between zones one and two was that

during zone two there were more occurrences of herbs and QM taxa. However, Pinus,

Corylus and Betula were still the most dominant taxa. Poaceae, which were smaller than 40

μm and therefore deemed not to be from cultivated grass, reached 2.2% of the total pollen

sum. Ericaceae, Cyperaceae, Artemisia, Chenopodiaceae, Ranunculaceae and Rumex

appeared more frequently in the pollen diagram. Nuphar, a freshwater plant taxon, appeared

in zone two which was somewhat conflicting with the stratigraphy which indicated a brackish

water environment. The general trend was that tree pollen decreased in favour of shrub, dwarf

shrub and herb taxa. There were charcoal fragments throughout zone two.

Pollen Zone Three

Pollen zone three is between 190 and 97 cm and coincides with the upper part of the gyttja.

This pollen zone covers a time span of about 1530 years between 4260 and 2730 BC (6210 –

4680 cal years BP) during the latter part of the Mesolithic, the Early Neolithic and part of the

Middle Neolithic. The upper boundary of zone three, according to CONISS, should have

been around 86 cm which is perhaps somewhat linked to the change in stratigraphy at 79 cm.

However, owing to the importance of indicator species such as Hordeum-type and Plantago

lanceolata which were present at the onset of zone four the upper boundary was placed at 97

cm. Pinus, Betula, Corylus and Alnus were the most dominant taxa in this zone. Picea was

first seen in the pollen record at 180 cm depth but only one grain was observed. A second

Picea grain was observed at 110 cm depth. Poaceae was low during the first part of zone

three but then increased at around 115 cm depth. Herbs such as Cyperaceae, Artemisia and

Rumex were all fairly consistent throughout zone three, whereas Chenopodiaceae was more

sporadic. Equisetum spores also appeared relatively consistent throughout zone three whereas


33

Polypodiaceae increased towards the end of zone three. Charcoal fragments were fairly

constant throughout zone three.

Pollen Zone Four

Pollen zone four differed the most from the others. Zone four was between the depths of 97

and 40 cm, which includes some of the gyttja, the upper calcareous gyttja and the fen peat.

The time interval of zone four was about 2330 years between 2730 and 400 BC (4680 – 2350

cal years BP). This spanned part of the Middle Neolithic, the Late Neolithic, the Bronze Age

and the beginning of the Iron Age. Pinus, Corylus, Betula and Poaceae were the most

abundant taxa in the pollen record. The onset of zone four was defined by the onset of the

human impact indicator taxa Hordeum-type and Plantago lanceolata (Fig.10). Herbs, namely

Poaceae and Cyperaceae began to increase in abundance at 75 cm and 45 cm respectively.

Two pollen grains from the Poaceae family, which were larger than 40 μm in diameter, and

not identified as Hordeum-type, were seen in zone four. These grains were identified as being

Cerealia-type (Fig. 10), since it was not possible to identify them to a lower taxonomic level.

During zone four, pollen from other herbs such as Saxifraga-type and Apiaceae appeared in

the pollen record. Towards the top of zone four, the number of Polypodiaceae and Equisetum

spores increased. Charcoal fragment observations remained relatively consistent within zone

four. Observations of Pediastrum coincided with the upper calcareous gyttja in stratigraphy

which was indicative of a freshwater environment.

Figure 10. Pollen grains under 1000X magnification. A/ Cerealia-type seen through phase contrast microscope. B/ c.f

Hordeum-type. C/ Chenopodium. D/ Plantago lanceolata.

Nichola Strandberg

34

Discussion

Chronology

The age depth model followed a linear trend with most samples becoming younger in an

upwards vertical direction within the stratigraphy. However, sample Ua-54786 did not fit this

trend. The dating for this sample was based on bulk sediments. This date when corrected for

the reservoir age affect and once calibrated appeared to be about 1000 years younger than

expected. This could be due to bioturbation or reworking of the sediment. Downward

penetration of roots can also be a source of contamination (Kaland et al., 1984) but since only

the soluble fraction of the bulk sample was dated this should have been avoided. Younger

humic acids which may percolate downwards may also contaminate bulk sediments (Björck

and Wohlfarth, 2001). Another reason for the younger than expected date could be caused by

poor correlation between cores. As previously stated, cores from different holes within the

2x2 m grid around the master core were needed in order to subsample for bulk sediments.

The gyttja was difficult to correlate due to a lack of clear stratigraphic boundaries. However,

the correlation of the gyttja, with an average accumulation rate of about 0.06 cm per year

would have needed to be around 60 cm out which is unlikely. Bulk sediment dating of the

calcareous gyttja was avoided as fragments of limestone would have resulted in an infinite

age. Limestone can also be taken up by molluscs and foraminifera and could significantly

increase 14

C ages, this is known as the hard water effect (Grimm et al., 2009).

Once calibrated and plotted with a 95% confidence interval, radiocarbon date Ua-54320

appeared to be older than the date Ua-54321, which was immediately below it in the

stratigraphy (Fig. 7). Both dates Ua-54320 and Ua-54321 were derived from Betula seeds

within the lower calcareous gyttja. Perhaps reworking of the sediment or re-deposition was

the reason for sample Ua-54320 appearing to be older than sample Ua-54321. It was unclear

which date should be omitted from the age depth model. However, date Ua-54320 was

omitted from the age-depth model since the Betula seeds may well have been remobilized

and redeposited. At the time of deposition of the Betula seeds used for radiocarbon date Ua-

54320, Lina Mire was a lake and older material may well have been redeposited by water

flowing into the lake from streams, overland flow or erosion of the banks. Given to the fact

that the calcareous gyttja was dense and full of shell fragments it is perhaps unlikely that

Betula seeds could have penetrated downwards. The macrofossils for dating were originally

removed from fourteen different parallel cores; these cores were spaced closely together

within just a 2 x 2 m grid. However, due to the uneven bathymetry of the basin, the small

discrepancy in dates could be due to poor correlation between lower calcareous gyttja in the

parallel cores despite correlation of the lower calcareous gyttja was relatively strait forward.

Another issue with the chronology was that bulk sediment radiocarbon date Ua-54784, which

was used to calculate the reservoir age for the Littorina Sea at 201 cm depth, was subsampled

from a different parallel core to the parallel cores in which the Betula seeds were retrieved at

201 cm. It would have improved accuracy to retrieve the terrestrial macrofossils from the

same core as the bulk sediment was subsampled in order for a more direct comparison of


35

dates. However, terrestrial macrofossils were scarce; in many cases, subsampling from

fourteen parallel cores resulted in no terrestrial macrofossils being found.

In order to construct an age-depth model, the radiocarbon dates based on bulk sediment

samples had a reservoir age subtracted from them prior to calibration. Since the Baltic shelf is

highly influenced by freshwater river runoff the reservoir age can be discussed as an offset

from IntCal09 (Lougheed et al., 2013) which is a terrestrial calibration curve for the Northern

hemisphere. The reservoir age is affected by both marine water containing older carbon and

river runoff containing relatively younger atmospheric 14

C and terrestrial carbon giving

“true” ages of when the organics grew on land and stopped growing. Both shelves and coastal

locations are affected by these factors.

The present day reservoir age of bulk sediments from the Baltic Sea has been calculated from

dating macrophytes and mollusc shells with known ages, this reservoir age is 300-400 years

(Olsson, 1996). However, reservoir ages of 650–850 years for surface sediments in the Baltic

Sea have been determined by Erlenkeuser et al., (1973). These examples show that even

calculating reservoir ages for the present Baltic Sea is not straightforward.

According to Lougheed et al., (2012), who have carried out a study in the Gotland Basin, the

reservoir age associated with Baltic sediments has decreased throughout the Holocene. This

could be due to the shallowing of the Baltic basin and reduction in marine 14

C. A collection,

from a museum, of pre-bomb mollusc shells was used to calculate reservoir ages for the

Baltic including coastal Gotland (Lougheed et al., 2013). A reservoir age of 866 years from a

location 16 km north of Lina Mire was calculated(Lougheed et al., 2013).

In a shore displacement study at Lake Lilla Harsjön, Eastern Sweden, Hedenström and

Possnert (2001) determined reservoir ages varied over time. They calculated that bulk

sediments from the coastal Littorina Sea had reservoir ages of 1100-700 years. The reservoir

age decreased with time and was about 400 years after the isolation of the lake and close to 0

years in the freshwater sediments.

This study of Lina Mire estimates the reservoir age of the Littorina Sea to around 451 years,

which is significantly less than what Hedenström and Possnert, (2001) and Lougheed et al.,

(2013) calculated. However, the reservoir age for Lina Mire is only based on the comparison

between four and a half Betula seeds and one bulk sediment sample at one level in the

stratigraphy. Terrestrial macrofossils were scarce in the Littorina sea gyttja, ideally more

terrestrial macrofossils would have been found so that bulk sampling was not required and

the uncertainty of reservoir effect could have been avoided.

The difficulty with reservoir ages calculated for the Littorina Sea at Lina Mire is that little is

known about the proximity to the shoreline or of freshwater inputs from rivers at this time

during the Littorina Sea. There has only been a limited amount of research into the coastal

reservoir ages and the modification of these ages by freshwater runoff (for example Cage et

al., 2006). Many studies have had to use regional estimates for reservoir age based on the

open ocean which is far from ideal (Lougheed et al., 2013).

Nichola Strandberg

36

Quaternary Geology and Mire Stratigraphy

Much of the natural history of the area of Lina Mire can be learned from the Quaternary

accumulations map of the area surrounding Lina Mire (Fig. 4). The calcareous gyttja at the

surface directly to the west of the mire was probably formed when Lina Mire was a

freshwater lake. The calcareous gyttja at the surface shows the extent of the old lake which

would have been formed during the earliest freshwater lake phase. When the transects (Fig.

5) are compared to the surface geology (Fig. 4) it appears that the first freshwater lake

covered a larger surface area than the second lake. Till further to the west of Lina Mire was

probably deposited during the last deglaciation as no Quaternary depositions older than that

have been found on Gotland (Svensson, 1989). It is likely that the wave washed sediment and

postglacial sand were reworked when the Lina Mire basin was a bay or lagoon. Svantesson

(1976) has investigated the tills of northern Gotland which are calcium carbonate and clay

rich but boulder poor and the distribution and depth of the till is uneven. The till is usually

covered by younger deposits. Eriksson (1992) commented that most glacial deposits on

Gotland have been reworked by wave action because the whole of Gotland has been

submerged during the earlier Baltic Sea stages.

The stratigraphy of the mire is complex and there was probably a hiatus in the record. Since

the mire was once joined with the Baltic, the mire stratigraphy can be compared with other

Quaternary deposits usually found in the Baltic basin. Different sediment types of the Baltic

basin can usually be identified by the stratigraphic properties and by the diatom species they

contain (Ignatius et al., 1981). The stratigraphic order of units in the Baltic basin are rather

regular from the south of the Baltic Sea to the northern Gulf of Bothnia (Ignatius et al.,

1981).

The bluish clay, seen in the master core stratigraphy at 354-400 cm, was interpreted as clay

from the Ancylus Lake. The Ancylus Lake shoreline, drawn after Svensson (1989) was based

on beach ridges; these approximately follow the 30m contour line (Fig. 3). Lina Mire was,

during the Ancylus Lake phase, below the highest shoreline. Ancylus clay is homogeneous,

which indicates that the ice retreat was distant. It was not possible to radiocarbon date the

clay as there were no macrofossils and very little organic carbon.

According to Svensson (1989) Ancylus Lake deposits began to be deposited at Lina Mire at

around 9500 cal years BP. Ignatius et al., (1981) stated that older Ancylus clay sediments

tend to be sulphide rich whereas the younger Ancylus deposits tend to be homogenous grey

or even bluish and can sometimes be faintly laminated. The reddish clay seen during the

coring at site 14 on the most southerly transect was probably from the Yoldia Sea or Baltic

Ice Lake. The Baltic Ice Lake formed as a proglacial lake after the retreat of the

Fennoscandian Ice Sheet and was drained at about 11,600 cal years BP. The Yoldia Sea was

formed after the drainage of the Baltic Ice Lake and lasted for about 900 years (Björck,

2008). Yoldia Sea clays can have a reddish tint but both Yoldia Sea clays and Baltic Ice Lake

clays can be varved (Winterhalter, 1992). Without dating of the reddish clay it is impossible

to say with any certainty when it was deposited.


37

According to Jerbo (1961) the boundary between the Ancylus Lake and the Littorina Sea

deposits in the Baltic basin is usually sharp. However, at Lina Mire there were additional

stratigraphical units inbetween the Ancylus clay and Littorina gyttja. There was coarse sand

immediately above the Ancylus clay, then a thin layer of clay, and then fine sand. The sand

layers represent high energy periods in the record. The sand could have been deposited by

wave action. The sand in the upper part was finer; this indicates transgressive succession as

finer grains are deposited in deeper water. However, it is known that the Ancylus Lake was

generally in a regressive phase at this time. The sand layers could also have been deposited

by longshore drift or storm events were sand from the till was reworked and sorted by wave

action. It is possible that around the time the sand was deposited there was some erosion in

the area. However, there are no dates from the clay or sand so it is impossible to tell if there is

a hiatus in the record or how long the hiatus may represent.

The Ancylus Lake regression was caused by a drop in eustatic level which occurred about

10,200 cal years BP (Björck, 2008). According to Svensson (1989) the Ancylus regression

was rapid in the beginning (5-10 m) followed by a slow regression. It is thought that the

Ancylus Lake found a new outlet between the islands of Zealand and Funen (Björck, 2008).

At 307-339 cm depth there was calcareous gyttja in the master core stratigraphy. The C/N

ratio indicated that the source of the organic matter was mixed. The C/N ratio was about 11;

according to Jones et al., (2013) a C/N ratio between 10 and 20 indicates a mixed source

between terrestrial and aquatic matter. The lower calcareous gyttja unit was dated with three

radiocarbon dates, one of which has been omitted from the age-depth model. The lower

calcareous gyttja formed relatively quickly during about 480 years and between about 7030 –

6550 BC (8980 – 8500 cal years BP). This was the first isolation of the basin to form a

freshwater lake and it is indicated by an increase in organic carbon and calcium carbonates

(Fig. 8). The C/N ratio indicated that organic matter originated from both aquatic and

terrigenous sources.

The lower calcareous gyttja was generally thicker and more widespread than the upper

calcareous gyttja (Fig. 5). The isolation of the lake was probably not caused by gradual

isostatic uplift but rather by a forced regression in sea level caused by a drop in eustatic sea

level. Svensson (1989) said that the first isolation of the Lina Mire basin, after the Ancylus

Lake stage, occurred around 6650 BC (8600 cal years BP), which is about 380 years later

than seen in this study (which indicates the first isolation at around 7030 BC (8980 cal years

BP). Since the present study has better dating control the older date of isolation, as presented

in this study, is probably the more accurate date. The freshwater lake phase persisted until the

Littorina transgression.

According to (Björck, 2008) the onset of the Littorina Sea began around 6550 BC (8500 cal

years BP). The Littorina Sea shoreline was drawn after Svensson (1989); some sections of

this shoreline follow the 20 m contour line. The 20m contour line gives an approximation of

how the bay may have looked during the Littorina Sea stage (Fig. 3). Lina Mire was below

this shoreline and was probably a relatively sheltered bay throughout the Mesolithic and

subsequent periods. This understanding of the environment is fundamental to understanding

the pollen record and the depositional environment. The transport of pollen grains from the

Nichola Strandberg

38

open sea would be very different from that of an enclosed bay. As previously stated,

archaeological finds at Svalings (RAÄ Gothem 202:1) were covered with Littorina Sea

deposits. This indicates that the Littorina Sea level reached beyond the present day 10 m a.s.l.

contour level (Fig. 3). The contours are based on modern day elevation above sea level (Fig.

3). The elevation and accumulation thicknesses have changed over thousands of years.

However, the countour lines give some indication of the extent of the Littorina Sea bay at

Lina Mire.

The first Littorina Sea sediments in the master core stratigraphy appear at 307 cm depth

corresponding to an age of about 6550 BC (8500 cal years BP). Littorina gyttja is typically

soft and greenish in colour and has a high organic matter content of about 10-15% (Ignatius

et al., 1981). However, the organic matter content of the Littorina deposits in the present

study is 26.58%, and therefore higher than expected. This higher than expected organic

matter content is perhaps due to the proximity of the site to the coast and increased input of

allochthonous from the land. According to Björck (2008), the onset of the Littorina Sea is

usually seen as an increase in organic matter content in the sediment composition. Saline

water entered the freshwater Ancylus Lake and the rapid increase in salinity caused

flocculation and an increase in deposition of minerals which were suspended in the water

(Winterhalter, 1992). The decrease in suspended mineral particles allowed light to penetrate

further into the water and organic productivity increased due to the increase of the photic

layer (Winterhalter, 1992). The onset of the Littorina transgression at Lina Mire is reflected

in the organic matter content measurements as a slight increase in organic carbon. The

organic matter content then decreased slightly after the initial peak and stayed relatively

constant throughout the Littorina Sea phase. Variations in the C/N ratio prior to the

transgression showed a shift towards terrigenous organic matter prior to the Littorina

transgression. This was followed by a shift towards a lower C/N ratio which is due to there

being more aquatic organic matter than terrestrial as the lake was joined to the Littorina Sea.

The Littorina Sea phase persisted for about 4680 years at Lina Mire from 6550 BC (8500 cal

years BP) until about 1870 BC (3820 cal years BP). The Littorina sediments end at 79 cm in

the master core stratigraphy where gyttja was succeeded by calcareous gyttja. At this point

the lake became isolated for a second time.

Comparisons between different areas around the Baltic basin are not straightforward as uplift

rates varied. From this study alone it is impossible to tell if there was one main transgression

which began at about 6550 BC (8500 cal years BP) or if there were further transgressions

following this initial transgression. However, the three shifts to lower C/N ratios could be

caused by increases in aquatic organic matter related to a transgression. The resolution of the

C/N ratios (7 cm) was not high enough to see variations in detail. Rather, only general shifts

in the C/N ratio are observed. This study finds three shifts towards more terrestrial organic

matter followed by shifts back to aquatic organic matter during the Littorina Sea after the

initial transgression. C/N ratios may vary for other reasons than an increase in aquatic or

marine organic matter. A comparison between diatoms and C/N ratios in isolation basins in

Scotland by Mackie, et al., (2005) discussed how amounts of phytoplankton in marine

sediments may vary. The variations in phytoplankton would in turn affect the C/N ratio.


39

Freshwater and marine phytoplankton show similar ratios of carbon-to-nitrogen so it is

therefore not possible to tell if water was marine or freshwater purely from C/N ratios.

According to Sampei and Matsumoto (2001) C/N ratios should not be used as an indicator for

source material when the organic matter content is low (less than 1%), as inorganic nitrogen

can lower the C/N ratio. However, the organic matter content of the measured samples was

typically around 20%.

The three shifts towards terrestrial carbon, which were followed by shifts back to more

aquatic organic matter, during the Littorina Sea phase, could be caused by terrestrial organic

matter entering the bay due to deforestation from human activities. Another reason for the

increases in terrigenous organic carbon may have been that the bay almost became isolated

due to isostatic uplift. As a semi enclosed bay terrigenous inputs of organic matter may have

been more influential then aquatic sources. The shifts back to predominance of aquatic

organic matter may have occurred when the bay was flooded by brackish water again.

These three shifts towards aquatic organic matter during the Littorina Sea phase at Lina Mire

occurred at about 4560 BC (6510 cal years BP), 4040 BC (5990 cal years BP) and 3220 BC

(5170 cal years BP). According to Björck (2008) there was a steady transgression of the

Littorina Sea until about 6000 cal years BP although some minor transgressions possibly

occurred up to 5000 cal years BP. This steady transgression was caused by gradual melting of

the North American Ice Sheet. According to Saarse et al., (2009c) the transgressive trend of

the Littorina Sea at Saaremaa, Estonia began around 8300–8200 cal years BP and persisted

until 7300 cal years BP. This study finds a general shift from aquatic organic matter at Lina

Mire until around 3220 BC (5170 cal years BP) although there were variations in the C/N

ratio. After that point there was a shift towards terrestrial organic matter. In order for more

concrete conclusions to be drawn about the Littorina Sea transgressions a shore displacement

study would be required.

The second isolation of the basin was not well dated as terrestrial macrofossils were scarce.

The scarcity of terrestrial macrofossils was interesting in itself, as terrestrial macrofossils

were very abundant in the lower calcareous gyttja. This is perhaps an indication that the

environment was more open this time which fewer trees, such as Betula, close to the lake.

The C/N ratios indicate terrestrial organic matter during the isolation of the basin (C/N ratio

of 25) and then a mixed source of organic matter. This indicates that the lake may have

experienced high inputs of terrestrial organic matter during the isolation or that basin may

have dried out allowing plants to grow on the surface. However, there was no evidence of the

lake drying out in the stratigraphy and organic matter content actually declined around the

time of the isolation. Perhaps one explanation for the relatively high C/N ratios during the

second isolation was deforestation in the catchment. Deforestation may have led to an

increase in allochthonous material entering the basin.

Units above and below the upper calcareous gyttja were dated (Fig. 7). It can be said that this

freshwater lake phase occurred between 79 and 57 cm depth in the master core stratigraphy,

and lasted around 1050 years from 1870 to 820 BC (3820 – 2770 cal years BP). This

freshwater lake phase persisted for more than twice as long as the first freshwater lake phase

at Lina Mire. Lakes are dynamic and the size and shape of the lakes would have changed over

Nichola Strandberg

40

time due to water level change and uplift. However, from the stratigraphy of the mire it can

be assumed that the first freshwater lake in the Lina Mire basin was larger and deeper than

the second lake stage despite existing for a shorter period of time (Fig. 5). The Quaternary

deposits map (Fig. 4) also showed the extent of one of the previous lake phases, which was

probably from the first lake phase. However, it is known that the mire has dried out and the

surface elevation of the mire has decreased by about 1.6 m since it was drained in the 1940’s.

It could be that the upper part of the mire has dried out more than the lower parts. It is

therefore difficult to make comparisons between the two freshwater lake phases directly from

transects of the mire.

It is likely that isostatic uplift rather than a regression caused the second isolation of the

basin. It is thought that the transgressive trend of the Littorina Sea ended around 6000 cal

years BP and the eustatic sea level stopped rising (Björck, 2008). Land uplift created new

land which humans could use. As previously discussed, there are numerous archaeological

sites around Lina Mire which illustrate how important the area has been historically (Fig. 3).

The isolation of the lake from the Littorina Sea may have put an end to the use of the inland

water system as a sailing route. The apparent shift in C/N towards aquatic organic matter

during the second lake phase could actually be a reflection of conditions in the lake becoming

more eutrophic with increased abundances of phytoplankton. The lake began to infill and

became a mire about 820 BC (2770 cal years BP). Fen peat probably accumulated from when

the lake began to overgrow to until the mire was drained in the 1940’s and the water table

was lowered. According to a comparison between modern elevation data and the levelled

surface elevation of the mire before the drainage (Generalstabs kartan) the surface elevation

of Lina Mire has reduced by about 1.6 m between the 1940’s and 2009 or after (Lantmäteriet,

2016). This reduction in elevation was caused by lowering of the water table, which in turn

oxidised the fen peat. Compaction from agricultural vehicles has probably contributed to the

reduced elevation of the mire. The accumulation rates for fen peat and gyttja at Lina Mire

have been calculated (Fig. 8) as around 0.06 cm per year. However, these accumulation rates

are probably inaccurate due to the 1.6m elevation reduction previously discussed. The fen

peat probably accumulated at higher rates than shown in this study.

Pollen

The local pollen assemblage zones and Baltic Sea stages are compared with climate

variations for the Holocene for the Baltic region by Borzenkova, et al. (2015), the Blytt-

Sernander climatic scheme and Archaeological divisions after Stenberger (1979) (Fig. 11).


41

Figure 11. A summary of the Baltic Sea stages seen at Lina Mire, including the local pollen assemblage zones, the Blytt-

Sernander Climatic Scheme with calibrated dates, a summary of Holocene climate shifts after Borzenkova et al., (2015)

and archaeological divisions after Stenberger (1979).

Nichola Strandberg

42

Pollen Zone One

Pollen zone one and two were within the Mesolithic timescale on Gotland. This was also

during the, Boreal and all of the Atlantic climatic periods (Fig. 11). According to research by

Borzenkova et al., (2015), this was a period of relatively cool climate around the Baltic

region.

From archaeological finds it is evident that there were people living close to Lina Mire while

it was a bay connected to the Littorina Sea. The archaeological finds at Svalings (RAÄ

Gothem 202:1) which were submerged during the Littorina transgression are an example of

this. Pollen concentrations were generally low, perhaps owing to there being sparse

vegetation or poor preservation. Charcoal concentrations were also low. Mesolithic people on

Gotland were hunter-gatherers and probably had a limited impact on vegetation except for

gathering wood. Pinus pollen was predominant throughout most of the pollen record for Lina

Mire and the same can be said for zone one. However, there were variations in the Pinus

pollen percentage. The decline in Pinus pollen during zone one coincided with the Littorina

transgression. According to Österholm (1989) much of the Pinus that grew along the

coastlines was buried by the earlier Ancylus transgression. The same mechanism could be the

cause of the Pinus decline during the Littorina transgression. Alnus reacted in a similar way

as Pinus decreased around the time of the Littorina transgression. Corylus increased where

Pinus and Alnus decreased.

However, Pinus pollen can be transported long distances and may not purely reflect local

changes in vegetation (Birks et al., 1988). The predominance of Pinus at Lina Mire

substantiate the research carried out by Sernander (1894), Pettersson (1958) and Påhlsson

(1977) who postulated that there were mainly Pinus forests on Gotland during the Boreal

period. Towards the end of pollen zone one Salix appeared in the pollen record. There was no

clear evidence of human impacts in zone one.

According to Pettersson (1958) Ulmus and Corylus immigrated to Gotland during the Boreal.

Ulmus and Corylus were present throughout the whole pollen record in this study, perhaps

because the earliest analysed samples were from the late Boreal. According to Påhlsson

(1977), by the late Boreal stable forests began to occur on Gotland. Påhlsson (1977), who

analysed pollen from Lojsta, central Gotland, described that towards the end of the Boreal

period Betula expanded as Pinus decreased which can be attributed to wetter climate

conditions which occurred just prior to the Atlantic phase. This study finds a similar trend.

However there were relatively low pollen count of the sample from 270 cm depth (70 pollen

grains) providing an unrepresentative picture of the pollen assemblage. Another cause of the

perceived decrease in Pinus pollen during zone one could be suppression by Corylus pollen

which peaks at the same depth in the stratigraphy.

According to Österholm, (1989) there were well established Pinus forests around the

coastline of Gotland during the Boreal phase. Betula was present where there was more

fertile soil. Österholm (1989) also stated that Corylus, Ulmus and Quercus arrived on Gotland

during the Boreal phase. This study shows that Corylus, Ulmus and Quercus were present on


43

Gotland during the Boreal phase but does not identify the timing of their migration to the

island. These tree taxa probably arrived on Gotland in the earlier part of the Boreal period.

Österholm (1989) stated that Tilia, Fraxinus and Ulmus migrated to Gotland during the

Atlantic phase. This study finds the first instance of Fraxinus at Lina Mire about 5650 BC

(7600 cal years BP) which was indeed during the Atlantic period. However, this study finds

that Tilia and Fraxinus were present, if not in large quantities, as early as the Boreal.

The decrease in Corylus pollen at the end of zone one is perhaps related to the 8.2 ka event.

Seppä et al., (2007) found that Corylus and Ulmus, which are thermophilus taxa, decreased

from 10-15% to 5% during the 8.2 ka event. This study finds that Corylus pollen decreased

from 39% to 12% between 6610 – 5650 BC (8560 – 7600 cal years BP). However, the

resolution of samples analysed around this period was not high enough to show the decline in

detail. It is not possible to show how climate and migration patterns of taxa have impacted

the vegetation of Gotland through analysis of just one core at one location. Polypodiaceae

spores increased from 0% to 8% during the same time Corylus pollen decreased.

Pollen Zone Two

This zone spanned the Mesolithic archaeological period and Atlantic climate period. During

pollen zone two, about 5490 – 4260 BC (7440 – 6210 cal years BP) there were more taxa in

the pollen record. Generally, tree pollen decreased while Corylus and herb pollen taxa

increased. Corylus pollen production typically depends on the environment in which the trees

or shrubs are growing; if the area is open, then more pollen is produced than in a dense forest

(Eriksson, 1992). This may indicate that the area around Lina Mire became more open or an

actual increase in Corylus. Corylus is heliophytic and therefore prefers open environments to

dense forest (QMUL, 2001). Therefore, peaks in Corylus within pollen diagrams may

indicate forest clearance. According to Simmons (1996) Corylus is more resistant to fire than

other taxa so peaks in Corylus seen with simultaneous peaks in charcoal may indicate

Mesolithic human impacts of vegetation. However, no clear peak in charcoal was seen during

zone two.

The changes in the pollen record could be due to Late Mesolithic deforestation. Wallin

(2010) discussed the link between a decline in tree pollen and a peak in charcoal, around the

late Atlantic period, which coincided with the latter part of the Mesolithic, with axes found

from that period. Deforestation may have resulted in more light being available and more

herbs being able to grow. Increases in herb taxa pollen during zone two reflect vegetational

changes rather than environmental changes as Lina Mire was a bay throughout this period.

Some of the herb taxa which appeared during zone two were Poaceae, Artemisia,

Chenopodiaceae, Plantago lanceolata, Rumex and Filipendula. Filipendula is a tall herb and

may suggest vegetation change (Ralska-Jasiewiczowa and Rzętkowska, 1987). Rumex can

indicate some human influence; however more concrete assumptions could be drawn if

Rumex was accompanied by a clear peak in charcoal or other indicator taxa (Karlsson, 1992).

When Artemisia, Chenopodiaceae and Plantago lanceolata occur together it can be

indicative of coastline weeds (Miller and Robertsson, 1981). Plantago lanceolata can also

indicate grassland or ley farming (Burrichter, 1969).

Nichola Strandberg

44

In a study of shore displacement and vegetation development on the south-eastern coast of

Sweden (Yu et al., 2004) where Poaceae and Polypodiaceae spores occur together it

indicated a meadow environment. According to Rannap et al., (2004) people around the

Baltic region have been grazing animals in areas which have risen from the sea for thousands

of years. This was advantageous as the land was already free from trees and no labour was

required to deforest the area. This uplift of the land created a niche habitat for flora and fauna

where light loving plants could flourish. However, it is perhaps unlikely that there was

grazing as early as 6000 BC (7850 cal years BP) as humans were probably hunter-gatherers

during the Mesolithic on Gotland. According to Österholm (1989), the Atlantic forests of

Gotland were dense and dark and as such the growth of ground flora such as Poaceae and

herbs was suppressed by the dense canopy. This would have been a poor habitat for grazing

animals but well suited to wild boar. For hunter-gatherers there would have been a choice of

diet but a marine diet was perhaps the most important.

Another interpretation of the increase in Poaceae pollen in zone two may be that the pollen

originated from Phragmites. Phragmites, an aquatic grass, is one of the only Poaceae types

which is not associated with human impacts (Fægri and Iversen,1989). According to Fægri

and Iversen (1989) Phragmites pollen are relatively small (typically about 26 μm) compared

to other Poaceae pollen grains. Since all Poaceae pollen grains under 40 μm were grouped

together Phragmites pollen grains are included in this total. This may indicate that the

increase in Poaceae pollen in zone two may reflect Phragmites growing around the bay.

Phragmites tolerate brackish water (Moeslundet et al., 1990) and can grow in a wide range of

water depths (Hannon and Gaillard, 1997).

There is a peak in freshwater aquatic taxa during zone two. During this time the bay was

brackish as it was connected to the Littorina Sea. One explanation for the occurrence of

freshwater aquatic taxa in a brackish water bay could be that pollen flowed into the bay from

freshwater lakes and streams further inland. According to Campbell (1999) pollen

redeposited into lakes can be a source of error. Charcoal fragments were present in zone two

but no clear peak is shown.

Quercus remained somewhat constant during zones two and three which was probably due to

the more favourable climate conditions of the Atlantic period. According to Borzenkova et

al., (2015) the Holocene thermal maximum occurred around the Baltic region between 5550

– 3550 BC (7500 and 5500 cal year BP). In a pollen diagram from northern Finland Pinus

pollen and Polypodiaceae spores decreased due to the temperature increase (Seppä and Birks,

2001). At Lina Mire Polypodiaceae spores declined from around the same time 5650 BC

(7600 cal years BP). During the same period Pinus pollen declined from 59% to 21% at 3860

BC (5810 cal years BP). In Sweden and Estonia Tilia and Quercus expanded after 5050 BC

(7000 cal year BP) (Borzenkova et al., 2015). At Lina Mire Quercus showed no pronounced

trend of increase but Tilia increased from 2-6% during the Holocene Thermal Maximum.

Pollen Zone Three

Pollen zone three encompassed the last part of the Mesolithic and most of the Neolithic

period; Lina Mire was still a bay of the Littorina Sea at this time. This was also the time of


45

the Atlantic chronostratigraphic division until around 5000 cal years BP and then the Sub-

Boreal phase. The climate was generally warm as this period was still during the Holocene

climate maximum.

Many of the same pollen taxa which first appear in zone two persist in zone three; however,

there was a decrease in Salix, Poaceae and Cyperaceae pollen. There was an increase in

Equisetum spores. The presence of Equisetum indicated a wetland environment (Veski et al.,

2005a) and possibly the overgrowing of lake shorelines (Ralska-Jasiewiczowa and

Rzętkowska, 1987). Alnus increased throughout zone three and peaked at 19%. Alnus usually

grows by rivers, streams, lakes, fens or swamps (Karlsson, 1992). This supports the idea of an

increase in wetlands or freshwater in the area. However, the decrease in Poaceae pollen,

which as previously discussed may be from Phragmites is more difficult to explain. One

explanation may be that the shoreline was displaced either further inland (a transgression) or

was displaced outwards towards the Littorina Sea (regression). In this case the Phragmites

may have followed the shoreline and disappeared from the Lina Mire basin.

There were two Picea pollen grains found during zone three, the earliest corresponds to an

age of 4130 BC (6080 cal years BP). Österholm (1989) stated that Picea was established on

Gotland during the Boreal period, however at Lina Mire the earliest Picea was only identified

from the Atlantic period. It could be the case that Picea existed on Gotland as early as in the

Boreal, but was not represented in the Lina Mire pollen record. According to Hicks (1986),

Picea does not produce much pollen; however, the pollen produced is well dispersed. Picea

pollen can be transported long distances, even over open seas, and they can be found in

pollen records from sites where there are no Picea trees. However, Sugita et al., (1999)

explained that Picea pollen grains are heavy and may not contribute much pollen in terms of

long distance transport. It could therefore be argued that the few Picea pollen grains found

were transported long distances or rather that some scattered Picea trees have existed on

Gotland since the Boreal period.

There were also some Juniperus pollen grains identified during zone three. Juniperus can

indicate openness and dry meadow conditions (Veski et al., 2005b). It is known that land was

rebounding and that new land was being formed. Water systems upstream and further inland

of Lina Mire would have been isolated before Lina Mire itself. These water systems and lakes

may have been discharging freshwater into the Lina Mire bay. Reworked spores from

Equisetum and aquatic taxa pollen may have washed into the bay from upstream lakes.

Pollen Zone Four

Pollen zone four is where human impacts are most likely to have affected the vegetation

around Lina Mire. The time periods for this zone were the Late Neolithic, the Bronze Age

and some of the Early Iron Age. This was during the Sub-Boreal and part of the early Sub-

Atlantic chronostratigraphic divisions. The general temperature trend was declining during

much of this period (Borzenkova et al., 2015). Throughout zone four, tree pollen decreased

and Corylus also decreased from 48% at the onset of zone four to 4% at the end. Wind

pollinated tree taxa, such as Pinus, Corylus and Alnus, typically produce more pollen than

herb taxa, even compared to Rumex which produces large amounts of pollen (Traverse,

Nichola Strandberg

46

2007). Thus the shift in vegetation type during zone four reflects a real change in the

vegetation; however it is unclear if the decrease in Corylus pollen percentage was

suppression by an increase in herb pollen or an actual decrease in Corylus. Herb taxa

increased and the most notable increase was Poaceae pollen which increased from 2% to

21%. The increase in Poaceae pollen may be partly driven by an increase in Phragmites

pollen. As the land was gradually uplifted the shoreline was displaced in regressive trend.

The shoreline vegetation would have migrated with the shoreline; this shoreline vegetation

may have included Phragmites.

As previously mentioned, Corylus is a thermophilus taxa (Seppä et al., 2007) and therefore

some of the decline in Corylus throughout zone four could be attributed to the cooling trend

throughout the last 4500 years of the Holocene. A pollen diagram from southern Sweden also

showed this trend of declining Corylus (Jessen et al., 2005).

This study finds no evidence of a decline in Tilia around 2050 BC (4000 cal years BP),

perhaps owing to the relatively low pollen counts or to local factors on Gotland and the area

Lina Mire. However, Tilia did decline from 3.6% to 0.5% between 1920 BC and 400 BC

(3870 – 2350 cal years BP). This decline in Tilia could be linked to agricultural management

(Hultberg, 2015). Similarly, no clear evidence of a sudden decline in Ulmus was seen at Lina

Mire in this study. At Ageröds Mosse, Southern Sweden, the Ulmus decline occurred about

3770 BC (5720 cal years BP) (Skog and Regnell, 1995). Österholm (1989) stated that there

was a relatively small decline in Ulmus on Gotland at about 3200 BC (5150 cal years BP).

This study found a small decline in Ulmus pollen at Lina Mire from 2.6% to 0% between

3170 BC (5120 cal years BP) and 2800 BC (4750 cal years BP). This is in agreement with the

Ulmus decline described by Österholm, (1989). However, the Ulmus decline at Lina Mire is

not clear. This result could be explained by relatively low pollen counts, a higher resolution

study would be needed to investigate the Ulmus and Tilia declines in more detail.

The most important human impact indicators in zone four are the taxa which may have been

cultivated. This is the Hordeum-type and the Cerealia-type pollen which first appeared in the

pollen record at 2630 BC (4580 cal years BP) and 970 BC (2920 cal years BP) respectively.

The Cerealia-type pollen grains found were not identified to a lower taxonomic level but

were probably from either Avena-type or Triticum-type. As previously discussed, Lina Mire

was still connected to the Littorina Sea around the Late Neolithic and Early Bronze Age. It is

possible that Lina Mire was then part of an important inland water system. Gothemshammar

has been found to be from 900 – 700 BC; Lina Mire would have been isolated from the

Littorina at this stage. Gothemshammar was built around 1000 years after the isolation of the

lake from the Littorina Sea.

According to Badr et al., (2000) Hordeum vulgare was probably first cultivated in the fertile

crescent about 10,000 years ago. Hordeum vulgare was probably first cultivated from

Hordeum spontaneum, a wild variety of Barley. Barley was one of the first crops which came

with agriculture to Europe during the 6th and 5th millennia BC (Jones et al., 2008).

According to Jones et al., (2008) Wild Barley grows naturally in south-west Asia and Turkey.

Wild Barley tends to flower early in the season in its native arid environment in order to

avoid the hottest and driest part of the year. However, in Northern Europe the growing season


47

is much longer, thus in order for Barley to be more productive it would have to flower later in

the year. A mutation found in Wild Barley which is grown in Iran could have enabled Wild

Barley to flower later in the year in Northern Europe. This is contrary to the idea that Wild

Barley mutated to flower later in the year as it spread northward with agriculture. Bogucki

(1996) who studied the spread of agriculture through Europe suggested that agriculture

spread to Scandinavia around 4000 BC (5950 cal years BP). The findings of this study

indicated that cultivation of Hordeum started around 2630 BC (4580 cal years BP) around

Lina Mire. However, cattle rearing activity was more difficult to identify than cultivation and

may have started much earlier than cultivation.

According to Sillasoo et al., (2009) some cereal type taxa belong to wild grass species. It is

therefore difficult to separate what is natural and what is anthropogenic. For example,

Glyceria fluitans of which the pollen belongs to the Hordeum group was used for food in

western Russia and in Europe until the 19th

Century. Hordeum itself is associated with

natural, wet habitats (Kuusk et al., 1979). However, Estonia does not have many natural

occurrences of cereal type taxa (Sillasoo et al., 2009).

The earliest cereal type pollen was Avena and Hordeum-type at Mustjärve, Central Estonia

about 4700 14

C years (Veski, 1998) and Kõrenduse, Estonia about 3215 BC (5165 cal years

BP) (Pirrus and Rõuk, 1998). Avena and Hordeum-type pollen were also the earliest cereal

pollen types at Rõuge, southern Estonia at about 2630 BC (4580 cal years BP) (Poska et al.,

2004). This evidence of Avena and Hordeum-type cultivation is supported by a charred

Hordeum spontaneum grain from the Iru settlement in Estonia 2700 BC (4650 cal years BP)

(Jaanits et al., 1982). In Finland, Barley (Hordeum vulgare) is also the earliest cereal pollen

and was dated to about 1690 – 1270 BC (3640–3220 cal years BP 3200 ± 170 14

C BP)

(Vuorela and Lempiäinen, 1988). Similarly, Barley (Hordeum vulgare) is also the earliest

cereal seen in Latvia and was found from the time of the late Neolithic about 2050 – 1550 BC

(4000– 3500 cal years BP) (Rasiņš and Taurina, 1983). Later during the pre-Roman Iron Age,

Barley and Emmer (Triticum dicoccum) were the most abundant cereals. Secale pollen is first

seen in Estonia about 500 BC (2450 cal years BP) (Poska et al., 2004); (Niinemets and

Saarse, 2006). According to Österholm (1989) Secale pollen was found from the end of the

Bronze Age and the beginning of the Iron Age and in such amounts as to indicate cultivation

of Secale. This study has not found Secale specifically but finds that cultivation was probably

underway around Lina Mire during the Bronze Age and Iron Age.

Hordeum is an autogamous plant and produces large amounts of pollen. However much of

the pollen remains in the hulls and is therefore poorly distributed. It is therefore common that

this pollen type is not found in the pollen records even if they are close to cultivated areas

(Behre, 1981). However, if the site itself was once cultivated it is likely that threshing on the

cereals resulted in large quantities of pollen being incorporated into the soil (Behre, 1976).

Pollen from Hordeum is very poorly dispersed during flowering but is released when

harvesting and threshing occurs. Pollen is also deposited along the route where the harvest is

taken (Vuorela, 1973). A study by Welten (1967) in Switzerland at a Neolithic lake shore

dwelling showed large differences in Cerealia pollen between sites only 13 metres apart.

Pollen diagrams are therefore somewhat unreliable indicator for prehistoric human activities

Nichola Strandberg

48

and additionally, the absence of Cerealia-type pollen does not mean that cultivation was not

taking place (Behre, 1981). Franzén & Hjelmroos (1988) analysed snow from Southern

Sweden and discovered Hordeum-type, Plantago lanceolata and Urtica pollen. It was of

course not possible to identify where the pollen originated from with certainty but it was

suspected that the origin was Denmark, over 200 km away. Pollen grains can also travel

thousands of kilometres, for example Hjelmroos & Franzén (1994) found that pollen grains of

Secale-type, Triticum-type and small mineral particles in Northern Sweden, close to the

Arctic Circle, probably originated in Italy and North Africa. It is therefore important not to

place too much emphasis on only a few pollen grains.

It is not certain that Hordeum was cultivated close to Lina Mire as grains could have

originated from wild plants or transported by the wind. It is a possibility that Hordeum was

cultivated, threshed or transported by humans very close to Lina Mire. However, when

Hordeum was first seen in the pollen record Lina Mire was a bay of the Littorina Sea. It may

be the case that Hordeum was grown near to the bay or threshed close to the bay.

It is interesting that Hordeum-type was not replaced by Cerealia-type in the pollen record but

that both grew simultaneously during the Bronze Age. Is it difficult to say if humans

preferred Cereals to Hordeum or if they cultivated both at the same time? Another

perspective is that humans preferred to cultivate Cereals but Hordeum remained and grew as

a weed.

Taxa other than cultivated crops can act as indicators of human activity. Plantago lanceolata

occurred at the same depths as Hordeum-type. In rotational cultivation perennial species are

common (Burrichter, 1969). The most important of these indicators is Plantago lanceolata

which usually indicates undisturbed grassland and an important ley farming taxa. Modern

analogues also show that Plantago lanceolata recolonises abandoned agricultural land and is

therefore an indicator of fallow land (Behre, 1981). It is not only the farming method, i.e.

rotational or continuous farming which is important for understanding weed species. The

implements used for farming are also important as some weeds are more resistant to some

farming techniques. Some methods may rip apart the soil but not destroy penetrating organs;

in that case the spread of perennial species such as grasses and Plantain family would be

favoured (Behre, 1981).

Pollen and Charcoal Taphonomy

Charcoal concentration rates were calculated (Fig. 7) and the charcoal was also calculated as

a sum normalised against pollen and shown in the pollen percentage diagram (Fig.9). It is

known that people have lived in the area of Lina Mire since the Mesolithic. However, it is not

clear if charcoal fragments relate to natural fires or human activity as there is no clear peak in

charcoal. Charcoal was relatively constant in the whole pollen record. There are, as with

pollen, many taphonomic factors which affect charcoal distribution, preservation and

identification. Counting charcoal on the pollen slide is a convenient method of calculating the

microscopic charcoal abundance. However, since pollen preparation and counting is a long

process it is not always possible to have a contiguous or high resolution record (Mooney and

Tinner, 2011). The resolution for parts of the stratigraphy at Lina Mire was very low, in the


49

upper part of the stratigraphy the resolution was every 2.5 or 5 cm whereas the lower part was

every 20 or 30 cm. According to Gardner and Whitlock (2001) macroscopic charcoal does

not travel as far as microscopic charcoal which can be viewed on a pollen slide. This means

that it may be difficult to differentiate between local fires and regional fires.

In theory microscopic charcoal can be transported over long distances (Clark, 1988a). This is

especially the case with convection currents of which are generated during wildfires

(Patterson et al., 1987). Microscopic charcoal could have originated from fires as far away as

20–100 km (Conedera et al., 2009), thus it is unclear if charcoal was from a local or regional

scale. However, microscopic charcoal counted with pollen is within a size range which is

difficult to lift, but once taken up into the air it is suspended for a long time before being

deposited (Clark, 1984). Charcoal counted with pollen is also a size which is

underrepresented near the burning site as it tends to be transported away by winds or

convection currents (Clark, 1984). Due to aerodynamics and cohesion more charcoal stays on

the ground than gets transported into lakes (Clark, 1984). This could mean that the charcoal

was underrepresented in much of the stratigraphy. Even so, charcoal accumulation rates were

relatively higher in the lake and Littorina bay phases than for the fen peat. Another issue with

charcoal is that recent human activity could have remobilised allochthonous charcoal which

was stored in the catchment (Mooney and Tinner, 2011). Handling during the pollen

preparation may have resulted in a higher charcoal count as charcoal is brittle (Clark, 1984).

There can be problems visually departing charcoal from other dark coloured material on the

pollen slides (Patterson et al., 1987).

There are questions about how representative microscopic charcoal is as a means of

reconstructing fire history. In order for results from a single sediment core to be robust, the

charcoal counts must be high enough (Finsinger and Tinner, 2005). According to Finsinger

and Tinner (2005) charcoal fragment counts need to be 200-300 in order reduce errors in

calculating charcoal concentration rates to less than 5%. The total sums of charcoal and

added Lycopodium spores counted in this study would need to be far higher in order to show

a more representative picture. The charcoal counts for this study are probably not relevant as

so few charcoal particles were counted.

It has been discussed how plant taxa are affected by climate, human activities and

environmental change. One additional factor which has not been discussed so far is to what

extent the limestone bedrock may have affected the soil makeup and which plants could grow

on Gotland. According to Svensson (1989), who analysed pollen on Gotland and mainland

Sweden, there were no major differences caused by the limestone bedrock as most of the taxa

which appeared in the pollen record of indifferent to soil pH.

Pollen can be affected by many factors between being released from the plant to being

analysed. Probably the most important of these factors is the difference between different

taxa in pollen production (Campbell, 1999). Entomophilous species produce less pollen than

anemophilous species. This means that entomophilous species may be underrepresented in

pollen diagrams (Lowe and Walker, 2014). Self-pollinating (autogamous) species such as

Hordeum (Behre, 1981) produce very little pollen. Tilia however produce large amounts of

pollen despite being insect pollinated. Fagus sylvatica, which does not grow wild on Gotland

Nichola Strandberg

50

(Nordstedt, 1920), is wind pollinated but only produces small amounts of pollen (Lowe and

Walker, 2014).

Differential deposition and redeposition are also factors which must be taken into account.

Knowledge of the depositional environment is important, for example if the plant which

produced pollen was likely growing around a lake margin, on the surface of a mire or further

away (Lowe and Walker, 2014). At Lina Mire it has been revealed from the stratigraphy that

the environment of deposition changed numerous times. Throughout most of the pollen

record presented here, Lina Mire was a lake or an enclosed bay. The largest changes in the

pollen record occurred as the freshwater lake infilled and became a mire, which occurred

around 820 BC (2770 cal years BP). It is likely that change in the local environment has

affected the pollen record and that perhaps the record shows a more local signal where there

was fen peat. According to Tauber (1965), where there are forests, airborne pollen reaches

the surface of a mire by two ways. These are from either raindrop impact or through the

canopy of the forest between tree trunks. There are additional factors relating to the

movement of pollen through the canopy, such as how dense the forest was, the thickness of

the foliage, the size or shape of the mire or lake, the wind speed and what time of year the

trees release pollen. It is possible to try to try to understand these factors by monitoring

modern day pollen dispersal and deposition using pollen traps (Gosling et al., 2003). This has

however, not been carried out for this study.

According to Giesecke and Fontana (2008) the size of a lake will influence which scale the

pollen record shows. For example, a large or an open lake or mire will receive pollen from

the region whereas a small or enclosed lake or mire may show a more local signal. It could be

assumed that the first freshwater lake phase of the Lina Mire basin shown in this study was

larger and or deeper than the second stage. Therefore, pollen from the first freshwater lake

phase represent vegetation on a more regional scale, as does also the pollen from the Littorina

Sea phase (when the basin was a bay). As previously discussed, it is also important to

consider pollen transported by streams (Brown et al., 2007). There are pollen that are

remobilised and deposited into the stratigraphy later. Once deposited, mixing and

bioturbation could redistribute the pollen grains (Lowe and Walker, 2014). In a similar way

pollen grains can be redistributed if an edge of the lake or bay collapses, or if there is

overland flow of water (Campbell, 1999). According to Clymo and Mackay (1987) there can

be some redistribution of pollen grains on a mire surface. They state that larger pollen grains

remain trapped whereas smaller pollen grains can migrate downwards. However, when

compared to peat accumulation rates this movement is somewhat insignificant.

Pollen grains and spores can show signs of damage due to chemical, physical or biological

factors. Oxidation, which is exposure to air, can cause such damage to pollen grains.

Polypodium spores are quite resistant to damage whereas some pollen grains can be

completely destroyed, for example Urtica (Lowe and Walker, 2014). This means that some

spores and pollen grains may be under-represented in the pollen record. As Lina Mire was

drained and the accumulations became oxidised is likely that many grains have been

damaged. At Lina Mire, the most damaged pollen grains occurred at around 100 cm depth; it

is possible that these gyttja deposits have been oxidised.


51

During the analysis of pollen grains under the microscope there can be identification

problems. In this study some pollen grains have been identified to the species level, for

example Plantago lanceolata. Other grains have been identified to the generic level for

example Betula. Poaceae and Cyperaceae have only been identified as far as the family level.

This mixture of taxonomic levels means that an accurate reconstruction of the plant

communities is not possible as within, for example, the family level of taxonomic

identification, there is a large difference in ecological preferences (Lowe and Walker, 2014).

In order to reduce the error, the pollen sum should be at least 500 arboreal pollen grains in

forested areas and 500 pollen grains of arboreal and non-arboreal in open areas (Berglund and

Ralska-Jasiewiczowa, 1986). However, when counting pollen where there have been human

impacts they recommend a minimum count of 1000 pollen grains at each depth so that the

important indicator species are not missed. They recommend a pollen count of 2000 for Late

Holocene human impact pollen investigations. This study falls short of these suggested pollen

sums owing to time restraints. Since the pollen sums were on average 250, and one pollen

sum was as low as 70, some of the rarer indicator species may have been missed. When the

added Lycopodium spores were included in the pollen sum added Lycopodium spores only

made up an average of 5.85% of the total. In order for the pollen sum and Lycopodium sum to

be comparable with the indigenous pollen it would have been preferable to have close to

equal amounts of each so that half of the pollen and spores counted were added Lycopodium

spores. It is likely that low Lycopodium spore counts mean that the pollen and charcoal

concentrations (Fig.7) are somewhat unreliable. In hindsight it may have been beneficial to

increase the amount of Lycopodium tablets added to all of the samples and reduce the weight

of the subsample. For example, the fen peat had on average 127,000 pollen grains per gram

of material, 12 Lycopodium tablets should provide a ratio of indigenous pollen grains to

added Lycopodium spores close to 1:1. Since there were so few Lycopodium spores and the

pollen concentrations per gram are calculated using Lycopodium spores, it would be best to

increase the amount of tablets, added gradually, until the ratio became equal.

Conclusions

The Baltic Sea Stages and Development of the Lina Mire Basin

Lina mire was submerged during the Ancylus Lake phase. There was then a period of high

energy and possibly some erosion around this time. The period of high energy was probably

caused by wave action during the Ancylus regression. The regression was caused by a drop in

the eustatic level of the Ancylus Lake.

Between about 7030 – 6550 BC (8980 – 8500 cal years BP) a small freshwater lake was

formed in the Lina Mire basin. The lake existed for about 480 years.

At about 6550 BC (8500 cal years BP) the Littorina transgression reconnected the lake with

the sea and the Lina Mire basin became a brackish water bay. This transgression was caused

by an increase in eustatic sea level. Lina Mire became an enclosed bay with a narrow

connection to the open sea; this persisted for about 4680 years at until about 1870 BC (3820

cal years BP).

Nichola Strandberg

52

After about 1870 BC (3820 cal years BP) the basin was once again isolated, this time due to

isostatic uplift. A freshwater lake existed for 1050 years until 820 BC (2770 cal years BP).

The isolation of the basin meant that the area could not be used as an inland water system

anymore. Gothemshammar was built around 1000 years after the isolation of the lake from

the Littorina Sea.

At about 820 BC (2770 cal years BP) the lake overgrew and infilled to become a mire. Fen

peat accumulated until the mire was drained during the 1940’s. The mire surface elevation

level fell by about 1.6 m in the north of the mire after the drainage as the water table was

lowered.

Vegetational Development around Lina Mire

Pollen zone one, 6900 – 5490 BC (8850 – 7440 cal years BP). During this time there was

mainly Pinus forest around Lina Mire. There would have been little to no human impacts on

vegetation as humans were hunter-gatherers during this time.

Pollen zone two, 5490 – 4260 BC (7440 – 6210 cal years BP) is where conditions became

more open. This shift to open conditions was perhaps caused by isostatic uplift creating new

land or by forest clearance by humans.

Pollen zone three, 4260 – 2730 BC (6210 – 4680 cal years BP) showed an increase in

wetland taxa and aquatic taxa as the land surrounding Lina Mire was uplifted although the

basin was still a bay of the Littorina Sea.

Pollen zone four, 2730 – 400 BC (4680 – 2350 cal years BP). This was the period which was

most likely to have been influenced by humans, the landscape was more open with fewer

trees and shrubs and more herbs. Hordeum-type and the Cerealia-type pollen first appeared

in the pollen record at 2630 BC (4580 cal years BP) and 970 BC (2920 cal years BP)

respectively. The interpretation of these cereal types being cultivated was substantiated by

occurrences of Plantago lanceolata, a ruderal taxon, within the same pollen assemblages.

This indicates that cultivation around Lina Mire may have started during the Late Neolithic.

Acknowledgements

I would like to thank Helene Martinsson-Wallin from the Institute of archaeology and ancient

history for inviting me to work on the project ‘I Tjelvars fotspår’ (In the Footsteps of

Tjelvar). Thank you to Martina Hättestrand from the Department of Physical Geography,

Stockholm University for her feedback on the manuscript, supervising me during laboratory

work and the writing of my thesis. Thanks to Jan Risberg at the Department of Physical

Geography, Stockholm University, for helping with the field work, laboratory work and

writing. Many thanks to Erik Wallin and Anton Uvelius (Campus Gotland) for all their help

with the field work; without their help it would not have been possible to collect all of the

material required for dating. Thanks to Britta Sannel from the Institute of Physical Geography

Stockholm University, for help identifying macrofossils. Also thanks to Elin Norström from

the Department of Geological Sciences, Stockholm University, for advice on C/N ratios.

Thank you to Yusuke Yokoyama from the Atmosphere and Ocean Research Institute,

Department of Earth and Planetary Sciences, University of Tokyo for C/N ratio


53

measurements. Thanks to Sven Karlsson from the Department of Physical Geography,

Stockholm University, for help with pollen identification and laboratory work. I would also

like to thank Cecilia Bandh from the Department of Environmental Science and Analytical

Chemistry, Stockholm University, for help with the microbalance. Thank you to Sofia

Kjellman, master’s student, Stockholm University, for advice with the preparation of C/N

ratios and help with software. Thank you to Erika Modig and Alexander Strandberg for proof

reading the text and providing helpful feedback. Huge thanks to Taariq Sheik and Veronica

Nord for useful discussions about pollen preparation methods and identification. Finally

thanks to Aleftin Barliaev, master’s student, Stockholm University, who I have worked with

on this project. I would also like to thank Stefan Wastegård who was my examiner and

provided useful comments on the text. This study was funded by Institute of Archaeology and

Ancient History, Uppsala University and by the Gerard De Geer Foundation 2016 stipend.

Nichola Strandberg

54

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64

Appendix

Table 3. Radiocarbon dates and calibrations; radiocarbon dates from bulk sediments have had the reservoir

age subtracted prior to calibration.

Laboratory

number

Depth

(cm)

Stratigraphic

unit

Sample

material

14C

age

BP

Reservoir

age years

Calibrated

years BP

(IntCal13.14C)

95% confidence

interval

Calibrated

years BC

(IntCal13.14C)

95% confidence

interval

Ua-54489 41 Fen peat

2 Carex

seeds and

25

Cladium

mariscus

seeds

2339

± 28

-

2317 -2384

86.1%

2387-2432 8.9%

435 – 368 86.1%

483 – 438 8.9 %

Ua-54979 52 Fen peat

1 Betula

and 7

Cladium

mariscus

seeds

2448

± 29 -

2360-2541

54.6%

2631-2701

26.3%

2581-2618

11.1%

2562-2579 2.9%

592 – 411 54.6%

752 – 682 26.3%

669 – 632 11.1%

630 – 613 2.9%

Ua-54322 97 Gyttja 2 Betula

seeds

4142

± 60 - 4524-4835 95%

2886 – 2575

95%

Ua-54782 121 Gyttja

Gyttja

bulk

sample

5030

± 31 451

5271-5326

49.9%

5120-5169 16%

5406-5446

14.5%

5065-5112

13.6%

5171-5182 0.9%

5220 -5220

0.1%

3377 – 3322

49.9%

3220 – 3171

16%

3497 – 3457

14.5%

3163 – 3116

13.6%

3233 – 3222 0.9

%

3271 – 3271

0.1%

Ua-54783 175 Gyttja

Gyttja

bulk

sample

5695

± 32 451

5922-6028

68.6%

6046-6068 4.1%

6076-6118

14.5%

6151-6176 7.8%

4079 – 3973

68.6%

4169 – 4127

14.5%

4227 – 4202

7.8%

4119 – 4097

4.1%

Ua-54784 201 Gyttja

Gyttja

bulk

sample

6018

± 32 451 6286-6443 95%

4494 – 4337

95%

Ua-54415 201 Gyttja

4.5

Betula

seeds

5567

± 51 6286-6443 95%

4493 – 4341

95%

Ua-54785 225 Gyttja

Gyttja

bulk

sample

6472

± 33 451

6782-6949

94.4%

6758-6761 0.5%

5000 – 4833

94.4%

4812 – 4809

0.5%

Ua-54786 270 Gyttja Gyttja 6235 451 6499-6658 95% 4709 – 4550


65

bulk

sample

± 32 95%

Ua-55698 276 Gyttja

3.5

Betula

seeds

6862

± 51 -

7595-7794

94.4%

7814-7818 0.6%

5845 – 5646

94.4%

5869 – 5865

0.6%

Ua-54319 309 Calcareous

gyttja

9 Betula

seeds

7777

± 43 - 8451-8631 95%

6682 – 6502

95%


gyttja

13 Betula

seeds

8111

± 40 -

8986 -9135

92.1%

9178-9201 1.6%

9221-9239 1.3%

7186 – 7037

92.1%

7252 – 7229

1.6%

7290 – 7272

1.3%


gyttja

15 Betula

seeds

8072

± 38 -

8967-9094

73.9%

8780-8832 9.9%

8862-8920 8.3%

9100-9121 1.9%

8953-8963 0.9%

8935-8935 0.1%

7145 – 7018

73.9%

6883 – 6831

9.9%

6971 – 6913

8.3%

7172 – 7151 1.9

%

7014 – 7004

0.9%

6986 – 6986

0.1%

Table 4. The coring location coordinates are provided in latitude and longitude All depths are (m) a.s.l. and empty values

indicate that the stratigraphic layer was not present or that coring was not deep enough to find the layer.

Coordinates (m) 57.579866

18.661445

57.578143

18.664239

57.577180

18.665471

57.576246

18.667325

Coring location

number (Northern

transect)

1 2 3 4

Distance between

coring locations

(m) west-to-east

258.86 125.1 151.42

Fen peat surface 8.93 8.90 8.93 8.26

Upper calcareous

gyttja surface 8.30

7.73

Gyttja surface 8.01 8.25

7.60

Lower calcareous

gyttja surface 6.05

5.06

Sand surface 6.51 5.85

4.73

Bluish clay surface 6.48

4.68

Coordinates (m) 57.575743

18.645268

57.573402

18.650568

57.572094

18.653005

57.571150

18.655212

Coring location

number (Middle

transect)

5 6 Master core (7) 8

Distance between

coring locations 415.27 200.89 167.60

Nichola Strandberg

66

(m) west-to-east

Fen peat surface. 9.35 9.59 9.07 9.01

Algae gyttja

surface 8.79

Upper calcareous

gyttja surface 8.62 8.64 8.61

Gyttja surface 8.9 8.39 8.33 8.31

Lower calcareous

gyttja 7.5 6.74 5.97 4.46

Clay surface. 6.45

Sand surface 6.7 6.38 5.69

Bluish clay surface 6.32

Coordinates (m)

57.574

551

18.634

655

57.572

077

18.638

791

57.569

858

18.641

491

57.569

311

18.643

119

57.568

287

18.645

629

57.567

422

18.647

578

57.566

717

18.648

924

57.564

888

18.652

548

57.564

100

18.654

284

Coring location

number

(Southern

transect)

9 10 11 12 13 15 15 16 17

Distance between

coring locations

(m) west-to-east

364.21 291.20 110.98 189.83 158.80 106.17

3 299.74 136.03

Fen peat surface 9.39 9.28 9.27 9.58 9.47 9.12 9.16 8.92 8.83

Upper

calcareous/Algae

gyttja surface

8.79 8.48 8.81 8.9 8.92 8.27 8.66 8.07 7.71

Gyttja surface

8.43 8.52 8.83 8.22 7.921 8.41 7.77 7.27

Lower calcareous

gyttja surface 6.88 6.77 6.71 6.52 6.17 6.86

Sand surface 8.59 6.39 6.32 6.13 5.98 5.62 6.31

5.02

Bluish clay

surface 6.30

5.42

4.98

Reddish clay

surface 5.07

67

Table 55. C/N ratios

Sample

name

Depth

(cm)

C/N

Ratio Error

227-01 61 11.18 ±0.53

227-02 68 11.27 ±0.53

227-03 75 15.11 ±0.71

227-04 82 25.2 ±1.19

227-05 89 11.26 ±0.53

227-06 96 11.38 ±0.54

227-07 103 11.36 ±0.54

227-08 110 10.77 ±0.51

227-09 117 10.41 ±0.49

227-10 124 12.38 ±0.58

227-11 131 11.21 ±0.53

227-12 138 11.44 ±0.54

227-13 145 10.99 ±0.52

227-14 152 10.82 ±0.51

227-15 159 10.63 ±0.5

227-16 166 10.65 ±0.5

227-17 173 9.76 ±0.46

227-18 180 10.2 ±0.48

227-19 187 12.48 ±0.59

227-20 194 11.57 ±0.54

227-21 201 10.59 ±0.5

227-22 208 9.84 ±0.46

227-23 215 10.44 ±0.49

227-24 222 10.85 ±0.51

227-25 229 12.19 ±0.57

227-26 236 9.96 ±0.47

227-27 243 9.67 ±0.46

227-28 250 9.62 ±0.45

227-29 257 9.58 ±0.45

227-30 264 10.64 ±0.5

227-31 271 9.59 ±0.45

227-32 278 10.66 ±0.5

227-33 285 13.38 ±0.63

227-34 292 15.05 ±0.71

227-35 299 14.03 ±0.66

227-36 306 16.21 ±0.76

227-37 313 17.48 ±0.82

227-38 320 17.29 ±0.81

227-39 327 11.36 ±0.54

227-40 334 15.04 ±0.71

68

Table 6. Trees, herbs, shrubs, dwarf shrubs, spores and aquatic taxa with Latin, English and Swedish name.

Trees

Abies Fir Ädelgran

Acer Maple Lönn

Alnus Alder Al

Betula Birch Björk

Carpinus Hornbeam Avenbok

Cupressaceae Conifer/Cypress family Cypressväxter

Fagus Beech Bok

Fraxinus Ash Ask

Larix Larch Lärk

Picea Spruce Gran

Pinus Pine Tall

Quercus Oak Ek

Salix Willow Pil

Sambucus-type Elderflower Fläder

Sorbus-type Rowan Rönn

Tilia Linden or Lime Lind

Ulmus Elm Alm

Shrubs

Corylus Hazel Hassel

Juniperus Juniper En

Dwarf Shrubs

Ericaceae Heather Ljung

Herbs

Apiaceae

Artemisia Mugwort et al., Malörtssläktet

Aster-type Asters Astersläktet

Cerealia-type Cereal Sädesslag

Chenopodiaceae Goosefoot et al., Ogräsmållor

Cyperaceae Sedges et al., Halvgräs

Filipendula Dropwort et al., Älggrässläktet

Hordeum-type Barley or wild barley Kornsläktet

Lactuceae Dandelion et al., Maskrossläktet

Linum austriacum Flax Klipplin

Linum bienne Pale flax Linsläktet

Lobelia Lobelias Lobelior

Menyanthes Trifoliata Bogbean/Buckbean Vattenklöver

Plantago Lanceolata Plantain/Lamb's tongue/ribleaf Svartkämpar

Poaceae Grass Gräs

Potentilla-type Cinquefoils Fingerörtssläktet

Primula Farinosa Bird's-eye primrose Majviva


69

Ranunculaceae Buttercup Smörblomma

Ranunculas Arvenis Corn buttercup Åkerranunkel

Rumex Common sorrel Ängssyra

Saxifraga-type Saxifrages Bräckesläktet

Scheuchzeria palustris Pod grass Kallgräs

Teucrium Germanders Gamandrar

Utricularia Bladderworts Bläddresläktet

Veronica Veronica Veronikasläktet

Spores

Equisetum Horsetail Fräkensläktet

Polygonum Trampörtssläktet

Polypodiaceae Polypod ferns Stensöteväxter

Sphagnum Peat moss Vitmossor

Aquatics

Elodea Waterweeds Vattenpester

Nuphar Water-lily Gulnäckrossläktet

Nymphaeaceae Water lilies Näckrosväxter

Stratiotes aloides Water soldiers Vattenaloe

Trapa natans Water caltrop Sjönöt

Typha Bulrush Kaveldunssläktet

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