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1.
The extent of the Barents-Kara Sea ice sheet (northern Europe and Russia) during the Last Glacial Maximum (LGM), in Marine Isotope Stage (MIS) 2 is controversial, especially along the southern and northeastern (Russian High Arctic) margins. We conducted a multi-disciplinary study of various organic and mineral fractions, obtaining chronologies with 14C and luminescence dating methods on a 10.5 m long core from Changeable Lake (4 km from the Vavilov Ice Cap) on Severnaya Zemlya. The numeric ages indicate that the last glaciation at this site occurred during or prior to MIS 5d-4 (Early Middle Weichselian). Deglaciation was followed by a marine transgression which affected the Changeable Lake basin. After the regression the basin dried up. In late Middle Weichselian time (ca 25–40 ka), reworked marine sediments were deposited in a saline water body. During the Late Weichselian (MIS 2), the basin was not affected by glaciation, and lacustrine sediments were formed which reflect cold and arid climate conditions. During the termination of the Pleistocene and into the Holocene, warmer and wetter climate conditions than before led to a higher sediment input. Thus, our chronology demonstrates that the northeastern margin of the LGM Barents-Kara Sea ice sheet did not reach the Changeable Lake basin. This result supports a modest model of the LGM ice sheet in northern Europe determined from numeric ice sheet modelling and geological investigations.  相似文献   

2.
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3.
This study presents a multi‐proxy record from Lake Kotokel in the Baikal region at decadal‐to‐multidecadal resolution and provides a reconstruction of terrestrial and aquatic environments in the area during a 2000‐year interval of globally harsh climate often referred to as the Last Glacial Maximum (LGM). The studied lake is situated near the eastern shoreline of Lake Baikal, in a climatically sensitive zone that hosts boreal taiga and cold deciduous forests, cold steppe associations typical for northern Mongolia, and mountain tundra vegetation. The results provide a detailed picture of the period in focus, indicating (i) a driest phase (c. 24.0–23.4 cal. ka BP) with low precipitation, high summer evaporation, and low lake levels, (ii) a transitional interval of unstable conditions (c. 23.4–22.6 cal. ka BP), and (iii) a phase (c. 22.6–22.0 cal. ka BP) of relatively high precipitation (and moisture availability) and relatively high lake levels. One hotly debated issue in late Quaternary research is regional summer thermal conditions during the LGM. Our chironomid‐based reconstruction suggests at least 3.5 °C higher than present summer temperatures between c. 22.6 and 22.0 cal. ka BP, which are well in line with warmer and wetter conditions in the North Atlantic region inferred from Greenland ice‐cores. Overall, it appears that environments in central Eurasia during the LGM were affected by much colder than present winter temperatures and higher than present summer temperatures, although the effects of temperature oscillations were strongly influenced by changes in humidity.  相似文献   

4.
The Tibetan Plateau is a topographic feature of extraordinary dimension and has an important impact on regional and global climate. However, the glacial history of the Tibetan Plateau is more poorly constrained than that of most other formerly glaciated regions such as in North America and Eurasia. On the basis of some field evidence it has been hypothesized that the Tibetan Plateau was covered by an ice sheet during the Last Glacial Maximum (LGM). Abundant field- and chronological evidence for a predominance of local valley glaciation during the past 300,000 calendar years (that is, 300 ka), coupled to an absence of glacial landforms and sediments in extensive areas of the plateau, now refute this concept. This, furthermore, calls into question previous ice sheet modeling attempts which generally arrive at ice volumes considerably larger than allowed for by field evidence. Surprisingly, the robustness of such numerical ice sheet model results has not been widely queried, despite potentially important climate ramifications. We simulated the growth and decay of ice on the Tibetan Plateau during the last 125 ka in response to a large ensemble of climate forcings (90 members) derived from Global Circulation Models (GCMs), using a similar 3D thermomechanical ice sheet model as employed in previous studies. The numerical results include as extreme end members as an ice-free Tibetan Plateau and a plateau-scale ice sheet comparable, in volume, to the contemporary Greenland ice sheet. We further demonstrate that numerical simulations that acceptably conform to published reconstructions of Quaternary ice extent on the Tibetan Plateau cannot be achieved with the employed stand-alone ice sheet model when merely forced by paleoclimates derived from currently available GCMs. Progress is, however, expected if future investigations employ ice sheet models with higher resolution, bidirectional ice sheet-atmosphere feedbacks, improved treatment of the surface mass balance, and regional climate data and climate reconstructions.  相似文献   

5.
Late-glacial (17–11 cal ka BP) pollen records from midwestern North America show similar vegetation trends; however, poor dating resolution, wide-interval pollen counts, and variable sedimentation rates have prevented the direct correlation with the North Atlantic Event Stratigraphy as represented in the Greenland ice-core records, thus preventing the understanding of the teleconnections and mechanisms of late-Quaternary events in the Northern Hemisphere. The widespread occurrence of late-glacial vegetation and climates with no modern analogs also hinders late-glacial climate reconstructions. A high-resolution pollen record with a well-controlled age model from Crystal Lake in northeastern Illinois reveals vegetation and climate conditions during the late-glacial and early Holocene intervals. Late-glacial Crystal Lake pollen assemblages, dominated by Picea mariana and Fraxinus nigra with lesser amounts of Abies and Larix, suggest relatively wet climate despite fluctuations between colder and warmer temperatures. Vegetation changes at Crystal Lake are coeval with millennial-scale trends in the NGRIP ice-core record, but major shifts in vegetation at Crystal Lake lag the NGRIP record by 300–400 yr. This lag may be due to the proximity of the Laurentide ice sheet, the ice sheet's inherent slowness in response to rapid climate changes, and its effect on frontal boundary conditions and lake-effect temperatures.  相似文献   

6.
The extent of the last British–Irish Ice Sheet (BIIS) in northern Scotland is disputed. A restricted ice sheet model holds that at the global Last Glacial Maximum (LGM; ca. 23–19 ka) the BIIS terminated on land in northern Scotland, leaving Buchan, Caithness and the Orkney Islands ice‐free. An alternative model implies that these three areas were ice‐covered at the LGM, with the BIIS extending offshore onto the adjacent shelves. We test the two models using cosmogenic 10Be surface exposure dating of erratic boulders and glacially eroded bedrock from the three areas. Our results indicate that the last BIIS covered all of northern Scotland during the LGM, but that widespread deglaciation of Caithness and Orkney occurred prior to rapid warming at ca. 14.5 ka. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

7.
The behaviour of ice sheets as they retreated from their Last Glacial Maximum (LGM) positions provides insights into Lateglacial and early Holocene ice‐sheet dynamics and climate change. The pattern of deglaciation of the Laurentide Ice Sheet (LIS) in arctic fiord landscapes can now be well dated using cosmogenic exposure dating. We use cosmogenic exposure and radiocarbon ages to constrain the deglaciation history of Clyde Inlet, a 120 km long fiord on northeastern Baffin Island. The LIS reached the continental shelf during the LGM, retreated from the coastal lowlands by 12.5 ± 0.7 ka (n = 3), and from the fiord mouth by 11.7 ± 2.2 ka (n = 4). Rapid retreat from the outer fiord occurred 10.3 ± 1.3 ka (n = 6), with the terminus reaching the inner fiord shortly after 9.4 ka (n = 2), where several moraine systems were deposited between ca. 9.4 and ca. 8.4 ka. These moraines represent fluctuations of the LIS during the warmest summers since the last interglaciation, and this suggests that the ice sheet was responding to increased snowfall. Before retreating from the head of Clyde Inlet, the LIS margin fluctuated at least twice between ca. 7.9 and ca. 8.5 ka, possibly in response to the 8.2 ka cold event. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

8.
《Quaternary Science Reviews》2007,26(19-21):2505-2525
New Zealand's climate during the Last Glacial Maximum (LGM) has been investigated using the United Kingdom Met Office global (HadAM3H) and regional model (HadRM3H). All models were set up according to the glacial conditions as specified by the Paleoclimate Modelling Intercomparison Project (PMIP), although SSTs and sea-ice were supplied from a set of prior coupled model (HadCM3) runs. The simulated climate of New Zealand during the LGM was mainly compared against a control simulation which was set up for pre-industrial conditions. New Zealand's simulated LGM climate was cooler than today, varying spatially between 2.5 and 4 °C. There was an increase in seasonality in temperature with the seasonal cooling being largest during winter. Excluding the Alpine/Fiordland region, the largest cooling geographically took place in the east of the South Island (ESI). Annual mean precipitation was reduced but there were significant regional and seasonal variations. The main band of precipitation along the West Coast shifted westwards, resulting in a reduction in precipitation over those regions in the Southern Alps that receive the largest amount of precipitation in today's climate. The westerly circulation increased considerably over the North Island and the northern part of the South Island, but did not change much over the rest of the South Island. The stronger westerly wind accentuated the cooling over the western and northern parts of the North Island and it probably reduced the occurrence of incursions of tropical lows over the north of the North Island. The westerly winds were weaker over New Zealand during winter, which appears to be related to enhanced blocking activity during that season. The number and the strength of the southerlies increased, and they were capable of bringing very cold polar air over most of the country. The east of the South Island was affected especially by these cold winds.The simulated cooling during the LGM is not sufficient to limit forest growth. It is proposed here, that together with the general drier and colder conditions, it was the increase in seasonality and extremes of climate that limited the growth of certain vegetation types.  相似文献   

9.
Cosmogenic 36Cl was measured in bedrock and moraine boulders in the Za Mnichem Valley (High Tatra Mountains). The post‐LGM deglaciation of the study area occurred about 15.9 ka ago. The northernmost part of the valley slopes was ice‐free around 15 ka ago. The terminal moraine on the valley threshold was finally stabilized 12.5 ka ago during the Younger Dryas cold event (Greenland Stadial 1). At that time, the Za Mnichem glacier was 1.3 km long and had an area of 0.57 km2. The AAR equilibrium line of the glacier was located at 1990 m a.s.l., which corresponds to an ELA depression of ～500 m compared to today. The mean summer temperature was colder by 4°–4.5°C than the present‐day temperature. The mean annual temperature was colder by 6°C than today. Such conditions suggest a decrease of the annual precipitation by ～15–25% compared with the present‐day annual average. These data indicate a probable uniform temperature change across central and western Europe, with the precipitation being the most significant factor affecting the mass balance of mountain glaciers. The spatial distribution of balance data suggests increasing continentality towards the east during the Younger Dryas.  相似文献   

10.
<正>Considerable controversy exists over whether or not extensive glaciation occurred during the global Last Glacial Maximum(LGM) in the Larsemann Hills.In this study we use the in situ produced cosmogenic nuclide ~(10)Be(half life 1.51 Ma) to provide minimum exposure ages for six bedrock samples and one erratic boulder in order to determine the last period of deglaciation in the Larsemann Hills and on the neighboring Bolingen Islands.Three bedrock samples taken from Friendship Mountain(the highest peak on the Mirror Peninsula,Larsemann Hills;～2 km from the ice sheet) have minimum exposure ages ranging from 40.0 to 44.7 ka.The erratic boulder from Peak 106(just at the edge of the ice sheet) has a younger minimum exposure age of only 8.8 ka.The minimum exposure ages for two bedrock samples from Blundell Peak(the highest peak on Stornes Peninsula,Larsemann Hills;～2 km from the ice sheet) are about 17 and 18 ka.On the Bolingen Islands(southwest to the Larsemann Hills;～10 km from the ice sheet),the minimum exposure age for one bedrock sample is similar to that at Friendship Mountain(i.e.,44 ka).Our results indicate that the bedrock exposure in the Larsemann Hills and on the neighboring Bolingen Islands commenced obviously before the global LGM(i.e.,20-22 ka),and the bedrock erosion rates at the Antarctic coast areas may be obviously higher than in the interior land.  相似文献   

11.
The sediment succession of Lake Emanda in the Yana Highlands was investigated to reconstruct the regional late Quaternary climate and environmental history. Hydro-acoustic data obtained during a field campaign in 2017 show laminated sediments in the north-western and deepest (up to ̃15 m) part of the lake, where a ̃6-m-long sediment core (Co1412) was retrieved. The sediment core was studied with a multi-proxy approach including sedimentological and geochemical analyses. The chronology of Co1412 is based on 14C AMS dating on plant fragments from the upper 4.65 m and by extrapolation suggests a basal age of c. 57 cal. ka BP. Pronounced changes in the proxy data indicate that early Marine Isotope Stage (MIS) 3 was characterized by unstable environmental conditions associated with short-term temperature and/or precipitation variations. This interval was followed by progressively colder and likely drier conditions during mid-MIS 3. A lake-level decline between 32.0 and 19.1 cal. ka BP was presumably related to increased continentality and dry conditions peaking during the Last Glacial Maximum (LGM). A subsequent rise in lake level could accordingly have been the result of increased rainfall, probably in combination with seasonally high meltwater input. A milder or wetter Lateglacial climate increased lake productivity and vegetation growth, the latter stabilizing the catchment and reducing clastic input into the lake. The Bølling-Allerød warming, Younger Dryas cooling and Holocene Thermal Maximum (HTM) are indicated by distinct changes in the environment around Lake Emanda. Unstable, but similar-to-present-day climatic and environmental conditions have persisted since c. 5 cal. ka BP. The results emphasize the highly continental setting of the study site and therefore suggest that the climate at Lake Emanda was predominantly controlled by changes in summer insolation, global sea level, and the extent of ice sheets over Eurasia, which influenced atmospheric circulation patterns.  相似文献   

12.
Trimlines separating glacially abraded lower slopes from blockfield‐covered summits on Irish mountains have traditionally been interpreted as representing the upper limit of the last ice sheet during the Last Glacial Maximum (LGM). Cosmogenic 10Be exposure ages obtained for samples from glacially deposited perched boulders resting on blockfield debris on the summit area of Slievenamon (721 m a.s.l.) in southern Ireland demonstrate emplacement by the last Irish Ice Sheet (IIS), implying preservation of the blockfield under cold‐based ice during the LGM, and supporting the view that trimlines throughout the British Isles represent former englacial thermal regime boundaries between a lower zone of warm‐based sliding ice and an upper zone of cold‐based ice. The youngest exposure age (22.6±1.1 or 21.0±0.9 ka, depending on the 10Be production rate employed) is statistically indistinguishable from the mean age (23.4±1.2 or 21.8±0.9 ka) obtained for two samples from ice‐abraded bedrock at high ground on Blackstairs Mountain, 51 km to the east, and with published cosmogenic 36Cl ages. Collectively, these ages imply (i) early (24–21 ka) thinning of the last IIS and emergence of high ground in SE Ireland; (ii) relatively brief (1–3 ka) glacial occupation of southernmost Ireland during the LGM; (iii) decoupling of the Irish Sea Ice Stream and ice from the Irish midlands within a similar time frame; and (iv) that the southern fringe of Ireland was deglaciated before western and northern Ireland.  相似文献   

13.
Zhong, W., Cao, J., Xue, J., Ouyang, J., Wang, H., Tang, X. & Gao, X. 2012 (January): Carbon isotope evidence of last glacial climate variations in the tropical NW Leizhou Peninsula, South China. Boreas, Vol. 41, pp. 102–112. 10.1111/j.1502‐3885.2011.00224.x. ISSN 0300‐9483. Bulk organic δ13C values of sediment sequences are commonly used to indicate past climatic changes, although the causes and mechanisms leading to the observed organic carbon isotope responses are presently not fully understood. Based on two sedimentary sequences, namely a peat profile and a fluvial and swamp sequence from the tropical NW Leizhou Peninsula in South China, we interpret more negative bulk organic δ13C values to suggest wetter and warmer conditions, implying a stronger East Asian (EA) summer monsoon, and less negative δ13C values to indicate drier and cooler conditions, reflecting a weakening of the EA summer monsoon. A warm and wet period occurred between c. 48.0 and 28.0 cal. ka BP. In the study region, a climate shift occurred at c. 22.0 (or 20.0) cal. ka BP, and the driest and coldest period occurred between c. 19.0 and 16.0 cal. ka BP. After c. 12.0 cal. ka BP, the climate changed towards wetter and warmer conditions. Several possible millennial‐scale dry and cold oscillations characterized possibly by C4 plants, or by more positive organic δ13C values during the period when C3 plants dominated, are cautiously and tentatively interpreted as showing a similarity with Heinrich events and other cold millennial‐scale oscillations evidenced from a Greenland ice core and Chinese stalagmite. We demonstrate that bulk organic δ13C records of sedimentary sequences in the study region have potential for indicating the changes in vegetation composition that were closely associated with climate variation during the last glacial period.  相似文献   

14.
Lake Ladoga hosts preglacial sediments, although the Eurasian ice sheet overrode the area during the LGM. These sediments were first discovered by a seismic survey and are investigated using a 22.75‐m‐long core. Its upper 13.30 m comprise Holocene and Lateglacial sediments separated from the lower 11.45 m of preglacial sediments by a hiatus. They consist of highly terrigenous lacustrine sediments, which according to OSL dating, were deposited during an early stage of the last ice age (MIS 5). The palynological data allow a first reconstruction of the Early Weichselian environmental history for northwestern Russia. Birch and alder forests with broad‐leaved taxa dominated during MIS 5d (c. 118–113 ka), suggesting a climate more favourable than in the Holocene. A high content of well‐sorted sands and poorly preserved palynomorphs indicates a shallow‐water environment at least temporarily. More fine‐grained sediments and better preserved organic remains suggest deeper water environments at the core location during MIS 5c (c. 113–88 ka). Pine and spruce became dominant, while broad‐leaved taxa started to disappear, especially after c. 90 ka, pointing to a gradual climate cooling. An increase in open herb‐dominated habitats at the beginning of MIS 5b (c. 88–86 ka) reflects a colder and dryer climate. However, later (c. 86–82 ka) pine and spruce again became more common. Birch and alder forests dominated in the area c. 82–80 ka (beginning of MIS 5a). Although open treeless habitats also became more common at this time, a slight increase in hazel may point to somewhat warmer climate conditions coinciding with the beginning of MIS 5a. The studied sediments also contain numerous remains of freshwater algae and cysts of marine and brackish‐water dinoflagellates and acritarchs documenting that the present lake basin was part of a brackish‐water basin during the Early Weichselian, probably as a gulf of the Pre‐Baltic Sea.  相似文献   

15.
We present a high‐resolution reconstruction of the vegetation and climate dynamics during the penultimate interglacial, corresponding with Marine Isotope Stage (MIS) 7, based on detailed palynological analyses of lacustrine sediments from Lake El'gygytgyn, northeastern Siberia. The analysed sediments were deposited between 246 and 181 ka ago (late MIS 8 to early MIS 6.6). The interglacial vegetation was characterized by herb and shrub (mainly alder and birch) dominated plant communities. Pollen‐based biome reconstruction shows a dominance of the tundra (TUND) biome, thus indicating rather open vegetation. Warmer intervals (MIS 7.5, 7.3 and 7.1) were marked by an increase in the cold deciduous forest (CLDE) biome scores and a synchronous decrease in the cold steppe (STEP) biome scores. The thermal maximum occurred during MIS 7.1, as indicated by the highest CLDE biome scores occurring in this period, and lasted ~10 ka, possibly favoured by the high precession‐related summer insolation and the legacy of the preceding mild and dry stadial (MIS 7.2). In contrast, MIS 7.3 and 7.5 were characterized by shorter durations (~4 ka) and lower summer temperatures. The preceding cold glacial and stadial (MIS 8 and 7.4, respectively) might have led to an extensive distribution of permafrost that hindered vegetation development during the subsequent warm intervals. MIS 7.4 and 6.6 were cold and wet, probably triggered by low obliquity values and coevally low precession‐related summer insolation. As a result, these periods were marked by significantly reduced summer temperatures and an enhanced snow‐ice albedo feedback. The obtained reconstructions provide potential scenarios for future climate changes and allow a better understanding of the relationship between vegetation, climate and external/internal forcings in the high latitudes.  相似文献   

16.
张晓  张旭 《地学前缘》2022,29(5):322-333
千年尺度气候突变事件是第四纪冰期普遍存在的气候现象。这些事件可以被分为两类,一类为Dansgaard-Oeschger Event (DO事件),另一类为海因里希(Heinrich Stadial,HS)事件,后者有时也被认为是一种特殊的DO事件,因此也被称为 HS-DO事件。HS事件期间北大西洋冰架的融化一般对应DO振荡的冷相位,这与通常认为的冰架在较冷气候下体积增加并不相符。这两类事件在北大西洋重建数据中表现得最为明显,但其气候影响具有全球性。由于没有显著的外强迫驱动这两类气候突变事件,自20世纪90年代首次被确认以来,HS-DO事件一直是古气候界关注的重点,且人们对其触发机理仍没有定论。本文基于目前对这两类千年事件的研究现状,集中总结了目前已有的可反映千年事件的重建数据,利用已有的模拟工作,重点回顾了现有的机制理论,评述了目前研究DO事件以及HS-DO事件的局限性,并对其后续工作,尤其是模拟部分,进行了展望。  相似文献   

17.
Houmark‐Nielsen, M. 2010: Extent, age and dynamics of Marine Isotope Stage 3 glaciations in the southwestern Baltic Basin. Boreas, 10.1111/j.1502‐3885.2009.00136.x. ISSN 0300‐9483 The southwestern Baltic region is known as a major crossroad for the expansion of Pleistocene glaciers from the Scandinavian Ice Sheet (SIS). At the peak of the Last Glacial Maximum (LGM, 25–20 kyr BP), steady‐flowing inter‐stream glaciers expanded radially from the major ice divide over central Scandinavia. During the subsequent deglaciation phase (20–15 kyr BP), streaming ice was flowing through the Baltic gateway onto the North European lowland. The lithology and directional ice‐flow properties of pre‐LGM till formations of Baltic provenance in Denmark (the Ristinge till and Klintholm till) suggest that the ice‐sheet dynamics during the Marine Isotope Stage (MIS) 3 glacier expansion were similar to those for the post‐LGM advances. Increasing geological evidence indicates that glaciers extended onto the Circum‐Baltic lowlands during MIS 3. Reconstructions of flow paths and estimates of the basal ice‐sheet coupling in Denmark suggest that southward flow of the SIS through the Baltic was probably the result of ice streaming. Despite methodological uncertainties, available OSL and 14C dates indicate that glaciers advanced at least twice during the mild second half of the Middle Weichselian (c. 75–25 kyr BP), most probably in connection with Dansgaard‐Oeschger (D‐O) events 14–13 (54–46 kyr BP) and 8–5 (35–30 kyr BP). The chronology and dynamics of glacier expansion in the southwestern Baltic in response to long‐term cooling trends, the contemporary presence of a low Arctic biota in large parts of Scandinavia and of possible leads or lags in relation to North Atlantic climate changes during MIS 3 are discussed.  相似文献   

18.
Understanding Antarctic Ice Sheet dynamics related to global climate change is of scientific and societal interest as the future behaviour of the ice sheet under the currently changing climate is unknown. We present beryllium‐10 (10Be) analysis of a high‐resolution marine sediment core from the Adélie Basin near the eastern Wilkes Land margin, which is susceptible to marine ice sheet instability due to the low‐lying nature and down‐sloping trough of the Wilkes Subglacial Basin. Combined with a newly constructed age model using compound specific radiocarbon dates, the data reveal three events associated with high meteoric 10Be at ca. ~10 ka, ca. ~6.5 ka and from ca. ~4 ka. We interpret these high meteoric 10Be events to be derived from the deposition of 10Be released from the ice sheet during meltwater discharge. In particular, the shift to higher meteoric 10Be concentration at~4 ka may correspond to changes in climate patterns at this time. Copyright © 2019 John Wiley & Sons, Ltd.  相似文献   

19.
The distribution of ice‐rafted detritus (IRD) is studied in three cores from the western Svalbard slope (1130–1880 m water depth, 76–78°N) covering the period 74–0 ka. The aim was to provide new insight into the dynamics of the Svalbard–Barents Sea Ice Sheet during Marine Isotope Stages (MIS) 4–1 to get a better understanding of ice‐sheet interactions with changes in ocean circulation and climate on orbital and millennial (Dansgaard–Oeschger events of stadial–interstadial) time scales. The results show that concentration, flux, composition and grain‐size of IRD vary with climate and ocean temperature on both orbital and millennial time scales. The IRD consists mainly of fragments of siltstones and mono‐crystalline transparent quartz (referred to as ‘quartz’). IRD dominated by siltstones has a local Svalbard–Barents Sea source, while IRD dominated by quartz is from distant sources. Local siltstone‐rich IRD predominates in warmer climatic phases (interstadials), while the proportion of allochthonous quartz‐rich IRD increases in cold phases (glacials and stadials/Heinrich events). During the Last Glacial Maximum and early deglaciation at 24–16.1 ka, the quartz content reached up to >90%. In warm climate, local iceberg calving apparently increased and the warmer ocean surface caused faster melting. During the glacial maxima (MIS 4 and MIS 2) and during cold stadials and Heinrich events, the local ice‐sheets must have been relatively stable with low ablation. During ice retreat phases of the MIS 4/3 and MIS 2/1 transitions, maxima in IRD deposition were dominated by local coarse‐grained IRD. These maxima correlate with episodes of climate warming, indicating a rapid, stepwise retreat of the Svalbard–Barents Sea Ice Sheet in phase with millennial‐scale climate oscillations.  相似文献   

20.
Woolly mammoths were large, herbivorous, cold-adapted mammals of the Late Pleistocene. The diet and habitat requirements of the species set certain constraints on the palaeoenvironments it could occupy. The relationship between the mammoth’s shifting range and changing environments can be explored using independent data on ice sheet configuration, temperature, and vegetation, provided the locality and age of the fossil remains can be validated. Here we present a comprehensive record of occurrence of the woolly mammoth in the circum-Baltic region of northern Europe during the last glaciation, based on a compilation of radiocarbon-dated remains. The record shows that the mammoth was widespread in northern and north-eastern Europe during Marine Isotope Stage 3 (MIS 3), at 50,000–30,000 calibrated years ago (50–30 ka). The presence of the species up to 65°N latitude supports the restriction of the Scandinavian Ice Sheet (SIS) during MIS 3. The widest distribution range round 30 ka was followed by a decline that led to the disappearance of mammoths from the area during the maximum extent of the SIS, from 22 to 18 ka. The woolly mammoth re-colonized the Baltic region and southern Scandinavia after the onset of the late-glacial deglaciation at 17 ka. The late-glacial record suggests a markedly fluctuating population changing its range in tune with the rapid environmental changes. The last appearance of mammoth in our study region was in Estonia during the Younger Dryas (Greenland Stadial 1; GS1) at about 12 ka. The two major periods of occurrence during MIS 3 and the late-glacial stadial suggest that mammoth had a wide tolerance of open to semi-open tundra and steppe-tundra habitats with intermediately cold climate, whereas the 22–18 ka disappearance suggests a major southward and/or eastward retreat in response to extremely cold, glacial conditions near the SIS margin. The final regional extinction correlates with the re-forestation during the rapid warming at the Younger Dryas–Holocene boundary.  相似文献   

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