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1.
The sediment core NP05‐71GC, retrieved from 360 m water depth south of Kvitøya, northwestern Barents Sea, was investigated for the distribution of benthic and planktic foraminifera, stable isotopes and sedimentological parameters to reconstruct palaeoceanographic changes and the growth and retreat of the Svalbard–Barents Sea Ice Sheet during the last ～16 000 years. The purpose is to gain better insight into the timing and variability of ocean circulation, climatic changes and ice‐sheet behaviour during the deglaciation and the Holocene. The results show that glaciomarine sedimentation commenced c. 16 000 a BP, indicating that the ice sheet had retreated from its maximum position at the shelf edge around Svalbard before that time. A strong subsurface influx of Atlantic‐derived bottom water occurred from 14 600 a BP during the Bølling and Allerød interstadials and lasted until the onset of the Younger Dryas cooling. In the Younger Dryas cold interval, the sea surface was covered by near‐permanent sea ice. The early Holocene, 11 700–11 000 a BP, was influenced by meltwater, followed by a strong inflow of highly saline and chilled Atlantic Water until c. 8600 a BP. From 8600 to 7600 a BP, faunal and isotopic evidence indicates cooling and a weaker flow of the Atlantic Water followed by a stronger influence of Atlantic Water until c. 6000 a BP. Thereafter, the environment generally deteriorated. Our results imply that (i) the deglaciation occurred earlier in this area than previously thought, and (ii) the Younger Dryas ice sheet was smaller than indicated by previous reconstructions.  相似文献   

2.
Erbs‐Hansen, D. R., Knudsen, K. L., Gary, A. C., Jansen, E., Gyllencreutz, R., Scao, V. & Lambeck, K. 2011: Late Younger Dryas and early Holocene palaeoenvironments in the Skagerrak, eastern North Atlantic: a multiproxy study. Boreas, 10.1111/j.1502‐3885.2011.00205.x. ISSN 0300‐9843 A high‐resolution study of palaeoenvironmental changes through the late Younger Dryas and early Holocene in the Skagerrak, the eastern North Atlantic, is based on multiproxy analyses of core MD99‐2286 combined with palaeowater depth modelling for the area. The late Younger Dryas was characterized by a cold ice‐distal benthic foraminiferal fauna. After the transition to the Preboreal (c. 11 650 cal. a BP) this fauna was replaced by a Cassidulina neoteretis‐dominated fauna, indicating the influence of chilled Atlantic Water at the sea floor. Persisting relatively cold bottom‐water conditions until c. 10 300 cal. a BP are presumably a result of an outflow of glacial meltwater from the Baltic area across south‐central Sweden, which led to a strong stratification of the water column at MD99‐2286, as also indicated by C. neoteretis. A short‐term peak in the C/N ratio at c. 10 200 cal. a BP is suggested to indicate input of terrestrial material, which may represent the drainage of an ice‐dammed lake in southern Norway, the Glomma event. After the last drainage route across south‐central Sweden closed, c. 10 300 cal. a BP, the meltwater influence diminished, and the Skagerrak resembled a fjord with a stable inflow of waters from the North Atlantic through the Norwegian Trench and a gradual increase in boreal species. Full interglacial conditions were established at the sea floor from c. 9250 cal. a BP. Subsequent warm stable conditions were interrupted by a short‐term cooling around 8300–8200 cal. a BP, representing the 8.2 ka event.  相似文献   

3.
Core MD95‐2011 was taken from the eastern Vøring Plateau, near the Norwegian coast. The section between 250 and 750 cm covers the time period from 13 000 to 2700 cal. yr BP (the Lateglacial and much of the Holocene). Samples at 5 cm intervals were analysed for fossil diatoms. A data‐set of 139 modern sea‐surface diatom samples was related to contemporary sea‐surface temperatures (SSTs) using two different numerical methods. The resulting transfer functions were used to reconstruct past sea‐surface temperatures from the fossil diatom assemblages. After the cold Younger Dryas with summer SSTs about 6°C, temperatures warmed rapidly to about 13°C. One of the fluctuations in the earliest Holocene can be related to the Pre‐Boreal Oscillation, but SSTs were generally unstable until about 9700 cal. yr BP. Evidence from diatom concentration and magnetic susceptibility suggests a change and stabilization of water currents associated with the final melting of the Scandinavian Ice Sheet at c. 8100 cal. yr BP. A period of maximum warmth between 9700 and 6700 cal. yr BP had SSTs 3–5°C warmer than at present. Temperatures cooled gradually until c. 3000 cal. yr BP, and then rose slightly around 2750 cal. yr BP. The varimax factors derived from the Imbrie & Kipp method for sea‐surface‐temperature reconstructions can be interpreted as water‐masses. They show a dominance of Arctic Waters and Sea Ice during the Younger Dryas. The North Atlantic current increased rapidly in strength during the early Holocene, resulting in warmer conditions than previously. Since about 7250 cal. yr BP, Norwegian Atlantic Water gradually replaced the North Atlantic Water, and this, in combination with decreasing summer insolation, led to a gradual cooling of the sea surface. Terrestrial systems in Norway and Iceland responded to this cooling and the increased supply of moisture by renewed glaciation. Periods of glacial advance can be correlated with cool oscillations in the SST reconstructions. By comparison with records of SSTs from other sites in the Norwegian Sea, spatial and temporal changes in patterns of ocean water‐masses are reconstructed, to reveal a complex system of feedbacks and influences on the climate of the North Atlantic and Norway.  相似文献   

4.
《Quaternary Science Reviews》2007,26(3-4):463-478
The changes in flow and character of the warm Atlantic Water through the last 17,500 cal yr are reconstructed from the distribution of benthic foraminifera species, planktonic and benthic foraminifera abundances, stable oxygen isotopes and lithology in two cores from the western and northern shelf of Svalbard. The results show almost continuous presence of Atlantic Water at the shelf areas since >14,500 cal yr BP. The Bølling and Allerød intervals stand out as periods of highest bottom waters temperatures. The strong inflow of saline, but chilled Atlantic Water during the early Holocene was followed by cooling and freshening of the bottom waters during the mid- and late Holocene. The two records reveal synchronous oceanographic changes that are closely tied to changes in the flow of Atlantic Water recorded further south in the Nordic seas. The early Holocene warming was not just an effect of higher solar insolation, but was also due to increased heat flux from the stronger Atlantic Water inflow driven by wind force and/or thermohaline circulation.  相似文献   

5.
Articulated molluscs, sea urchins and barnacle fragments close to the Vedde Ash Bed in a shallow marine deposit on the west coast of Norway have been 14C dated. The weighted mean of four dates from a sediment slice 8 cm thick centred on the Vedde Ash Bed is 10920 ± 24 14C yr BP. The most accurate 14C age of the Vedde Ash from terrestrial plant macrofossils is 10310 ± 50 yr BP. The difference is the 14C reservoir age for coastal water at the west coast of Norway during the mid‐Younger Dryas and equals 610 ± 55 yr. This is 230 yr older than the reservoir age for the Bølling/Allerød and for the present day in this area. The result supports earlier conclusions of a higher reservoir age for the Younger Dryas in the North Atlantic and Nordic Seas, although our reservoir age of 610 ± 55 yr is a few hundred years younger. This suggests that the 14C reservoir age at Vedde Ash time may increase from coastal water towards the open North Atlantic and Nordic Seas. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

6.
A detailed shoreline displacement curve documents the Younger Dryas transgression in western Norway. The relative sea‐level rise was more than 9 m in an area which subsequently experienced an emergence of almost 60 m. The sea‐level curve is based on the stratigraphy of six isolation basins with bedrock thresholds. Effort has been made to establish an accurate chronology using a calendar year time‐scale by 14C wiggle matching and the use of time synchronic markers (the Vedde Ash Bed and the post‐glacial rise in Betula (birch) pollen). The sea‐level curve demonstrates that the Younger Dryas transgression started close to the Allerød–Younger Dryas transition and that the high stand was reached only 200 yr before the Younger Dryas–Holocene boundary. The sea level remained at the high stand for about 300 yr and 100 yr into Holocene it started to fall rapidly. The peak of the Younger Dryas transgression occurred simultaneously with the maximum extent of the ice‐sheet readvance in the area. Our results support earlier geophysical modelling concluding a causal relationship between the Younger Dryas glacier advance and Younger Dryas transgression in western Norway. We argue that the sea‐level curve indicates that the Younger Dryas glacial advance started in the late Allerød or close to the Allerød–Younger Dryas transition. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

7.
《Quaternary Science Reviews》2004,23(20-22):2231-2246
Palaeoclimatic changes through the last 1200 calibrated years have been documented by high-resolution multi-proxy studies of three cores from about 400 m water depth on the North Icelandic shelf. Benthic and planktonic foraminiferal assemblages and stable isotope values, as well as ice rafted debris (IRD) concentrations, are compared with diatom-based sea-surface water temperatures and the reconstructed mean temperature for the Northern Hemisphere. Changes in surface and bottom water characteristics are mainly due to variations in the strength of the relatively warm, high-salinity Irminger Current and the cold East Icelandic Current. The time period between 1200 and around 7–800 cal. (years) BP, including the Medieval Warm Period, was characterized by relatively high bottom and surface water temperatures due to the inflow of Atlantic water masses. After that, a general temperature decrease in the area marks the transition to a period with increased influence of the East Icelandic Current and, at the sea floor, the Norwegian Sea Deep Water. This corresponds to the transition to the Little Ice Age. After about 3–400 cal. BP, the inflow of cold East Icelandic Current was further enhanced. In particular, this had a strong influence on the surface waters, while the sea floor was under some influence of Atlantic water masses, resulting in stratification of the water masses. There is no clear indication of any warming in the area during the last decades.  相似文献   

8.
High resolution cores from the upper continental slope, northern Norwegian Sea, document rapid climatic fluctuations during the latest deglaciation and the Holocene. Based on down-core analysis of planktic and benthic foraminifera, stable oxygen and carbon isotopes, carbonate and organic carbon and radiocarbon dating, the following evolution is proposed: sea-ice cover broke up, the surface ocean warmed and an in situ benthic foraminiferal fauna was established at 12 500 BP. The Younger Dryas was characterized by reduced sedimentaion and foraminiferal production, due to surface ocean cooling. At the end of the Younger Dryas there were major shifts in both surface and bottom water conditions. The surface ocean warmed to temperatures similar to modern levels within < 100 years, reaching a maximum at about 9200 BP when foraminiferal production was high. A benthic foraminiferal assemblage indicative of bottom water conditions similar to present conditions was established at 10 000 BP. This was followed by a gradual decline in nutrients or an increase in ventilation of the bottom water throughout the Holocene. A gradual surface ocean cooling of c . 2°C ended around 6500 BP followed by a second warming that culminated at 2000 BP. The warming at the end of the Younger Dryas and the succeeding older Holocene temperature maximum correlate to a June insolation maximum in the northern hemisphere. In addition, fluctuating surface temperatures in the Holocene may be driven by variations in inflow of Atlantic Water.  相似文献   

9.
Sediment proxy records from a continuous, 1.5 million year long deep‐sea sediment core from a site in the western Norwegian Sea were used to obtain new insights into the nature of palaeoceanographic change in the northern North Atlantic (Nordic seas) during the climatic shift of the Mid‐Pleistocene Revolution (MPR). Red‐green sediment colour and magnetic susceptibility records both reveal significant differences in their mean values when comparing the intervals older than 700 000 yr (700 ka) with those from the past 500 kyr. The timing and duration of these changes indicates that the MPR in the Nordic seas is characterised by a gradual transition lasting about 200 kyr. Together with further sedimentological evidence this suggests that the mid‐Pleistocene climate shift was accompanied by a general change in ice‐drift pattern. It is further proposed that prior to the onset of the major late Pleistocene glaciations in the Northern Hemisphere a significant proportion of the ice in the eastern Nordic seas originated from a southern provenance, whereas later it dominantly came from the surrounding landmasses. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

10.
A late Quaternary deep-water stratigraphic framework has been established for the deep-water areas (>450m) of the northern Rockall Trough and Faeroe-Shetland Channel. Four stratigraphic units (1–4) are identified; these are primarily biostratigraphic units based on dinoflagellate cyst evidence. Unit 1 represents the late Weichselian glacial (pre-13 000 yr BP); unit 2 the Late Glacial Interstadial (11 000-13 000 yr BP); unit 3 is of Younger Dryas age (10 000-11 000 yr BP); and unit 4 represents the Holocene interglacial (post-10 000 yr BP). This stratigraphy is supported by the discovery of the mixed Vedde Ash (10 600 yr BP) and North Atlantic Ash zone 1, and the Saksunarvatn Ash (9000–9100 yr BP), concentrated in units 3 and 4 respectively. The sedimentology indicates that the oceanographic regime underwent a major change between the glacial and interglacial stages. This is marked by the onset of strong bottom current activity, allied to the restoration of overflow of the Norwegian Sea Deep Water into the North Atlantic, towards the end of the Younger Dryas Stadial. Despite intense bioturbation and bottom-current reworking the basic stratigraphic framework is maintained. Recognition of two volcanic ash markers enables correlation with established onshore and offshore sequences of marine and non-marine environments.  相似文献   

11.
This paper presents an event stratigraphy based on data documenting the history of vegetation cover, lake‐level changes and fire frequency, as well as volcanic eruptions, over the Last Glacial–early Holocene transition from a terrestrial sediment sequence recovered at Lake Accesa in Tuscany (north‐central Italy). On the basis of an age–depth model inferred from 13 radiocarbon dates and six tephra horizons, the Oldest Dryas–Bølling warming event was dated to ca. 14 560 cal. yr BP and the Younger Dryas event to ca. 12 700–11 650 cal. yr BP. Four sub‐millennial scale cooling phases were recognised from pollen data at ca. 14 300–14 200, 13 900–13 700, 13 400–13 100 and 11 350–11 150 cal. yr BP. The last three may be Mediterranean equivalents to the Older Dryas (GI‐1d), Intra‐Allerød (GI‐1b) and Preboreal Oscillation (PBO) cooling events defined from the GRIP ice‐core and indicate strong climatic linkages between the North Atlantic and Mediterranean areas during the last Termination. The first may correspond to Intra‐Bølling cold oscillations registered by various palaeoclimatic records in the North Atlantic region. The lake‐level record shows that the sub‐millennial scale climatic oscillations which punctuated the last deglaciation were associated in central Italy with different successive patterns of hydrological changes from the Bølling warming to the 8.2 ka cold reversal. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

12.
In the Nordic Seas, the Arctic front (AF) marks the boundary between the waters of the North Atlantic Drift/Norwegian Current and those of the Arctic domain. Long- or short-term shifts in the position of the AF may affect climate conditions in the northern hemisphere. Arctic water masses are also the loci of modern open ocean convection; hence, defining these areas in the past is important for reconstructing and modelling ocean circulation and its variability. C37 alkenones are biomarkers for some algae of the Class Prymnesiophyceae (e.g. coccolitho-phorids such as Emiliania huxleyi). These alga occur in most parts of the oceans, in ice-free conditions, and are found nowadays throughout the Nordic Seas. We have related the sedimentary abundance of the tetraunsaturated C37 alkenone (C37:4) to two types of water masses in the Nordic seas. In locations affected by Atlantic water masses percentages of C37:4 are less than 5%, whereas in Arctic type water masses these increase to more than 5%. We propose that this observation can be used as a modern analogue to reconstruct the position of the AF in North Atlantic Quaternary sediments. Using this novel molecular proxy we can infer that the southward migration of the AF in the NE Atlantic reached ≈ 50 °N during the last glacial maximum (LGM), but perhaps only 60 °N during the Younger Dryas, and that ocean conditions free of sea ice prevailed throughout the Northern North Atlantic in summer.  相似文献   

13.
Mangerud, J., Gulliksen, S. & Larsen, E. 2009: 14C‐dated fluctuations of the western flank of the Scandinavian Ice Sheet 45–25 kyr BP compared with Bølling–Younger Dryas fluctuations and Dansgaard–Oeschger events in Greenland. Boreas, 10.1111/j.1502‐3885.2009.00127.x. ISSN 0300‐9483. We present 32 accelerator mass spectrometry (AMS) 14C dates obtained on well‐preserved bones from caves in western Norway. The resulting ages of 34–28 14C kyr BP demonstrate that the coast was ice‐free during the so‐called Ålesund Interstadial. New AMS 14C dates on shells aged 41–38 14C kyr BP are evidence of an earlier (Austnes) ice‐free period. The Ålesund Interstadial correlates with Greenland interstadials 8–7 and the Austnes Interstadial with Greenland interstadials 12–11. Between and after the two interstadials, the ice margin reached onto the continental shelf west of Norway. These events can be closely correlated with the Greenland ice core stratigraphy, partly based on identification of the Laschamp and Mono Lake palaeomagnetic excursions. We found that the pattern of the NGRIP δ18O curves for the two periods Greenland Interstadial (GI) 8 to Greenland Stadial (GS) 8 and GI 1–GS 1 (Bølling–Younger Dryas) were strikingly similar, which leads us to suggest that the underlying causes of these climate shifts could have been the same. We therefore discuss some aspects of glacial fluctuations during the Bølling–Younger Dryas in order to elucidate processes during Dansgaard–Oeschger events.  相似文献   

14.
We present two new quantitative July mean temperature (Tjul) reconstructions from the Arctic tree-line region in the Kola Peninsula in north-western Russia. The reconstructions are based on fossil pollen records and cover the Younger Dryas stadial and the Holocene. The inferred temperatures are less reliable during the Younger Dryas because of the poorer fit between the fossil pollen samples and the modern samples in the calibration set than during the Holocene. The results suggest that the Younger Dryas Tjul in the region was 8.0–10.0°C, being 2.0–3.0°C lower than at present. The Holocene summer temperature maximum dates to 7500–6500 cal yr BP, with Tjul about 1.5°C higher than at present. These new records contribute to our understanding of summer temperature changes along the northern-European tree-line region. The Holocene trends are consistent in most of the independent records from the Fennoscandian–Kola tree-line region, with the beginning of the Holocene thermal maximum no sooner than at about 8000 cal yr BP. In the few existing temperature-related records farther east in the Russian Arctic tree line, the period of highest summer temperature begins already at about 10,000 cal yr BP. This difference may reflect the strong influence of the Atlantic coastal current on the atmospheric circulation pattern and the thermal behaviour of the tree-line region on the Atlantic seaboard, and the more direct influence of the summer solar insolation on summer temperature in the region east of the Kola Peninsula.  相似文献   

15.
The upwelling region off northwest Africa is one of the most productive regions in the world ocean. This study details the response of surface‐ and deep‐water environments off Mauritania, northwest Africa, to the rapid climate events of the last deglaciation, especially the Bølling–Allerød (15.5–13.5 ka BP) and Younger Dryas (13.5–11.5 ka BP). A high accumulation rate gravity core GeoB7926‐2, recovered at ～20° N, 18° W, was analysed for the grain size distribution of the terrigenous sediment fraction, the organic carbon content, diatom and benthic foraminifera communities. Humid conditions were observed during the Bølling–Allerød with a high contribution of fluvial sediment input. During the Younger Dryas intensified trade winds caused a larger sediment input of aeolian dust from the Sahara and more intense upwelling with higher primary productivity, as indicated by high diatom concentrations. The abrupt and large increase of organic matter caused low oxygen conditions at the sea floor, reflected by the poor benthic foraminiferal fauna and the dominance of the low‐oxygen‐tolerant foraminiferal species Bulimina exilis. This is surprising since low‐oxygen conditions have not been recorded during modern times at the sea floor in this region, despite present‐day intensive upwelling and high primary productivity. After the Younger Dryas, more humid conditions returned, diatom abundance decreased and B. exilis was replaced by typical deep‐sea species as found in the region today, indicating the return of more oxygenated conditions at the sea floor. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

16.
New records of planktonic foraminiferal δ18O and lithic and foraminiferal counts from Eirik Drift are combined with published data from the Nordic Seas and the “Ice Rafted Debris (IRD) belt”, to portray a sequence of events through Heinrich event 1 (H1). These events progressed from an onset of meltwater release at ～19 ka BP, through the ‘conventional’ H1 IRD deposition phase in the IRD belt starting from ～17.5 ka BP, to a final phase between 16.5 and ～15 ka BP that was characterised by a pooling of freshwater in the Nordic Seas, which we suggest was hyperpycnally injected into that basin. After ～15 ka BP, this freshwater was purged from the Nordic Seas into the North Atlantic, which preconditioned the Nordic Seas for convective deep-water formation. This allowed an abrupt re-start of North Atlantic Deep Water (NADW) formation in the Nordic Seas at the Bølling warming (14.6 ka BP). In contrast to previous estimates for the duration of H1 (i.e., 1000 years to only a century or two), the total, combined composite H1 signal presented here had a duration of over 4000 yrs (～19–14.6 ka BP), which spanned the entire period of NADW collapse. It appears that deep-water formation and climate are not simply controlled by the magnitude or rate of meltwater addition. Instead the location of meltwater injections may be more important, with NADW formation being particularly sensitive to surface freshening in the Arctic/Nordic Seas.  相似文献   

17.
Comparatively little research has been undertaken on relative sea‐level (RSL) change in western Iceland. This paper presents the results of diatom, tephrochronological and radiocarbon analyses on six isolation basins and two coastal lowland sediment cores from the Stykkishólmur area, northern Snæfellsnes, western Iceland. The analyses provide a reconstruction of Lateglacial to mid‐Holocene RSL changes in the region. The marine limit is measured to 65–69 m above sea level (asl), with formation being estimated at 13.5 cal ka BP. RSL fall initially occurred rapidly following marine limit formation, until ca. 12.6 cal ka BP, when the rate of RSL fall decreased. RSL fell below present in the Stykkishólmur area during the early Holocene (by ca. 10 cal ka BP). The rates of RSL change noted in the Stykkishólmur area demonstrate lesser ice thicknesses in Snæfellsnes than Vestfirðir during the Younger Dryas, when viewed in the regional context. Consequently, the data provide an insight into patterns of glacio‐isostatic adjustment surrounding Breiðafjörður, a hypothesized major ice stream at the Last Glacial Maximum.  相似文献   

18.
Expansion of fresh and sea‐ice loaded surface waters from the Arctic Ocean into the sub‐polar North Atlantic is suggested to modulate the northward heat transport within the North Atlantic Current (NAC). The Reykjanes Ridge south of Iceland is a suitable area to reconstruct changes in the mid‐ to late Holocene fresh and sea‐ice loaded surface water expansion, which is marked by the Subarctic Front (SAF). Here, shifts in the location of the SAF result from the interaction of freshwater expansion and inflow of warmer and saline (NAC) waters to the Ridge. Using planktic foraminiferal assemblage and concentration data from a marine sediment core on the eastern Reykjanes Ridge elucidates SAF location changes and thus, changes in the water‐mass composition (upper ˜200 m) during the last c. 5.8 ka BP. Our foraminifer data highlight a late Holocene shift (at c. 3.0 ka BP) in water‐mass composition at the Reykjanes Ridge, which reflects the occurrence of cooler and fresher surface waters when compared to the mid‐Holocene. We document two phases of SAF presence at the study site: from (i) c. 5.5 to 5.0 ka BP and (ii) c. 2.7 to 1.5 ka BP. Both phases are characterized by marked increases in the planktic foraminiferal concentration, which coincides with freshwater expansions and warm subsurface water conditions within the sub‐polar North Atlantic. We link the SAF changes, from c. 2.7 to 1.5 ka BP, to a strengthening of the East Greenland Current and a warming in the NAC, as identified by various studies underlying these two currents. From c. 1.5 ka BP onwards, we record a prominent subsurface cooling and continued occurrence of fresh and sea‐ice loaded surface waters at the study site. This implies that the SAF migrated to the southeast of our core site during the last millennium.  相似文献   

19.
Few well‐dated records of the deglacial dynamics of the large palaeo‐ice streams of the major Northern Hemisphere ice sheets are presently available, a prerequisite for an improved understanding of the ice‐sheet response to the climate warming of this period. Here we present a transect of gravity‐core samples through Trænadjupet and Vestfjorden, northern Norway, the location of the Trænadjupet – Vestfjorden palaeo‐ice stream of the NW sector of the Fennoscandian Ice Sheet. Initial ice recession from the shelf break to the coastal area (~400 km) occurred at an average rate of about 195 m a−1, followed by two ice re‐advances, at 16.6–16.4 ka BP (the Røst re‐advance) and at 15.8–15.6 ka BP (the Værøy re‐advance), the former at an estimated ice‐advance rate of 216 m a−1. The Røst re‐advance has been interpreted to be part of a climatically induced regional cold spell while the Værøy re‐advance was restricted to the Vestfjorden area and possibly formed as a consequence of internal ice‐sheet dynamics. Younger increases in IRD content have been correlated to the Skarpnes (Bølling – Older Dryas) and Tromsø – Lyngen (Younger Dryas) Events. Overall, the decaying Vestfjorden palaeo‐ice stream responded to the climatic fluctuations of this period but ice response due to internal reorganization is also suggested. Separating the two is important when evaluating the climatic response of the ice stream. As demonstrated here, the latter may be identified using a regional approach involving the study of several palaeo‐ice streams. The retreat rates reported here are of the same order of magnitude as rates reported for ice streams of the southern part of the Fennoscandian Ice Sheet, implying no latitudinal differences in ice response and retreat rate for this ~1000 km2 sector of the Fennoscandian Ice Sheet (~60–68°N) during the climate warming of this period.  相似文献   

20.
Blomvåg, on the western coast of Norway north of Bergen, is a classical site in Norwegian Quaternary science. Foreshore marine sediments, named the Blomvåg Beds and now dated to the Bølling‐Allerød from 14.8 to 13.3 cal. ka BP, contain the richest Lateglacial bone fauna in Norway, numerous mollusc shells, driftwood, and flint that some archaeologists consider as the oldest traces of humans in Norway. The main theme of this paper is that the Blomvåg Beds are overlain by a compact diamicton, named the Ulvøy Diamicton, which was interpreted previously as a basal till deposited during a glacial re‐advance into the ocean during the Older Dryas (c. 14 cal. ka BP). Sediment sections of the Blomvåg Beds and the Ulvøy Diamicton were exposed in ditches in a cemetery that was constructed in 1941–42 and have subsequently not been accessible. A number of radiocarbon and cosmogenic 10Be exposure ages demonstrate that the diamicton is not likely to be a till because minimum deglaciation ages (14.8–14.5 cal. ka BP) from the vicinity pre‐date the Ulvøy Diamicton. We now consider that sea ice and icebergs formed the Ulvøy Diamicton during the Younger Dryas. The Scandinavian Ice Sheet margin was located on the outermost coastal islands between at least c. 18.5 and 14.8 cal. ka BP; however, no ice‐marginal deposits have been found offshore from this long period. The Older Dryas ice margin in this area was located slightly inside the Younger Dryas margin, whereas farther south it was located slightly beyond the Younger Dryas margin.  相似文献   

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