Lake Torfadalsvatn: a high resolution record of the North Atlantic ash zone I and the last glacial-interglacial environmental changes in Iceland SVANTE B J ~ R C K , OLAFUR ING~LFSSON, HAFLIDI HAFLIDASON, MARGRET HALLSDOTTIR AND N. JOHN ANDERSON

Bjorck, S . , Ingolfsson, O., Haflidason, H., Hallsdottir, M. & Anderson, N. J. 1992 (March): Lake Torfadalsvatn: a high resolution record of the North Atlantic ash zone I and the last glacial-interglacial environmental changes in Iceland. Boreas, Vol. 21, pp. 15-22. Oslo. ISSN 0300-9483.

B o r n A

High resolution environmental records with a refined chronology are essential to understand, reconstruct and model the climate dynamics of the last glacial-interglacial transition. Sediments from Lake Torfadals- vatn in northern Iceland contain at least four primary volcanic tephras that belong to ash zone I in the North Atlantic deep-sea cores. We chemically define these basaltic/rhyolitic tephras and the high resolution allows us to date them to about 10,800, 10,600, 9300 and 8900 BP. This detailed tephrostrati- graphy will act as a refined dating and correlation tool in the North Atlantic region and enable calibration between different absolute chronologies. The pollen stratigraphy of the sediments suggests that by 10,400 I4C years BP plant colonization of coastal north Iceland had begun. The pollen stratigraphy shows a succession of pioneer plants, from open tundra vegetation towards birch-juniper woodland, which probably also reflects a transition from a cool climate at 10,400 BP to conditions similar to today’s sub-polar oceanic climate around 9200 BP. Diatom data largely concur with the climatic information from pollen, indicating gradually increasing productivity in the lake.

Svunre Bjorck & Olafur Ingd[fson, Department of Quaternary Geology, Lund University, Tornaoagen 13, S-223 63 Lund, Sweden; Hajidi Hapidason, Department of Geology, University of Bergen, Alligatan 41, N-5007 Bergen, Norway; MargrCt Hullsddttir, Science Institute, University of Iceland, Jardfruedahus Haskdlans, IS-101 Reykjavik, Iceland; N . John Anderson, Geological Survey of Denmark, Thoruvej 8, DK-2400 Copenhagen K , Denmark; 11th November, 1991 (revised 20th January, 1992).

The last glacial termination, defined as Termina- tion I in the deep-sea cores (Shackleton et al. 1983), has been the focus of multidisciplinary research to reconstruct and understand the pat- tern, dynamics and mechanisms of events during the last glacial/interglacial transition. The rela- tionhsip between the Atlantic’s conveyor system (Broecker & Denton 1989) and the extent and timing of the polar front migrations (Ruddiman & McIntyre 1981) were of vital importance for the rapid climatic changes we see in circum- Atlantic terrestrial records between 1 1,000 and 9000 BP. Iceland has a key position to monitor these migrations, but up to now no continuous Icelandic paleoenvironmental records beyond 9700 BP have been published (Hallsdbttir 1991; Ingolfsson 1991). We now present a record that reaches beyond 10,600 BP.

The key requirement when dealing with geo- logical intervals of short duration is a high reso- lution chronology. During recent years intensive research has been aimed at relationships between the different chronologies that are used for study-

ing the termination of the Pleistocene, obtained from 14C, U/Th, varve and tree-ring dating meth- ods (Stuiver et al. 1991; Bard et al. 1990; Bjorck et al. 1987; Lotter 1991; Becker & Kromer 1986; Becker et al. 1991). Tephra horizons have proved to be excellent stratigraphic time markers in many areas due to their instantaneous fall-out, large areal distributions, and the ease with which they may be identified in different depositional environments (Thorarinsson 1944; Einarsson 1986). Therefore they are very useful for strati- graphical correlation. For example in central and northern Europe the Laacher See tephra is a widely used Late Weichselian tephra layer (van den Bogaard & Schminke 1985), and in the NW Europe/N Atlantic region the Vedde Ash (Mangerud et al. 1984) of Younger Dryas age is becoming an increasingly important time marker and time calibration horizon.

In the North Atlantic deep-sea cores, ash zone I has a key position within Termination I (Rud- diman & McIntyre 1976). However, due to low sedimentation rates, bioturbation, low C content

16 Svantr Bjorck et 01. BOREAS 21 (1992)

and other dating problems it has been difficult to I4C date this zone in detail and usually only two tephra layers can be distinguished ( SjBholm et al. 1991), the Vedde Ash (Mangerud et al. 1984) dated to c. 10,600 BP . and the Saksunarvatn Ash (Mangerud et al. (1986) dated to c. 9 100 BP. Ash zone I is originally defined on the basis of colour- less glass shards, but basaltic shards of several geochemical populations are also frequent in the same marine stratigraphic level (Kvamme et al. 1989). I t has been shown that the rhyolitic com- ponent of ash zone I and the Vedde Ash proba- bly originated from one single eruption, but the low resolution in the deep-sea sediments has not allowed for using other geochemical populations for dating or correlation purposes. Although it can be stated on the basis of the geochemistry of the tephras that Iceland is the only possible source for these tephra populations, the land- based Icelandic tephrochronology has not been extended far enough back in time to allow corre- lation with ash zone I (Sigurdsson & Loebner I981 ). There are, however. isolated occurrences of ash zone I tephras in Iceland: Norddahl (1983) described the Skogar tephra, an extensive tephra deposit in glaciolacustrine sediments in Fn- joskadalur. central north Iceland. Norddahl & Haflidason ( 1990) and Norddahl (1991) corre- lated it with the Vedde Ash. Hjort et crl. (198s) described a tephra deposit from Hzlavik, on the extreme northwest coast of Ice- land, which Kvamme (1988) correlated with the Saksunarvatn ash in the Faeroe Islands. We can now present a high resolution record of ash zone I , based on I4C-dated lake sediments from north- ernmost Iceland.

Results A s a result of a new deglaciation concept for Iceland (Ingolfsson & Hjort 1990; Ingolfsson 1991) a project was initiated with the aim of retrieving sediment cores from lakes on its ex- [reme north coast to study the late Weichselian- tarly Holocene paleoenvironmental changes in northernmost Iceland. Our hypothesis was that I he relatively low-relief Skagi peninsula ( Fig. 1 B) probably had not been seriously affected by any extensive Younger Dryas glaciation in Iceland. As the peninsula carries numerous lakes, it would be possible to obtain Late Weichselian lake sedi- ments from a key area of the last glacial/inter-

glacial transition. Two of the lakes cored during a week of fieldwork in March 1990 contained distinct tephra horizons in their oldest sediments. The thickest sequence of supposedly Late Weich- selian -early Holocene sediments was found in Lake Torfadalsvatn (Fig. IA). The lake has an area of 0.4 km2, and is situated in the northwest- ern corner of the Skagi Peninsula (Fig. IB). Its present threshold was levelled to 46. I m a d . , but has been lowered almost 1 m by man. Its original threshold is thus estimated to 47 m a.s.1.

Lithostratigraphy and chronology After having cored through 10.3 m of sediments a 'false bottom' was reached, which turned out to be a 22cm thick, very compact tephra. Below this horizon another 1.43 m of sediments was pene- trated before the coring came to a complete stop at 1 1.95 m. In this lower part of the sequence (Fig. 1A) several rather thin (0.2-1.5cm) tephras oc- cur. The bulk sediments in the lowermost 1.07 m of the sequence consist of silty clays and clays. Above follows 36 cm of gyttja clay and clay gyttja which is overlain by the 22 cm thick tephra. This is in turn covered by 74 cm of clayey gyttjas mixed with tephra particles before another thin but distinct tephra horizon appears (Fig. 1A).

Based on the sediment lithology and our de- glaciation hypothesis we assumed that the lowest part of the core was of pre-Holocene age. The location of Lake Torfadalsvatn, a t least 200 km from any active volcanic area (Fig. 1 b), makes its tephra horizons potential time markers of large areal distribution. Its tephrostratigraphy could thus be of great importance to understand the complexity of ash zone I. For this reason several levels were samples for I4C dating (Table 1). As very few organic macro remains were present in the sediments. mainly bulk sediments had to be

T d h , 1. Radiocarbon dates from Lake Torfaddlsvaln.

Depth belo\* Obtained aye sediment ''C yrs BP Dated Type of surface (cm) ( I In) material dating Lab. no.

954.5 -959.5 6000 140 Bulk Conv. Lu-3285 1035 1036 8 5 4 0 i 2 3 0 Bulk AMS Ua-I892 1051 1053 8 8 6 0 i 2 5 0 Bulk AhlS Ua-1891

1060 Y I X O ~ Z l O Mosses AMS Ua-1890 I085 1086 98YOi290 Bulk AMS Ua-1889 1095 1096 Y470k20U Bulk AMS Ua-1888

1121.5 1122.5 10.550 i 240 Bulk AMS Ua-1887

BOREAS 21 (1992) Ash zone I, Iceland 17

10.0

10.5

11.0

11.5

%. \ + \

\ I I I 1 I 1 I I I I I I

6000 7000 8000 9000 10.000 11,000 14C y e a r s BP

Fig. I . A. Lake Torfadalsvatn's lower sediment sequence including the most distinct tephra horizons. The seven I4C datings are shown to the right as horizontal lines with 20 errors. The age/depth curve is based on the dates and the age of the correlated Vedde Ash (marked with a dot). C B. The location of the Skagi Peninsula in relation to the active volcanic zones of Iceland. 0 C. The geographic position of Iceland in the North Atlantic. Ash zone I tephras have been recognized in many deep-sea cores from this region as well as in lacustrine records from bordering land areas.

dated. The carbon content in the two lowermost submitted levels was too low to allow for I4C dating. The seven obtained ages were fairly con- sistent and the shape of the age/depth curve (Fig. 1 A) indicates a transition from glacial conditions with high sedimentation rates (very high mi- nerogenic and low organic sedimentation) into postglacial conditions with lower rate. Our ex- trapolated sedimentation curve suggests that the oldest sediments were deposited before the Younger Dryas and the lowermost 1.5 m of sedi- ments before 9000 BP. The time resolution is thus 5-10 times higher than in deep-sea cores.

Tephrostratigraphy As several tephra fall-outs in Lake Torfadalsvatn can be distinguished it gives us an opportunity to

separate, date and chemically define different tephra populations deposited during the same time period as ash zone I.

After lithological and chemical studies of all the tephra horizons recorded in the lower part of the core (Fig. 1A) we conclude that at least five tephra horizons are primary tephra fall-outs of basaltic and rhyolitic compositions (Fig. 2). They are characterized by a sharp lower boundary, a compact zone consisting of >95% volcanic particles (ejecta), and a well-defined geochemical composition (Tables 2 and 3). They are all rela- tively fine-grained with a maximum grain size of 125-250 pm.

The oldest primary tephra, Tv-1, is the 1 .O cm thick black horizon at 11.13 m with a tholeiitic basalt composition (Table 2). The compositional range is limited, characterized by relatively high

BOREAS 21 (1992)

A Tor fada lsvatn

A l O 6 7 m

+ 1 1 1 3 m

T i 0 2 (7;)

B T o r f a d a l s v a t n (11.05 m)

7 4 e ' 2 ' 5

FeO' ( " to )

h q . 2. A TiO,:FeO* \ariation diagram of I'our basaltic tephra horimn3 in Lake l'orfadals\ atii. The encircled area marks the niain chemical distribution of the Saksunarvatn ash population i Mangerud ''1 ( I / 1986). ~~ R . FeO*:K,O variation dingraiii or the r l iyo l i t i c - in tem~edia te -ba~~l~~~ horimn 1 T!-2) at i I .05 ni iit Ldke Tortiidalsriitn 7 h e small dots show the chem- ical disrributioii of the Vedde A s h (Maiigerud er d 1983) and the line 01' highest lrequenc! is tentatiiely indicated

TiO? (2.8%) and AI,O, (15.3%) contents (Fig. 2A). It was found to have a very similar geo- chemical composition to tephra layer I-Thol-2 in ash zone 1. Kvamme et al. (1989) correlated it to the Saksunarvatn ash. The Torfadalsvatn se- quence shows that it i s a separate and signi- ficantly older ash layer. probably dating from 10,700- 10,800 BP (Fig. IA).

The tephra at 11.05 m, Tv-2, is a distinct 1.0- 1.5 cm thick, greyish-black horizon consisting of a mixture of rhyolitic and basaltic-intermediate glass particles of transitional alkali basalt compo- sition (Table 2). The chemcial character of this tephra is best described by the two distinctive populations of rhyolitic and basaltic-intermediate composition illustrated in the FeO*:K,O varia- tion diagram by two separate chemical trends (Fig. 2B). These two populations are very good criteria for a firm correlation of this tephra layer with the Vedde Ash (Table 3 and Fig. 2B), dated to about 10.600 BP (Mangerud rt trl. 1984).

Another tholeiitic basalt tephra horizon, Tv-3, occurs at 10.67m. It is blackish, 0.3cm thick, and consists of glass shards characterized by a low TiOz content ( 1.2%) and high MgO and CaO contents (Table 1 ) . This tephra has the same geochemical population as population I-THOL-1 in ash zone I previously dated to 10,200- 11.000 BP in deep-sea cores (Kvamme et (11.

1989). We data i t to c, 9200BP. As Tv-3 and I-THOL-I most likely correspond to the same volcanic event we think that this age difference well illustrates the problems of obtaining a reli- able ''C chronology in marine sediments with low time resolution.

The blackish 22 cm thick tephra at 10.52-

l i rhk 3 Microprobe analyses of four basaltic tephra horizons in Lake Torfadalsvatn (Tv-I, Tv-3, Tv-4 and Tv-5). The mean of inajor clernent microprobe analyses ( 1 7 ) for the basaltic horizons given together with the standard deviation (u) for each element. All aiial!se, are expressed iii weight '',, Total iron is expressed as FeO* The analyses were performed on an ARL-SEMQ electron niicroprobe. with accelerating coltage of 15 kV. beam current of 10 nA. and a beam diameter of 6&10 pm.

T\-1 f\-l TI -4 Tv-5 - ~- ~ ~ _ _ _ ~ _ _ _ _

Oxidc ( t i = I?) a (11 = 7 ) 4 ( I 7 = 9) 4 ( n = 5) u

47 0 7 2 71

l i 79 13 10

( J 13 6 31

1 I 09 ' .X I 0.46

(0.95) (0 30) I 0 38) ( 0 . 5 0 ) ( 0 06) (0.86) (0.74) (0.26) (0.06)

39.36 1.22

14.47 10.10 0.19 8.71

13.68 I91 0.11

(0.45) (0.08) (0.15) (0.10) (0.08) (0.25) (0.27) (0.14) (0.06)

48.9 I 2.84

13.43 13.76 0.27 6.02

10.60 2.56 0.43

(0.45) (0.16) (0.43) (0.23) (0.04) (0.29) (0.33) (0.23) (0.05)

48.05 4.32

13.26 14.49 0.19 5.23 9.57 3.08 0.75

(0 61) (0.08) (0.16) (0.15) (0.02) (0 20) (0.17) (0.13) (0.02)

1 old1 911 40 99 81 98 82 98 94

BOREAS 21 (1992) Ash zone I, Iceland 19

Table 3. Microprobe analyses of the composite rhyolitic-basaltic tephra horizon in Lake Torfadalsvatn, Tv-2, and at the Vedde Ash stratotype (Mangerud ef al. 1984). Compared to Table 2 the end members of the basaltic intermediate trend are added. The beam diameter was 8- 12 pm. The sodium content in the rhyolitic glass shards is depleted compared to the original concentration. The rate of sodium loss during analysis of the rhyolitic glass shards can be as much as 50% of the original concentration. The same standards were applied as in other relevant and comparable works.

Tv-2 Vedde Ash

Oxide (n = 7) U bas-int trend (n = 21) U bas-int trend

Total

71.53 0.31

13.81 4.01 0.21 0.28 1.47 2.72 3.37

97.71

(0.83) (0.21) (0.13) (0.24) (0.12) (0.17) (0.16) (0.44) (0.14)

46.87-58.71 4.65-2.70

13.03- 13.35 15.03-9.20 0.25-0.20 5.23-2.58 9.96-5.63 3.13-2.65 0.91- 2.10

77.87 0.3 1

13.25 3.79 0.15 0.21 I .23 2.1 1 3.21

(0.97) (0.14) (0.28) (0.16) (0.09) (0.04) (0.12) (0.39) (0.38)

47.26- 58.34 4.52 -2.71

12.54 - I 3.3 I 14.74-10.19 0.24 0.28 4,s: I,?

3 ' ~ 15

lJ..,/ i.. '

97.13

10.30 m, Tv-4, is of tholeiitic basalt composition. I t is interrupted several times by thin laminae ( 1 mm) of diatomite indicating a rhythmic tephra deposition over some time. The chemical analyses were performed on the initial phase of this unit, i.e. the lowermost 1-2 cm. The chemical charac- ter is similar to Tv-I, but with a slightly lower Al,O, content (Table 2) and a less compositional range (Fig. 2A) than Tv- I . The chemical charac- ter matches well with the Saksunarvatn ash (Mangerud et al. 1986), dated to c. 9100 BP. In contrast to earlier datings of this tephra we have dated both the upper and the lower contacts to the surrounding sediments. We date it to c. 8900 BP. The large areal distribution of this tephra, as indicated by previous findings of it in deep-sea cores, in Haelavik on northwestern Ice- land and on the Faeroe Islands, establishes it as an important Preboreal-Boreal marker horizon in the whole North Atlantic region.

The uppermost tephra at 9.56m, Tv-5, is 0.5 cm thick, blackish, and of transitional alkali basalt composition. It is of similar geochemical composition as the basaltic part of the Vedde Ash, but has slightly lower contents of CaO and K,O (Table 2) . Traces of tephra particles with this chemical character have been analysed from the North Altantic. The age of this tephra is, however, only about 6000 BP (Fig. lA), so from a chronological viewpoint it does not belong to ash zone I. Although it has not been possible to correlate it to any known tephra, its occurrence, just above ash zone I, is regarded as important.

Pollen stratigraphy and diatom data

Attempts to find pollen and spores in the sedi- ments were only partly successful. The lower- most 70-90 cm of sediments are barren (Fig. 3 ) both with regard to pollen and diatoms, and here the organic C content varies between 0.07 and 0.9%. Around 10,400 BP the first traces of a terrestrial vegetation can be found in the sedi- ments. Poaceae pollen dominate completely, but among the other pollen types Dryas octopetulu, Saxifraga oppositifolia, Caryophyllaceae and Thalictrum alpinum are common. The presence of these pioneer plants together with the ex- tremely low pollen influx values indicates a harsh environment. However, compared with the previous barren period a major environmental change had taken palce. Snow- and icefree ground was accessible for plants to colonize and the climate was suitable for certain plants. To- gether with the sudden presence of long-trans- ported Pinus pollen this may indicate that the polar front had already shifted to a northerly position at around 10,400 BP ~ earlier than usu- ally suggested from the deep-sea cores, but more in line with detailed NW European terrestrial records (Bjorck 1979; Lowe & Walker 1980; Atkinson et al. 1987; Bjorck & Moller 1987; Lemdahl 1991) and with Greenland ice core data (Dansgaard et al. 1989), as well as recently tephra-dated diatom stratigraphies in the Norwe- gian Sea (Karpuz & Schrader 1990). The earliest diatom assemblages in Lake Torfadalsvatn are

20 Sitante Bliirck et ul. BOREAS 21 ( 1992)

0 5 t - - ~ ~. .~~ ~ ~~~ ~ ~~~~ ~ 3 B a r r e n Sedlmenls

IJ 2 0 2 5 0 503 i o m 0 %

b"q .i Summari/cd pollen diagram from Lake Torfadalsvatn Content of organic carbon ( % of dry weight). total influx of non-long dislliiicc pollen grains (grains cm ' y r - I), relative percentages of 14 different pollen types. and the primary tephras arc: related tu age I "C grs BP x 10') as estimated from the age/depth curve (Fig. IA). Percentage curves (incl. curves enlarged by 10 x ) l o r the i'ollouing pollen t!pes are shown. 1 = D r w s ocroperaltr. 2 = TIiu/icrruni ulpintrm, 3 = Butrychiuni und., 4 = Juniperus 1 o r i 7 1 1 ~ 1 1 1 1 1 ~ . 5 = .S'ci\!/rqqu ~p[ i i~\ i t i f idI i i type. 6 = Su1i.r und.. 7 = 0.1,rriu drgynu, 8 = Brtu/u p u h r m w , 9 = Betulu nana, 10 = Koenijpu fdundr<u. 1 1 = ( i i lrhcr p d u r r u . 12 = Poomw. 13 = Arlrnmii i und.. and 14 = Pinus und. The sum of primary pollen grains varied hctueen I O X iind 585. The pcrcenlage, of long distance pollen grains were calcukited on the sum of pollen grains + sum of Arternbiu .I lld Pi/fil.S

dominated by benthic F v u g i h i u species, which indicate low plankton productivity with high wa- ter transparency. This is similar to what has been found at many late-glacial sites in NW Europe (e.g. Haworth 1976).

Around 9900 BP the pioneer vegetation had becomc more varied, with additional plants such a s for example O.~yrici d ig jm and Koetiigirr is- / m i / i w . The slowly increasing organic production in the lake and its surroundings is indicated by the gently increasing carbon and pollen influx values (Fig. -7). The diatom assemblage also be- comcs more mixed, with a small planktonic com- munity present. indicating that the conditions for biological production within the lake itself im- proved as climate ameliorated. However. effects o f the ash falls on nutrient conditions in the lake cannot be ruled out, and will be the scope of a separate study.

At 0200 BP the complete dominance of mesic indicators together with the rapidly rising carbon and pollen influx values indicates a humid climate with distinctly rising temperatures. This suggests that the glacial/interglacial transition on northern Iceland was conipletcd by 9200 BP, when this part of the North Atlantic in general has been suggested to have experienced an early Holocene temperature maximum ( Kellogg 1975: Balsam 1981; Kuddiman & McIntyre 1981; Karpuz & Schrader 1090).

The thick tephra fall-out at 8900BP seems to have had a severe impact on the environment in and around the lake. The pollen influx curve (Fig. 3 ) suggests that it may have taken several hundred years before vegetation had recover- ed. and the diatom data suggest that nutrient concentrations in the lake increased dramati- cally, resulting in massive bloom of the plank- tonic Asterionella ,furmosa. A more detailed presentation of the diatom data will be made clsewhere.

Conclusions We conclude that the Lake Torfadalsvatn se- quence contains a high resolution tephra record for the last glacial/interglacial transition. Apart from the two previously defined tephra layers, the Vedde Ash and the Saksunarvatn ash, we re- solve some of the stratigraphic problems related to the Saksunarvatn ash and redate the I-THOL- 1 ash. An additional ash zone I tephra, Tv-1, previously named I-Thol-2 and tentatively corre- lated with the Saksunarvatn ash, is defined and dated. This means that we can now date, and stratigraphically and chemically define, four tephras (Tv-1 to Tv-4) that belong to ash zone I (Table 4). The complexity of this zone is now largely sorted out, which gives us a refined dating

BOREAS 21 (1992) Ash zone I , Iceland 21

Table 4. Levels, designated abbreviations, estimated ages and likely correlations of the five studied primary tephra horizons in Lake Torfadalsvatn.

Bard, E., Hamelin, B., Fairbanks, R. G. & Zindler, A. 1990: Calibration of the I4C timescale over the past 30,000 years using mass spectrometric U-Th ages from Barbados corals. Nature 345, 405-410.

Sediment Tephra Estimated age Likely depth abbreviation (I4C yrs BP) correlation

9.56m Tv-5 6000 10.52m Tv-4 8900 Saksunarvatn ash 10.67111 Tv-3 9200 I-THOL-I 11.05 m Tv-2 10,600 Vedde Ash 11.13m Tv-I 10,800 I-Thol-2

and correlation tool for use in continental and marine paleoclimatological studies in and around the North Atlantic region. Our next step will be to look for these Late Pleistocene/early Holocene tephra horizons in the Swedish varved clays to establish correlation between the I4C chronology and the clay-varve based Swedish Time Scale (Cato 1987; Bjorck et al. in press).

The sequence in Lake Torfadalsvatn contains the first Icelandic terrestrial, biostratigraphic data from the last glacial/interglacial transition. They show the vegetational succession from an open tundra around 10,400 BP, with more humid and mild conditions around 9200, and the develop- ment towards birch-juniper woodland in late Boreal times. The data suggest that the rate of post-glacial climatic change was subdued in northern Iceland compared to northwestern Europe.

Acknowledgetnents. - The study is financed by the Swedish Natural Science Research Council (NFR), Icelandic Council of Science (Visindasjodur), Kungliga Fysiografiska Sallskapet in Lund, and the Norwegian Research Council for Science and the Humanities (NAVF) through the Klimbre project. Halldor PCtursson at the Museum of Natural History in Akureyri helped with the field logistics, Per Sandgren and Thorsteinn Saemundsson helped with the corings, Ole Tumyr assisted with the microprobe analyses, and Ingibjorg S. Jonsdottir gave us information about Icelandic plant ecology. The study is a part of IGCP-253: Termination of the Pleistocene, North Atlantic Seaboard Programme (NASP).

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