Quaternary Science Reviews 25 (2006) 3228–3245 Marine 14 C reservoir ages for 19th century whales and molluscs from the North Atlantic Jan Mangerud a, , Stein Bondevik b , Steinar Gulliksen c , Anne Karin Hufthammer d , Tore Høisæter e a Department of Geoscience and Bjerknes Centre for Climate Research, University of Bergen, Alle´gt. 41, N-5007 Bergen, Norway b Department of Geology, University of Tromsø, N-9037 Tromsø, Norway c National Laboratory for 14 C Dating, Norwegian University of Science and Technology, N-7491 Trondheim, Norway d Natural History Collections, University Museum of Bergen, N-5007 Bergen, Norway e Department of Biology, University of Bergen, HIB—Thormøhlensgt. 55, N-5020 Bergen, Norway Accepted 2 March 2006 Abstract In order to compare radiocarbon dates on marine and terrestrial samples the former have to be corrected for a reservoir age. We present reservoir ages from dating 21 whales collected 1860–1901 and recalculating dates of 23 molluscs collected 1857–1926. Most of the whales were caught along the coast of Norway, but one is from France and one from Iceland. We assume the former mainly lived in the North and equatorial Atlantic and in the Norwegian Sea. Whales feed only on pelagic organisms and will provide the reservoir age for the open ocean surface water. However, they travel long distances and will integrate the reservoir ages of the different water masses along their way. Molluscs (dated from Norway, Spitsbergen and Arctic Canada) are stationary and monitor the sea water passing their dwelling site, but some also take up carbon from particulate food or sediment pore water. Coastal water also often contains some continental carbon. We present two different views on how to analyze and interpret the data. Mangerud recommends to use reservoir ages based on a combination of the whale and mollusc dates, i.e. 380730 and 360730 yr relative to Intcal04 and British oak, respectively, and a DR value of 20730 for the surface water in the N-Atlantic and Norwegian Sea. Bondevik and Gulliksen maintain that the reservoir age—and DR—along the Norwegian coast is latitude dependant, with DR-values increasing from 3722 in the South to 105724 at Spitsbergen. Whales, reflecting North Atlantic open ocean surface water have lower DR (7711) than most molluscs. r 2006 Elsevier Ltd. All rights reserved. 1. Introduction The marine reservoir age is defined as the 14 C-age- difference between a sample which acquired its carbon from the ocean water and a sample that contempora- neously obtained its carbon from the atmosphere (Stuiver et al., 1986). In the present day ocean-surface water the reservoir ages vary from 350 to 1500 yr (Reimer and Reimer, 2001). In order to correlate marine and continental events accurately, and to calibrate marine 14 C-dates to calendar years, a better knowledge of the reservoir ages in space and time is necessary. The main purpose of this paper is to report 22 radiocarbon dates of 21 whales from the North Atlantic and the Nordic seas, caught 1860–1901. One incitement for this study of whale bones was that some authors reported and used considerably lower reservoir ages for whales than for molluscs (Forman et al., 1987; Dyke et al., 1996), whereas we had taken for granted they were more or less the same in areas with minor variation in the surface reservoir age (Landvik et al., 1987; Bondevik et al., 1995). We also report improved, re-calculated reservoir ages for the 23 marine shells published earlier (Mangerud, 1972; Mangerud and Gulliksen, 1975). The molluscs are sta- tionary, and in theory they should monitor the 14 C content of the sea water passing their dwelling site during their life time. Whales, on the other hand, move across large ocean ARTICLE IN PRESS 0277-3791/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2006.03.010 Corresponding author. Tel.: +47 55 58 35 04; fax: +47 55 58 36 60. E-mail address: [email protected] (J. Mangerud).
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ARTICLE IN PRESS
0277-3791/$ - se
doi:10.1016/j.qu
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Quaternary Science Reviews 25 (2006) 3228–3245
Marine 14C reservoir ages for 19th century whales and molluscs fromthe North Atlantic
Jan Mangeruda,�, Stein Bondevikb, Steinar Gulliksenc,Anne Karin Hufthammerd, Tore Høisætere
aDepartment of Geoscience and Bjerknes Centre for Climate Research, University of Bergen, Allegt. 41, N-5007 Bergen, NorwaybDepartment of Geology, University of Tromsø, N-9037 Tromsø, Norway
cNational Laboratory for 14C Dating, Norwegian University of Science and Technology, N-7491 Trondheim, NorwaydNatural History Collections, University Museum of Bergen, N-5007 Bergen, Norway
eDepartment of Biology, University of Bergen, HIB—Thormøhlensgt. 55, N-5020 Bergen, Norway
Accepted 2 March 2006
Abstract
In order to compare radiocarbon dates on marine and terrestrial samples the former have to be corrected for a reservoir age. We
present reservoir ages from dating 21 whales collected 1860–1901 and recalculating dates of 23 molluscs collected 1857–1926. Most of the
whales were caught along the coast of Norway, but one is from France and one from Iceland. We assume the former mainly lived in the
North and equatorial Atlantic and in the Norwegian Sea. Whales feed only on pelagic organisms and will provide the reservoir age for
the open ocean surface water. However, they travel long distances and will integrate the reservoir ages of the different water masses along
their way. Molluscs (dated from Norway, Spitsbergen and Arctic Canada) are stationary and monitor the sea water passing their
dwelling site, but some also take up carbon from particulate food or sediment pore water. Coastal water also often contains some
continental carbon. We present two different views on how to analyze and interpret the data. Mangerud recommends to use reservoir
ages based on a combination of the whale and mollusc dates, i.e. 380730 and 360730 yr relative to Intcal04 and British oak,
respectively, and a DR value of 20730 for the surface water in the N-Atlantic and Norwegian Sea. Bondevik and Gulliksen maintain that
the reservoir age—and DR—along the Norwegian coast is latitude dependant, with DR-values increasing from �3722 in the South to
105724 at Spitsbergen. Whales, reflecting North Atlantic open ocean surface water have lower DR (7711) than most molluscs.
r 2006 Elsevier Ltd. All rights reserved.
1. Introduction
The marine reservoir age is defined as the 14C-age-difference between a sample which acquired its carbonfrom the ocean water and a sample that contempora-neously obtained its carbon from the atmosphere (Stuiveret al., 1986). In the present day ocean-surface water thereservoir ages vary from 350 to 1500 yr (Reimer andReimer, 2001). In order to correlate marine and continentalevents accurately, and to calibrate marine 14C-dates tocalendar years, a better knowledge of the reservoir ages inspace and time is necessary.
e front matter r 2006 Elsevier Ltd. All rights reserved.
The main purpose of this paper is to report 22radiocarbon dates of 21 whales from the North Atlanticand the Nordic seas, caught 1860–1901. One incitement forthis study of whale bones was that some authors reportedand used considerably lower reservoir ages for whales thanfor molluscs (Forman et al., 1987; Dyke et al., 1996),whereas we had taken for granted they were more or lessthe same in areas with minor variation in the surfacereservoir age (Landvik et al., 1987; Bondevik et al., 1995).We also report improved, re-calculated reservoir ages forthe 23 marine shells published earlier (Mangerud, 1972;Mangerud and Gulliksen, 1975). The molluscs are sta-tionary, and in theory they should monitor the 14C contentof the sea water passing their dwelling site during their lifetime. Whales, on the other hand, move across large ocean
ARTICLE IN PRESSJ. Mangerud et al. / Quaternary Science Reviews 25 (2006) 3228–3245 3229
areas and somehow monitor the 14C content of the oceanwater along their route. Therefore molluscs and whalesmay have different marine reservoir ages even if they werecollected at the same site.
We also consider whether it is true that whale bones andmollusc shells are in isotopic equilibrium with the sea waterwhen the animals die—and the answer is ‘‘not always’’; forwhales because C in bone collagen is fixed during thegrowth period of mammals, i.e. potentially decades beforethe whales were caught, and for molluscs because theybuild their shells throughout their life, and for some speciesbecause they take C from other sources than sea water.
To calculate the reservoir ages we needed the 14C age ofthe atmosphere corresponding to the year our molluscs andwhales were collected. For this we used the published 14Cages of tree rings. Here we encountered another problem,namely that the 14C age of tree rings in IntCal04 (Reimeret al., 2004), which for the last few hundred yearsmainly reflects NW-American Douglas fir, differsslightly from the 14C ages of British oak (McCormacet al., 1998). The differences are up to 60 yr around 1900AD when some of our samples were collected. We havetherefore calculated the reservoir ages relative to the 14Cage of both the tree rings in IntCal04 and British oak,respectively.
2. Samples and calculation methods
2.1. Samples
All of the dated whale bones are from the collections inthe Zoological Museum at the University of Bergen. Thekey information is given in Table S1 and the site ofcollection in Fig. 1. The whale skeletons were at that time(late 1800s) prepared either by boiling and then pickingaway the meat, by sinking the carcass in the sea, byburrowing it in sandy soil until the skeleton was clean orleaving the carcass on the beach for the nature to take careof preparation. There are no records regarding which ofthese techniques was applied for each skeleton. However, itis unlikely that any of the methods would influence the14C/12C ratio of the bone collagen. We used an electrichollow corer with diameter 4 cm to sample the bones.Sample lengths were 1–4 cm.
The dated shells are also from the collections in theZoological Museum. Details are given in Table S2 andlocations in Fig. 1. According to the curator at the time,Johanne Kjennerud, all were probably collected alivebecause they were collected by zoologists, although thatwas not specified on the labels and thus cannot beguaranteed. If some of the shells were empty at the timeof sampling, they would then provide artificially highreservoir ages. Note that we have not re-measured theshells, only re-calculated their ages from the measure-ments by Mangerud and Gulliksen (1975), as explainedbelow.
2.2. Preparation of samples and measurements
Collagen was extracted from the whale bones by usingthe Longin method (Longin, 1971), and an additionalalkali treatment after demineralization was included toremove humic contaminants. The shells were thoroughlywashed, periostracum scraped off and the outer parts, onaverage 12% by weight, were removed by HCl etchingbefore dating.All samples were converted to CO2 and measured by gas
proportional counting. To obtain high precision themeasurements were performed in two periods with durationof several thousand minutes each, separated by 2–5 months.Background and oxalic standard samples were frequentlymeasured in each period. Age calculation follows recom-mendations given in Stuiver and Polach (1977).When we originally published the results for the molluscs
we conservatively calculated the ages as if they weremeasured in one period, and we rounded off theuncertainty upwards (Mangerud and Gulliksen, 1975).Now we have recalculated the ages and errors as preciselyas the measurements allow. This recalculation resulted inminor changes, less than 10 yr for almost all samples, butthe standard deviations decreased. Note also that wecalculate reservoir ages in a different manner as explainedbelow.
2.3. Calculation of marine reservoir ages
The marine reservoir age (Mres) is defined as (Stuiveret al., 1986):
Mres ¼14C age of marine water�14C age of contem-
poraneous terrestrial plants.The recent reservoir age is commonly found by dating
museum samples of marine organism collected before themain input of fossil-fuel-carbon to the atmosphere andcompare the date with the 14C dated tree ring record.However, as discussed in subsequent sections, the 14C contentof these animals are not always in equilibrium with the oceanwater in which they live. We will therefore introduce the termmarine water reservoir age for the apparent age of thedissolved inorganic carbon in ocean water.Another complication is that there are regional differ-
ences in the 14C content in the atmosphere. The IntCal04(Reimer et al., 2004) assumes a well mixed atmosphere forthe northern hemisphere, but for some periods thereapparently are differences between western North Americaand the British Isles (Knox and McFadgen, 2004). This ismost probably due to the influence of CO2 exchangebetween the ocean surface water and the atmosphere, andthe variation of this difference over time (Fig. 2) isprobably mainly caused by variation in upwelling alongthe west coast of N-America (Knox and McFadgen, 2004).However, one cannot completely rule out the possibilitythat the British oak values are influenced by a fossil-fuel-effect from Belfast industry (Paula Reimer, written.com.2005).
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Fig. 1. Map showing the location of the samples, except the molluscs from Arctic Canada. Here is given the marine water reservoir age relative to British
oak. Details on locations, etc. are given in Tables S1 and S2. Whales and molluscs in red and blue numbers respectively.
J. Mangerud et al. / Quaternary Science Reviews 25 (2006) 3228–32453230
In this paper we compare our 14C-ages with the northernhemisphere standard for 14C-calibration, IntCal04 (Reimeret al., 2004), from which also Marine04 (Hughen et al.,2004) is produced. When necessary we have interpolatedbetween the 5 yr increments given in IntCal04. In theperiod of interest, late 19th and early 20th century,IntCal04 is based on several datasets, including tree-ringsof Douglas fir from the northwest coast of USA, andBritish oak from northern Ireland. The data for Douglas firis based on 14C dates of 1–2 yr tree-rings, while the Britishoak dates are on decadal blocks (McCormac et al., 1998),thus having a much lower resolution. Consequently theIntCal04 curve for the relevant time period is dominated bythe northwest American data. While the British oak andDouglas fir data largely agree for much of the period from1320 to 1950, there are a few exceptions, among which theperiod of interest here is the most striking, with a difference
of more than 60 yr around AD 1900 (Fig. 2). We also givereservoir ages calculated relative to British oak because weconsider that these better reflect the processes in this areaand therefore are more relevant to use for correctingmarine dates from older parts of the Holocene where theIntCal04 curve is more strongly influenced by dates of treerings from Europe. In Fig. 2 we have plotted IntCal04together with means for British oak. The latter are thedecadal dates from McCormac et al. (1998) which we haveplotted from the table of ‘‘y smoothed calibration curveat yearly intervals’’ in Knox and McFadgen (2001). Wealso used the latter for calculating reservoir ages relative toBritish oak.We will also point out that when we originally calculated
the reservoir ages for the molluscs (Mangerud, 1972;Mangerud and Gulliksen, 1975) reliable terrestrial datawere not available. We therefore compared the 14C age of
Fig. 2. Uncorrected radiocarbon ages (71s) of all dated whales and
molluscs plotted with the year of collection (death) as horizontal scale.
Also shown are curves of InCal04 (Reimer et al., 2004) and Marine04
(Hughen et al., 2004) both with71s, and for British oak (71s)(McCormac et al., 1998). The latter is plotted from Knox and McFadgen
(2001) who stated the mean standard error is 874 yr; here we use 712 yr.
J. Mangerud et al. / Quaternary Science Reviews 25 (2006) 3228–3245 3231
the mollusc with the calendar year age of the sample.According to the definition we now compare the 14C age ofthe mollusc with the 14C age of the tree ring of the sameyear; the difference being the reservoir age (Stuiver et al.,1986). Because the 14C ages of tree rings around 1900s areabout 50 yr older than the calendar year, these newreservoir ages are about 50 yr younger than the oldestimates (Bondevik et al., 1999).
2.4. Calculation of DR
For calibration of 14C dates of surface-water marinesamples, the calibration curve Marine04, which shouldrepresent a ‘‘mean global ocean’’, has been constructed(Hughen et al., 2004). For the last 10,500 cal yr thiscurve is calculated by using an atmosphere–ocean diffusionmodel with the 14C dates of tree-rings from Intcal04 asinput data. For each region (and period) one has to find aDR value which expresses the difference from the ‘‘globalocean.’’ We have calculated DR values by subtracting the14C-age given by Marine04 for the relevant year from the14C age of the sample (Tables S1 and S2). ‘‘The relevantyear’’ is the year of collection when calculating what webelow call ‘‘whale DR’’ and ‘‘mollusc DR’’, and the yearwhen C was fixed in bone collagen or shell carbonate whencalculating the ‘‘marine water reservoir DR.’’ As explainedbelow this latter is 5 yr before collection for molluscsand 10 and 20 yr for small and large whales, respectively.Note that we have combined the standard deviationsof the sample and Marine04 age when giving our DR
values. When necessary we have interpolated between thefive years increments given in the table of the Marine04ages.
3. Carbon sources and residence times
3.1. Whales
Mammals and other animals take up C only bydigestion, i.e. through the food and drink. The datedwhales feed only on plankton or on pelagic animals(Table 1) higher up in the food chain than plankton. Wepostulate that C in phytoplankton is in isotopic equili-brium with sea water and also that the turnover of Cthrough the marine food chain from phytoplankton to, e.g.fish is so fast that the time can be neglected for 14C dating.The soft tissue of whales should therefore have a reservoirage representative for the sea water in which the whaleslive. Whales travel far and the 14C reservoir age measuredon whales should be a kind of a ‘‘mean’’ for the wateralong their routes (Table 1). A main problem with thewhales is that we know their living areas only in a generalway; We cannot track the routes for each individual whale.However, the standard material for 14C dating of whales
is not meat but bone collagen. It has been shown that mostof the collagen in human bones is locked-in during thegrowth period, i.e. before the person is about 20 yr old(Geyh, 2001). Later the turnover of C in collagen is veryslow, although it varies between different skeletal elements(Shin et al., 2004). The implication is that one has tosubtract a correction for the residence time of C in thecollagen when dating human bones. Geyh (2001) found,e.g. that for a 65-yr-old person a correction of 32 yr shouldbe subtracted. To our knowledge no similar study ofresidence time of C in whale bones exists, but we assumehumans are more or less representative for all mammals.Some whales can be old, up to 200 yr is reported forbowhead whales (George et al., 1999), so the bone reservoir
age may potentially be significant. However, there is amajor difference between humans and whales becausewhales continue to grow throughout most of their lives,although certainly fastest when they are young. This meansthat the younger parts of whale bones have a 14C-activityclose to the contemporaneous sea water. We were notaware of the problem of bone reservoir age when we datedthe whales, but as we sampled the outer part of the bonesthe bone reservoir age is likely minimized. The implicationof the bone reservoir age in this connection is that the bonedates reflect the isotopic composition of sea water at thetime C was fixed in the collagen. To obtain the marinewater reservoir age, the bone reservoir age has to besubtracted.We present two sets of reservoir ages and DR values
(Tables S1 and Table 2). The first set is called ‘‘whalereservoir age’’ and ‘‘whale DR’’ and is calculated relative tothe year of collection (death). The other set is called‘‘marine water reservoir age’’ and ‘‘marine water DR’’, withthe intention that it will provide the values of the sea water.For these values we have assumed that C is fixed in thebone collagen 10 and 20 yr before death in the small andlarge whales, respectively, but at death for the ‘‘baby’’
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Table 1
Typical living areas and diet used by the dated whales
Species Global distribution of the species Probable living area for the relevant individ Food
Toothed whales
Globicephala melas North-Atlantic (and southern
oceans), cold temperate waters
North Atlantic. Oceanic and littoral. Prefer
deep waters. Most frequently found at the
edge of the continental shelf.
Primarily squids, but also gregarious
fishes.
Lagenorhynchus
acutus
North Atlantic, cold temperate
waters
North Atlantic. Oceanic. Common at the
edge of the continental shelf.
Mainly squids and gregarious fishes.
L. albirostris North Atlantic, cold temperate
waters
Atlantic Ocean. Oceanic, more rarely
littoral. Wider migration and wider South
and North distribution than L. acutus.
Mainly squids and gregarious fishes.
Orcinus orca World wide North Atlantic. Oceanic and littoral. Gregarious fishes, mammals and squids.
Physeter catodon World wide Atlantic Ocean, but not the North Sea
Basin. Long migration North–South.
Oceanic and littoral.
Mainly large squids, but also fishes.
Deep diver.
Hyperoodon
ampullatus
North Atlantic, Arctic-cold
temperate waters
Atlantic Ocean, from Spain to Svalbard.
Oceanic.
Mainly squids, but also fishes and
invertebrates. Deep diver.
Mesoplodon bidens North Atlantic and Baltic Sea,
temperate waters
North Sea, to ca 591N. Oceanic, relatively
deep waters.
Squids and fishes.
Baleen whales
Eubalaena glacialis Temperate to tropical waters,
northern hemisphere
Atlantic Ocean. Littoral, more rarely
oceanic.
Small crustacean, i.e Calanus
finmarchicus.
Balaenoptera
acutorostrata
World wide, northern to tropical
waters
North Sea, relatively stationary. Littoral,
more rarely oceanic.
Fish and crustacean.
B. borealis World wide, cold temperate to
tropical waters
North Atlantic. Oceanic, primarily deep
waters.
Fish, squids and crustaceans. In the
North Atlantic, small crustaceans.
B. musculus World wide, Arctic to tropical
waters
North Atlantic Ocean. Oceanic, rarely
littoral. Long range North–South
migrations.
Crustaceans, i.e. Thysanoessa inermis
and Meganyctiphanes norvegica.
B. physalus World wide, Arctic to tropical
waters
North Atlantic Ocean. Oceanic, rarely
littoral.
Crustacean and fishes, more rarely
squids
Megaptera
novaeangliae
World wide, cold temperate to
tropical waters; wide migrations
North Atlantic Ocean, (not in the North
Sea Basin). Oceanic and littoral.
Crustaceans and fishes.
The information is mainly according to Tomelin (1967), Ellis (1980) and Balcomb and Minasian (1984).
-6010 20 30 40 50 600
-50-40-30-20-10
0102030405060
Years before death
ΔR 23 years
Fig. 3. Plot shows the resultant mean marine water reservoir age for all
Norwegian whales when postulating that C was fixed in the collagen the
year of death (collection) and 10–50 yr earlier, respectively. Note that in
this paper we have postulated C-fixing 10 and 20 yr before collection for
small and large whales, respectively.
J. Mangerud et al. / Quaternary Science Reviews 25 (2006) 3228–32453232
(Table S1). However, because our whale samples werecollected during the long atmospheric 14C-plateau1820–1880 (Fig. 2), an error in this assumption will causevery small differences in reservoir ages and DR values. Asseen from Fig. 3 the mean DR for whales from Norwaywould be only 23 yr less with a postulated C-fixing 50 yrbefore death compared with uptake the year of death. Thedifference is even less with the time of C-fixing we haveused.
3.2. Mollusc shells
For molluscs the carbonate shells (calcite or aragonite)are almost exclusively used for dating. The molluscs buildtheir shells with C from two sources; dissolved inorganiccarbon (mainly bicarbonate) in the sea water and metaboliccarbon. The processes involved in the carbonate precipita-tion are not fully understood, but food is digested andsubsequently CO2 for shell formation produced byrespiration, whereas water apparently also have otherpathways to the carbonate precipitation centres (McCon-naughey, 1989; Klein et al., 1996; Hickson et al., 1999). In athorough review Wheeler (1992) maintains that the ratio
between the two sources probably depends on the speciesand the physiological state of any given organism. From adating point of view it is useful to distinguish between C
ARTICLE IN PRESSJ. Mangerud et al. / Quaternary Science Reviews 25 (2006) 3228–3245 3233
from particulate food and water, respectively, although weare not always able to identify the source. Most of the foodparticles will stem from the marine food chain starting withphytoplankton assimilating C from sea water and thus thisfood will also have the marine water reservoir age.
Mangerud (1972) and Mangerud and Gulliksen (1975)concluded that the shell carbonate is almost in isotopicequilibrium with sea water bicarbonate, and because thesepapers have been the standard references for datingmolluscs in this part of the world, other scientists havealso often ignored the possibility of other C sources.However, it is clear that some of the carbon for the shell istaken from the food or from sediment pore water whichboth may have a different C source than sea water. Tanakaet al. (1986) concluded that Balanus sp., Littorina littorea,and also filter feeding bivalves such as Mytilus edulis andMya arenaria, from the New Haven Harbour on the Eastcoast of US had taken up to 60% of the C in their shellsfrom food consisting of remnants of terrestrial plants,sewage particles, etc. that had a sea water reservoir age ofzero. However, McConnaughey et al. (1997) maintain thatTanaka et al. (1986) used an erroneous formula so theamount should be reduced to maximum 25%. Otherstudies also report that the contribution from metabolicallyderived C varied from 5–20% in various bivalve species(Klein et al., 1996; Hickson et al., 1999; Lorrain et al.,2004). More seriously for dating, Arthur Dyke (GeologicalSociety of America Annual Meeting, 2002) reported thatthe deposit feeder Portlandia arctica yielded up to 2500-yr-older 14C ages than the filter feeder Mya. truncata from thesame bed (England et al., 2003). They found that highapparent ages for P. arctica are common in areas withcarbonate bedrock. The explanation may be that Portlan-
dia digested particles with ‘‘old’’ C. However, probably atleast some (possibly most) of the ‘‘old’’ C was taken fromambient sediment-pore-water that was 14C-depleted bysolution of carbonate rock fragments. Also recent shells ofP. arctica yielded higher reservoir ages than filter feeders(Forman and Polyak, 1997). In almost enclosed Danishinlets (called fjords, but concerning water circulationtotally different from Norwegian fjords) filter feedingbivalves obtained reservoir ages up to 500 yr more thanfound in open-ocean-sea-water outside the inlets (Heier-Nielsen et al., 1995). They concluded that ground waterfrom carbonate rocks brought dissolved ‘‘old’’ C into thesea water, and the effect is then the same as often called‘‘hard water effect’’ in lakes. When we below report lowerreservoir ages in shallow coastal water in southernNorway, the effect might be the opposite, viz. that runoffhere has negligible reservoir ages.
The apparent 14C age of particulate food may be calledthe food reservoir age, and it may be both older andyounger than the marine water reservoir age. Two aspectshave to be considered in this connection: First, the foodselection strategy and digestion processes of the differentspecies, and second, which C sources other than sea waterare available at the locality where the animal lived.
For both problems the relative amount of C from differentsources is decisive. In surface waters where the marinephytoplankton production is high, other C sources will bediluted. In deep water, and other places with lowproduction, alternative sources will have a much largerinfluence.Balanids and most bivalves are filter feeders, i.e. they
consume particles suspended in the water (Ruppert et al.,2004). This is favourable when considering shells for datingbecause these species filter and digest particles, normallyphytoplankton, suspended in sea water. However, organicdetritus on the sea bottom, to a large extent also remnantsof marine organisms having a normal marine reservoir age,may be re-suspended and thus be ingested by the filteringbivalves. The bivalves are able to sort out and reject theheavier mineral particles, although this sorting mechanismis not 100% effective (Ruppert et al., 2004). Because theyfilter sea water, C taken directly from water should alsoreflect the sea water. All molluscs we have dated in thisstudy are filter feeding bivalves, except two gastropods.The two gastropods (Buccinum and Neptunea) are both
carnivores. Among gastropods are found all kinds offeeding types; carnivores, herbivores, browsers, depositfeeders, filter feeders and parasites (Ruppert et al., 2004).Again, as long as they feed on recently produced marinefood, none of them should cause any problems for 14Cdating. However, in low production areas, or where much‘‘old’’ food is exposed, they may yield ages that are too old.Those consuming seaweed exposed at low tides or organicparticles of terrestrial origin will obtain too low reservoirages compared with sea water at the site.Some species of bivalves which occur in Norwegian-
Svalbard waters, although not used in the present study,should be avoided for dating. Most important are membersof the group Protobranchia, including, e.g. the generaPortlandia, Yoldia, Yoldiella, Nucula, Nuculana and Pseu-
domalletia. These sub-surface deposit feeders eat and digestwhat they find of organic matter buried in the sediment.They do have a rejection system for mineral particlesalthough less efficient than the other bivalves (Ruppertet al., 2004). Possibly even more important is that theambient water is the sediment-pore-water which often hashigh reservoir ages. It is also possible that these (and other)bivalves somehow consume carbonate particles and use thecarbonate for shell building. In the group Tellenoideamany species, in Norwegian waters represented by, e.g.Macoma, Tellina, Abra, Scrobicularia and Gari, are surfacedeposit feeders (Ruppert et al., 2004). The probability ofgetting old carbon is of course less for these than for thesub-surface deposit feeders, but again these species shouldbe avoided whenever possible, although the ambient wateris ‘‘normal’’ sea water.The main concern for ‘‘contamination’’ of food is old C.
Organic C with ages from decades to some few thousandyears will be accessible on or near the surface in areas withlow sedimentation rates and active bioturbation. Evenmore serious is ‘‘non-finite old’’ 14C which will stem from
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-160
-120
-80
-40
0
40
-40
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40
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1840 1850 1860 1870 1880 1890
R
Nor
way
, all,
non
-wei
ghte
d
N-N
orw
ay, a
llS
-Nor
way
, all
S-N
orw
ay, e
xcep
t 565
, 870
, 869
S-N
orw
ay,
565,
870
, 869
S-N
orw
ay, 5
65, 8
70, 8
69N
orw
ay b
efor
e 18
80N
orw
ay, b
alee
nN
orw
ay, t
ooth
edN
orw
ay, a
ll, v
s yr
col
lect
ion
Means relative toyear of C-fixing
Nor
way
, all,
wei
ghte
d
Year of C-fixing
869
870
565
Fig. 4. Marine water DR values (relative to Marine04) calculated for all14C dates of whales from Norway. Left panel shows the individual values
plotted with the year of C-fixing as horizontal axis. Right panel shows
mean values for different populations. To the extreme right is also plotted
the mean value for all whales relative to the year of collection, i.e. what in
this paper is called the ‘‘whale DR’’ value. On the left panel the three
samples of the least oceanic species, Balaenoptera acutorostrata, are
marked with sample no, and their mean given in the right panel.
J. Mangerud et al. / Quaternary Science Reviews 25 (2006) 3228–32453234
exposed bedrock or sediments, or oil and gas seepage.Some molluscs in the families Thyasiridae (e.g. Thyasira
sarsi and T. flexuosa) and Lucinidae (in Norwegian watersrepresented by Lucinoma and Myrtea) obtain some of its Cfrom symbiotic (or other) bacteria potentially utilizing oilor gas, including methane (Le Pennec et al., 1995;McConnaughey et al. 1997; Dando et al., 2004), and thuswill give too old ages. Along most of the inshore coast ofNorway there are only gneisses and other rocks almostdevoid of C, so most places old C is not a major problem(See ‘‘Old C available’’ in Table S2). This is different on thecontinental shelf and on Svalbard where sedimentary rocksare exposed. Thus, e.g. dates on the sub-surface depositfeeder Nuculana pernula from Bellsund, Svalbard yieldedages 12.8 ka (T-6000) and 12.6 ka (Ua-280) in an areawhere the oldest shore line is dated to about 11 ka(Mangerud et al., 1992). Mangerud et al. accepted thesedates, but here we consider that the Nuculana datesprobably are about 1600 yr too old due to carbonate andcoal in the sediment.
Carbon with higher 14C activity than sea water is mainlyderived from C dissolved in fresh water and remnants ofland plants brought out by rivers, although sea weedexposed at low tides also partly assimilate C directly fromthe atmosphere (Tanaka et al., 1986). This is especiallyrelevant in closed bays or near river mouths. If the seawater reservoir age is 400 yr and we use the extremeexample cited above, that 25% stems from recent terrestrialplants, then the reservoir age of the shell would be 300 yr.
Molluscs build their shells during their entire life and C isfixed during the shell building process, meaning that theumbo will have slightly higher reservoir ages than the shellmargins. A larger volume of the younger than the olderparts of the shell was removed before dating. Most of ourdated molluscs have a maximum life span of 5–20 yr. Theexception is Arctica islandica for which a 374-yr-oldindividual is reported (Schone et al., 2005). Indeed theage for the inner (to a large extent umbo) part of Arctica
from Iosen (T-954A and B, Table S2), is older than theouter part, but not significantly different even at the 67%level. When calculating marine water reservoir ages and DR
values, we have postulated that the C was fixed 5 yr beforecollection for all our shells. Because the ages in IntCal04represent 5 yr means, this should in theory represent fixingof C in the period 2.5–7.5 yr before the mollusc wascollected. We also present what we call ‘‘mollusc reservoirage,’’ where we have used the year of collection to estimatethe parameters.
4. Discussion
The following discussion and conclusions (Sections 4and 5) present the interpretation of Mangerud. Alternativeinterpretations by Bondevik and Gulliksen are given inSection 6 as an contribution added after the manuscriptwas accepted for printing. Sections 4 and 5 are notmodified after Bondevik and Gulliksen wrote their
contribution, but I will note that I have calculated thatthe w2/(n-1) values for DR are 0.34 for the group ‘‘Atlanticwater molluscs’’ and 0.93 for the group ‘‘Whales fromNorway except outlier and Atlantic water molluscs’’ inTable 2.
4.1. Trends in the whale results
In Fig. 4 we have presented the ‘‘marine water DR’’ valuesfor all whales from Norway and mean values for selectedgroups. The pattern would not be much different if we hadpresented ‘‘marine water reservoir ages’’ (Table S1 andTable 2). We have omitted the two whales from Iceland andFrance because we do not know if they ever were inNorwegian waters. They are almost the youngest and oldest,respectively, and would not influence mean values much.There is a slightly lower mean DR for N-Norway
compared with S-Norway, but due to the low number ofsamples, the value for N-Norway is strongly influenced bythe abnormal low reservoir age of sample T-13245. If weomit this value the DR of N-Norway is higher than forS-Norway. There is no apparent difference between baleenand toothed whales. The mean DR for whales caughtbefore 1880 is also close to the mean for all whales.Apparently Balaenoptera acutorostrata is the least oceanicof the whales (Table 1), and indeed the mean for the threesamples of this species is lower than for the total or for anyother sub-population (Fig. 4, samples 565, 869, 870), butoverlap well within one standard deviation.In view of the low number of samples and the small
differences between the sub-groups, we will treat all whales
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98Whales Molluscs
95
90
80
70
605040
30
20
10
200 300 400 200 300 400 500
5
2
%
Marine water reservoir age vs. British oak
98
95
90
80
70
605040
30
20
10
5
2
%
Fig. 5. Marine water reservoir ages (relative to British oak) for all whales caught in Norway and all molluscs from Norway–Spitsbergen, plotted on a
normal probability paper (where a Gaussian distribution will be a straight line). The cumulative frequency is plotted as (i�0.5)100/n. The three youngest
molluscs are the shallow water samples (Fig. 7) and the two oldest are from Spitsbergen. Both populations show a nearly Gaussian distribution, but the
whales have a narrower age range.
-15055° 60° 65° 70° 75° 80°
-100
-50
0
50
100
150
200
250
Latitude N
ΔR
Old C in bedrock near the collection siteNo old C, shallow waterNo old C, deeper water
Fig. 6. Marine water DR for all molluscs (except Arctic Canada) plotted
on an S–N-profile. Black sign is used for molluscs living in areas where
‘‘old’’ C potentially is available—apparently that does not influence the
reservoir ages for these filter feeders. For the others these from shallow
water (less than about 50m) are shown in green and from deeper water in
red.
J. Mangerud et al. / Quaternary Science Reviews 25 (2006) 3228–3245 3235
from Norway as one group. The differences represent therandom dating uncertainties, but also real differences dueto natural geographical and temporal (period of samplecollection) variability of the reservoir age, and theassumption of C-fixing 10 and 20 yr before death. Thedistribution is almost Gaussian (Fig. 5), except thatT-13245 stands out as an outlier. In the further discussionand in the conclusions, we use the means when the outlier isexcluded.
4.2. Trends in the mollusc results
The two carnivorous gastropods (Buccinum and Neptu-
nea, Table S2) have ‘‘normal’’ DR and reservoir agescompared with the other molluscs, indicating that theyhave fed on recent marine food. They are thereforeincluded in the following calculations. In Table S2 wehave indicated locations where carbonate rocks or otherold C can be expected at the site where the molluscs werecollected. Fig. 6 shows that, except for Pseudamussium
from Brevikfjord (no. 3 from left in Fig. 6, DR ¼ 129), theyhave not higher DR than molluscs from areas without oldC. The reason is probably that the dated molluscs are filterfeeders and therefore did not digest any, or at least notmuch, C from the sediments. Neither is the mentioned datefor Pseudamussium significantly different from the otherseven on a one standard deviation criterion. This does notprove that none of the shells were influenced by old C, butwe have not omitted any shell from the calculations on thiscriterion.
For molluscs from the coast of S-Norway there is adistinct trend with lower DR values and reservoir ages withshallower water (Fig. 7), although the number of analysed
shells is small. This trend is most likely the result of‘‘young’’ atmospheric and terrestrial-organic carbonbrought out with run-off from land.Another trend is increasing DR and reservoir ages from
south to north along the Norwegian coast (Figs. 6 and 8).This was explained by Mangerud (1972) and Mangerudand Gulliksen (1975) as a result of the increasing admixingof Atlantic water into the coastal current. However, theincrease in DR is not very marked when the shallow watersamples discussed above and the Spitsbergen samples areremoved. This is further discussed in the section on watermasses below.
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0
50
100
150
200
250
300
350
150 200 250 300 350 400 450 500 550 600
Reservoir age (yrs) vs British oak
Dep
th (
m)
Fig. 7. Marine water reservoir ages for molluscs from the coast of
S-Norway, calculated relative to British oak and plotted versus depth. The
value for the inner fraction for Arctica from Iosen (T-954B) is plotted with
an X at 15m instead of 10, in order to distinguish it from the others. The
outer fraction (plotted at 10m and age 284760 yr) should be more
relevant here. The diagram shows lower values at shallow depth.
Marine water reservoir age vs British oak
250 300 350 400 450 years
,,,,
,,,,
Fig. 8. Mean marine water reservoir ages calculated as unweighted
population means for groups of whales and molluscs relative to
radiocarbon ages of British oak tree-rings. Note the mean (marked with
a dot) of molluscs and whales from the Atlantic water.
J. Mangerud et al. / Quaternary Science Reviews 25 (2006) 3228–32453236
4.3. Comparison between whale and mollusc dates
As neither the whale 14C-ages nor the 14C-ages of theanalysed molluscs seem to have been significantly affectedby metabolic carbon with higher or lower content of 14Cthan the ambient water-masses, the discussion below islimited to the relationship of the animals to these watermasses. We have plotted the marine water reservoir agesaccording to increasing ages (Fig. 5), in order to facilitate acomparison of the age pattern of the two groups; all whaledates and all mollusc dates except those from ArcticCanada. The similar distribution is striking. This is even
stronger if we consider that the three youngest molluscdates are the three shallow water samples discussed above(Fig. 7) and that the two oldest mollusc dates are fromSpitsbergen. Therefore a main conclusion is that reservoirages of the molluscs and whales mainly reflect the samewater masses, and that there is no reason to assume thatwhales generally have considerably lower reservoir ages asearlier thought by some scientists as mentioned in theintroduction. The similarity between the reservoir ages ofanimals with such different uptake of C also indicates thatthe ages accurately represent the real marine waterreservoir ages.
4.4. Accuracy of the reservoir ages relative to water masses
Dating uncertainties are given as standard deviations onthe individual dates. If these were the only uncertaintiesthen more precise values could be calculated as weightedmeans and standard deviations (Geyh and Schleicher,1990). However, we consider that there are uncertainties inthe order of some decades also in the accuracy of the datesrelative to the identified water masses due to: thepostulated time of C fixing before collection, influence ofother C-sources on mollusc shells, which water masses thesamples really reflect, short-term fluctuations of reservoirages at a given site and, not at least, which tree ring agesare most relevant for comparison. For groups in Table 2this latter factor alone causes differences of up to 48 yr forreservoir ages calculated relative to IntCal04 or Britishoak, respectively. This has lead us to apply a simplestatistical treatment and thus to calculate only populationmeans and standard deviations for most sub-populations,and the weighted means only for some groups (Table 2).Given these uncertainties, in the following we suggest thata simple approach is best and recommend using one marinewater reservoir age for larger areas within an oceaniccirculation system rather than accept detailed regionalcorrections (e.g. along the coast of Norway) that in thelong run may not stand further tests—with the risk that wepropose an oversimplification.
4.5. Relation between the reservoir ages and water masses
The surface water relevant for this study, i. e. the upper200–300m of water, is completely dominated by the NorthAtlantic current water with an original salinity slightlyabove 35% which flows into the Norwegian Sea betweenScotland and Iceland (Fig. 9) (Orvik and Niiler, 2002;Blindheim and Østerhus, 2005; Drange et al., 2005). Alongits way north in the Norwegian Sea the water becomescooler and thus denser and descends below the less salinepolar ocean water West of Spitsbergen and in the BarentsSea. Another part of the current turns into the GreenlandSea where the water sinks and forms deeper water massesor it returns with the East Greenland current. The totalinflux of Atlantic water to the Norwegian Sea is estimatedto 7.7 Sv but the flux varies from year to year (Blindheim
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Fig. 9. Simplified picture of the surface circulation in the North Atlantic Ocean and the Nordic seas.
Atantic waterCurrent towards N
Continental Shelf
Fjord
Inflow ofAtlanticwater
RIVERSNorwegian
Coastal Current (towards N)
Fig. 10. Schematic cross-section of the water masses and circulation on
the Norwegian continental shelf and in the fjords.
J. Mangerud et al. / Quaternary Science Reviews 25 (2006) 3228–3245 3237
and Østerhus, 2005). The North Atlantic current is mainlya continuation of the Gulf Stream, but it entrains somewater of other origin and therefore potentially different 14Creservoir ages along its way. The C-exchange rate with theatmosphere also varies, due to, e.g. change in storminess,temperature and efficiency of the biological pump,although this is an area of net uptake of C from theatmosphere (Skjelvan et al., 2005). Thus one should expectsome fluctuations of unknown magnitude in the reservoirage on time scales from hours to the 60-yr-collection-period of our samples. However, the water flow is so fastthat any decay of 14C during transport can be neglected; Awater mass would use less than a year from the entrance tothe Norwegian Sea until it descends in the North.
Brackish water with salinities 10–20% flows out of theBaltic Sea, mixes with more saline water masses of Atlanticcurrent origin and continues northwards as the Norwegiancoastal current (Fig. 9) (Blindheim, 1987). This water forms
a wedge on top of the Atlantic water (Fig. 10), varying inthickness and width during the year. Outside Bergen themean annual salinity in the coastal current 1936–1989 was32.270.9%, with the lowest salinity of 29.071.9%
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occurring in July and August (Aure and Strand, 2001). Atthe northern tip of Norway the corresponding values are34.270.2% and 33.870.3%. The increasing salinity andreduced annual fluctuations northwards are due toincreasing in-mixing of Atlantic water. Mangerud (1972)and Mangerud and Gulliksen (1975) concluded that thereservoir ages increase from South to North along thecoastal current, and explained this by the increasingamount of Atlantic water. However, as stated above, thistrend is no longer so clear in the present data set (Fig. 8),and if we consider the marine water reservoir age relative toIntCal04 it disappears if we compare ‘‘deep waterS-Norway+North Sea’’ (432741 yr) with ‘‘N-Norwayand Barents Sea’’ (437714) (Table 2). Also, the hypothesisimplies that the Atlantic water has a higher reservoir agethan coastal water in N-Norway, which is not supported bythe present data. Our present interpretation concerningreservoir ages is that the Norwegian current water (at leastNorth of Bergen) can be considered as consisting ofAtlantic water with a small addition of fresh water fromrunoff. The reservoir ages of filter-feeding molluscs in seawater strongly influenced by Baltic water (Reimer andReimer, 2005) or coastal runoff (as ‘‘Molluscs, S-Norway,shallow water’’ in Fig. 8) are only some few decades lowerthan the Atlantic water reservoir ages. Therefore the smallfresh water content in the coastal current has no significantimpact on the reservoir age of the water.
We emphasize that the heavier Atlantic water descendsbelow the coastal current and fills the deep parts of theNorwegian fjords. Although the fjords are up to 1300mdeep, the deep water in the fjords is the same as the surfaceAtlantic water outside the coast (Fig. 10). In the openfjords discussed here, the deep water is renewed so oftenthat also the reservoir age is identical to that of the Atlanticwater. The inflow is counterbalanced by a less salinesurface current due to run-off from land. In the upper fewmetres of the fjord the salinity will therefore fluctuatestrongly through the year with a freshening gradient towardsriver mouths. The largest run-off is during snowmelt inSpring and early Summer, the same period as major algaeblooming and thus C-uptake takes place. We consider thatthe lower reservoir ages in the shallowest water (Fig. 7) iscaused by the higher 14C-activity in the run-off. This alsomeans that we should expect a variability of several decades,possibly centuries in extreme brackish situations, but wehave too few samples to answer this question.
The whales are obvious candidates for characterizing thereservoir ages of surface waters because they only consumepelagic food. Most whales in our collection commonlytravelled South to the North and equatorial Atlantic Ocean(Table 1), the latter with slightly lower reservoir ages(Reimer and Reimer, 2005). Some may also have been inthe slightly ‘‘older’’ water in the Greenland Sea, so thewhales almost certainly have a reservoir age influenced bydifferent water masses and therefore a larger range in agethan should be expected for a more stationary population.However, as mentioned above, we are not able to track the
routes of each whale and therefore neither to map regionaldifferences that might be reflected in their reservoir ages.Nevertheless, the distribution of their reservoir ages isalmost Gaussian. We therefore consider that the whalesdominantly have grown up and lived in the open Northand equatorial Atlantic Ocean and the Norwegian Sea andthus that the mean reservoir ages for the whales arerepresentative for these waters. We consider that the bestnumbers are the means when the outlier (T-13245) is leftout; i.e. the marine water reservoir ages of 369730 and353735 relative to IntCal04 and British oak, respectively,and a DR value relative to Marine04 of 5732 (Table 2). Ifthese whales truly had represented one age population,then the weighted means with their standard deviationswould have been a better measure, i.e. the means wouldhardly change but the standard deviations would be only6–8 yr (Table 2).According to the description of the oceanic circulation
above, the water in the North Atlantic which flows into theNorwegian Sea should have almost the same reservoir ageuntil it descends below the polar water. We have selectedthe mollusc samples that should be best related to thiswater, and then included the samples from the North Sea(T-957 and -1533), deeper water samples from S-Norway(T-952, -953, -959), all samples from the coast ofN-Norway (T-958, -1534, -1535, -1536) and the samplefrom the Barents Sea (T-1537). The main uncertainty inwhich samples to include were two samples from south-western Norway, T-954A and B, and T-956. These wereexcluded because they appeared as ‘‘young surface water’’in Fig. 7, but they were collected on the outer islands, in thegeographical domain of the coastal current. If these threesamples were included, the means for ‘‘Atlantic water’’would be about 20 yr younger than given in Table 2, i.e.even closer to the whale values.If both whales and molluscs incorporated carbon from
the same Atlantic water one should expect them to haveidentical marine water reservoir ages. However, the meanreservoir age relative to British oak for the 10 ‘‘Atlanticwater molluscs’’ is almost 50 yr higher than for the 19 ‘‘allwhales from Norway, except outlier’’, and even morerelative to IntCal04 (Table 2). We consider that thesimplest explanation is that the whales obtained someyoung C from the ocean farther South, but it could also bedue to influence of old C on the molluscs, wrongassumptions on time of C-fixing, or some combination ofthese factors. We will also point out that more molluscthan whale samples stem from the period with the largestdifference between British oak and IntCal04 tree ring dates(Fig. 2).We conclude from the discussion of oceanic circulation
and our dating results that it at present is most reasonableto use one single marine water reservoir age for the entireNorth Atlantic current and its extension North to theBarents Sea, including also the parts of the Norwegiancoastal current dominated by the Atlantic water, althoughthere are differences between sub-populations. We also
J. Mangerud et al. / Quaternary Science Reviews 25 (2006) 3228–3245 3239
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consider that the most accurate numbers will be obtainedby a mean somehow combining the whale and molluscdates. A baseline is that this mean does not change muchwhether we calculate the one way or the other, or includeor exclude some groups of samples (Fig. 8). In Table 2 wepresent means for 29 samples including all Norwegianwhales except the outlier (19) and the Atlantic watermolluscs (10). However, again we consider that theweighted standard deviations (6 and 7 yr) are too small toreflect the natural variability. In the last line of Table 2 wetherefore propose some rounded off values using theweighted means but standard deviations close to popula-tion standard deviations.
The reservoir ages are lower in the fresher, uppermostsurface water along the inner coast and in the fjords(Fig. 7). Here one should expect a gradient in reservoir agetowards river mouths, and regional differences dependingon salinity, source of water, etc. However, even in thefjords fully marine water dominate at a depth of some fewtens of metres, so the error may not be too large using theAtlantic water numbers and just consider that it will beslightly too large. The pattern has to be much bettermapped in order to obtain more accurate reservoir ages forthe surface water in the fjords.
The East Spitsbergen current consists of cold surfacewater flowing out of the Arctic Ocean (Fig. 9). It turnsaround the southern tip of Svalbard and flows northwardsalong the west coast where our samples were collected(Fig. 1). However, the Atlantic water is found below thispolar water and enters the fjords at some depth. We cannotdecide if our samples were collected from one or the other,or a mixture of these water masses. The mean reservoir agefor the Spitsbergen samples is higher than those from theAtlantic water (Fig. 8) which Mangerud and Gulliksen(1975) explained by the influence of the polar water in theEast Spitsbergen current. This conclusion is still supportedby the means obtained now (Fig. 8, Table 2), but thedifferences are not significant even on a one sigma level.For marine water reservoir ages the differences between‘‘Atlantic water’’ and Svalbard are 15761 and 35762relative to IntCal04 and British oak, respectively (Table 2).In order to understand and determine reservoir ages in thismixing zone between polar and Atlantic waters more datesare necessary to clearly characterize each of the watermasses; especially for the East Spitsbergen current. Forexample Forman and Polyak (1997) obtained smallreservoir ages, less than 300 yr, for two molluscs fromFranz Josef land, east of Svalbard and certainly within thearea of this polar water. Therefore we recommend applyingthe Atlantic water corrections in the region of Svalbarduntil better dates are obtained. We will also mention theprominent occurrence of rocks containing old carbonaround Svalbard raising the possibility that (some of) oursamples are contaminated.
The two dates from Arctic Canada represents older polarwater there, but is here only presented because of the re-calculation, and they are not further discussed.
5. Conclusions and recommendations
�
With the recent developments in 14C dating, includingcalibration to calendar years and revision of marinereservoir ages, it becomes increasingly important thatscientists specify original dates, and how they havecorrected them. � Carbon is fixed in our bone collagen when humans are
about 20 yr old and we assume a similar situation forother mammals, including whales. We therefore distin-guish between the ‘‘marine water reservoir age’’ and the‘‘whale reservoir age’’.
� The marine water reservoir age for an ocean area should
be obtained by comparing the marine dates withterrestrial dates from the adjacent-down-wind continentin order to reflect the natural processes. In publisheddata sets there is a difference of up to 60 yr around 1900AD between tree ring dates from British oak and theages given by IntCal04; the latter being stronglyinfluenced by NW-American trees. We therefore givereservoir ages relative to both scales, and consider thatfrom a process point of view those related to British oakare best, whereas IntCal04 is based on far more data.
� We consider that the 19 whales caught in Norway (i.e.
omitting those from Iceland and France and one outlier)provide the reservoir age for the North (and equatorial?)Atlantic Ocean and the western Norwegian Sea. Thepopulation means are 369730 and 353735 yr, relativeto IntCal04 and British oak, respectively, andDR ¼ 5732 relative to Marine04. These values shouldbe relevant for open ocean organisms such as planktonicforaminifers, but below we propose slightly differentvalues based on combination with molluscs fromAtlantic water.
� We identified ten molluscs that had lived in Atlantic
water along the coast of Norway. Mean marine waterreservoir ages are 435731 and 399735 yr relative toIntCal04 and British oak, respectively.
� We recommend using the same reservoir age and DR
value for the entire part of the North Atlantic currentthat flows into the Norwegian Sea, all the way from theNorth Atlantic to the Barents Sea and including theparts of the Norwegian coastal current dominated byAtlantic water and even the coasts of Svalbard. Basedon this study we recommend marine water reservoir ageswhich are the means of the mentioned 29 whale andmollusc dates; i.e. 380730 and 360730 yr obtained bycomparing with tree ring dates in IntCal04 and onBritish oak, respectively. Alternatively we recommend aDR value of 20730 yr relative to Marine04.
� Shallow water samples from S-Norway, probably
influenced by fresh water gives lower reservoir ages.The amount of correction should be evaluated indivi-dually. The simplest would be to use the Atlantic watercorrections given above, and accept that it is a too largecorrection.
ARTICLE IN PRESSJ. Mangerud et al. / Quaternary Science Reviews 25 (2006) 3228–3245 3241
6. Alternative discussion and recommendations by Bondevik
and Gulliksen
We disagree with Mangerud’s discussion and recom-mendations given above that one single reservoir ageshould be used all the way from the North Atlantic to theBarents Sea (Fig. 1) and from the coast to the open ocean.We clearly find that our dataset of DR values and reservoirages, R(t) (Tables S1 and S2) show different populationsthat statistically cannot be combined into one singleestimate. Here we explain how we have treated the datasetstatistically, discuss trends in the dataset, and finally giverecommendations based on this analysis.
6.1. Reservoir age dynamics
DR values should be used to make inferences about thedifferent water masses instead of reservoir ages,R(t ¼ time), which varies over time. The marine reservoirage, as defined earlier (Section 2.3), is the differencebetween the 14C age of marine water and the 14C age of theatmosphere at a given time. It varies constantly because therapid fluctuations in atmospheric 14C content are smoothedout in the large marine carbon reservoir (Fig. 2). If sampleswith different collection dates are measured, the variabilityof reservoir ages will also contain variations induced byfluctuations in the difference between the atmospheric andmarine 14C content. Consequently, reservoir ages cannotunveil regional differences p100 yr unless the carbon in thesamples is contemporaneous (Stuiver et al., 1998). Thisproblem was discussed in Stuiver et al. (1986), and to solveit they introduced DR as the regional offset from a globalmean reservoir age, R(t). Consequently, to estimateregional differences from samples containing non-contem-poraneous carbon only DR values should be considered.
6.2. Statistical methods
We have used the well-known w2 test to check if theinternal variability in a group of DR values (and reservoirages) is consistent with the standard measurement errorson the individual measurements (cf Ward and Wilson,1978; Ascough et al., 2005). The deviation of a singlemeasurement (Ri) from the pooled (weighted) mean (Rp)should on average be close to the measurement error (Ei).w2 is the sum of squared ratios between deviations anderrors, given as
Xn
1
Ri � Rp
� �2=E2
i ,
and should therefore be close to the number of measure-ments (n), or more precisely the degrees of freedom, (n�1).Thus, if the quantity w2=ðn� 1Þ is p1 it means thatmeasurement uncertainties explain the variance, whilevalues 41 indicates that the group has additional variance.We have used this normalized w2 to investigate the
consistency of the results for the different groups ofsamples.All of the different groups of shells (except Arctic
Canada) and the two whale groups have w2/(n�1) valueso1 for DR values, indicating that the measurementuncertainties explain the variance within the group. Wehave thus combined the measurements and calculatedpooled (weighted) means of DR for each group (Table 3)based on the measurement uncertainties. On the otherhand, reservoir ages R(t), which are temporal averages overthe carbon fixation period of the samples within a group,show larger w2/(n�1) values indicating larger variability(Table 3).The w2/(n�1) values calculated for the reservoir ages,
R(t), of the whales and two of the mollusc groups(Spitsbergen and Arctic Canada) are larger than 1 (Table 3).This is a strong indication that there is additional varianceto the measurement errors of the reservoir age estimates.We have estimated the measurement standard deviation bymultiplying the pooled error by
ffiffiffiffinp
; which is the acceptedratio between population standard deviation and thestandard error of the population mean. The additional orexternal variance is then obtained by subtracting themeasurement variance from the total population variance(see explanations in Table 3). In this way we found theexternal standard deviation for the whales to be 18–24 yr.The whales were caught between 1860 and 1901, whichcorresponds to 1845–1881 for the year of carbon fixing(Section 2.4). The differences between atmospheric (Britishoak) and marine 14C ages (Marine04 model) vary ca 30 yrduring this period (Fig. 2). It is plausible that most of theexternal variation in the reservoir ages is caused by thisvariation in R(t). This test shows that using reservoir ageestimates from samples collected over some decades toestimate regional differences should be avoided.If the Marine04 model (Stuiver et al., 1986; Hughen
et al., 2004) is correct, the temporal variations will becancelled out when the DR data from a specific region areanalysed. As shown in the last two columns in Table 3 thisis exactly the case, i.e. for the shells on Spitsbergennormalized w2 for DR is 0.61 and for the combined whaledata set (both toothed and baleen species) the normalizedw2 for DR is E1. For the baleen whales there is a slightindication of excess variance in DR, and a closer examina-tion of the combined data set reveals that a very small, butprobably not significant, excess variance might be indi-cated. The uncertainty of the recommended DR mean valueis increased correspondingly (Table 3).
6.3. Implications for different regions
Both toothed- (n ¼ 10) and baleen whales (n ¼ 10) showsimilar DR values (7711, 7728; Table 3). This indicatesthat the different food sources do not influence thereservoir ages. There is also no relationship between DR
values and the location of where these animals were caught(Table S1). The whales are clearly younger than all the
J. Mangerud et al. / Quaternary Science Reviews 25 (2006) 3228–32453242
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-40
Spitsbergen (4)
N.Norway + B.Sea (5)
S.Norway, deep (5)
S.Norway, shallow (6)
All whales (20)
S.Norway, all (11)
-20 20 40 60 80 100 120 1400
ΔR Molluscs
ΔR Whales
Δ R
Fig. 11. Bondevik and Gulliksens contribution: pooled (weighted) DR
values for different populations show a clear trend with increasing values
towards North. Whales are younger than most of the different groups of
molluscs. No. of samples within each group are in parentheses.
J. Mangerud et al. / Quaternary Science Reviews 25 (2006) 3228–3245 3243
different mollusc groups except for those from shallowwater in southern Norway (Table 3; Fig. 11).
The molluscs belong to five different populations;shallow water (p100m) southern Norway (n ¼ 6); deeperwater southern Norway (n ¼ 5); northern Norway andBarents Sea (n ¼ 5); Spitsbergen (n ¼ 4) and ArcticCanada (n ¼ 3). All of these different groups, except ArcticCanada, have w2/(n�1) valueso1 for the DR values.Shallow water molluscs in southern Norway (�3722)have the lowest DR value, being lower than the deepermolluscs from the same area (46726). DR values ofshallow water molluscs from northern Norway (71721)are significantly larger than the shallow water molluscsfrom southern Norway (�3722) and smaller than DR
values from Spitsbergen (105724) (Fig. 11).The DR values clearly increase northwards along the
Norwegian coast (Fig. 11). Mangerud and Gulliksen (1975)explained this with more mixing of Atlantic water into the‘‘younger’’ coastal current. However, we now see that thewhales, representing North Atlantic open ocean water, areyounger than most of the molluscs collected along theNorwegian coast. One reason for this could be that thecoastal water contains small amounts of ‘‘old’’ carbon andthat this amount increases northwards along the coast.Another factor could be that open ocean water has a higherair-sea exchange rate of carbon due to storms and higherwind speed. According to modelling, a 20% increase inwind speed over the North Atlantic could reduce reservoirages with about 50 years (Bard et al., 1994).
For all shell samples, except Arctic Canada, the normal-ized w2 values indicate that the actual groups of samplesrepresent homogeneous water masses. When differencesbetween group means are evaluated the standard error ofthe mean should be considered—and not the much largerstandard deviation of the group population. We are ofcourse aware of the low number of samples, but feel thatthe latitudinal dependence of DR is clearly demonstratedand also that the whales, that represent open ocean
Norwegian Sea/Atlantic water, are younger than mostgroups of molluscs along the coast.
6.4. Conclusion and recommendations
�
Reservoir ages, R(t), are time dependant and varies overdecades. Normalized w2-tests show that some of ourgroups of R(t), collected over a time span of 60 yr, haveexternal variance in addition to measurement errors.These external variances cancel out for the same groupswhen we analyze DR values. Thus, for samples collectedover some decades, only DR values should be used toestimate variance between different water masses. � A group of 20 whales caught mainly along the
Norwegian coast have a DR value of 7711. This valuerepresents the surface water in the Norwegian Sea andNorth Atlantic and could be used to correct 14C ages ofplanktonic foraminifera and also other 14C ages oforganisms that lived in the open Norwegian Sea/NorthAtlantic.
� DR values measured on stationary molluscs along the
Norwegian coast are latitude dependant and increasenorthwards (Fig. 11). 14C ages of shells from the coast ofsouthern Norway that from deposits/species lived inshallow water (o 100m, i.e. from practically allQuaternary marine deposits onshore) should be cor-rected using a DR value of �3722 yr. Shells/benthicforaminifera that lived in deeper water (4100m) insouthern Norway should be corrected for a DR value of46726 yr; samples from Northern Norway with a DR
value of 71721 and Svalbard with a value of 105724.
� The recommendations above are given for ocean
circulation and exchange of 14C between atmosphereand surface ocean similar to today’s situation. Forsamples spanning the Holocene these recommendationsare probably fine. However, a recent study showsrelatively large variation in reservoir ages through lateglacial times at the coast of southern Norway (Bondeviket al., 2006).
Acknowledgements
We sincerely thank Jane Ellingsen who finalized theillustrations, Ulysses S. Ninneman who critically read themanuscript and corrected the English language, PaulaReimer and Rob Witbaard who critically read the manu-script and suggested improvements, and the journalreviewers Steve Forman and especially Mebus Geyh whoproposed several improvements—all before Section 6 wasadded. The work was funded by the Research Council ofNorway. It is a contribution to the ‘‘Icehus’’ project.Author contributions: Mangerud proposed this research,
he wrote the first draft for all sections except Section 6 anddid the calculations for Tables S1 and S2 and Table 2. He isalone responsible for some sections and co-responsible forthe others, except Section 6. Bondevik co-designed the
ARTICLE IN PRESSJ. Mangerud et al. / Quaternary Science Reviews 25 (2006) 3228–32453244
sampling strategy for the whales, collected these samplesand is co-responsible for Sections 1 and 2. Gulliksenperformed the C-14 dates and is co-responsible forSections 1 and 2. Bondevik and Gulliksen are aloneresponsible for Section 6. Høisæter is co-responsible forSection 3.2. Bondevik, Gulliksen and Høisæter also readother sections and proposed editorial improvements. Hufth-ammer co-designed the sampling strategy for the whales,produced Table 1 and is co-responsible for Section 3.1.
Appendix A. Supplementary data
Supplementary data associated with this article can befound in the online version at doi:10.1016/j.quascirev.2006.03.010.
