Late Weichselian Marine 14C Reservoir Ages at the Western Coast of Norway

Late Weichselian Marine 14C Reservoir Ages

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Quaternary Research52, 104–114 (1999)Article ID qres.1999.2048, available online at http://www.idealibrary.com on

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at the Western Coast of Norway

Stein Bondevik

Department of Geology, University of Bergen, Alle´gaten 41, N-5007 Bergen, Norway

Hilary H. Birks

Botanical Institute, University of Bergen, Alle´gaten 41, N-5007 Bergen, Norway

Steinar Gulliksen

Radiological Dating Laboratory, NTNU, Sem Sælandsvei 5, N-7034 Trondheim, Norway

and

Jan Mangerud

Department of Geology, University of Bergen, Alle´gaten 41, N-5007, Bergen, Norway

Received October 28, 1998

fois

consin) and Holocene deposits. A precise correlation betweenc trial,a andf afli-d herd

tion( ics s in ar gesi edt 975).F id-Yo d inle enc 00 yrd

al forc striale orthA theSa timef aireds al inc thew

A shallow marine Late Weichselian deposit on the outer coast ofestern Norway contains both terrestrial plant material and articu-

ated marine shells. We have 14C dated both types of material fromight different stratigraphic levels covering the time interval 12,300 to1,100 14C yr B.P. The difference between 14C-dated terrestrial plantaterial and marine shell material (the marine reservoir age) ranges

rom 200 to 525 yr, with a weighted average of 380 6 32 yr. This islmost identical to the present reservoir age of 379 6 20 yr forouthern Norway. In the mid-Younger Dryas (YD) interval the res-rvoir age in the North Atlantic (55°N–65°N) was 700–800 yr,onsiderably greater than the present reservoir age and the age weave measured for the Bølling–Allerød interval. The reason for this

ncrease during the YD is probably a combination of reduced inflowf surface waters to the North Atlantic and more extensive sea-iceover. Evidence from marine cores show that the southeastern Nor-egian Sea experienced rapid fluctuations in the inflow of warmtlantic surface water during the period 12,300 to 11,000 yr B.P.owever, the reservoir age apparently did not increase during these

older periods (Older Dryas I and II). The reason is probably that, inontrast to the YD, these colder periods did not last long enoughnd/or were of too limited extent to alter the reservoir age of thecean. A comparison of the obtained 14C dates with the varve 14Chronology from Lake Suigetsu indicates an age of 12,770 cal yr B.P.or the AL/YD boundary. © 1999 University of Washington.

Key Words: Late Weichselian; shallow marine deposit; 14Ceservoir age; western Norway.

INTRODUCTION

Radiocarbon dating is now the most important toolstablishing precise time frames for Late Weichselian (W

033-5894/99 $30.00opyright © 1999 by the University of Washington.ll rights of reproduction in any form reserved.

104

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limate records or other events identified in marine, terresnd ice-core successions is a priority objective for ongoing

uture research (e.g., Lowe and NASP Members, 1995; Hason et al., 1995). Such correlations rely mainly on tadiocarbon method and require a correction of marine14Cates due to the reservoir age of the ocean.The reservoir age is closely related to ocean circula

Stuiver et al., 1983). Today the inflow of warm Atlanturface water to the North Sea and Norwegian Sea resulteservoir age of ca. 400–500 yr in the North Atlantic. Chann inflow of Atlantic water through time may have influenche reservoir age in this area (Mangerud and Gulliksen, 1oraminifera and shell fragments within the Vedde Ash (mounger Dryas) in North Atlantic cores are 700–80014C yrlder than terrestrial plant material within the same Ash be

akes (KocKarpuz and Jansen, 1992; Bardet al.,1994; Austint al., 1995; Haflidasonet al., 1995). Therefore, it has beoncluded that the reservoir age was greater by 300–4uring the Younger Dryas.Ash beds are synchronous time markers and are ide

omparing14C ages for contemporaneous marine and terrenvironments. However, in the Norwegian Sea and Ntlantic only the Vedde Ash bed (ca. 10,300 yr B.P.) andaksunarvatn Ash bed (ca. 9000 yr B.P.) (Birkset al., 1996)re available for this purpose during the Late Weichselian

rame. To overcome these limitations, we have dated pamples of marine molluscs and terrestrial plant materiores from a shallow marine deposit at Kulturmyra atesternmost coast of Norway (Fig. 1).

001 apifl tota iss d ti rvoa rvaw anc

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sea coresm

LATE WEICHSELIAN MARINE 14C RESERVOIR AGES 105

The Kulturmyra sequence includes the time interval 12,31,100 yr B.P. (14,500–12,800 cal yr B.P.), a period with ructuations of the inflow of warm Atlantic surface watershe Norwegian Sea (Lehman and Keigwin, 1992; Koc¸ Karpuznd Jansen, 1992; Haflidasonet al.,1995). The purpose of thtudy was to measure the marine reservoir age directly anf these rapid fluctuations had any influence on the resege of the Norwegian Sea. Our main result is that the resege for the Bølling–Allerød interval was 3806 32 yr on theestern coast of Norway, close to the present value,onsiderably less than the Younger Dryas reservoir age.

SETTING

The studied site, Kulturmyra, is a 7- to 9-m-deep bocated on the strandflat at the outermost coast of weorway (Figs. 1 and 2). Today the surface of the basin is at 2.5 m altitude. Between 13,000 and 11,000 yr B.P.,eglaciation, the threshold of the basin was 2–5 m below

evel (Svendsen and Mangerud, 1990). At that time Kulturm

FIG. 1. Map of the Norwegian Sea region showing the present surfaentioned in the text (HM 79-6/4; Koc¸ Karpuz and Jansen, 1992; and Tr

–d

estir

oir

d

nrng

ereaa

as a shallow marine basin located ca. 300 m from the she proximity to the shore enabled terrestrial plant matTPM) derived from the surroundings to be deposited inarine sediments, together with articulated shells on the

oor. The dated plant fragments are mostly leaves andtems very unlikely to have been reworked before depositihe basin. We assume that the TPM has approximatelame real ages as the molluscs.Today Atlantic Water and Norwegian Coastal Water do

ate along the Norwegian coast. Atlantic Water entersorwegian Sea in the Faeroe–Shetland area (Fig. 1); it

emperature of about 9°C and a salinity above 35‰.orwegian Coastal Water, with salinities below 35‰, iixture of Atlantic water, brackish water from the Baltic Snd runoff from the Norwegian mainland. The Coastal Wixes with deeper Atlantic Water in such a way that

alinity along the Norwegian coast increases northwardud, a permanent hydrographic station ca. 100 km north otudied site, summer temperatures in water,50 m deep ar

circulation, the location of Kulturmyra, and the location of the two deep.1; Lehman and Keigwin, 1992).

ceoll 3

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BONDEVIK ET AL.106

1–12°C, and winter temperatures are 5–6°C. The salinetween 33.0 and 33.5‰ year around (Aure and Øste993).

METHODS

A piston corer provided 2-m-long core sections witiameter of 11 cm. To make certain we obtained enoaterial for dating, three parallel cores were collected

han 1 m apart. The cores were X-ray radiographedxamination of sedimentary structures and as an a

ocate articulated shells. The cores were easily correlateatching sedimentary structures and the Vedde Ashample intervals ranged from 1 to 6 cm and consistedolume of 100 to more than 500 cm3 of sediment, consumng three halves of the cores. This material was sieved am after soaking in water overnight. The componentPM were selected under a stereo-microscope and ided. Only material of undoubted terrestrial origin wicked for radiocarbon dating. The fragments were cleaf silt and other contamination and air-dried. All TPamples were more than 12 mg dry weight before bubmitted for preparation in the Trondheim radiocaraboratory (Table 1). From the marine material (MM) orticulated shells were used for dating. In the lower pa

FIG. 2. Kulturmyra is located on Bergsøya at the outer Norwegianacustrine deposits and supports bog vegetation. Kulturmyra was a shallfter deglaciation now lies at ca. 20 m altitude on Bergsøya.

isn,

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25fti-

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he core a cod bone (Gadus morhua) was found and dateTable 1, Fig. 3).

Both TPM and MM samples were prepared and targetsroduced at the Radiological Dating Laboratory in Trondhehe 14C content was measured by accelerator mass spectry (AMS) analysis at the T. Svedberg Laboratory, Uppniversity, Sweden (TUa numbers, Table 1). The outer

ions (.23%) of the shell samples were dissolved. All14C agesre reported as conventional radiocarbon ages (Stuiveolach, 1977).The total organic carbon content was determined with a

2 LECO carbon analyzer. Magnetic susceptibility was mured with a Bartington MS2 instrument using a 12-iameter ring sensor.d18O and d13C were measured withinnigan MAT 251 mass spectrometer.

RESULTS

The Late Weichselian deposits are found in the lower pahe stratigraphy of the basin. They are part of a shallowpward sequence from glacialmarine, through shallow mand into lacustrine sediments.The studied sequence can be divided into four units (Fig

he lower, from 797 to 880 cm, is a gray silty clay with saaminae having a very low total organic carbon (TOC) con

st close to the open Norwegian Sea. Today the basin is filled in with mmarine basin ca. 12,700–10,000 yr B.P. The shoreline of 12,700 yr B.Pmed just

coaow

( np teM ana t1 oir

a f thea

owns ofs d in

TABLE 1

T

T

T

T

T

T

T

T

T

T

T

T

T

T

T

T

TT


Fig. 3). These sediments are interpreted as having beeosited during and immediately after deglaciation. Articulaacoma calcareaat the transition between the laminated snd the overlying silty clay at 828–829 cm was dated3,1656 55 yr B.P. (TUa-1902, not corrected for reserv

Radiocarbon Ages of Terrestrial Plant Material and

Laboratorynumber

Depth(cm)

Sed. vol.(cm3) Material dated

Ua-1896 593–597 150 TPM: Leaves ofSalix herbacea, S. polaris, DryaSalix budscale and capsule. Seeds ofD. octopeCarex trigonous,Carex nigratype,Comarum pTerrestrial mosses (Racomitrium, PolytrichumsDrepanocladus uncinatus, Fissidens cristatupalustre, A. turgidum, Distichium capillaceum

Ua-1891 593–597 MM:Litorina littorea

Ua-1897 609–611 100 TPM: Leaves ofSalix herbacea, S. polaris, Dryaviviparum. Salixtwig, bud, budscale, capsuleCochlearia,Gramineae,Carex lenticular,SileneTerrestrial mosses (Racomitrium, Polytrichum,Fissidens osmundoides, Aulacomnium turgid)

Ua-1892 608–610 MM: ArticulatedMytilus edulis

Ua-1898 620–623 351 TPM: Leaves ofSalix herbacea, S. polaris, Dryaviviparum, Saxifraga oppositifolia, Salixvegetaof Dryas, Cochlearia,Gramineae,Saxifraga opJuncus.Terrestrial mosses (Racomitrium, PolyPohlia, Dicranum).


Ua-1885 635–639 435 TPM: Leaves ofSalix herbacea, Dryas, Salixbud,viviparumbulbil, seeds ofSaxifraga cespitosaintermedia, S. saginoidestype,Juncus,GramineTerrestrial mosses (Racomitrium, Polytrichum,Drepanocladus uncinatus, Dicranum, AulacoRhytidiadelphus squarrosus, Tortulacf. norveg


Ua-1899 659–661 200 TPM: Leaves ofSalix herbacea, S. polaris, Dryaviviparum, Salixtwig, budscales, Seeds ofDryaCarex trigonous. Terrestrial mosses (RacomitriuBryum, Drepanocladus uncinatus, Dicranum).


Ua-1887 672–675 335 TPM: Leaves ofSalix herbacea, Dryas, PolygonSalix bud, budscale, capsule, Seeds ofDryas,GCarex trigonous,Sagina intermedia.Terrestrial(Racomitrium, Polytrichum, Bryum, Dicranum).


Ua-1900 683–688 475 TPM: Leaves ofSalix herbacea, S. polaris, Dryaviviparum. Salixfemale flower. Seeds ofDryasCochlearia.Terrestrial mosses (Racomitrium, PBryum, Pohlia, Fissidens).


Ua-1889 720–726 580 TPM: Leaves ofSalix polaris, Dryas, Salixbud, bOxyria fruit. Terrestrial mosses (Racomitrium,juniperinum, Polytrichumsp.,Bryum, AulacomTortula cf. norvegica).


Ua-1901 738 Jawbone from Cod (Gadus morhua L.)Ua-1902 828–829 MM: ArticulatedMacoma calcarea

* Assumed value, not measured.

de-ddo

ge, Table 1) and gives a minimum age for delgaciation orea.The next unit, between 735 and 797 cm, is an olive-br

ilty gyttja with higher TOC values and many fine laminaeeaweed. Only a few terrestrial plant fragments were foun

rine Material from Core 505-04-01/02, Kulturmyra

Dry weight(mg)

Sample size(mg C)

14C age(yr B.P.)

Reservoir ageMM–TPM

d13C(‰ PDB)

ctopetala,, Cochlearia,stre.Bryum,ulacomnium

18.0 1.4 11,1256 65 224.5

1.9 11,4456 55 3206 85 1.3

olygonumeds ofaulis.um,

35.5 2.1 11,0656 60 226.5

2.0 11,5656 45 5006 75 1.9

olygonumparts, seedsitifolia,um, Bryum,

14.2 1.4 11,6006 90 225.8

2.1 11,8256 55 2256 105 20.4

ygonumginaarex.

um,ium turgidum,

13.0 1.6 11,6156 70 226.5

1.8 12,0156 60 4006 92 0.8

olygonumramineae,Polytrichum,

13.7 1.5 11,9056 85 223.5

3.1 12,1056 60 2006 104 0.7

viviparum.ineae,sses

12.8 1.7 11,8106 70 226.0

0.9 12,3356 65 5256 96 2.6

olygonummineae,

trichum,

19.7 2.6 11,8706 60 223.9

2.1 12,2506 50 3806 78 1.2

cales,trichum

turgidum,

6.5 1.2 12,3156 95 227.8

2.2 12,6856 55 3706 110 1.58

2.3 13,1106 125 15.0*0.5 13,1656 55 0.2

Mean and standard deviation 3656 116Weighted mean 3806 32

Ma

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s, P. Se

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trich

Pol, Saae,CBrymn

ica).

s, Ps,Gm,

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s, P,Graoly

udsPolynium

t a-w thn sef sizuoc 5%g dM edm thp

ytt

w rtic-u yc org ed tot ughf l thea s thes w not

580c f silt.I

laf

BONDEVIK ET AL.108

his part, insufficient for reliable14C measurements. The seeed (mostlyFucus serratusand an unidentified type wiarrow tubular dichotomously branching thalli) was not u

or radiocarbon dating. Littoral marine algae photosynthesing a mixture of the contemporaneous atmospheric CO2 andlder CO2 from the seawater (Raven, 1994).F. serratusgainsarbon from air during emersion, probably similar to the 2ained by its higher-shore relativeF. spiralis (Madsen anaberly, 1990). Therefore it would likely yield a reducarine reservoir effect and would not be suitable forresent study.Between 580 and 735 cm the deposit is an olive-gray g

FIG. 3. Stratigraphic log, total organic content, magnetic susceptibilitrom core 505-04-01/02. *behind14C date is uncorrected age of the marin

de

e

ja

ith silt and fine sand containing abundant broken and alated shells. Most shells areMytilus edulisthat are commonloncentrated in zones.Mytilus is normally attached to hardravelly surfaces (Yonge, 1976) and was probably wash

he basin floor during storms. Terrestrial plant material, enoor 14C dating, was found within these sediments. In generamount of TPM and sand increased upward (Table 1) aite approached the shore due to isostatic uplift. We sarace fossils or evidence of bioturbation.

The upper unit, defined by sharp boundaries at 542 andm, is coarse sand and fine gravel supported in a matrix on the middle, the Vedde Ash (Mangerudet al.,1984) forms a

nd radiocarbon dates of both terrestrial plant fragments and marine articuted shellshells.

y, ae s

distinct 2-cm-thick bed. The lower boundary was interpreted tob ld.A mi ent posi thi 95

res ef but tht nM ew htea

toL M( ent 80f iths tchi ageo them1 en1f ,0a inew itt lieb ala ref ao mn agf r.

R

d tM ths n ot ad ThT fram s tl oulh gb asw olTo nr ort

to the basin floor from the rocky sides of the basin. Onlya havea enceb e isc rangew

V

le 1),a 00 yrB hicht mon-tD andh eN obli-gna tad,V hera at oft un-t mert n ofr entm eanJ ) fort 5 kmn

theY asa cticdT asa tot ast ofG

soc pidi d ice-r sea( 2;H ca.1 (ODI TheS Nor-w

uth-w aus,1 notr ationa andB atec f Kul-t the


e the Allerød/Younger Dryas (AL/YD) boundary in the fie14C date of 11,1256 65 yr B.P. (TUa-1896, Table 1) fro

mmediately below the lower contact confirms that it represhe AL/YD boundary. The coarse sediment likely was deted by local sea ice, which transported material fromntensely frost-weathered YD shore (Blikra and Longva, 19

The eight pairs of14C dates for the TPM and the MM ahown relative to depth in Figure 3. The MM14C dates arrom 200 to 525 yr older than the TPM dates (Table 1),here is no obvious correlation of age as a function of dephe studied sequence. The mean of the difference betweeM and TPM dates is 3656 116 yr. If the differences areighed according to their standard deviations, a weigverage of 3806 32 yr is obtained.The radiocarbon ages were matched (Pearson, 1986)

ake Suigetsu14C chronology built from AMS dates of TPKitagawa and van der Plicht, 1998) by varying the sedimation rate and and using the weighted reservoir age of 3or the marine dates (Fig. 4). The best fit was obtained wedimentation rate of 0.105 cm/year. According to this mang, the AL/YD boundary at 580 cm in Kulturmyra has anf 12,770 cal yr B.P. In contrast, the AL/YD boundary inarine varved deposits in the Cariaco basin (Hughenet al.,998), shown by gray-scale measurements, occur betwe3,050 and 12,900 cal yr B.P. When matching the14C dates

rom the Cariaco basin with the Suigetsu data between 15nd 12,000 cal yr B.P., we found that the best fit is obtahen 128 yr is subtracted from the Cariaco time scale. W

his adjustment, the AL/YD boundary in the Cariaco basinetween 12,770 and 12,940 cal yr B.P., very close to the cge boundary we found for Kulturmyra. In the GRIP ice co

rom the Greenland ice sheet, the AL/YD boundary has anf 12,705 ice-core yr B.P (J. P. Steffensen, personal comication). However, the establishment of a precise cal yr

or the AL/YD boundary is beyond the scope of this pape

DISCUSSION

eal Age Difference between Samples in a Pair

Our study depends on the assumption that the TPM anM had no age difference when deposited together in

hallow marine basin. The TPM derives from the vegetatiohe hillside surrounding the basin and was transportedeposited in the basin, together with the marine shells.PM consists of tiny leaves, seeds, and delicate mossents that are very unlikely to have been in transit acros

and surface for a long time before deposition. If so, they wave been decomposed and destroyed before reachinasin. We assume that the TPM, when deposited in the bas probably formed that year and was no more than 2 yrhe dated MM consists of seven samples ofMytilus edulisandne sample ofLittorina littorea. Both species normally live oocky surfaces, and so the shells were most likely transp

ts-

e).

tinthe

d

the

-yra-

ca.

00dhsyrsgeu-e

heen

ndeg-hedthein,d.

ed

rticulated shells were dated, and they probably did notny significant age when deposited. The real age differetween the TPM and the MM within the same samplonsidered to be less than 30–50 yr, the possible ageithin a 3- to 5-cm-thick sample (Table 1).

egetation and Climate

The plant assemblages, based on the macrofossils (Tabre similar through the sequence between 12,300 and 11,1.P. (14,500–12,770 cal yr B.P.). The vegetation from w

hey originated was treeless and dominated by arctic andane taxa. The prostrate shrubsSalix herbacea, S. polaris,andryas octopetalawere associated with sedges, grasses,erbs such asPolygonum viviparumthat are common in thorwegian mountains today. Among the mosses are theate montane taxaAulacomnium turgidumand Tortula cf.orvegica. A. turgidumandSalix herbaceanow occur as lows 430 m altitude on the coastal mountains of Møre (Sågsøy, ca. 25 km south of Kulturmyra), but at much higltitudes inland. The Kulturmyra assemblage resembles th

he low- and mid-alpine vegetation in the Norwegian moains today. This correlates with a cool climate and sumemperatures of 5–7.5°C (see Birks (1994) for a discussioegional Allerød climate in western Norway). The presean July temperature at Kulturmyra is ca. 13°C, and the m

anuary temperature is ca. 2.5°C (values from Aune (1993he nearest climate stations at Ålesund and Vigra, ca. 2orth of Kulturmyra).Mytilus edulis is present throughout the core below

D/AL boundary. The presence ofM. edulishas been usedn indicator of warmer-than-present conditions in the Aruring the Holocene climatic optimum (Hjortet al., 1995).odayM. edulis is not found in higher Arctic waters, suchround Svalbard (Hjortet al., 1995), but it penetrates far in

he southeastern Barents Sea and along the western coreenland (Peacock, 1989).Two colder periods, Older Dryas I and II (OD II is al

alled the inter-Allerød cold period), are evident from a rancrease in polar fauna, sea-ice diatom assemblage, anafted debris in cores from the southeastern NorwegianLehman and Keigwin, 1992; Koc¸ Karpuz and Jansen, 199aflidasonet al., 1995). The events have been dated to2,300–12,000 yr B.P. (OD I) and 11,800–11,500 yr B.P.

I) (the ages were corrected for a reservoir age of 440 yr).candinavian ice sheet advanced during OD I along theegian coast (Mangerud, 1970, 1977).Indications of two colder periods in pollen records in soestern Norway are inferred to represent OD I and II (P988). However, macrofossil studies in that area haveevealed any small oscillatory changes in the local vegett that time (Birks, 1993, and unpublished data; van Dinterirks, 1996, and unpublished data). Similarly, no climhanges were detected at Kråkenes to the southwest ourmyra for this time, either in the local vegetation or in

a dv hab nsT tha set maa het seb to ts w-a tiof semb thi thet hel ged onap rvas d.

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arec -m d att andK fam gure5 lciticl e pre-p

da ,1

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BONDEVIK ET AL.110

quatic ecosystem (Birkset al.,in press). However, the Allerøegetation along the western Norwegian coast may noteen sensitive to small, brief (ca. 200 yr) climatic oscillatiohe vegetation was well developed and was analogous tobove the tree line in Norway today. Betula trees were ab

heir nearest occurrences being in southern Sweden, Dennd the British Isles (van Dinter and Birks, 1996). Ot

hermophilous plant taxa were also absent. Allerød aslages of aquatic animals and diatoms at Kråkenes Lakeouth of Kulturmyra consisted of taxa typical of cool, lolpine climates, and quantitative temperature reconstruc

rom pollen, chironomid, cladocera, and coleoptera aslages from the Allerød at Kråkenes are all consistent with

nterpretation (Birkset al., in press). This suggests thaterrestrial vegetation was in equilibrium with the climate. Tack of evidence at Kulturmyra for local vegetation chanuring the studied time period is consistent with this regiicture. The samples are widely spaced at ca. 150-yr inteo short fluctuations (;200 yr) may not have been sample

o the Marine Samples Represent Open Ocean Conditio

Today the difference in salinity between the coastal waround Kulturmyra and the open Norwegian Sea is a–2‰. Mytilus edulis tolerates an extremely wide salin

FIG. 4. Radiocarbon ages with 1s error from Kulturmyra core 505-04-0998). A reservoir age of 380 yr was subtracted from the marine ages.etween AL/YD is at 580 cm and shows a calendar age of 12,770 yr B

ve.at

nt,rk,

rm-he

ns-

is

slls,

?

rsut

ange, from 4 to 5‰ to above 35‰ (inner Baltic to fuarine conditions). (Bayneet al.,1976). To check if the wate

rom the area where the shells precipitated the carbonatenfluenced by any fresh water, and for that reason doeecord thetrue 14C reservoir age of the ocean, we perform18O measurements on the shells. Isotopic ratios of oxygenarbon can be related to salinity because of the diffesotopic composition of ocean and fresh water. A linear rionship has been demonstrated betweend18O in M. edulisandalinity in the seawater where the shells calcified (Ingramet al.,996; Mook, 1971).Thed18O values obtained from the shells in Kulturmyra

ompared in Figure 5 withd18O values from planktonic forainifera in the Norwegian Sea and North Sea that calcifie

he same time (Koc¸ Karpuz and Jansen, 1992; Lehmaneigwin, 1992). The mussel shell (M. edulis) is composed on outer calcitic layer and an inner aragonitic layer. Thed18Oeasurements of the shells from Kulturmyra shown in Fiare from the inner aragonitic layer, because the outer ca

ayer had already been dissolved when the samples werared for the14C measurements.Aragonite is enriched ind18O relative to calcite precipitate

t the same temperature (Tarutaniet al., 1969; Grossman984). The average difference betweend18O from Mytilus and

2 curve-matched to the Lake Suigetsu chronology (Kitagawa and van dt fit was obtained with a constant sedimentation rate of 0.105 cm/yr. Ty

1/0Bes.P.

f ou2 em -t set

as 1).B avd ordva er LaW . Td eas relat hat urs edt rap

during spring and summer and slow or absent during the colderw frac-t thef d bea day.T withv nedr

inr thei n thes s int havei

V

thed ne-o era pen-d rates)ra At-l tingm 900.Ws t thei oms thec ivingh ta e be-t ownh ver,d t thec ange8 aver e fors 0)e sti se-q e dif-f strials egianc oft

thei ea.H dis-t in,1 ftedd yrB ryas( ns.

i win1 terNe ocf tot hellc orwg out2 r tht inpuo .


oraminifera from the Norwegian Sea (HM 79-6/4) is ab.25‰ d18O (Fig. 5). Because thed18O measurements of thussels are from aragonite and thed18O values of the plank

onic foraminifera are from calcite, the real difference is cloo 3‰ d18O (Tarutaniet al., 1969).

The present salinity (S)–d18O relationship for the North Sehows a S:d18O ratio of 1:;0.3 (Israelson and Buchardt, 199ecause of cold climate and retreating glaciers in Scandinuring the AL/BØ, fresh water must have been much mepleted ind18O than today. A change to more negatived18Oalues in fresh water would increase the S:d18O ratio (Rohlingnd Bigg, 1998). A ratio of S:d18O 5 1:0.5–0.6 would be moreasonable for the North Sea/Norwegian Sea during the

eichselian (E. Jansen, personal communication, 1998)eviation of d18O from foraminifera in the Norwegian Suggests that the salinity at Kulturmyra, using the linearion S:d18O 5 1:0.6, would have been about 4–6‰ less that in the open ocean. However, surface temperatures dummers were probably higher in coastal waters comparhe open ocean, as they are today. Growth in shells is

FIG. 5. d18O isotopes fromM. edulisfrom Kulturmyra compared tod18Osotopes from planktonic foraminifera from Troll 3.1 (Lehman and Keig992) and HM 79-6/4 (Koc¸ Karpuz and Jansen, 1992) in the southeasorwegian Sea. (See Fig. 1 for location). Note that thed18O values onM.duliswere made on aragonite that is enriched ind18O relative to calcite. Tompare thed18O values from Kulturmyra with thed18O values from theoraminifera, thed18O curve from Kulturmyra should be shifted 0.5–0.9‰he left indicating a difference of about 3‰. Considering that the salcified under higher temperatures than the foraminifera in the open Nian Sea, the difference ind18O corresponds to a salinity difference of ab–3‰ between the two water masses. This difference is only 1–2‰ large

oday and shows that the shells calcified in marine water with very littlef fresh water. Radiocarbon ages are not corrected for a reservoir age

t

r

iae

tehe

-ningtoid

inter months (Seed, 1976). If we assume a 2°C higherionation temperature for the shells in Kulturmyra thanorams in the Norwegian Sea, the salinity difference woulbout 2–3‰, only 1–2‰ larger than the difference is tohis shows that the shells calcified in salty, marine waterery little input of any fresh water, indicating that the obtaieservoir age is representative of the open ocean.

The d18O andd13C values of the dated shells are shownelation to the reservoir ages (Fig. 6). There is no trend insotope ratios versus the reservoir ages. The variations itable isotopes of the shells, probably reflecting variationemperature and salinity of the waters, do not seem tonfluenced the reservoir ages.

ariation in Reservoir Age Present and 10,000–12,30014CYears B.P.

The most appropriate definition of a reservoir age isifference between14C ages of samples grown contemporausly in the atmosphere and in the actual reservoir (Stuivetl., 1986). The marine reservoir age is time and space deent due to reservoir parameters (size, carbon exchangeestricting its response to variations in the14C/12C ratio of thetmosphere. An estimate of reservoir ages for the North

antic was made by Mangerud and Gulliksen (1975) by dauseum samples of molluscs collected about AD 1eighted mean reservoir ages of 4306 20 and 4706 30 yr for

outhern and northern Norway, respectively, indicated thanfluence of fresh water (from the Baltic Sea and run-off frouthern Norway) on the Atlantic water decreased inoastal current northward along the Norwegian coast gigher reservoir ages. Reliable atmospheric14C data were novailable; thus, the estimate was based on the differenc

ween the radiocarbon age of the samples and their knistoric age before AD 1950, that is about 50 yr. Howeendrochronological calibration data have revealed thaorresponding terrestrial radiocarbon ages are in the r0–100 yr B.P. (Stuiver and Becker, 1993), and we hecalculated the present (i.e., ca. AD 1900) reservoir agouthern Norway as 3796 20 yr, close to Olsson’s (198stimate of 3706 25 yr. More important, it is also almo

dentical to the reservoir age found for the Kulturmyrauence, calculated as the weighted mean radiocarbon ag

erence between marine shells and contemporary terreamples. It shows that the reservoir ages along the Norwoast during Bølling–Allerød were quite similar to thoseoday (Fig. 7).

The last deglaciation was marked by rapid changes innflow of Atlantic surface waters into the Norwegian Sigh-resolution marine records show three periods with

inct increases of polar foraminifera (Lehman and Keigw992), diatoms (Koc¸ Karpuz and Jansen, 1992), and ice-raetritus (Haflidasonet al.,1995) between 12,500 and 10,000.P. The most prominent of these is the Younger D

11,000–10,000 yr B.P.) return to almost glacial conditio

,n

se-

ant

14C ages within or close to the Vedde Ash in marine succes-so lan(1V ab hil ashsc t thm tingt olda thii facw a-icc dW

altn urit hei senC an7 urvm Lak

S rvoira nce( heoJ1 f theo se oft

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ledc m1 evet ellm trenb onst r as

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BONDEVIK ET AL.112

ions in the North Atlantic are 700–800 yr older than14C agesf terrestrial plant material within the same ash bed onKoc Karpuz and Jansen, 1992; Bardet al.,1994; Austinet al.,995; Haflidasonet al., 1995). Determining a14C age for theedde Ash on the shelf and in the deep Sea is problemecause of bioturbation, depth of the dated molluscs w

iving, reworking of older sediments, and ice rafting ofhards (Austinet al., 1995). Nevertheless, Bardet al. (1994)oncluded, after a correction of the bioturbation bias, thaean14C age is still about 11,000–11,100 yr B.P., indica

hat the reservoir age of the sea surface was 300–400 yrt that time in the North Atlantic than today. The reason for

s probably a combination of reduced convection of suraters to the North Atlantic and an increase of the seover during the Younger Dryas (Bardet al.,1994; Stocker anright, 1996).Even though the southeastern Norwegian Sea was

ately influenced by cold and temperate water masses dhe period 12,000–11,000 yr B.P., the data presentedmply that the reservoir age was not higher than at preonsidering the limited number of paired samples (Figs. 3, Table 1), there is no obvious trend in the data set. By catching the dated sequence to the chronology from

FIG. 6. d13C and d18O values in relation to their reservoir ages. Filircles show values obtained from measurements on pure aragonite fro4C-dated shells. The open circles are from shells located at the same lhe core as the dated shells and are measurements from the entire shight thus be a mixture of both calcite and aragonite. There is noetween reservoir ages and isotope ratios indicating that small variati

emperature and salinity do not seem to have influenced the reservoiignificantly.

d

ticle

e

ersee

er-ngret.dee

uigetsu we obtained a good fit using the weighted resege of 380 yr for the marine14C ages throughout the sequeFig. 4). The rapid climate shifts of the OD I and OD II in tcean did not last more than 200–400 yr (Koc¸ Karpuz andansen, 1992; Lehman and Keigwin, 1992; Haflidasonet al.,995), possibly not long enough to alter the reservoir age ocean significantly, or these variations were missed becau

he sample density.Numerical models suggest that the cover of sea ice i

actor that contributes most to higher reservoir ages duhe YD (Stocker and Wright, 1996). The Norwegian coas partly ice-free during the late-glacial period. Theref

he reservoir ages we have found for the western Norweoast between 11,000 and 12,300 yr B.P., almost identicresent values, may not apply to areas farther west to

celand and Greenland where the ocean was more eively covered by sea ice during Late Weichselian time (t al., 1993). New radiocarbon ages of the Vedde Asharine cores outside Iceland confirm this picture, with

reasing ages toward the west (H. Haflidason, pers

thel inanddin

ges

FIG. 7. Reservoir ages from historic shells (Mangerud and Gullik975) from southern Norway, from the Vedde Ash Bed in the North AtlaBardet al.,1994, Austinet al.,1995, Haflidasonet al.,1995) and Kulturmyran the outermost coast of western Norway (this study). The weighted resge from Kulturmyra between 14,500 and 12,800 cal yr B.P. is 3806 32 yr,ery close to the present value of 3796 20 yrs. The reservoir age for tid-Younger Dryas Ash zone, the Vedde Ash Bed, is 700–800 yr.

communication, 1998). This might suggest that the mariner giac thN

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from eastern Svalbard and the Holocene marine climatic optimum.Polar

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eservoir ages for the Younger Dryas along the Norweoast are slightly lower than the 700 – 800 yr found fororwegian Sea–North Sea.

ACKNOWLEDGMENTS

Most of this paper was written during the spring and summer of 1hile the first author visited the Quaternary Research Center at theersity of Washington. He is most grateful to both staff and faculty auaternary Research Center. Dagfinn Bondevik helped with the corank Hague did the magnetic susceptibility measurements, Stig M

he TOC analysis, and Rune Søraas the13C/12C and18O/16O measurementystein Jansen helped with the interpretation of the oxygen isotopeohn Raven with information about seaweed photosynthesis. S.B. gppreciates financial support toward a PC from Hans and Helga Reuequest of 1997. The work is a contribution to the Strategic Univerogram at the University of Bergen, “Rapid Sedimentation andesolution Stratigraphy: Processes and Application,” funded by theearch Council of Norway. H.H.B. was supported during this work byorwegian Research Council.

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Late Weichselian Marine 14C Reservoir Ages at the Western Coast of Norway

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