The Last Glacial Maximum on Spitsbergen, Svalbard 2006 readings/Svalbard...lands of Svalbard (e.g., Spitsbergen and Nordaustlandet) (Forman, 1989). We do not include those glaciers

QUATERNARY RESEARCH 38, 1-31 (1992)

INTRODUCTION

When we started our investigations of the glacial history of Svalbard in 1981 we accepted the view that the Barents Ice Sheet had covered eastern Svalbard and parts of the Barents Sea (Fig. 1) during the late Weichselian. This view was mainly based on the classical argument of a major glacioisostatic updoming of the archipelago (Schytt et al., 1968), with the date for the 100-m shoreline on Kongsoya of 9800 yr B.P. (Salvigsen, 1981) being the final proof that this updoming was caused by the late Weichselian glaciation. This interpretation has been reinforced by growing evidence from the sea floor of the Barents Sea (El- verhoi and Solheim, 1983; Vorren et al., 1988; Elverhoi et al., 1990), and is now generally accepted, even though the area1 ex-

’ Present address: Agricultural University of Nor- way, Department of Soil Sciences, P.O. Box 28, N-1432 AS-NLH, Norway.

The Last Glacial Maximum on Spitsbergen, Svalbard

JAN MANGERUD, MAGNE BOLSTAD, ANNE ELGERSMA, DAG HELLIKSEN, JON Y. LANDVIK,’ IDA L#NNE,’ ANNE KATRINE LYCKE, OTTO SALVIGSEN,*

TOM SANDAHL, AND JOHN INGE SVENDSEN

University of Bergen, Department of Geology, Section B, Ail&t. 41, N-5007 Bergen, Norway; and *Norwegian Polar Research Institute, P.O. Box 158, N-1330 Oslo Lufthavn, Norway

Received April 4, 1991

Most scientists have concluded previously that the west coast of Spitsbergen, Svalbard, remained ice-free during the late Weichselian, between 25,000 and 10,000 yr B.P. We conclude that the glaciation was more extensive. Terraces that were postulated to have been ice-free are covered by a thin, late Weichselian till. Sudden drop in the marine limit and basal radiocarbon dates of raised glaciomarine sediments demonstrates that the glaciers in the main fjords, Isfjorden and Van Mijentjorden, terminated west (outside) of the fjord mouths. Basal radiocarbon dates from glaciomarine clay above till in cores from the continental shelf west of Spitsbergen yielded ages of about 12,500 yr B.P., from which we conclude that the ice extended to the shelfedge. Based on the extent of amino acid diagenesis in radiocarbon-dated molluscs, the duration of the maximum extension of the late Weichselian glaciation was short, certainly less than 10,000 years. During the ice-free period preceding that glaciation, at least back to 40,000 yr B.P., the glaciers on Svalbard were not significantly larger than at present, as shown by marine deposits close to the glacier snouts. Many radiocarbon dates place deglaciation of the outer coast at about 12,500 yr B.P. At about 10,000 yr B.P., the rest of the archipelago rapidly became ice-free. 0 1992 University of Washington.

tent and thickness of the Barents Ice Sheet is still debated.

Although there is a general consensus that a large ice sheet covered the northern and central Barents Sea during the late Weichselian, a major disagreement remains about the glacial limit on western Spitsber- gen. According to some reconstructions, the entire archipelago was covered by the Barents Ice Sheet (Grosswald, 1980; Den- ton and Hughes, 1981). However, all scientists who had done field work in the area before we started, and indeed later, concluded that the extreme west coast remained ice-free during the late Weichselian (Salvigsen, 1977, 1979; Salvigsen and Ny- dal, 1981; Salvigsen and efsterholm, 1982; Troitsky et al., 1979; Boulton, 1979, 1990; Boulton et al., 1982; Miller, 1982; Miller et al., 1989; Forman and Miller, 1984; For- man, 1989). Some scientists also concluded that the middle and inner parts of Isfjorden and Van Mijenfjorden were ice-free

I

0033-5894/92 $5.00 Copyright 0 1992 by the University of Washington. All rights of reproduction in any form reserved.

2 MANGERUD ET AL.

100 200 25’ 300

. NORDAUSTLANDET ( \

BARENTS0YA

_. ”

I

20” 25” 30

FIG. 1. Map of Svalbard, giving place names outside the area shown in Figure 2. We follow the offtcial Norwegian naming; Svalbard is the name of the entire archipelago, whereas Spitsbergen is the main island only. Numbers give radiocarbon dates that provide minimum ages for the last deglaciation. The dates are given in lo3 yr B.P., rounded off to the nearest hundred years. Original references for the dates are given in circles, and are listed below. For most of the dates, the authors concluded that the date indicates the age of deglaciation, or a minimum age less than 200 yr younger than the deglaciation. However, based on the results by Mangerud and Svendsen (1990b), that assumption may be too optimistic. References: (1) Salvigsen, 1981; (2) Biidel, 1968; (3) Nagy, 1984; (4) Boulton, 1990; (5) Jonsson, 1983; (6) Salvigsen, 1978; (7) Karl&t, 1987; (8) @sterholm, 1986; (9) Blake, 1987; (10) Blake, 1981; (11) Hoppe, 1987; (12) Salvigsen and @sterholm, 1982; (13) Stankowski et al., 1989; (14) Forman et al., 1987; (15) Lehman and Forman, 1991; (16) Forman, 1990. We have subtracted 140 years from whalebone dates cited from 14 and 16, see text. Ages without reference are from the present paper.

LAST GLACIATION OF SPITSBERGEN 3

(Lavrushin, 1967, 1969; Troitsky et al., 1979; Troitsky, 1981; Boulton, 1979).

The main aim of this paper is to contrib- ute to a resolution of the described contro- versy on the limit of the last glacier, and to provide an improved description and interpretation of the late Weichselian glaciation on western Svalbard. Our evidence is based on extensive field work along the two main fjords, Van Mijenfjorden and Isfjorden (Fig. 2). This provided new stratigraphic and other geologic data for the reevaluation of earlier observations and interpretations, as well as samples for an extensive dating program. In this paper we also compile earlier published results, especially the relevant radiocarbon dates.

When we started the field work we adopted the working hypothesis that the entire study area had been ice-free, unless the opposite could be proven. One objective, therefore, has been to construct minimum models of the last glaciation. Our earlier reports demonstrate how our model has changed during the work: we soon found that there had been a glacier that extended at least to the mouth of Van Mijenfjorden (Mangerud et al., 1984, 1985; Landvik et al., 1987). Moving northward, we found that also Linnedalen, at the mouth of Isfjor- den, had been glaciated, but in that article we kept open the possibility that Isfjorden remained ice-free (Mangerud et al., 1987). Thus, to determine the glacial limit, we had to study the sea floor sediments in the fjord and on the continental shelf. Our conclusion in this paper is that the entire Van Mi- jenfjorden-Isfjorden area (except some summits) was ice-covered, and that the western limit for the last glacial maximum was on the continental shelf (Svendsen et al., 1992).

We restrict the term the Barents Ice Sheet to an ice sheet that was centered in the Barents Sea, including Kong Karls Land (Fig. 1). We propose that the term also be used for such ice sheets during earlier glaciations. The Barents Ice Sheet may have flowed onto land in Eurasia (e.g.,

Grosswald, 1980), and probably inundated most of Svalbard at some times. During other periods there were ice domes and/or separate glaciers situated on the main is- lands of Svalbard (e.g., Spitsbergen and Nordaustlandet) (Forman, 1989). We do not include those glaciers in the Barents Ice Sheet, even though they might have been in physical contact with it. Such a conceptual distinction between the Barents Ice Sheet and glaciers on Svalbard is useful to understand the glacial history of this area.

In this paper we first present the observations from the Van Mijenforden area, then Linnedalen and the coast around Is- tjorden, and finally cores from the floor of Isfjorden and the continental shelf (Fig. 2).

METHODS

Field Work

This paper is based on stratigraphical investigations of raised marine sediments, partly interbedded with tills. We spent days and weeks in digging sloped material to obtain large sections that in addition to verti- cal also provided lateral stratigraphic rela- tionships. We also mapped glacial striae, shorelines, and moraines. More detailed descriptions of some of the sites are given in unpublished (but available) candidates scientific theses (Master thesis) at the Uni- versity of Bergen (Elgersma and Helliksen, 1986; Lonne, 1986; Sandahl, 1986; Bolstad, 1987; Lycke, 1987). Elevations were measured either with a Paulin barometer with l-m resolution, or leveled. Directions were measured with a 360” compass, corrected for magnetic deviation.

Radiocarbon Dates

All samples have been dated either at the Trondheim Laboratory for Radiological Dating or at The Swedberg Laboratory, Uppsala University. At the Trondheim Laboratory (prefix T-, on samples) dating is performed by proportional counting, using COz gas. We have submitted small samples to Uppsala (prefix Ua-), for accelerator

P


mass spectrometry (AMS) dating. For samples with prefix TUa- the target was pre- paired in Trondheim, and the AMS measurements performed in Uppsala.

All samples are reported as recom- mended by Stuiver and Polach (1977) including a correction for isotopic fractionation to -25 per mil 13C on the PDB scale. A reservoir age of 440 yr is subtracted for all samples that have obtained their carbon from sea water (shells, seaweed, whalebones, etc.). This is a standard value used by the Trondheim Laboratory for the coasts of Norway including Svalbard, and is based on measurements of many prein- dustrial shells from these waters (Mangerud and Gulliksen, 1975); 440 yr is also the mean reservoir age for the Svalbard area for the last 9000 yr according to Stuiver et al. (1986). Whales acquire their carbon from larger oceanic areas and, thus, theoretically they may have different reservoir ages compared to the stationary molluscs. However, the reservoir ages obtained around the North Atlantic are nearly every- where 400-500 yr (Stuiver et al., 1986). We therefore use the same reservoir age for whales and shells, in contrast to Forman et al. (1987), who use 300 yr for whales and 425 yr for shells.

Amino Acid Diagenesis

In this paper we use amino acid diagenesis for three purposes: (1) to ensure that radiocarbon samples of shell fragments consist of only one age population; (2) for a first-order age estimate of samples of “old” or non-finite radiocarbon age; and (3) for

modeling of diagenetic temperatures (especially ice-covered or not) for samples of postulated age.

All samples were analyzed at the Bergen laboratory (prefix BAL-). Full descriptions for some of the samples are given by Bol- stad (1987); methods follow Miller and Mangerud (1986). In this paper we report only the epimerization of isoleucine to allo- isoleucine for the total fraction, expressed as D/L ratios (by some labeled aIle/Ile). All reported D/L ratios are from the species Mya truncata or Hiatella arctica, which have similar epimerization rates (Miller, 1982).

For paleotemperature estimates (especially the 87-m terrace in Linnedalen and Kapp Ekholm) we have used a D/L ratio of 0.011 for living shells, and the Arrhenius parameters 28.1 kcal/mole for the activa- tion energy and 16.45 for the intercept (Miller, 1985). For radiocarbon-dated shells that lived, and were uplifted, soon after deglaciation (11,500 to 10,000 yr B.P.), we obtained a mean D/L value of 0.016 ? 0.003 for 42 analyses from different sites on the west coast of Spitsbergen. Solving the temperature equation for this D/L value (0.016) predicts an effective diagenetic temperature of - 3.7”C which is close to the current mean annual temperature at Istjord Radio, just W of Linnedalen ( - 4.7”C for 1951- 1975; Steffensen, 1982).

VAN MIJENFJORDEN-BELLSUND

Minimum Age of Deglaciation

Radiocarbon dates from the Bellsund-

FIN. 2. Map of the study area. Radiocarbon dates are given in IO3 yr B.P. The ages are rounded off slightly different compared to Figure 1. In this map the first digit in the assay is given unaltered, to make comparison with Tables l-6 easier. Thus, in this figure 9980 is cited as 9.9, whereas in Figure 1 it is cited as 10.0. Only the oldest dates from each site that provide meaningful minimum ages of deglaciation are cited. Dates in squares are from sediment subsequently overrun by ice. Location of cores from the sea floor are given by core number (03/04; 01/02; and 144). Shaded areas show present day glaciers. Contour interval is 200 m both on the sea floor and on land. All names ending -d. are shortenings for -dalen (which means valley in Norwegian). Other shortened names are: Blomesl., Blomesletta; Pet., Petuniabukta; Billefj., Billefjorden; Ekhohn, Kapp Ekholm; Bohem.fl., Bohe- mannflya; Erdm.fl., Erdtmanflya; M&en., Mbeneset (the site SE of the island of Akseloya); Rech.fj., Recherchetjorden.

6 MANGERUD ET AL.

TABLE 1. RADIOCARBON DATES~ FROM BELLSUND, VAN MIJENFJORDEN, AND AGARDHBUKTA (FIG. 2)

Laboratory No.

T-6000

Ua-280

T-5991

T-4865

T-5995 T-5273

T-571 1

T-4843

T-4842

T-5363

T-5362

T-5368

T-5369

Age (yr B.P.) Material Locality

12,830 2 210

12,570 2 160

11,230 k 120

11,020 * 110

10,840 -+ 110 10,230 ” 140

9580 k 110

9640 + 240

9600 ? 180

10,330 + 140

10,040 * 110

10,500 ?I 200

10,130 _’ 150

Shells

Shells

Shells

Shells

Shells Shells

Shells

Shells

Shells

Seaweed

Shells

Shells

Shells

Skilvika

Skilvika

Skilvika

Ytterdalen

Y tterdalen Mlseneset

Miseneset

Vassdalen

Vassdalen

Frysjadalen

Frysjadalen

Bromelldalen

Bromelldalen

Field sample No. and description

Svalbard-84-747. Paired Nuculana pernula in a laminated, extremely finegrained clay, just above a till.

Svalbard-84-225. Accelerator date of a similar sample as the conventional date T-6000 above.

Svalbard-84-426. Fragments of Hiatella arcrica from a diamicton, interpreted as slump-deposit, overlying the clay described under T-6000. Only fragments with D/L ratios between 0.015 and 0.017 were dated.

Mya truncata and Hiatella arctica related to terrace at 64 m altitude (Landvik et al., 1987).

As T-4865. Sa-83-49 Hiatella arctica and Mya truncata in

living position in the lower part of foresets in a terrace at 40 m altitude. Just east of the main gully cutting through the large terrace.

Hel-Elg 240-83. Shell fragments, mainly Balanus, in low angle topsets in terrace at 30 m altitude. Just west of main gully.

Hel-Elg 28-82. From sections along the seashore, south of the mouth of the river. Just above a basal till.

Hel-Elg 26-82. Mya truncata, and Hiatella arctica. Similar position to T-4843.

Hel-Elg 323-83. Section along western margin of present delta. Plant remains in silt, probably contorted by subsequent local ice advance. The sample had an estimated content of terrestrial plant remains of IO-30%; therefore, a reservoir age of only 350 yr was subtracted.

Hel-Elg 324-83. Macoma c&area in living position in undisturbed silt above the silt with T-5363.

Hel-Elg 266-83. Yoldiella lenticula, Portlandia arctica, Nucula tenuis, Macoma calcarea in living position in a SO-cm thick clayey silt. Above the silt is a diamicton, interpreted as a till deposited by a local Younger Dryas readvance down Bromelldalen. The section is situated 2.3 km from the sea, east side of the valley.

He)-Elg 243-83. Macoma calcarea, and Mya truncata in living positions at the base of a silt just above the Younger Dryas till described under T-5368.


TABLE I-Continued

Laboratory No. Age (yr B.P.) Material Locality Field sample No. and description

T-5713 10,650 2 170

T-5109 9980 2 140 Shells

T-5216 Tln- 146

9910 f 130 10,340 2 110

T-5710 9590 i 110

T-4844 9050 + 130

T-4937 9870 2 140

Plant remains

Wood Shells

Shells

Shells

Plant remains

Bromelldalen Hel-Elg 336-83. Same silt bed as T-5369, stratigraphically slightly higher. Small remnants of plants, mainly herbs and mosses, but also Picea and Betula nana, found in a lense. Compared to the shell dates, these long transported plant remains yield slightly to high age.

Bromelldalen Hel-Elg 120-82. Mya truncata, and Mucoma calcarea in living positions, top of the 6-m thick silt from which T-5369 and T-5713 were collected.

Bromelldalen Sa 83-48. Picea sp., 30 m altitude. Sveagruva From 9 m below surface in a terrace at 40 m

altitude (Punning et al., 1976). According to Punning (personal communication, 1984), the sample is not corrected for isotopic fractionation, and thus has a “built-in” correction for reservoir age of 410 yr compared to 440 yr for our samples.

Kjellstromdalen Hel-Elg 123-82. Along the west bank of the river from Lundstromdalen is 2-3 m silt above bedrock. Hiatella arctica from base of silt.

Kjellstromdalen Hel-Elg 69-82. Mya truncata and Hiatella arctica collected on the surface of a ridge at 49 m, some few hundred meters west of T-5710.

Agardhbukta Sa 82-17. Grass and mosses in delta foresets at approximately 50 m altitude in Vreringsdalen (Salvigsen and Mangerud. 1991).

a The dates are listed from west to east. The table includes dates giving minimum ages of the deglaciation. Thus, for both this and the following tables only the oldest dates obtained from each site are included.

Van Mijenfjord area that give unambiguous minimum ages for the deglaciation are listed in Table 1. Most of the samples were collected from the lower part of marine muds underlain by till, or from marine terrace gravels that we infer were deposited shortly after deglaciation. The dates show a consistent pattern. We have obtained 20 dates from Van Mijenfjorden east of Ak- seloya (the island nearly blocking Van Mi- jenfjorden; Fig. 2) giving ages between 10,650 and 9500 yr B.P. The oldest are plotted in Figure 2. We conclude that deglaciation of Van MijenfJorden occurred about 10,500 yr B.P. Both areas we studied west of Akseloya yielded older minimum ages

of deglaciation (11,000 to 12,830 yr B.P.; Fig. 2).

Stratigraphy at Skilvika

Along the shore from Skilvika to Renar- dodden on the south coast of Bellsund (Fig. 2) are extensive sections in Quaternary sediments (Fig. 3) (Semevskij, 1967; Troitsky et al., 1979). Our detailed investigations of these sections will be reported in a forthcoming paper by Landvik et al. Above the bedrock are two basal tills (formations 1 and 2, Fig. 3) where till fabric demonstrates WNW ice flow. This flow direction shows that the glacier that deposited the tills terminated west of Bellsund. The tills are

MANGERUD ET AL.

Holocene sublittoral sand

Till from glacer out Recherchefjorden.

‘Cryoturbation and weathering

Bouldery foresets deposlted from Scottbreen SW of the site

Marine sand and silt

Till

TI I I

FIG. 3. Simplified lithostratigraphy for the site at Skilvika (Fig. 2). Ice flow directions (to the left) are based on till fabrics and foreset dip in formation 4. The youngest flow direction in each formation is shown by stipled arrows. The younger radiocarbon dates are given in Table 1; the non-finite dates will be described in a forthcoming paper by J. Y. Landvik et. al.

overlain by marine silts and sands (formation 3) from which shell yielded non-finite radiocarbon ages of >49,000 yr B.P. (Fig. 3). The upper sand of formation 3 interfin- gers with the overlying formation 4, consisting of foresets of subangular boulders, which we interpret to have been deposited directly from the glacier terminus during an advance (toward the NE) by the local glacier Scottbreen. Paired shells from this sand yielded non-finite radiocarbon ages also. Troitsky et al. (1979) interpreted the boulder bed (formation 4) to be of late We- ichselian age, based on a TL-age of 26,000 yr. Our radiocarbon dates clearly contra- dict this assertion and show that the deposit is significantly older.

On top of formation 4 is an unconformity marked by cryoturbation and frost weath-

ering, representing a long ice-free period with low relative sea level (probably of middle Weichselian age; see below). Above the unconformity is a till (formation 5) with fabric showing ice flow to the NNW in its lower part; thus, it was deposited by a glacier flowing out Recherchefjorden (Fig. 2), and ice flow was to the NE (from Scott- breen) in the upper part of the till. Lami- nated clay, up to 5 m thick, occurs directly above this till. The clay contains only two mollusc species, mainly Nuculana pernula, which is dated to 12,830 and 12,570 yr B.P. (Table I), and very few Pecten groenlan- dicus. Both the undisturbed laminations and the extremely poor fauna indicate a stressed environment. We conclude that a glacier terminus was nearby, and that the last deglaciation occurred about 13,000 yr B.P. The till (formation 5) was probably deposited by this glacier, although that age cannot be confirmed without dates beneath the till.

Shoreline Data for Bellsund-Van Mijenfiorden

Landvik et al. (1987) found that the direction of isobases north of Bellsund is ca. 150”. We placed the projection plane for a shoreline diagram for Van Mijenfjorden at a right angle to these isobases, parallel to the direction of maximum tilt of the oldest shorelines. The marine limits were projected into that plane; the locations are plotted in Figure 4, and briefly described in the Appendix.

The tilt of the marine limit shoreline north of Bellsund is basically unknown, because the entire mapped occurrence of the shoreline is parallel with the isobases (Landvik et al., 1987). We correlate the marine limit in this area (labeled Ytterdalen in Fig. 4) with a littoral gravel at Maseneset (Appendix), but neither the exact tilt of the shoreline nor the correlation is significant to our conclusions. Landvik et al. (1987) assumed an age of 11,000 yr B.P. for the marine limit in Ytterdalen, which is a safe minimum age; possibly it is older. How-

LAST OLACL4TI0N OF SPITSBERGEN

I Altitude of marine limit 4 Minimum elevation of marine limit

Distance (km) 5b 90 km

9

FIG. 4. A shoreline diagram for Van Mijenfjorden. The sites are projected into a plane at right angle to the isobase direction found by Landvik er al. (1987). The 11,000 yr B.P. shoreline is dashed because its tilt is poorly constrained. The important point is the drop in altitude from that line to the 10,300- 10,600 yr B.P. line, which shows that the ice front stayed at Maseneset for the period of that drop. The marine limit localities are described in the Appendix and located in Figure 2.

ever, the exact age of this line does not in- fluence our main argument, namely, that there is a drop in the elevation of the marine limit around Akseloya (Fig. 4). The only possible interpretation of that drop is that a glacier occupied Van Mijenfjorden when the marine limit west of Akseloya was formed.

According to the radiocarbon dates (Fig. 2), the middle parts of Van Mijenforden were rapidly deglaciated about 10,500 yr B.P., or soon after. Indeed, all the marine limits along the fjord fit into a straight line that is drawn through both them and the 10,300-10,600 yr B.P. shoreline in Ytter- dalen (Fig. 4). This is a strong argument for that being the age of the deglaciation, and for rapid deglaciation in Van Mijenfjorden. The very rapid emergence after 10,000 yr B.P. would clearly separate marine limits with age differences of some few hundreds of years, as demonstrated by the elevation of the 9600 yr B.P. shoreline (Fig. 4). The 9600 yr B.P. line is drawn through the marine limit terrace in Lundstromdalen, indirectly dated to that age (Table l), and the elevation of the 9600 yr B.P. shoreline as

read out of the relative sea-level curve for Ytterdalen (Landvik et al., 1987).

The Coast North of Bellsund

A well-developed gravel terrace at 64 m altitude, running along the foothill and dated to around 11,000 yr B.P., represents the postglacial marine limit (Landvik et al., 1987). The terrace is mapped along the entire coast, and into the valleys; thus, the western coast between Bellsund and Isfjor- den was completely ice-free 11,000 yr B .P. at the latest. The area below the marine limit is mainly covered by a thin veneer of beach gravel, and some prominent beach ridges, that provides no clues as to whether the area was covered by ice or not during the last glacial maximum. Well-preserved glacial striae occur in some valleys (Fig. 2), which suggest a “young” glaciation. No “old” marine deposits were found in the steep slopes above the postglacial marine limit.

LINNiDALEN

Linnedalen contains more pre-Holocene sediments than any other area along outer

10 MANGERUD ET AL.

Isfjorden. Furthermore, continuous sequences of postglacial sediments have been recovered from Linnevatnet, the largest lake on Svalbard. Linnedalen is the western-most tributary valley to Isfiorden and any glacier advance out of Isfjorden that passed beyond Linnedalen terminated on the continental shelf.

At several sites in Linnedalen fresh glacial striae indicate ice flow to the north (Fig. 2). One of the sites is Nimrododden, protruding from the shore of Isfjorden, but still without westerly striae. Till is rare in the area. Below we describe a till covering a beach terrace at 87 m altitude, and a till in the sections along Linneelva. In both cases fabric and other directional indicators show deposition by a northward-moving glacier. In all the tills, the clasts are derived from the bedrock in Linnedalen. In fact, exotic rocks are extremely rare in other sediments in the area (Musial, 1985), so there exists no positive indication of glacial transport from the east and across the valley.

It seems quite clear that the last glacier in Linnedalen moved northward, downvalley in Linnedalen, and terminated at the shore of Isfjorden. This may have been a deglaciation phase. However, evidence of ice flow out Isfjorden has not been recorded on land in this area.

Stratigraphy of Lake LinnCvatnet

Beneath the Holocene lacustrine sediments in Linnevatnet is a sequence of marine sediments that rests on till (Mangerud

and Svendsen, 1990b). Subbottom echo- sounding profiles indicate that the till is but a thin veneer on the bedrock, and thus that the last glaciation removed most preexist- ing sediments. This glacier must have filled the entire valley and terminated north of the lake. Periods of nondeposition are unlikely in closed basins like those cored in Linnevatnet, and we therefore postulate that the marine sedimentation started immediately after deglaciation. Radiocarbon samples from the lowermost marine sediments gave ages of around 12,300 yr B.P. (Table 2, Fig. 5). This proves that Linnedalen was indeed glaciated during the late Weichselian, and that the final deglaciation occurred shortly before 12,300 yr B.P., or, if we consider the standard deviation of the dates, possibly as late as 12,000 yr B.P.

Pre-Late Weichselian Marine Terraces, Overrun by Glaciers

On the east slope of the Linnedalen valley there is a staircase of shorelines from present sea level up to 87 m altitude (Fig. 5). Radiocarbon dates demonstrate that they are of Holocene or late-glacial age up to 65 m, and possibly up to 75 m. The high- est morphologically distinct terrace lies at 87 m (Fig. 6), and it is radiocarbon dated to ca. 36,000 yr B.P. (Table 3), which may be a minimum age. Our first assumption. from the distinct morphology was that the terrace had not been overrun by ice (Man- gerud et al., 1985), and thus that the area

TABLE 2.

Laboratory No.

Ua-1351 Ua-730 Ua-729 Ua-29 1 Ua-290 Ua-1350 Ua-732 Ua-279

RADIOCARBON DATES OF MARINE SHELLS FROM LINN~DALEN GIVING MINIMUM AGES

FOR DEGLACIATION

Age (yr B.P.)

11,740 f 130 11,560 * 160 12,320 ” 190 11,770 * 140 11,490 2 150 11,640 ” 130 12,300 2 190 11,000 +- 190

Sample

Linntvatnet, core 01, 780 cm (Mangerud and Svendsen, 199Ob). Linnkvatnet, core 01, 845 cm (Mangerud and Svendsen, 199Ob). Linnkvatnet, core 01, 928 cm (Mangerud and Svendsen, 199Ob). Linntvatnet, core 14, 1,160 cm (Mangerud and Svendsen, 199Ob). LinnCvatnet, core 14, 1,179 cm (Mangerud and Svendsen, 199Ob). Linrkvatnet, core 24, 642 cm (Mangerud and Svendsen, 199Ob). Linntvatnet, core 24, 686 cm (Mangerud and Svendsen, 199Ob). E valleyside, Svalbard 84-1174. One fragment of Mya truncata

from a terrace at 65 m altitude (Mangerud et al., 1987).


FIG. 5. Schematic cross section of LinnCdalen. It has not been demonstrated in the field that the till covering the 87-m terrace is the same as the till that occurs on the floor of the lake. All dates above the till provide minimum ages for the deglaciation; the oldest are from the basal part of the marine sediments on the floor of the lake. From Mangerud and Svendsen (199Ob).

had been ice-free for at least 36,000 years. This assumption was also compatible with the conclusions of, e.g., Lavrushin (1969), Troitsky (1981), and Boulton (1979), which were partly based on similar observations, including this terrace.

Morphologically identified shorelines have been used many places in the Arctic as evidence for a lack of glaciation after the

formation of the shoreline. Because we can now demonstrate that it has been overrun by ice, we will describe the 87-m terrace in some detail. The terrace is ca. 80 m long, 20 m wide, and has a 10 m high distal slope of gravel standing at the angle of repose. We dug four sections around the rim and two ditches in central parts of the terrace (Fig. 6). In all excavations two formations were

FIG. 6. Photo of the 87-m terrace toward south. The lake (Linndvatnet, 12 m altitude) is seen to the right. The three excavations in the northern end (marked l-3) show the width of the horizontal terrace surface, which is 20 m. The heaps from excavations 4 and 5 in the central part are marked. Excavation 6 was in the southern end, 80 m south of excavations 1-3.

12 MANGERUD ET AL.

TABLE3. RADIOCARBONDATESFROMLINNI~DALEN PREDATINGTHELASTGLACIATIONOFTHEVALLEY

Laboratory No. Age (yr B.P.) Material Locality Field sample No. and description

T-521 1

T-6618

T-8184

Ua-73 1

T-6003

T-6728

T-6001

T-6228

T-6226

T-6006

T-6224

36,100 + 800

35,900 ” 500

40,600 k 1100

38,100 2 800

>38,100

42,500 t 1700 - 1400

>43,100

50,200 + 4600 - 2900

28,600 2 500

>46,800

>44,400

Shells

Shells

Shells

Shells

Shells

Whalebone

Shells

Seaweed

Shells

Shells

Shells

87 m terrace

87 m terrace

Linntbreen

Linnevatnet

Linneelva

Linneelva

Linneelva

Linntelva

Solovjetskib

Solovjetskib

Solovjetskib

Sa 83-30. Myn truncata collected one meter below the surface (Mangerud et al., 1987).

Svalbard 1985-1001. Paired Mya truncnta from excavation 1 (Fig. 6). (Mangerud ef al., 1987).

Svalbard 1987-83. Fragments of Mya truncata from beach sand at 83 m altitude just outside the Little Ice Age moraines of the glacier at the head of the valley (Mangerud and Svendsen, 199Ob).

Core 05, 843 cm. One fragment of Mya truncata in a diamicton at the base of the core (Mangerud and Svendsen, 1990b).

Svalbard 1984-2001. Fragments of Mya truncata from the till (Fig. 8). Fragments with lowest D/L ratios were selected (Lonne and Mangerud, 1991).

Svalbard 1985-2098. From the youngest sediments below the till (Fig. 8) (Lonne and Mangerud, 1991).

Svalbard 1984-2063. Paired Macoma calcarea from formation C (Fig. 8) (Lonne and Mangerud, 1991).

Svalbard 1984-2006. Formation A (Fig. 8) (Lonne and Mangerud, 1991).

Svalbard 1984-l 149. Several fragments, mainly of Mya truncnta, from a slided silt in western part of Solovjetskibukta (Section 15, in Sandahl, 1986). Subsequent obtained D/L ratios of 0.021 and 0.020 (BAL-1260a,b) from the same collection support a young age, as the shells are found only 19 m altitude. However, the dated sample may represent a mixed age population of postglacial shells and non-finite old shells. Further east in Solovjetskibukta shells (sample T-6006) from a similar silt yielded a non-finite age. We are skeptical of this date, until it is reproduced on a single fragment.

Svalbard 1984-1060. Fragments of Mya truncata from a silt that in section 4 (Sandahl, 1986) apparently is the youngest unit predating the ice advance.

Svalbard 1984-l 152. Several shell fragments from a silt in section 13 b (Sandahl, 1986) that is correlated with T-6006.

found: (1) a lower gravel overlain by (2) a excavated to a depth of 2 m. The distinct diamicton. planar beds dip about 1O”W. Scattered shell

(1) The lower formation is a gravel with fragments occur in the gravel. In a more rounded to subrounded pebbles which we sandy facies in the NE part of the terrace


are frequent large Mya truncata in living position. We interpret the sandy gravel as a beachface facies developed on a small delta deposited from the brook immediately to the south of the terrace.

Before we discovered the till, we obtained a radiocarbon age of 36,100 + 810 yr B.P. (T-521 1) on shells 1 m below the top of the gravel. We later recollected shells from the excavated section (No. 1, Fig. 6), at least 1 m behind the original slope, and obtained an identical age of 35,900 + 500 yr B.P. (T-6618). The shells were buried beneath a low-permeability diamicton, and the surface vegetation is extremely sparse, strongly decreasing the risk of contamina- tion by young carbon. Still, we conserva- tively consider the dates to be minimum ages.

The shells have very low amino acid D/L ratios (Fig. 9). In the Discussion we use these ratios to estimate the duration of the glaciation that deposited the till. The question here is if the low D/L values can be used to test whether the radiocarbon dates of 36,000 yr B.P. give real ages or minimum ages only. No definite answer can be given, because at an annual temperature of, e.g., - 20°C the epimerization rate is so low that even the epimerization that occurs during 100,000 yr is well inside one standard deviation of the measurement precision.

(2) The upper formation is a diamicton, up to 60 cm thick, which thins toward the edges of the terrace. The boundary with the underlying gravel is sharp, and nearly horizontal. The upper half of the diamicton is loose, and is probably frost disturbed or a solifluction deposit. The disturbed sediment was the only part seen along the rim of the terrace before the excavations.

The lower half of the diamicton is gray, matrix-supported, massive, and hard. The pebbles and boulders are generally subangular, and significantly less-rounded than in the gravel beneath. Several boulders in the diamicton have a distinct stoss-and-lee morphology, typical of lodgment tills (Boul- ton, 1978). Figure 7 shows that the direction of glacial striae on boulders, and the long axis of both boulders and pebbles, all are parallel to the glacial striae in the valley. These observations show unambiguously that the diamicton is a basal till. We conclude that the terrace, despite its well- preserved morphology, was overrun by a glacier moving NNW, down the valley.

The Section along Linne’elva

Thick sections of Quaternary sediments are exposed along the lower course of the river Linneelva (Fig. 8) (Lonne and Man- gerud, 1991). Below the Holocene littoral

FIG. 7. Directional elements in the diamicton (basal till) on the 87-m terrace. (A) Fabric of the long axis of 100 pebbles, excavation 2. Schmidts net, lower hemisphere. (B) Fabric of the long axis of 100 pebbles, in the central part of the terrace (excavation 5). (C) Squares show the fabric of the long axis of 14 boulders (>20 cm) from different excavations. The lines show the direction of glacial striae on 10 different boulders. All directional elements show a NNW ice-flow direction, down the valley.

sediments (formation E, Fig. 8) is a massive, matrix-supported diamicton (formation D) that contains frequent striated pebbles. The diamicton is l-2 m thick and is mapped more or less continuously for 500 m along the sections. L@nne and Mangerud (1991) concluded that it is a basal till. Till fabric and glaciotectonic thrusting in the underlying sediments show that it was deposited by a northward-moving (valley) glacier.

higher D/L ratios for formation C could be due to longer submergence (about 10,000 yr) at this lower level. Alternatively, formation C might be older than the 87 m terrace.

In order to select the youngest fragments for (conventional) radiocarbon dating, the D/L ratios were measured for many shell fragments found in the till; the screened sample still yielded a non-finite age (~38,100 yr B.P., Table 3). Here we will also use the D/L ratios for till correlation. Figure 9 shows that there is a significant difference in the D/L ratios from formations

The youngest formation (C, Fig. 8) beneath the till is interpreted to represent a prograding beach, deposited during a falling relative sea level that was at 28 m during the 6

final stages of deposition. Formation C 5 4

0.025 * 0.005 (27)

probably was deposited during the sea-level 3 2

drop after the 87 m terrace was formed. The I 0

CHRONO. TRATIGRAPHY

)SITE RAPHY

‘4C DATES

1103 VI B.P I

Formarion B . . . . . . . . . . . . . . . . . ..~.C....

HOLOCENE 3 _ Formation A

q I I,“, , I .--

2 - 0.027 f 0.003 (17)

I 10.3

LATE WEICHSELIAN

>38.1

42.5

>43.1 :I shoreline I- -

‘I sequence

2 ? c%

D/L I 0 Y

Proglacial m.\\\.\\

5 2 channels and

5 debris 8 2 9 i--- w

Shallow marine,

proglacial fan

FIG. 9. The amino acid D/L ratios of the species Mya truncata and Hiatella arctica from described sections in Linnbdalen. The “83 m sand” is from Man- gerud and Svendsen (1990b), and is mentioned under Discussion. In this plot each individual measurement is plotted, also when there are more than one measurement on each specimen, e.g., the two low ratios in formation A are from one specimen. The means t 1 standard deviation and number of measurements in parentheses are given for each unit. The mean for formations A, B, and C together is 0.028 * 0.003. For the till (D) the mean for only Mya is 0.023 2 0.005. For the 87-m terrace a ratio of 0.028 is omitted because new measurements on the same sample gave 0.022; thus, the mean is slightly lower than cited by Mangerud and Svendsen (1990b). The 87 m terrace/83 m sand and formations A, B, and C represent two different D/L

14 MANGERUD ET AL.

FIG. 8. Composite lithostratigraphy for the section along LinnCelva, simplified from L@nne and Mangerud (1991). populations; both are included in the till.


A, B, and C underlying the till in the Lin- neelva section and the ratios from the 87 m terrace/83 m sand (described in the discussion section). Possible causes for the different D/L ratios are discussed above. The point here is that both populations are represented in the till (formation D) which therefore has to be younger than the 87-m terrace, and thus should be correlated with the till on that terrace.

THE SHORES OF ISFJORDEN

Shorelines

Boulton (1979) and Troitsky (1981) used “old” shorelines which they concluded were not overrun by ice to delineate the maximum limit of the last glacial advance. As described for the 87-m terrace above, and for the Kapp Ekholm section below, we can now demonstrate that some terraces that were assumed to have been beyond the late Weichselian ice limit, indeed have been overrun by ice. We do not know any “old” shorelines along Isfjorden that can be con- vincingly demonstrated to have escaped glaciation.

North

Izl

Boulton (1979) used a postulated drop in altitude of the marine limit from high, presumably pre-late Weichselian beaches in the outer fjord, to lower levels in the inner tjord, to delineate the last glacial maximum. We cannot see that the high terraces are documented. On the contrary, in Lin- nedalen, and also in Van Mijenfjorden and Bellsund, we conclude that the postglacial marine limits were much lower than those compiled by Boulton (1979).

Stratigraphy at Kapp Ekholm

Within the middle and inner parts of Is- fjorden only a few known stratigraphic sequences predate the last glaciation; the most important site is Kapp Ekholm (Figs. 2 and 10). This site was a key section that Lavrushin (1967, 1969), Troitsky (1981), and Troitsky et al. (1979) used to conclude that glaciers around Isfjorden never were much larger than today during the last 40,000 years. Boulton and Rhodes (1974), Boulton (1979), and Boulton et al. (1982) used Kapp Ekholm as a key section for their reconstruction of a very limited and young late Weichselian glaciation. Some

South

m II I 30m

+ & + + I I I

900 m I I I

o

700 500 300 100 0

LITHOLOGY:

m Gravel foresets (littoral) Marine silt and diamicton MW Middle Weichsellan

LW Lower Welchsellan

a silt, sand and gravel Glaciotectonically deformed m Bedrock

FIG. 10. A simplified profile of the sections at Kapp Ekholm. The stippled lines between each section show the correlations made during tieid work. For the formations discussed in this paper (the glaciotectonically deformed and formations above) these correlations are supported by radiocarbon dates and amino acid D/L ratios. Radiocarbon dates are indicated in lo3 yr B.P.; details for the Holocene dates are given in Table 4. The dates from older units will be described in a forthcoming paper by J. Mangerud and J. I. Svendsen. Note that the youngest till is found in sections V and VI only, but an unconformity could be mapped to the south, between the deformed and Holocene formations.

16 MANGERUD ET AL.

preliminary results of our investigations are presented in Mangerud and Svendsen (1990a). A full description will be given elsewhere; here we will present some results that are relevant for the last glacial advance.

A simplified stratigraphic diagram is shown in Figure 10. In the upper part is a glaciotectonically deformed formation that we have correlated from section II to VI. It consists of silt, sand, and gravel, containing molluscs with radiocarbon ages between 50,000 and 37,000 yr B.P.; here we conclude only that it is older than 40,000 yr B.P. The formation is not covered by till in sections II to IV. Troitsky and Punning have orally confirmed that their and Lavrushin’s (1969) section was measured at the site of our section II, and the descriptions can indeed be compared. In this part the deformations are large thrust planes which are nearly parallel to the primary bedding planes. The thrusts can hardly be discerned without cleaning large parts of the section. Presumably these thrusts were not observed by Lavrushin (1969), Troitsky et al. (1979), or Boulton (1979), and certainly not by Mangerud and Salvigsen (1984). Lavrushin (1969), Troitsky et al. (1979), and Punning and Troitsky (1984) concluded that the unit had not been covered by ice, and as they also had obtained non-finite radiocarbon ages from this unit, they concluded the area had been ice-free during the entire late Weichselian.

The mean D/L ratio for 30 measurements on 22 individuals of Mya truncata from the deformed formation is 0.026 Ifr 0.004. Un- der Discussion we use this ratio to calculate the duration of subsequent ice cover. Con- sidering that Kapp Ekholm is situated far inland and thus was covered longer by glaciers, and was submerged for longer periods during glacioisostatic high sea-level stands, than most west coast sites, the deformed formation should be correlated with sites on the west coast with lower D/L ratios. It can most easily be correlated with the 87-m terrace in Linnedalen. If this is

correct, it will also support a correlation of the youngest till at both sites.

Most dates on shell from the lower part of the postglacial sequence gave a minimum age of deglaciation 9900-9700 yr B.P. (Ta- ble 4). One shell fragment yielded an age of 11,050 t 150 yr B.P. (Ua-972, Table 4). However, we subsequently obtained a date of 9470 + 140 yr B.P. (TUa-71) from the same level, and 9730 + 180 yr B.P. (TUa- 70) directly beneath that sample. Thus, either the shell fragment yielding 11,050 yr B.P. is redeposited, or the date is errone- ous. Boulton (1979) reported a similar date (11,030 + 440 yr B.P., SRR-111, Table 5) from the upper till at his site 11, which is close to 140 m in Figure 10 (G. Boulton, personal communication, 1991). A possible interpretation is that there was a short ice- free period about 11,000 yr B.P., and that shells of that age were incorporated in the till and subsequently also redeposited in the postglacial sediments. Alternatively, both dates of 11,000 yr B.P. are too old. For either alternative, the final deglaciation is dated to just before 9900-9700 yr B.P.

Most folds and thrusts in the deformed unit show thrusting to the west, that is nearly perpendicular to Billefjorden. The sections are situated south of the mouth of the tributary valley (Mathisondalen); thus, the deformations were not caused by a local glacier flowing out that valley. The simplest interpretation is that the westerly deformations took place beneath a thick glacier that moved across Billefjorden. If this reconstruction is correct, there could not simul- taneously have existed an ice-stream out Billefjorden-Isfjorden. A further prediction from this ice flow direction is that the glacier also flowed across the land NW of Is- ljorden (Figs. 1 and 2), and that the ice front was located west of the coast between Is- fjorden and Kongsfjorden (Mangerud and Svendsen, 1990a).

Minimum Dates for the Deglaciation

In Figure 2 and in Tables 4 and 5 are compiled radiocarbon dates that give a min-


TABLE 4. RADIOCARBON DATES FROM THE LOWER PART OF THE POSTGLACIAL SEQUENCE AT KAPPEKHOLM

Laboratory No. Age (yr. B.P.) Material Section” Field sample No. and description

Ua-972

TUa-70

TUa-69

TUa-7 1

T-8322

T-8330

T-83 19

T-8323

Ua-974

T-8326

TUa-72

T-5666

T-8534

11,050 2 150

9730 XL 180

37,400 2 1600

9470 ? 140

9730 * 120

9810 ? 70

9690 k 70

8740 5 100

9910 + 130

8560 f 60

9760 ” 140

9530 1: 110

9080 t 110

Shells

Shells

Shells

Shells

Shells

Shells

Shells

Shells

Shells

Shells

Shells

Shells

Shells

I, 110

I, 110

I, 110

I, 110

I, 130

I, 160

II, 280

IV, 550

V, 650

v, 760

VI, 870

VI, 870

VI, 890

Svalbard 1988-696. One shell fragment from the base of a 20-cm thick reddish-brown silt overlying till. The sample was collected just above sample -695 described below. Samples TUa-69, -70, -71, and -72 were subsequently dated to test if the age obtained by Ua-972 could be reproduced.

Svalbard 1988-695b. One shell fragment from a few millimeters thick sand layer beneath stones along the boundary between the underlying till and the reddish-brown silt, described above.

Svalbard 1988-695a. A thick fragment from the same collection as TUa-70. The date shows that this fragment has been redeposited from older beds. The age has been calculated on the basis that infinite old calcite yields an age of 42,000 2 2500 yr B.P. with the same chemical preparation.

Svalbard 1988-697. One gastropode from exactly the same site as sample -696.

Svalbard 1988-235. Paired Hiatella arctica in sorted sand 5 cm above a IO- to 20-cm thick bed of reddish-brown silt.

Svalbard 1988-698. Balanus sitting on a boulder in a IO-cm thick lense of reddish-brown silt that was found in the boundary zone between the underlying (interglacial) gravel foresets and the overlying Holocene sand.

Svalbard 1998-78. Three individs of paired Hiatella arctica from the transition between a brownish silt and overlying fine sand. Sample collected less than 10 cm above a bed of angular pebbles that are thought to be the base of the Holocene at this locality.

Svalbard 1988-317. One large individ of Mya truncata from a boulder bed interpreted as an erosional lag at the base of the Holocene.

Svalbard 1988447. One individ of Lepeta from a laminated silt with reddish and grayish lamina, at the base of the Holocene sequence.

Svalbard 1988-438. One large individ of paired Mya truncata from the base of the Holocene. The underlying till is missing at this site.

Svalbard 1988-758. On top of the youngest till is 20-30 cm reddish-brown silt. Small Lepeta from the base of the silt.

Sa 81-08. Paired Mya truncata in the lowest part of the sand following above the reddish-brown silt described under sample 1988-758. This sample was collected by Salvigsen and Mangerud in 1981, but can easily be plotted into the section measured in 1988.

Svalbard 1988-522. Two large individs of Mya truncata in living position, from a zone rich in large Mya, 1.5 m above the till.

* The column “Section” refers to Figure 10, where arabic numbers are meters along the horizontal scale. Samples are listed from south to north.

Laboratory No.

T-6290

Age (yr. B.P.) Material Locality

9980 2 130 Shells Gronfjorden

T-6282 %80 2 110 Shells Erdmannflya

T-6281 9720 f 110 Shells Erdmantiya

Lu-2364 9510 2 90 Shells Bohemannflya

T-4407 9690 f 140 Shells Lyckholmdalen

SI-4308

Tln-275

9780 2 80 Shells

9480 f 110 Shells

Blomesletta

Adventdalen

U-132

U-128

9840 2 150 Shells

9980 f 140 Shells

Telttjellbekk

Kapp Ekholm

SRR-109

SRR-I11

9710 + 90 Shells Kapp Ekholm

11,030 + 440 Shells Kapp Ekholm

T-4406

Gd-2172

10,030 + 140 Wood Kapp Ekholm

11,940 * 200 Organic matter Petuniabukta

Gd-5248 9730 k 70 Shells Petuniabukta

18 MANGERUD ET AL.

TABLE 5. RADIOCARBON DATES FROM THE SHORES OF ISFJORDEN(FIG.Z)

Sample and description

Sa 84-19. Fragments of Mya iruncuta and Hiatella arctica at 12.5 m altitude in Holocene till deposited by Aldegondabreen.

Hiatella arcticn, 26 m altitude (Salvigsen et al., 1990).

Shell fragments 47 m altitude (Salvigsen er al., 1990).

Hiarella arctica, 20 m altitude (Salvigsen et al., 1990).

Sa 81-85. Myu truncutu in living position in sand, 10 cm above a till. Sample altitude is 32 m, but overlying beach sediments reach 48 m.

Mya truncuta from a beach ridge at 31 m altitude (P&we et al., 1982).

Terrace at 55 m altitude between Longyearbyen and Todalen. (Punning et al., 1982).

Shells from 56 m altitude (Feyling-Hanssen and Olsson, 1960).

Site called north of Phantomvika, same as others call Kapp Ekholm. Shells from 51 m altitude (Feyling-Hanssen and Olsson, 1960).

Whole valves of Mya truncutu (Boulton, 1979).

Fragment of Macoma calcarea in till (Boulton, 1979). According to G. Boulton (personal communication, 1991). the site is at 160 m in our section (Fig. 10).

Driftwood of Lurix at 57 m altitude. Thought to date the 67-m terrace (Salvigsen, 1984).

“A weathering mantle enriched with organic matter has been recognized on bedrock making up the base of a marine terrace of 10 m” (Stankowski et al., 1989). We reject this date, because if the area was ice-free that early, it was below sea level.

Shells in till from a postglacial readvance. (Stankowski et al., 1989).

Note. The table includes dates giving minimum ages of the deglaciation. Our new dates for the Kapp Ekholm section are given in Table 4. Field sample number is only given for unpublished dates. For dates from other laboratories than T-, U-, and Lu-, the corrections for reservoir age might be different from that used in this paper.

imum age for deglaciation. A few of them Most significant is that almost all dates are are from silt just above a till, and thus from land areas where glacial striae show should give an age close to the deglaciation. that the last ice movement was from local Some are from terraces that are known to glaciers in the hinterland, and thus give a be lower than the marine limit, and thus minimum age of when these glaciers with- somewhat younger than the deglaciation. drew from the shore.


The map shows that both the shores and the inner branches of the main fjord were ice-free about 10,000 yr B.P. The main body of Isfjorden may have broken up earlier. The dates from Linnedalen show that at least the outer part was ice-free 12,50& 12,000 yr B.P.

SEA FLOOR SEDIMENTS

Mangerud et al. (1987) concluded that the late Weichselian glaciers extended at least to the shores around Isfjorden, and that tidewater glaciers calving into the fjord possibly represented the glacial maximum. This minimum extension is further documented in the sections above. The only way to test that hypothesis was to investigate the stratigraphy on the sea floor. We therefore collected sediment cores from both Is- fjorden and the shelf west of the fjord mouth; a full description and discussion is given by Svendsen et al. (1991).

In an unglaciated area the preservation potential of sediments is considered to be larger on the floor of the fjord, especially in closed depressions, than above sea level. Thus, if Isfjorden remained ice-free, extensive pre-late Weichselian sediments, and indeed late Weichselian glaciomarine sediments, should have survived in the fjord basins. In the same way as for Linnevatnet, we argue that a grounded glacier provides the only mechanism to empty the closed depressions in the fjord floor, and that the basal dates of the marine sediments should date the last deglaciation. The practical problem was that the sediment thickness in most of the depressions is too thick to pen- etrate with conventional coring equipment.

Svendsen et al. (1991) provided two main arguments that Isfjorden was glaciated during the late Weichselian:

(1) The sediment thickness in Isfjorden (generally 10-20 m) is similar to the thickness recorded in Van Mijenfjorden (Elver- hoi et al., 1983), which we have demonstrated was glaciated until around 10,000 yr B.P. If Isfjorden had been ice-free for a much longer time (e.g., >80,000 yr, which

according to Miller ef al. (1989) was the last major glacial advance on Spitsbergen), the sediment thickness should have been significantly larger. Svendsen et al. (1991) obtained a date of 10,400 * 140 yr B.P. (Ua- 757) in the lower part of core 144 raised in the central part of Isfjorden (Fig. 2). The till boundary at this site is, according to the seismic stratigraphy, only 2-4 m deeper, and considering the assumed rapid sedimentation rate, the basal sediments should not be much older than this date.

(2) In the trough that forms the extension of Isfjorden onto the continental shelf (Fig. 2) several cores penetrated into a firm diamicton interpreted as a till (Fig. 11). De- rived fragments of shell in the diamicton were dated to >40,000 yr B.P. Dates from glaciomarine clay resting directly on the till yielded ages between 12,550 and 10,000 yr B.P. (Table 6). If the sequences are correctly interpreted, they indicate that a grounded glacier reached well onto the continental shelf shortly before 12,600 yr B.P. Preliminary interpretations of seismic profiles across the shelf and fjord obtained during a cruise in 1990 (Svendsen, Elverhoi, Solheim, Mangerud, unpublished data) support this interpretation.

(3) Ice-front deposits or substantial accu- mulations of sediments across the main fjord or inner shelf were not identified on the subbottom profiles. This contrasts to prominent moraines identified on the outer shelf, partly described by Otha (1981), which may represent the late Weichselian extension.

DISCUSSION AND CONCLUSIONS

Location of the Ice Front during the Late Weichselian Maximum

In Van MijenfJorden the ice front was at Akseloya at least from 11,000 to 10,500 yr B.P. This shows a definite minimum extension for the late Weichselian ice in this fjord. We have no conclusive observations to determine whether this was the maximum position, or whether it only represents

20 MANGERUD ET AL.

CORENO. 8WO4 8m3 8#02 wol 071137

271 270 271

General

stratigraptiy

olive rey mud ( !I olocene)

Diamicton (Ice dropped)

Grey mud (Deglaciation)

Firm diamicton t-W

5

FIG. 11. Lithostratigraphy and datings in cores from the continental shelf. Locations in Figure 2. Core 871137 was raised just west of cores 88101 and 88102. Modified from Svendsen et al. (1991).

a halt during the retreat from a maximum much farther west.

An argument for Akseloya being the maximum position is the lack of glacial evidence of proven late Weichselian age farther west. In the section at Skilvika, the only tills deposited by westerly ice movement (formations 1 and 2, Fig. 3) occur stratigraphically below beds with non-finite radiocarbon ages. The late Weichselian till at Skilvika (formation 5, Fig. 3) was depos-

ited by a glacier that came from the south (out Recherchefjorden) and obviously calved in Bellsund. However, this till may represent a deglaciation phase, and the till from the late Weichselian maximum may be missing.

If the conclusion for Isfjorden is correct, most probably the ice front also at Bellsund was on the continental shelf, well outside the coast, during the maximum extension. Even though this conclusion cannot be

TABLE 6. RADIOCARBON DATES” FROM CORES RAISED FROM THE FLOOR OF ISFJORDEN AND THE SHELF (FIG. 2)

Laboratory No. Age (yr B.P.) Core No.

Depth in core (cm) Dated species

TUa-45 10,240 f 260 88-04 83 TUa-46 >4o,ooo 88-04 142

TUa-47 >40,000 88-04 210 TUa-44 11,610 2 180 88-03 105 T-8182 10,070 2 90 87-137 296 Ua-756 10,110 f 140 87-137 373

TUa-38 12,080 t 940 88-01 88 TUa-39 11,610 5 330 88-01 136

TUa-40 11,680 2 180 88-01 204 TUa-41 10,810 + 120 88-02 140 TUa-42 12,550 f 150 88-02 220

Ua-757 10,400 * 140 87-144 362

Acmaea rubecula? Unidentified shell fragment in diamicton

interpreted as till. As TUa-46. Nucula tenuis Neptuna denselirata Nuculana pernula Nucuia tenuis Nucula tenuis Astarte elliptica Unidentified mollusc Nucula tenuis Unidentified mollusc

u All dates are cited from Svendsen et al. (1991).


demonstrated from land-based observations, it is not in conflict with these observations.

In Linnedalen all observations show that a north-flowing glacier occupied the valley just prior to 12,300 yr B.P., and that it at least reached Isfjorden. Based on the sea floor evidence, this valley glacier merged with a major glacier in Isfjorden, terminat- ing on the shelf. We cannot decide if Linnedalen was covered by thick ice at an earlier stage, which moved across the valley, but we found no signs of such an ice flow.

We conclude that the glacial limit was west of all cored sites on the shelf west of Isfjorden (Fig. 2). This will be further tested, and the maximum position more precisely located, by analyses of seismic records and a number of new cores collected in 1990.

Immediately to the north of Isfjorden the situation is completely different. On Prins Karls Forland, along the coast from Istjor- den to Broggerhalvoya, and around Kongs- fjorden, sediment sequences and shorelines older than 40,000 yr B.P. which were not covered by till, are reported to occur fre- quently (Salvigsen, 1977, 1979; Salvigsen and Nydal, 1981; Troitsky et al., 1979; Boulton, 1979, 1990; Boulton et al., 1982; Miller, 1982; Miller et al., 1989; Forman and Miller, 1984; Forman, 1989). All the mentioned authors agree that these sites have not been overrun by late Weichselian glaciers.

The question then arises if our interpretation of large fjord glaciers extending well onto the shelf in the Istjorden-Van Mijen- fjorden area is compatible with the sug- gested restricted late Weichselian glaciation just north of Isfjorden. One hypothesis that possibly could accommodate both interpretations is to postulate low net accu- mulations of snow along the west coast, and that the glaciers out Istjorden and Van Mijenfjorden were ice streams draining parts of the Barents Ice Sheet proper. The

latter was probably to a large degree the case. However, our reconstruction of the glaciers in Linnedalen and out Recherche- fjorden demonstrate a depression of the equilibrium line altitude along the west coast that is incompatible with the minor readvances postulated to the north of Is- fjorden.

On both sides of Liefdefjorden, in the NW part of Spitsbergen (Fig. l), Salvigsen (1979) and Salvigsen and Jbsterholm (1982) mapped end moraines and ice-marginal channels that they concluded represent the late Weichselian maximum. The moraines are correlated with submarine moraines from Raudfjorden to Danskeoya (Liestol, 1972; Salvigsen, 1977, 1979). If correctly interpreted, they show that fringes of the coast remained ice-free, and can in that sense support a restricted glaciation also farther south, e.g., around Kongstjorden. However, the moraines show an ice cap centered on the northwest coast, which demonstrates a considerably larger depression of the equilibrium line altitude than postulated by the reconstruction of the late Weichselian maximum by, i.e., Forman (1989). This argument is valid even if the moraines mapped by Salvigsen should represent a deglaciation phase from the late Weichselian maximum.

If our reconstruction of the glacial maximum in Isfjorden is valid, it also provides other arguments for more extensive ice north of Isfjorden. It is impossible to reconstruct a glacier in Isfjorden that did not cover the southern localities postulated to have remained ice-free (Forman, 1989), even though the key localities on Brogger- halvoya (Forman and Miller, 1984; Miller et al., 1989; Boulton, 1990) could be outside that glacier limit.

If there was an ice stream restricted to IsfJorden, a thick sequence of sediments should have been found in the depression of Forlandssundet (the sound between Prins Karls Forland and Spitsbergen, Fig. 2), because the sound according to this interpre-

22 MANGERUD ET AL.

tation had been ice-free for >80,000 yr (Miller ef al., 1989). The preliminary anal- ysis of the 1990 cruise observations shows only thin sediments, and thus suggests that the sound was indeed glaciated.

Our interpretation of the glaciotectonic structures at Kapp Ekholm suggests that there has been ice flow across land toward the coast between Isfjorden and Kongstjor- den, and thus a more westerly maximum position in that area than mapped by For- man (1989).

We conclude that in Van Mijenfjorden and Isfjorden, the late Weichselian glacial maximum was much larger than researchers working in the area have concluded before, and that the ice front was situated on the shelf well outside the present coast. Ac- tually, from the available observations we find it most probable that the glacier terminated along the shelf edge between the continental shelf and slope (Fig. 2). From this we also deduce that the glacier reached the shelf in the area between Isfjorden and Kongsfjorden, even though there is an apparent conflict between this conclusion and published observations, for which the solu- tion has to come from future research.

Reconstruction of the Glacier(s)

As indicated in the introduction, the ice- age glaciers on Spitsbergen can be considered as two systems. One is the large Bar- ents Ice Sheet to the east, which was mainly marine-based. The source of precipitation for this ice sheet is not at all clear. The main dome was well east of the mountains on Spitsbergen; thus, precipitation from due west was not likely. The glacial advance to the late Weichselian maximum in Svalbard (Fig. 13) lagged several thou- sand years compared to the expansion of the Scandinavian Ice Sheet (Mangerud, 1991; Andersen and Mangerud, 1990). Thus, one can speculate that snowfall over eastern Svalbard increased due to stronger southwesterly winds over the eastern Nor- wegian Sea and ice-free parts of the Barents Sea, set up by a glacial anticyclone around

the Scandinavian Ice Sheet (COHMAP Members, 1988). Alternatively, the Barents Ice Sheet could (partly) have been fed from the Arctic Ocean. This ice sheet dominated the pattern of glacioisostatic uplift of all Svalbard.

The other system is local glaciers, exem- plified by the glaciers existing today, but also including possible ice domes on Spits- bergen. Researchers who reconstruct the smallest late Weichselian glacial expansion maintain that local glaciers advanced somewhat at this time (Boulton, 1979; Forman, 1989). These local glaciers, even though they were larger than today, had some com- mon features: Their dynamic behavior was independent of the Barents Ice Sheet. Their mass balance also was different, although the local climate was influenced by the Bar- ents Ice Sheet. They were mainly land- based, but with most outlet glaciers calving in the sea. As they were facing the Norwe- gian Sea, we can assume they were nour- ished by precipitation from that direction. The growth and decay of these glaciers could be out of phase with the Barents Ice Sheet. If Isfjorden had remained ice-free, the glaciers to the NW of the fjord would have been isolated from the Barents Ice Sheet (Forman, 1989).

We concluded that during the glacial maximum the ice front was at least west of all coring sites on the continental shelf (Fig. 2). A “minimum model” based on this ob- servation would be ice streams out of Is- fjorden and Van Mijentjorden, with tributary glaciers from ice fields on the land areas between the fjords. This glacier would be so thick in the eastern part that it certainly was contiguous with the Barents Ice Sheet. Probably it also drained western parts of that ice sheet. This model could possibly be compatible with the assumption of an ice-free coast north of Isfjorden, as discussed above. An alternative “maximum model” would be an ice sheet that covered the entire area, and moved more independently of the topography. This could either be the Barents Ice Sheet that


overran Spitsbergen or, more probably, a composite ice sheet with one or more domes over Spitsbergen. The maximum model is even more realistic if the ice front was as far west as the edge of the continental shelf (Fig. 2).

We have no observations that demonstrate unambiguously that either of the two models (or an intermediate one) is correct or false. If the maximum model should be right, it would obtain a pattern very similar to the minimum model during deglaciation. Thus, even though nearly all observations of glacial striae (Fig. 2) show ice flow along the fjords and down the tributary valleys, that does not prove the minimum model to be correct for the glacial maximum. Even on the hard metamorphic bedrock along the coasts of Scandinavia, nearly all striae re- flect the flow directions for short intervals during deglaciation only.

Only two observations show ice move- ments independent of topography, and thus support the maximum model. One is the described glaciotectonic deformations at Kapp Ekholm. The second is a section in Gangdalen, midway between Isfjorden and Van Mijenfjorden (Fig. 2), where local glaciation that developed into a regional west- ward moving glacier can be found through both a lower and the uppermost till (Land- vik and Salvigsen, 1985). However, this sequence is not dated, and theoretically even the youngest till may be older than the last glaciation.

Age and Duration of the Last Glacial Maximum

The end of the last glaciation is, for ob- vious reasons, better dated than the onset. We obtained several dates of about 12,500 yr B.P. (Fig. 2), the oldest being 12,830 yr B.P. from Skilvika. Similar ages were obtained north of Isfjorden; the oldest date reported there is 13,100 + 190 (B-10968) (Forman et al., 1987). As this date was corrected for a reservoir age of only 300 yr for whales, the age should be cited as 12,960 yr B.P. to be comparable with those reported

by us. The glacial maximum has to predate these ages.

We use amino acid D/L ratios to calculate a maximum duration of the last glaciation (Mangerud et al., 1987). The principle is simple. The epimerization reaction is highly temperature-dependent (Miller and Brigham-Grette, 1990). With a present-day mean annual temperature of about - YC, the process is very slow, and with even lower ice-age temperatures it nearly stops. However, when sites were overrun by “warm-based” glaciers that deposited till, the ground temperature was close to 0°C. Also, when a site is inundated by the sea, the temperature in the sediments is around zero (+2”(J). Several sites covered by late Weichselian till have such low D/L ratios that they can have experienced 0°C for a very limited time. Here we describe the calculations for the 87-m terrace in Linnedalen in some detail.

To obtain the maximum possible duration of ice over the terrace, we assume that emergence occurred immediately after the shells died. The D/L ratios (Fig. 9) define the maximum length of time the terrace can have experienced temperatures as warm as 0°C (Fig. 12). The 0°C line, starting at the known D/L value of 0.016 (the amount of epimerization since deglaciation), inter- cepts the mean D/L value for the 87-m terrace at 3000 yr, which therefore is the maximum duration for the glaciation. If we use the lower end of the error bar for the terrace (0.021), the glaciation could have lasted 5000 yr. One could add another 1000 yr for the uncertainty for the postglacial D/L ratio. Still, the D/L ratios constrain the duration of the ice cover as short, certainly less than 10,000 yr. Linnedalen was deglaciated about 12,500 yr B.P. Using the time periods given above, the glaciation commenced after 23,000 yr B.P., and probably after 18,000 yr B.P. (Fig. 13). If the terrace had been ice-covered more than once, which we consider unlikely, the cumulative duration still must be <lO,OOO yr.

In these calculations we have assumed

24 MANGERUD ET AL.

AGE (yr B.P.)

0 to 000 20 000 30 000 40 000 ~011”“““““““““‘~‘~~‘~~~~““““‘~)

FIG. 12. Possible temperature histories for the shells from the 87-m terrace, based on amino acid epimerization rates. The numbers on the lines are degrees Celsius, and the slope of each line gives the epimerization rate for that temperature. The D/L value (or 1 standard deviation) for the 87-m terrace is plotted as a bar at 36,000 yr B.P. If the real age is higher, the bar should be moved to the right, but the slope of the lines would not change. The individual D/L measurements are given in Figure 9. The curves are drawn from two ends. One curve is drawn as a straight line from the present day through the known D/L ratio for 11,000 yr B.P. (0.016) until it reaches the time of deglaciation (12,000 yr B.P.). From that point the curve is drawn with the epimerization rate at O”C, because it is known that the terrace for some time was covered by a glacier at the pressure-melting point. The other curves are drawn backward from the mean D/L value of the terrace, and shown in three alternatives with slopes for epimerization rates of -lo”, -IS”, and -20°C respectively, in addition to a horizontal line (stipled). The curves show that the site could have experienced 0°C for some few thousands of years only before 12,000 yr B.P., and that the ground temperature for the rest of the time back to 36,000 yr B.P. (or more) must have been - 15°C or colder.

that all the epimerization took place during a short interval of 0°C and thus that the temperature for the rest of the period back to 36,000 yr B.P. (or more) was so low (- 15°C or lower) that no significant epimerization took place (Fig. 12). If some epimerization occurred during that period, the glaciation must have been even shorter.

Another modification that must be considered is that the basal temperature of the glacier covering the site may have changed, even though it was at the pressure melting point when the till was deposited. Some estimates for the maximum duration of a cold- based glacier can be read from the diagram (Fig. 12). Extrapolation of the postglacial line (- 3.7”C), which is a realistic temperature at the base of a cold-based valley glacier, gives an intercept with the mean D/L

for the terrace in 5000 yr. If the temperature was as low as - lo”C, the intercept would be in 20,000 yr. However, these are maximum estimates omitting the period at 0°C and also the intermittent period with temperatures between zero and the given value. We conclude that 10,000 yr is a rea- sonable estimate of the maximum time of ice cover, including a possible period of cold-based ice.

Mangerud and Svendsen (1990b) reported a glacially overridden deposit of beach sand at 83 m, just outside the Little Ice Age moraines of the glacier at the head of Linnedalen. The shells had identical D/L values (Fig. 9) to those in the 87-m terrace and a radiocarbon age of 40,610 + 1120 yr B.P. (T-8184). Thus, the calculations above are strongly reinforced. Furthermore, this


Front of NOIdMSklbklbrWll

Kapp Ekhdm II

FIG. 13. Time-distance diagrams for the glacier front in Isfjorden (upper) and Van Mijenfjorden (lower). Horizontal distances are measured along the middle of the fiords starting at the front of present glaciers (Nordenskifildbreen and Edvardbreen). The deglaciation pattern is constructed from radiocarbon dates. The advance for Istjorden is based on the duration of ice cover, estimated from the amino acid D/L ratios. For Van Mijenfiorden we have no data for the time of advance.

site shows that the glacier was not larger than that of the Little Ice Age during the last ice-free period.

The deformed formation at Kapp Ekholm (Fig. 10) has shells with a mean D/L ratio of 0.026 + 0.004 and radiocarbon dates >40,000 yr B.P. Using the same assump- tions as at the 87-m terrace, the site was at 0°C for only 11,000 yr after deposition of these shells. Again, extreme low temperatures are postulated for the rest of the period back to NO,000 yr B.P., implying that relative sea level was below the site (Fig. 13).

The onset of the last glaciation deduced from these calculations is not yet supported by radiocarbon dates. A main reason for the lack of such dates is that relative sea level was below the present level during

this period (Boulton, 1979; Miller, 1982), so that no shells of that age occur in sections. Thus, the best hope of finding shells that lived just before the late Weichselian advance would be below present-day sea level, either as derived shells in tills, or in subtill sediments. However, the two shell fragments we dated thus far, from the till on the shelf (Fig. ll), yielded non-finite ages.

Starting Point for the Readvance to the Last Glacial Maximum

To understand how the glacier responded to climatic change, it is important to know whether the last glacial maximum represents a small advance of glaciers that already were large or whether it represents a major new build up of glaciers at this high latitude. This question is closely related to

26 MANGERUD ET AL.

the dating, discussed in the preceding chap- ter.

For Linnedalen we showed that the glacier (Linnebreen) was no larger than at present for a long period before the late Weichselian readvance. Thus, we conclude that the local glaciers on Spitsbergen ex- panded from a size comparable to or less than they have today.

At Kapp Ekholm we calculated above that sediments from the last ice-free period had been covered by glaciers and/or the sea for an integrated time of no more than 11,000 yr before the onset of the Holocene. A considerable part of that time has been glacial coverage, leaving some few thousands years for submergence of the site. This demonstrates that relative sea level at Kapp Ekholm must have remained close to or lower than at present for at least some 20,000 yr preceding the last glacial read- Vance. The uplift pattern from the last deglaciation (Forman, 1991) shows that relative sea level at Kapp Ekholm monitors glacial loading of the Barents Ice Sheet. Thus, the low relative sea level at Kapp Ekholm prior to the last glacial advance suggests that the Barents Ice Sheet also was small or nonexistent prior to the late Weichselian glacial built up. The conclusion is that the glaciers on and around Svalbard were not much larger than today when the advance to the last glacial maximum started sometime after 25,000 yr B.P.

Deglaciation

Deglaciation of the coast must have started by 12,500 yr B.P., the minimum ages we obtained. Lehman and Forman (1991) concluded it started at least 13,000 yr B.P. in the Kongsfjorden area, which is compatible with our dates. Probably the glacier on the shelf calved back fast when it started to retreat. We cannot determine if the retreat was initiated by global eustatic sea-level rise or by thinning of the glacier by melting. However, the retreat of the glacier in Linnedalen demonstrates that melt-

ing was an important process already during an early phase of deglaciation.

For the earliest part of the deglaciation, we have not been able to reconstruct a consistent pattern of glacier retreat and relative sea-level change. The radiocarbon dates indicate that both Linnedalen and Bellsund were ice-free well before 12,000 yr B.P. (Fig. 2). During deglaciation of an ice sheet, the marine limit is normally formed at the ice front, due to the fast isostatic uplift. However, the oldest age we obtained for the marine limit was 11,000 yr B.P., both in Ytterdalen north of Bellsund (Fig. 2) and in Linnedalen (Figs. 2 and 5). We see two possible explanations for this: (1) The age for the marine limit is about 12,500 yr B.P., and was followed by a slow drop in relative sea level until after 11,000 yr B.P. This is the age obtained by Forman et al. (1987) for the Kongsfjord area (Fig. 1). The sample in Yt- terdalen was collected at an elevation below the marine limit, but sedimentologi- tally correlated with it. In Linnedalen, the marine limit may be above the shoreline where the sample was collected. (2) There was a small transgression after 12,500 yr B.P., so that the marine limit really was formed around 11,000 yr B .P. We cannot resolve this problem.

A sudden drop in the marine limits indicates a halt in the glacial retreat at the mouth of Van Mijenfjorden. According to the shoreline diagram, the front reached Akseloya about 11,000 yr B.P. However, as discussed above, the dates from Skilvika show that Bellsund was ice-free already about 12,800-12,500 yr B.P. This means that the ice front already was at, or close to, Akseloya at that time. Two dates from Bro- melldalen (Fig. 2) suggest that the ice front withdrew from Akseloya as early as 10,600 yr B.P.; others show that it was before 10,300 yr B.P. At any rate, these dates indicate that the ice front halted at Akseloya for about 2000 yr B.P. This stillstand was probably mainly topographically dependent. Akselgya is a bedrock island that nearly completely closes the fjord. If the ice


front calved rapidly from the continental shelf into Bellsund, it would stop at Ak- seloya to obtain a new equilibrium profile. With slower calving, the glacier could also maintain that position with less accumula- tion than, e.g., a position in Isfjorden, where the loss through calving would be much larger.

Both the radiocarbon dates and the shoreline diagram indicate that the glacier in Van Mijenfjorden broke up very fast sometime between 10,600 and 10,300 yr B.P., all the way from the sill at Akseloya to the head of the fjord around Sveagruva (Fig. 13). There the retreat slowed down, and Lundstromdalen, only 15 km upvalley from Sveagruva, was not deglaciated until 9600 yr B.P. At Agardhbukta, on the east side of Spitsbergen (Fig. 2), Salvigsen and Mangerud (1991) obtained a minimum age for deglaciation of 9870 2 140 yr B.P. (T- 4937, Table l), suggesting that the east coast of Spitsbergen was ice-free before Lundstromdalen on the west side of the mountains. This was probably due to a fast calving in Stortjorden on the east side.

In Bromelldalen (Fig. 2), a local read- Vance after 10,500 yr B.P. is demonstrated by a till overlying marine sediments (Elg- ersma and Helliksen, 1986; see comment under the dating T-5368 in Table I). We cannot determine whether this readvance was a dynamic response to fast calving in Van Mijenforden, or whether it was climat- ically induced. A prominent beach ridge formed along the west coast between 10,600 and 10,000 yr B.P. was interpreted as an isostatic response to increased glacial loading (Landvik et al., 1987; Forman er al., 1987). Both the given observations point to ice growth in eastern Svalbard during the Younger Dryas chron. However, local glaciers on the west coast did not read- Vance during the Younger Dryas, and were, in fact, no larger than today (Mangerud and Svendsen, 1990b).

In Isfjorden we have not been able to identify any ice-front position across the middle or outer part of the fjord. Thus, the

retreat of the main fjord glacier is poorly dated. The outer part of the fjord was ice- free about 12,500 yr B.P. (Fig. 13). The pattern of glacial striae on both sides of the fjord shows that ice flow directions in later phases converged toward the fjord, indicating that the glacier in the main fjord had calved away. All shores and branches of the fjord became ice-free very rapidly close to 10,000 yr B.P.

In Figure 1 we have compiled minimum dates for the deglaciation of Svalbard. The earliest deglaciation was on the extreme west coast (12,500 yr B.P.). Along the north coast there are several dates that indicate deglaciation before 10,800 yr B.P. A strik- ing feature is that the head of all the fjords, and the entire eastern area, became ice-free at 10,000 yr B.P. or the following century. Many of the dates from the eastern area (Edgeoya, Kongsoya, Nordaustlandet) date marine levels close to the marine limit. The marine limit was formed at the time of deglaciation, and thus the dated levels probably were formed less than 100 yr after deglaciation. These dates suggest a nearly in- stantaneous disappearance of the last ice about 10,000 yr B.P. The isostatic uplift pattern (Forman, 1990) shows that this last event must have involved a large ice mass over eastern Svalbard and the Barents Sea. Before 10,000 yr B.P., the uplift along the ice-free coast of western Svalbard was slow (Landvik et al., 1987; Forman, 1990). Then, at 10,000 yr B.P. the entire archipelago sud- denly started to emerge rapidly.

If we compare relative sea-level curves in an E-W cross section over Svalbard (Forman, 1990) and western Scandinavia (Svendsen and Mangerud, 1987), the pat- terns are nearly identical, even though the amplitudes are larger over Scandinavia. Most significant are the two steps, with the large increase in glacioisostatic uplift rates at 10,000 yr B.P. In Scandinavia this is demonstrated to be correlated with the rapid glacial unloading after the Younger Dryas (Fjeldskaar and Kanestrom, 1981; Anundsen, 1985; Svendsen and Mangerud,

28 MANGERUD ET AL.

1987). This suggests also that for the Bar- ents Ice Sheet the fast uplift was caused by late-glacial unloading, but that the glacier had been thinner than over Scandinavia.

The pattern of deglaciation shows that the main process of ice retreat was calving. However, there is evidence that melting also was important, which indirectly may suggest that some of the calving was driven by initial thinning of the ice. Certainly all glaciers with ice fronts above the marine limit disappeared by melting. In Linnedalen, the glacier melted away long before the Isfjorden glacier had calved into the head of the fjord.

APPENDIX

Brief description of shoreline localities along Van Mijenfjorden is plotted in Figure 4. The sites are located on the map of Fig- ure 2.

Ytterdalen

This site is described in Landvik et al. (1987). The marine limit is a large beach, 64 m altitude, dated to 11,ooO yr B.P. Below this is another major beach at 50-52 m, probably formed during a stillstand ca. 10,500-10,000 yr B.P., and used in Figure 4 as the altitude for the shoreline for that period. For Ytterdalen, Landvik et al. constructed a complete sea-level curve; the 9600 yr B.P. level is read out of the curve and is not represented by a significant shoreline.

M&eneset

At Maseneset are large sections, 3UO m high, in a raised delta along the shore. The top of these terraces near the mountain slope is at 53 m altitude, which may represent the postglacial marine limit. The date 10,230 yr B.P. (T-5273, Table 1) is correlated to that level. However, 1 km to the east, littoral gravel is found up to 73 m (Landvik et al., 1987). That site is yet not well investigated, but represents an alternative for the marine limit. Both levels are plotted in the diagram.

Vassdalen

Three kilometers from the coast is a delta east of the river. The boundary between steeply inclined foresets, dipping S-SSW, and topsets is measured by Paulin altimeter to 65 m. Just south of this is a terrace at 66-67 m. In the diagram is shown a bar at 65-67 m.

Kalvdalen

North of the river at the mouth of Kalvdalen, 5.5 km from the sea, is a deposit with foresets dipping about 30” toward east. No terrace is developed. The top of the deposit was measured with a Paulin altimeter in poor weather conditions to be 70-73 m.

Semmeldalen

East of the river at the mouth of Sem- meldalen, is a large terrace at 71 m that is 1.2 x 2.5 km in area. This level is plotted as the postglacial marine limit. Above this terrace occur several smaller terraces in the interval 103-109 m altitude. We interpret those as being formed in an ice-dammed lake along a glacier out Reindalen.

Bliihukdalen

Just west of the mouth of Blihukdalen is a large raised delta, only 1 km from the shore of Kaldbukta. A section 200 m long and 40 m high shows gravel foresets dipping SE and E, indicating deposition by a glacial river from an ice-tongue in Reindalen. The foresets are discordantly cut by a bed l-l .5 m thick, interpreted as a beach gravel. Delta topsets were not identified, and the top surface is undulating. Thus the top altitude of 70 m is a minimum for the marine limit.

Gustavdalen (on Some Maps Called Nordenski+lddalen)

At the mouth of Gustavdalen is a marked terrace in the eastern valley slope. We consider its altitude, 83 m, as the marine limit. This is supported by unwashed till at 89 m, some 5 km further east.


Lundstremdalen

in altitude, to represent the marine limit in

In Lundstromdalen, close to the junction to Kjellstromdalen, is a section along the

the area.

east bank of the river showing from the base: bedrock; a basal till, 0.6 to 1.5 m thick, and with striations on boulders suggesting that it was deposited by an ice movement toward south; gravel foresets, 20 m thick and dipping downvalley; topsets, 2-3 m thick, consisting of rounded, cobbly gravel. The top of the deposit is a terrace, that is widely distributed in the area, especially along the west side of the valley. We assume this terrace, about 60 m

grafi, og glasiasjonshistorie i omr&det Skilvika, Bell- sund og Linnedalen, Isfjorden, vestlege Spitsber- gen, Svalbard.” Unpublished Cand. Scient. thesis, University of Bergen.

Boulton, G. S. (1978). Boulder shapes and grain size distribution of debris as indicators of transport paths through a glacier and till genesis. Sedimentology 25, 173-199.

Boulton, G. S. (1979). Glacial history of the Spitsber- gen archipelago and the problem of a Barents Shelf ice sheet. Boreas 8, 31-57.

No. 53. Boulton, G. S., Baldwin, C. T., Peacock, J. D., Mc-

Cabe, A. M., Miller, G. H., Jarvis, J., Horsetield,

Boulton, G. S. (1990). Sedimentary and sea level changes during glacial cycles and their control on glacimarine facies architecture. In “Glacimarine Environments: Processes and Sediments” (J. A. Dowdeswell and J. D. Scourse, Eds.), pp. 15-23. The Geological Society London Special Publication

ACKNOWLEDGMENTS

The project was funded by grants from the Norwe- gian Research Council for Science and Humanities (NAVF), Statoil and the Norwegian Polar Research Institute, which also provided logistical support. This is a contribution to the European Science Foundation project: Polar North Atlantic Margins, late Cenozoic Evolution (PONAM). Nils Flakstad, Truls Carlsen, Helge Nesteby, Ole Bjom Sandahl, and Asbjom Man- gerud were field assistants during different seasons. Reidar Nydal, Steinar Gulliksen, and Goran Possnert provided radiocarbon dates, and Hans Petter Sejrup amino acid D/L ratios. Jane Ellingsen and Dorotha Bhicher did the drawings. Most of this manuscript was written while Jan Mangerud spent a sabbatical year at Institute of Arctic and Alpine Research, University of Colorado. He thanks the faculty members at the institute, and, especially, John Andrews, Steve Forman, and Gifford Miller who critically read the manuscript, and also corrected the English language. We thank all persons and institutions mentioned.

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Documents

The Last Glacial Maximum on Spitsbergen, Svalbard 2006 readings/Svalbard...lands of Svalbard (e.g., Spitsbergen and Nordaustlandet) (Forman, 1989). We do not include those glaciers