2020 PALEOLIMNOLOGY/Overview

Past (J. A. Eddy and H. Oeschger, Eds.), p. 317. Wiley,

Chichester, UK.Schneider, S. H. (2003). Imaginable surprise. In Handbook of

Weather, Climate, and Water (T. D. Potter and B. R.

Colman, Eds.), p. 947. Wiley, Chichester, UK.

Stahle, D. W., et al. (1998). Experimental dendroclimatic recon-struction of the Southern Oscillation. Bulletin of the AmericanMeteorological Society 79, 2137–2152.

Stainforth, D. A., et al. (2005). Uncertainty in predictions of theclimate response to rising levels of greenhouse gases. Nature433, 403–406.

Timmermann, A., et al. (1999). Increased El Nino frequency in a

climate model forced by future greenhouse warming. Nature398, 694–697.

White, J. W. C. (2004). Do I hear a million? Science 304,

1609–1610.

PALEOLIMNOLOGY

Contents

Overview

Cladocera

Lake Chemistry

Marine Ostracods

Pigment Studies

OverviewM S V Douglas, University of Toronto, ON, Canada

ª 2007 Elsevier B.V. All rights reserved.

Introduction

Paleolimnology is the field of science that uses lakesediments to reconstruct past environmental condi-tions. Derived from the Greek paleo meaning ancientand limno meaning lake, paleolimnological studiesmake it possible to track how an environment haschanged over time, even if no prior measurementsexist for longer timescales, that is, hundreds to thou-sands of years. The field has become especially wellknown over the course of the past three decades,largely as a result of its rapid development as anapplied science. On one front, concern about thedegradation of Earth’s environmental conditions, lar-gely as a result of the impact of human activities, hassparked an increase in need for environmental assess-ments and the ability to manage anthropogenic activ-ity in the environment. On another front, studiesfocused on the natural development of environmentsare addressing issues such as global climate changeand other related topics. A challenge arises in manyinstances in trying to discern which effects werecaused by human activity and which were natural;paleolimnological studies can help distinguishbetween the two. Underlying this research is therequirement to establish the extent of the impactbeing studied and the rate of environmental change.However, such studies are often hindered from thebeginning because in order to assess the state of

current conditions, it is necessary to have a perspec-tive on how conditions have changed through time.In most cases, regardless of the time period beingconsidered, data on background conditions do notexist. The instrumental record is short and, in mostinstances, might only exist on a decadal scale versus acentennial scale. For example, temperature recordsmay exist for over 100 years in some instances butthese are rare. The same applies in the case of acidprecipitation. Many lakes have acidified within thelast five decades, but no pre-impact pH readingsexist. In most cases, instrumented environmentalreadings exist only for shorter periods: about half acentury or less. Paleolimnology provides the meansby which past environmental conditions can be deter-mined. Paleolimnological techniques can lengthenthe instrumental record by using proxy indicators ofthe environmental variable being investigated. Withthese longer records, baseline environmental condi-tions can be quantified and the natural variability ofthe system assessed. By reconstructing paleoenviron-mental conditions, it is possible to address manytopics concerning both, past- and present-day condi-tions. From these it will be possible to better under-stand and predict future trajectories of environmentalconditions on Earth.

Paleolimnology was slow to develop as a science.Early paleolimnological studies dating back to about1920 were largely descriptive (Frey, 1988); however,tremendous advances have been made over the ensu-ing decades and have transformed the science intoone that is quantitative, applied, and still expanding(Birks, 1998; Smol, 2002). This is largely due to thecoincidental timing of a serious environmental

Glacier1 2 3 4 5 6

Shrubtundra

Forest Farmagriculture

Time

Lake

Time

Airshed

Urban Industrial

Watershedboundary

Lakesediment1

23

456

Figure 1 Idealized diagram of a typical progression of events

within a postglacial lake and watershed captured within lake

sediment stratigraphies. Postglaciation is first followed by a nat-

ural succession of vegetative types leaving pollen and other

remnants behind in the sediment. Agricultural activities introduce

modified and/or exotic vegetation and enhance sediment and

nutrient runoff from within the watershed. Finally, urbanization

and industrialization typically introduce uniquely unnatural materi-

PALEOLIMNOLOGY/Overview 2021

problem, namely acid precipitation, and the develop-ment of personal computers (PCs) (Battarbee, 1991).Acid precipitation was affecting lakes and paleolim-nology was the science responsible for findinganswers to this problem (see Lake Chemistry). Theincreased computing power that PCs providedallowed for the development of complicated multi-variate analyses that could be applied to other envir-onmental challenges. The first internationalpaleolimnology symposium was held in 1967 andsince then, several scientific journals and mono-graphs (e.g., Berglund (1986) and Last and Smol(2001)) have been dedicated to paleolimnologicalresults. An early compendium of related chapters(Haworth and Lund, 1984) provided one of the firstcollections of paleolimnological papers. In-depthtextbooks have focused on the scientific applicationsof paleolimnology (Cohen, 2003; Smol, 2002). Whileearly studies might focus on one primary proxy indi-cator, the importance of multiproxy studies has beenrecognized and it is typical for multi-investigatormultiproxy international research studies to beundertaken. Paleolimnological developments havebeen rapid and significant since the mid-1970s.

als into watersheds, including many forms of organic contami-

nants, inorganic acids from atmospheric fallout, combustion

residuals (soot and metals), etc. A record of each of these

watershed events may be found in the sediment sequence of

lake sediments in their order of progression.

Lake as Archives

Lakes are archives of past environmental conditions.Their sediments represent an accumulation of biolo-gical, chemical, and physical components fromwithin and without the lake (Fig. 1). Materials mak-ing up the sediment matrix can be divided into one oftwo groups. Constituent material originating fromwithin the lake itself is termed autochthonous,whereas material originating from without the lake,such as in its watershed (catchment) or airshed, isreferred to as allochthonous. Sediment componentscan be further subdivided into biological, chemical,and physical groups. These are described below.Over time, as sediments build up, a time–depth rela-tionship is established with older sediments under-lying younger sediments, as per the Law ofSuperposition. Through the use of a sediment corer,it is possible to recover a vertical column of sedimentthat represents a period of deposition. By obtainingdeeper sediments, it is possible to sample further backin time. Figure 1 exemplifies a hypothetical exampleof how sediments from a lake formed in a glaciatedterrain might be able to capture past environments.In this example, the lake formed upon deglaciation ofthe region and the sediments captured the glaciola-custrine nature of the early lake through the varioussteps of landscape evolution (tundra, forest,and human-induced changes of agriculture andurbanization). From the time of their inception,

lakes start accumulating sediments and hence canserve as an archive spanning over several differenttimescales. For lakes whose sediments were notaffected (or removed) by recent glaciations, forexample, Lake Baikal (Russia), Lake Biwa (Japan),and African Rift Valley lakes, sediments have accu-mulated for millions of years. In areas that wereglaciated during the last ice age, for example, largeareas of North America and Europe, sediments mayoften represent only the Holocene or, approximatelythe past 10 kyr.

The Paleolimnological Method

Paleolimnological studies require a series of samplingand analyses with each requiring varying degrees ofexpertise (Fig. 2). This is termed the paleolimnologi-cal method. It includes several steps, starting with theretrieval of a sediment core. Once retrieved, a core issectioned, either on site or back in a laboratory, intosubsections which are partitioned for various ana-lyses including chronological dating, geochemical,and biological or proxy indicator analyses. Fromthe generated data, multivariate analyses are usedto reconstruct the environmental condition being

1

2

3a 3b

5

Sp.4Sp.3Sp.2Sp.1

4

Dat

e/tim

e

Dating andgeochemical

analysesProxy indicator

analyses

Figure 2 The paleolimnological method: major steps involved

in conducting a paleoenvironmental assessment are as follows.

(1) A sediment core is retrieved from a lake and subsectioned into

discrete intervals (typically 0.25–2.0 cm) for dating and proxy

analyses. (2). The thickness of the sampling interval determines

the temporal resolution of the final results. Thinner subsections

(0.25–0.5 cm) represent shorter time intervals but also require

more time and expense to process the added number of samples.

It is common for researchers to sample cores, finely near the

surface and more coarsely deeper in the core, in order to capture

recent events with the best possible resolution while also acquir-

ing adequate information about longer-term background or nat-

ural conditions. Subsections are then further divided and typically

shipped to separate laboratories for analysis of dating para-

meters, such as 210Pb or 137Cs, geochemical analyses, such as

mineral composition, total carbon, etc. (3a) and for analyses of

specific proxy indicators (3b) such as diatoms, pollen, and che-

mical contaminants. The results from dating analyses and model-

ing are then combined with those from the proxy indicators to

create a detailed history of each proxy indicator examined within

the lake sediment (4). Results from all the independent proxy

indicators are then combined and further analyzed using multi-

variate statistics (5) to yield a comprehensive reconstruction of

the history of events for the lake and its watershed.

(A)

(B) (C)

(D)

(E)

(F)

(G)(H)

(I)

Casing

Ice platform

(J)

a

dc

b

Figure 3 Examples of three commonly used corers: (A–D)

gravity corer: (A) A gravity corer with an open breach is lowered

down through the lake water slowly into the lake sediment (B).

Once seated in the sediment at the proper depth, a weighted

messenger is dropped down the coring line in order to trigger a

plunger that seals the top of the core (B and C). Sealing the top of

the gravity core creates a suction that holds the lake sediment

within the sampling tube until the core is retrieved to the lake

surface (D). (E–G) Freeze corer: A Frozen Finger (Freeze Core)

is filled with dry ice and ethanol and lowered into the sediment to

an appropriate depth (E–F). The core is left in the sediment until a

coating of material freezes firmly on the outside of the casing (F).

The core is then retrieved to the surface with a representative

stratigraphy attached to its casing. (H–J) A piston corer uses

suction in the same manner as a gravity corer to capture sediment

within a section of core tube. Typically deployed from a stable ice

platform (H), a rigid set of tubes is lowered close to the sediment

surface (I). The core tube (B) is then forced past the flange tip (A)

of the corer by means of a push rod (C) into the sediment while tip

remains locked in place with a control cable (D). Once the core

tube has been pushed to its furthest extent into the sediment, the

assembly is retrieved to the surface for subsampling. A rigid

casing is periodically used to guide piston cores into place

through the water column (H) and piston cores may be deployed

and retrieved sequentially in order to create one continuous

record for the entire sediment stratigraphy.

2022 PALEOLIMNOLOGY/Overview

studied. More often than not, a completed paleolim-nological analysis has enlisted the use of a variety oflaboratories, each specializing in one or more of thesteps.

Coring

The first step in the paleolimnological methodinvolves the retrieval of the sediment core.Particular attention must be given to this step as itforms the basis upon which the remainder of thestudy is established. The researcher must ensurethat an undisturbed core, representative of thedepositional environment, is recovered. Sediment

stratigraphy must be intact, otherwise incorrect infer-ences will be made and erroneous conclusions drawn.

There are a variety of different coring devices avail-able, each one suited to a particular type of lake and/or sediment type. Glew et al. (2001) describe thepractice and various techniques needed to obtain anundisturbed sediment core, and a dozen different clas-sifications of corers, many of which are common,albeit on a smaller scales, to oceanographic studies.Each one is designed to retrieve an undisturbed sedi-ment core from lakes of various types. Figure 3 illus-trates three commonly used sediment corers: gravity,freeze, and piston corers. Each one is best suited to aparticular kind of lake and sediment. In addition tothese three classes of corers, several other classes andvariants exist and are described in Glew (2001).Sediment corers are usually deployed from either aboat or, in cases where a lake may freeze over season-ally, from an ice platform (Figs. 4A and B).

(A)

(C)

(B)

(D)

Figure 4 Typical coring platforms can include two canoes lashed together (A) or the frozen ice surface of the lake (B). The sediments

recovered by gravity coring exhibit color changes reflecting different sediment matrices (C) or fine laminations as recovered from a

varved lake (D). Picture photo credits: A–C, M. Douglas and D. S. Lamoureux.

PALEOLIMNOLOGY/Overview 2023

2024 PALEOLIMNOLOGY/Overview

Gravity corers, as the name suggests, use the forceof gravity to penetrate the uppermost sediments. Thecorer, often made of brass or stainless steel, houses aplunger that can seal the top of a clear plastic orpolymer tube. The corer is slowly lowered throughthe water column, so as to prevent the formation of abow wave that would disturb the sediment–waterinterface. The mass of the corer should be sufficientto help force the tube into the sediments. Care mustbe taken not to overshoot and completely bury thecorer and core tube in the sediment, as the sediment–water interface represents the present-day conditionsand is an important reference point for the core.Once the person deploying the corer is certain thatthe corer has settled into the sediment, a messenger isdeployed down the core line to trigger the plunger.The plunger seals the top of the core tube so that thecorer and sediment core can be pulled up to the sur-face of the lake. Before breaking the surface–waterinterface, a bung (often made of rubber) must beinserted at the base of the core tube to plug it. Ifdeployed correctly, these sediment cores will reliablycollect an intact sediment–water interface and theunderlying sediment, up to 1 m or so in length,dependent upon the nature of the sediment matrixand the length of the core tube. Gravity cores areespecially well suited for studies that focus on therecent (past few centuries or less) past. So long asthe sediments are not too compacted, for example,clay or sand, cores can be successfully obtained.

Frigid finger, or frozen coring, is specialized andmore complicated than gravity coring. In this case,sediment is brought to the surface after having beenfrozen in situ. The corer consists of a box or tube thathas been sealed at one end. This end is either wedge-shaped or conical and has been weighted, often withlead. The corer is then filled with dry ice and ethanoland lowered gently into the sediment where itremains for roughly five to seven minutes, dependingon the ethanol–dry ice charge, while the sedimentfreezes on the outside of the corer. The carbon diox-ide gas, generated from the dry ice, escapes via asmall vent at the top of the corer. Upon retrieval onthe surface, the corer and its rind of frozen sediment(usually about 1 cm thick) are separated and the fro-zen sediment is transported and stored in a freezer,prior to analyses. This kind of coring does notrecover large amounts of sediment, but it is especiallyuseful in lakes where the sediment is very looselyconsolidated yet finely structured. For example, thesediment of meromictic lakes is often varved.Freezing such sediments in situ, as just described,preserves this structure. Again, depending upon thenature of the sediment and length of the coring appa-ratus, it is possible to retrieve sediment cores up to

2 m or more in length. Generally, however, shortercores are obtained. The specialized nature of thiscoring technique restricts its use to a certain extent.Because of transport regulations regarding dry ice(effectively, solid carbon dioxide), it is difficult,although not impossible, to use this technique invery remote areas.

Piston coring is used to obtain longer sedimentarysequences. The coring apparatus consists of a tube,which is connected to a handle at the top by a seriesof rods. Inside the tube is a piston, connected to thetop of the device by a strong wire cable, that can bepositioned at either end of the tube. With the pistonpositioned at the leading end of the core tube, thecorer is pushed into the sediment using the rods, untilit is directly above the sediment sequence to be recov-ered. The piston is then secured into place by holdingits connecting cable in place with a clamp, and thecore tube is then pushed one meter down past thepiston. This results in a core tube filled with sedimentthat is brought back to the surface of the lake bypulling up the rods. Another core tube is attached,and the process is repeated for the next depth inter-val. Generally, a researcher will work downwardsthrough the lake sediment, sequentially recoveringone meter of core at a time until an impenetrablelayer is met. In order to ensure that a continuoussediment sequence is obtained, and no depths remainunsampled, the researcher must overlap the coreintervals so that there are a few centimeters of over-lap between the bottom of one core section and thetop of the next lower interval. Because of problemswith rigidity and strength of the rods, casing is oftenused to guide and constrain them and the attachedcorer back to the same core hole. In addition, there isa limit to the length of the core sequence that can beobtained. A combined length of water depth and rodlength of no more than 20 m is generally the max-imum. Piston cores have been used to obtain entirepostglacial sequences (up to 11 m or more) in lakes.

The three methods described above can be used onrelatively small lakes and require little logistical sup-port. The equipment can even be transported by acoring team to remote areas without mechanicalassistance. However, core retrieval from the largerlakes of the world, such as lakes Biwa, Baikal,Titicaca, Great Salt Lake, and the Laurentian GreatLakes, require much more logistical planning andequipment. Thus for a long period, these lakesremained uncored. Recent design advances and aconcerted push by the paleolimnological communityhave resulted in long, multimillion year cores beingobtained. In some instances, drilling crews similar tothose used on oil rigs are employed to recover thecores. Drilling platforms can be deployed from

PALEOLIMNOLOGY/Overview 2025

specialized drill ships, such as those used by oceano-graphers, or from ingenious platforms designed foreasy transport and deployment on these large yetoften remote sites. The challenges and problems asso-ciated with these designs and large projects aredescribed by Leroy and Colman (2001). The effortsare rewarding as long, millennial-scale core recordscan be obtained. This is of especial interest to long-term global change studies.

Subsectioning

Upon retrieval of a core, it is extruded and subsec-tioned into intervals so that the sediment can bepartitioned for various subsequent analyses. Thiscan be done on site, immediately upon retrieval ofthe core, or it can be done back in a laboratory. Thedecision is based upon the nature of the sediment, thekind of core, as well as the location of the coring site.Frozen cores are transported intact, back to a freezerand laboratory, until further analyses. Gravity corescan be subsectioned on site, especially if the sedimentmatrix is loose and unconsolidated and/or if there is alikelihood of the sediments getting mixed duringtransport back to the lab. Piston cores are usuallyreturned to the lab in 1 m sections where they aresplit lengthwise. One half is preserved for thearchives and the other working half is subsectionedas necessary.

Dating Analyses – Geochronology

Once a sediment core has been obtained and theresearcher is assured that the core represents anunmixed stratigraphic column of sediments, theage–depth relationship can be used in the reconstruc-tions. According to the Law of Superposition,younger sediments will overlie older sediments. Thisis the basis of relative age dating. In most instances,an absolute chronology is desirable so that specificdates can be linked to past events. Paleolimnologistshave a number of dating techniques at their disposalto help resolve depth with respect to time. Each isappropriate for a certain age range and sediment type.These are covered in detail in the dating article (seeDating Techniques) and chapters in Last and Smol(2001). For events that have occurred within the past150 years, 210Pb and 137Cs radioactive isotopes arecommonly used. Another radioactive isotope, 14C hasbeen used to date lake sediments up to roughly 50 kyrof age. Accelerator Mass Spectroscopy (AMS) datingis helping to extend this age limit and refine datingchronologies. Other dating techniques include:Electron Spin Resonance (ESR), paleomagnetism,luminescence dating, varve chronology, amino acidracemization, tephrochonology, and marker beds of

pollen such as Ambrosia that can reflect specificevents such as European settlement of eastern NorthAmerica.

Proxy Indicator Analyses

Numerous proxy indicators can be teased out of thesediment matrix and analyzed to infer past environ-mental conditions. These can be grouped into threeclasses, namely biological, physical, and chemical.Table 1 lists some of the more commonly usedproxies for each class. A brief review of these indica-tors is discussed below. As it becomes common prac-tice to include proxies from each class in amultiproxy study, more robust and holistic paleolim-nogical reconstructions are achieved.

Biological indicators Numerous biological indica-tors including algae, algal pigments (see PigmentStudies), plants, zooplankton (see Cladocera), andinsects (see Overview) have been developed forpaleolimnological studies. Many of these proxies,such as algae and zooplankton, originate from withinthe lake (authochthonous) and can be used to recon-struct water chemistry and microhabitat availabilitythroughout the core sequence. Others are transportedinto the lake from outside the lake (allochthonous)via wind and water currents, and stored in the sedi-ment archives. Allochthonous proxies, including pol-len and insects, can be used to track vegetation shiftsand infer past temperatures.

In order to be used as a paleoindicator, a proxyindicator must possess several characteristics. Itneeds to reproduce quickly, be abundant, easily andconsistently identified, readily preserved in sedi-ments, and ecologically constrained to specific envir-onmental conditions. Ideally, the proxy containsdurable parts that do not easily decompose and arereadily identified.

The value of an indicator lies in the paleolimnolo-gist’s ability to quantify its environmental optima andtolerances. In so describing its environmental niche, orspace, it is therefore possible to link its occurrence in astratigraphic profile to specific environmental condi-tions. Until the advances in appropriate multivariatestatistics took place, precise quantification of theseenvironmental optima and tolerances was rare anddifficult. This calibration of indicators to environmen-tal conditions or variables is achieved by using sur-face–sediment training sets and is described brieflybelow and in detail in Smol (2002).

Physical and chemical indicators Examination ofthe physical and chemical sedimentary matrix hasrevealed a large number of sources for determining

Table 1 Examples of biological, physical and geochemical

proxy indicators used in paleolimnological analyses

Category Use or application

Biological

Algae

Diatoms Aquatic chemistry and microhabitats

Chrysophytes,

scales and cysts

’’

Desmids ’’

Pigments Aquatic chemistry and identification of

algal classes present

Insects

Coleoptera Aquatic chemistry and microhabitats

Chironomids ’’

Zooplankton,

Crustaceans

Ostracods ’’

Cladocera ’’

Copepods ’’

Sponges ’’

Pollen Terrestrial vegetation, aquatic

macrophytes

Phytoliths Terrestrial catchment vegetation,

especially grasses

Physical

Grain size Sediment source and processes of

sedimentation, turbulence

Loss-on-ignition Composition of sediment matrix as

inorganic, organic percentage

Mineralogy and

elemental

composition

Sediment source, water chemistry

Magnetic properties Sedimentation, erosion, dating

Fluid inclusions Aquatic paleochemistry and

paleoclimate

Fly ash and charcoal Industrialization: burning of fossil fuels,

fires

Geochemical

Organic matter

C : N

Alkenes and alkanes

Stable isotopes2H/1H, 15N/14N,13C/12C, 18O/16O

Paleoclimate, paleoproductivity

POP (persistant

organic pollutants)

Contaminant transportation

2026 PALEOLIMNOLOGY/Overview

paleoenvironmental conditions including paleocli-mates and other past environmental conditions.Listed in Table 1 are some of the more commonlyused indicators and some of their uses.

Progress in using isotopes preserved in lake sedi-ments has been rapid from the mid-1990s and isdescribed in literature of the time (Ito, 2001; Lenget al., 2005). Using different sediment fractions, suchas biogenic, and precipitate, various stable isotoperatios can be measured to reconstruct past waterchemistry variables (Table 1). These can be relatedto paleoclimatic conditions.

Data Analyses, Quantification andPaleoenvironmental Assessment

One of the greatest advances in paleolimnology hasbeen in data analyses leading to the quantification ofenvironmental change and paleoenvironmentalassessment. This big step brought paleolimnologyforward from a descriptive to a quantitative science.It was now possible to test hypotheses and quantifyenvironmental responses to ecological perturbations.As stated by both Birks (1998) and Smol (2002), thecreation of modern surface–sediment calibration ortraining sets provided a power to paleolimnologicalstudies that had previously been lacking. By linkingbiotic assemblages with their associated environmen-tal data, it is possible to quantify species–environ-ment relationships. The modern training set isconstructed by undertaking a field-intensive regionalsurvey of approximately 50 lakes. From each site, thesurface sediment (top 1 cm) is collected and the phy-sical and chemical water chemistry measured. Twodata matrices are then developed from these samplecollections. The first is composed of the relativeabundance of the biological proxy indicators in ques-tion for each site, for example, diatoms (can includeseveral hundred species). The second matrix consistsof the physical and chemical characteristics for eachsite. Using multivariate analyses, for example, multi-variate regression and canonical correspondence ana-lyses, it is possible to identify which environmentalvariables are contributing the most to the observedspecies’ distribution. Once each species’ environmen-tal optima and tolerance are calculated, it is possibleto construct transfer functions that will relate a spe-cies’ abundance throughout a stratigraphic profile toquantify values of the environmental variable beingreconstructed. A simplified description of the processis provided in Smol (2002).

It is also possible to conduct time-series and rate-of-change analyses on stratigraphic paleolimnologi-cal data (Birks, 1998). As longer and finer-resolutionstratigraphic records are being generated, answers toimportant questions can be obtained.

Applications

Paleolimnology has developed into a science with abroad spectrum of applications. These range fromdescribing long-term environmental changes to help-ing to solve environmental crises caused by anthro-pogenic causes. Paleolimnological analyses have beenconducted from every continent and nearly everypossible latitude on Earth, where lakes or paleolakesediments exist. Paleolimnological analyses have alsobeen proposed by exobiologists for potential work on

PALEOLIMNOLOGY/Overview 2027

other planets, including Mars (Doran et al., 2004;Lim and Cockell, 2002).

Some of the most important applied paleolimnolo-gical work focused on the human-induced problemsof acid precipitation and eutrophication. In bothinstances, success has largely been due to the useful-ness of diatoms in tracking these changes. Diatomspecies–environment responses are strong along apH and nutrient gradient and hence the sensitivityof this proxy to changing environmental conditions isremarkable. Reviews of these environmental pro-blems are detailed in Smol (2002) and inAntoniades (see Lake Chemistry).

It is possible to track the source of nutrients to alake via various vectors using paleolimnogical tech-niques. Surprisingly, even very remote lakes are suf-fering the consequences of elevated nutrient levels.Wolfe et al. (2001) documented the ecologicalchanges in Alpine lakes in Colorado Mountains,induced by anthropogenic atmospheric nitrogendeposition. The high elevation lakes’ algal assem-blages were sensitive to the added input of fixednitrogen and left a sedimentary signal. In a similarstudy, Blais et al. (2005) tracked elevated levels ofnutrients and pollutants such as persistent organicpollutants (POPs) that were being transported fromthe ocean environment back to Arctic lakes andponds via seabirds that were feeding in the adjacentmarine system. The POPs had been transported viaair currents to high latitudes. Zale (1994) was able touse the elevated levels of phosphorus and copper inAntarctic lake sediments to determine past penguinrookery populations. These birds were bioconcen-trating nutrients and metals from their marine dietof krill and some of their guano was leaching into anearby lake. Lifecycles of some salmon speciesinclude spawning in nursery lakes. Decomposingadult carcasses increase the level of nutrients inthese lakes. Using a combination of 15N isotopesand diatoms, it is possible to reconstruct the long-term population dynamics of these fish populationsover several millennia (Finney et al., 2002). Finally,in a parallel study of decomposing whale carcasses,Douglas et al. (2004) also used elevated levels of 15Nand diatom-inferred nutrients to track past humanoccupation (Thule Inuit) of a high Arctic winteringcamp for four centuries (AD 1200–1600).

Paleolimnological studies have been used to studylong-term environmental climate change. Kashiwayaet al. (2001) reconstructed major climatological andlimnological changes for the past 3.5 Myr of LakeBaikal, Russia. They related physical properties ofthe core to the effects of Milankovitch orbital para-meters. Using diatoms as the main proxy indicator,Laird et al. (2003) reconstructed the drought

intensity and frequency for the past two millenniaof the Northern Great Plains of North America bytracking diatom-inferred lake water salinity.Reported at subdecadal resolution, these data identi-fied droughts that lasted for centuries and wererelated to the same atmospheric circulation anoma-lies causing modern and potential future droughts.Bigler and Hall (2003) were able to directly linkdiatom assemblages as quantitative indicators of tem-peratures at a century-scale in northern Sweden.Pienitz et al. (2004) compiled a synthesis of the docu-mented environmental change at high latitudes. Aspredicted by general circulation models (GCMs)these high latitudes are already exhibiting the effectsof a warming climate. The effects of this recentwarming were documented for the circumarctic in adiatom- and zooplankton-based study of lake sedi-ments (Smol et al., 2005).

Lake sediment analyses contribute important datato large projects such as those defined by large inter-national collaborative efforts. The IGBP-PAGES PEPIII (Pole-Equator-Pole) is one such project. Focusedon the paleoclimate change of the last 200 kyr in atransect that crossed Africa and Europe, paleolimno-logical studies were the most common analyses used(Oldfield and Thompson, 2004) and included studiesof sea-level change on the Scandinavian coast(Hedenstrom and Risberg, 1999), paleolakes of theSahara (Gasse et al., 1987) as well as many others.The net result of all these efforts was a better under-standing of climate variation throughout this longtransect as well as the interactions between humansand climate over this same time period throughEurope, the Middle East and Africa. The complex-ities of the interactions between the Eurasian icesheets, the North Atlantic circulation and tropicalmonsoons for example, were illustrated and althoughadditional research is required, the long time seriesrecoverable from many of these geographic areasmeans that answers will be forthcoming.

Paleolimnology is continuing to develop at arapid pace. It is clear that the footprint of humanson the environment is not a delicate one and thatenvironmental managers will continue to rely heav-ily on this branch of science. As new environmentalproxy indicators are described and calibrated, andnew analytical techniques are developed, our under-standing of complex environmental interactions willincrease.

Glossary

Allochthonous Originating from without the system (e.g.,lake) in question (cf. autochthonous).

Anthropogenic Relating to human activity.

2028 PALEOLIMNOLOGY/Overview

Autochthonous Originating from within the system (e.g.,lake) in question (cf. allochthonous).

Law of Superposition When no reversal or mixing hasoccurred, younger sediments overlie older, deeper sedi-ments. This age–depth relationship provides a means ofrelative dating of lake sediment cores.

Meromictic Lake A lake whose bottom waters are chemi-cally more saline than overlying waters. Often thesebottom waters are anoxic and sediments can accumulateas varves.

Varves Sediment layers that occur as annual couplets. Inmany instances, a light layer represents summer accu-mulation and a dark layer represents winter accumula-tion of sediments.

See also: Beetle Records: Overview. Carbonate StableIsotopes: Lake Sediments. Chironomid Overview.Dating Techniques. Dendroclimatology. DiatomIntroduction. Diatom Methods: Quaternary GeologicalRecords. Diatom Records: Antarctic Waters.Paleobotany: Overview. Paleolimnology: Cladocera;Lake Chemistry; Pigment Studies. Phytoliths. PlantMacrofossil Methods and Studies: PaleolimnologicalApplications. Varved Lake Sediments.

References

Battarbee, R. W. (1991). Recent paleolimnology and diatom-based

environmental reconstruction. In Quaternary Landscapes(L. C. K. Shane and E. J. Cushing, Eds.), pp. 129–174.University of Minnesota Press, Minneapolis.

Berglund, B. (1986). Handbook of Holocene Palaeoecology andPalaeohydrology. Wiley, Chichester.

Bigler, C., and Hall, R. I. (2003). Diatoms as quantitative indica-tors of July temperature: A validation attempt at century-scale

with meteorlogical data from northern Sweden.

Paleogeography, Paleoclimatology, Paleoecology 189,

147–160.

Birks, H. J. B. (1995). Quantitative paleoenvironmental recon-

structions. In Statistical Modelling of Quaternary ScienceData. Technical Guide 5 (D. Maddy and J. S. Brew, Eds.), pp.161–254. Quaternary Research Association, Cambridge.

Birks, H. J. B. (1998). Numerical tools in paleolimnology – pro-

gress, potentialities and problems. Journal of Paleolimnology20, 307–322.

Blais, J. M., Kimpe, L. E., McMahon, D., et al. (2005). Arctic

seabirds transport marine-derived contaminants. Science 309,

445.Cohen, A. S. (2003). Paleolimnology: The History and Evolution

of Lake Systems. Oxford University Press, Oxford.

Doran, P. T., Priscu, J. C., Lyons, W. B., Powell, R. D., Andersen,

D. T., and Poreda, R. J. (2004). Paleolimnology of extreme coldterrestrial and extraterrestrial environments. In Long-TermEnvironmental Change in Arctic and Antarctic Lakes (R.

Pienitz, M. S. V. Douglas and J. P. Smol, Eds.), pp. 475–511.

Springer, Dordrecht.Douglas, M. S. V., Smol, J. P., Savelle, J. M., and Blais, J. M.

(2004). Prehistoric Inuit whalers affected Arctic freshwater

ecosystems. Proceedings of the National Academy of Science101, 1613–1617.

Finney, B. P., Gregory-Eaves, I., Douglas, M. S. V., and Smol,J. P. (2002). Fisheries productivity in the northeastern

Pacific Ocean over the past 2,200 years. Nature 416,

729–733.

Frey, D. (1988). What is paleolimnology? Journal of Paleolimnology1, 5–8.

Gasse, F., Fontes, J. C., Plaziat, J. C., et al. (1987). Biological

remains, geochemistry and stable isotopes for the reconstruc-

tion of environmental and hydrological changes in theHolocene lakes from North Sahara. Palaeogeography,Paleoclimatology, Paleoecology 60, 1–46.

Glew, J. R., Smol, J. P., and Last, W. M. (2001). Sediment corecollection and extrusion. In Tracking Environmental ChangeUsing Lake Sediments: Basin Analysis, Coring, andChronological Techniques (W. M. Last and J. P. Smol, Eds.)

vol. 1 pp. 73–105. Kluwer, Dordrecht.Haworth, E. Y., and Lund, J. W. G. (Eds.) (1984). Lake Sediments

and Environmental History: Studies in Palaeolimnology andPalaeoecology in Honour of Winifred Tutin. Leiscester

University Press, Bath, UK.Hedenstrom, A., and Risberg, J. (1999). Early Holocene shore

displacement in southern central Sweden as recorded in ele-

vated isolated basins. Boreas 28, 490–504.

Ito, E. (2001). Application of stable isotope techniques to inorganicand biogenic carbonates. In Tracking Environmental ChangeUsing Lake Sediments: Physical and Geochemical Methods(W. M. Last and J. P. Smol, Eds.) vol. 2 pp. 351–371.Kluwer, Dorderecht.

Kashiwaya, K., Sakai, H., Ryugo, M., Horii, M., and Kawai, T.

(2001). Long-term climato-limnological cycles found in a 3.5

million year continental record. Journal of Paleolimnology 25,

271–278.

Laird, K. R., Cumming, B. F., Wunsam, S., et al. (2003). Lake

sediments record large-scale shifts in moisture regimes across

the northern prairies of North America during the past twomillennia. Proceedings of the National Academy of Science100, 2483–2488.

Last, W. M., and Smol, J. P. (Eds.) (2001). TrackingEnvironmental Change Using Lake Sediments. Volume 1:Basin Analysis, Coring, and Chronological Techniques.Kluwer, Dordrecht.

Leng, M. J., Lamb, A. L., Marshall, J. D., et al. (2005). Isotopes inlake sediments. In Isotopes in Palaeoenvironmental Research(M. J. Leng, Ed.), pp. 147–184. Springer, Dordrecht.

Leroy, S. A., and Colman, S. M. (2001). Coring and drilling

equipment and procedures for recovery of long lacustrinesequences. In Tracking Environmental Change Using LakeSediments: Basin Analysis, Coring, and ChronologicalTechniques (W. M. Last and J. P. Smol, Eds.), vol. 1 pp. 107–135. Kluwer, Dordrecht.

Lim, D. S. S., and Cockell, C. S. (2002). Paleolimnology in the high

Arctic–implications for the exploration of Mars. InternationalJournal of Astrobiology 1, 381.

Oldfield, F., and Thompson, R. (2004). Archives and proxies along

the PEPIII transect. In Past Climate Variability through Europeand Asia (R. W. Battarbee, F. Gasse and C. E. Stickley, Eds.),

pp. 7–29. Springer, Dordrecht.Pienitz, R., Douglas, M. S. V. and Smol, J. P. (Eds.) (2004). Long-

Term Environmental Change in Arctic and Antarctic Lakes.Springer, Dordrecht.

Smol, J. P. (2002). Pollution of Lakes and Rivers: APaleoenvironmental Perspective. Arnold, London.

Smol, J. P., Wolfe, A. P., Birks, H. J. B., et al. (2005). Climate-

driven regime shifts in the biological communities of arctic

lakes. Proceedings of the National Academy of Science 102,

4397–4402.

PALEOLIMNOLOGY/Cladocera 2029

Wolfe, A. P., Baron, J. S., and Cornett, R. J. (2001). Anthropogenicnitrogen deposition induces rapid ecological changes in alpine

lakes of the Colorado Front Range (USA). Journal ofPaleolimnology 25, 1–7.

Zale, R. (1994). Changes in the size of the Hope Bay Adeliepenguin rookery as inferred from Lake Boeckella sediment.

Ecography 17, 297–304.

CladoceraM Rautio, Universite Laval, Quebec, QC, Canada

ª 2007 Elsevier B.V. All rights reserved.

Introduction

The Cladocera (Crustacea: Branchiopoda; see glos-sary) are a major component of the planktonic andbenthic crustacean fauna in lakes and ponds. Althoughtheir distribution, species number, and abundance canvary substantially among water bodies there areimportant similarities in the role they play in all aqua-tic ecosystems. They include the primary herbivores inlakes, and contribute to the recycling of nutrients in thewater column. In addition, they form a large portion ofplanktivorous fish and invertebrate diet. Because oftheir trophic position in the middle of the food web,they are subjected to both bottom-up and top-downforces and have a crucial role in carbon and energytransfer through the food web.

The high abundance of cladocerans in most of theworld’s freshwater habitats and the large range ofdifferent optimal tolerances to environmental condi-tions among species make cladocerans very powerfulin paleolimnological interpretation and hence in thedetection of changes in past environmental condi-tions. This group of organisms is evolutionarily old.The Cladocera have existed more than 100 millionyears and at least for the last 200,000 years no mor-phological changes have been observed (Frey, 1962;Hann and Karrow, 1993) which is essential whencomparing fossil remains with modern samples.

The aim of this chapter is to review the mechan-isms and observations that link subfossil cladoceransto a range of environmental conditions, from site-specific to global patterns. The first section reviewshow subfossil cladoceran research has rapidly devel-oped from taxonomic orientated approach to multi-disciplinary science that matches observation withecological processes. This is followed by a considera-tion of the most important factors that contribute tomaking cladocerans successful paleolimnologicalindicators. Finally, several case studies are presentedthat show how cladocerans have revealed

information about the past in multiple timescalesand abiotic–biotic process levels.

Short History of Cladoceran Researchin Paleolimnology

The taxon Cladocera was first recognized by Latreille(1829) but it took 100 years more before the study oftheir subfossil remains was introduced into paleolim-nology. The first quantitative study using animalmicrofossils in North America was published byDeevey (1942) and a few years later David G. Freyextensively promoted the use of cladocerans remainsin aquatic research with his numerous publications inthe mid-twentieth century (e.g., Frey, 1960; 1964).These first publications reported the occurrence ofone or a few cladoceran taxa and although they recog-nized the potential of cladoceran fossils as indicatorsof past environmental conditions their main emphasiswas to find out which species of cladocerans werepreserved in the sediment, how they could be identi-fied, and what was the general sedimentation processin a lake. The taxonomic guidelines that were set bythese pioneer studies are still valid and for many spe-cies still represent the best drawings of the remains.

During the 1960–1980s the use of cladocerans inpaleolimnological research increased rapidly.Sediment cores were collected from lakes acrossEurope and North America with the purpose of resol-ving community changes in time spans varying fromdecades to thousands of years (Goulden, 1964;Hofmann, 1984). Many of the studies also concen-trated on species distribution patterns using only sur-face sediments (Korhola, 1999) as it was now evidentthat a single sediment sample revealed the cladocerancommunity composition in a water body better than acareful and extensive limnological sampling over anumber of years (Frey, 1960). These studies linkedcladocerans to environmental variables such as tem-perature (climate), pH (acidification), and nutrients(eutrophication), initializing the use of cladocerans asindicators of the past. However, many studies alsoconcluded that the ecological indicator value of indi-vidual cladoceran species was variable and often ratherlow. Instead, interpretations should be based on theoverall structure and composition of the communityassemblage. The development of transfer functions in1990s resolved this problem (see Numerical AnalysisMethods). Transfer functions quantitatively recon-struct past environmental conditions in lakes. Theyare generated from a set of surface sediment samples(0–1 cm depth) usually collected from more than 20so-called training set lakes representing a large gradi-ent of environmental conditions. Statistical