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1.
Episodes of glaciation in the region north of Baffin Bay resulted in the erosion of Paleozoic carbonate outcrops in NW Greenland and the Canadian High Arctic. These events are recognized in the marine sediments of Baffin Bay (BB) as a series of detrital carbonate-rich (DC-) layers. BBDC-layers thin southward within Baffin Bay; thus, the contribution of Baffin Bay ice-rafted carbonate-rich sediments to the North Atlantic is probably slight, especially compared with sediment output from Hudson Strait during Heinrich events. We reexamine (cf. Aksu, 1981) a series of nine piston cores from the axis of Baffin Bay and across the Davis Strait sill and provide a suite of 21 AMS 14C dates on foramininfera which bracket the ages of several DC-layers. The onset of the last DC event is dated in six cores and has an age of ca. 12.4 ka. In northern and central Baffin Bay a thick DC-layer occurs at around 4 m in the cores and is dated >40 ka. There were three to six DC intervening events. The youngest BBDC event (possibly a double event) lags Heinrich event 1 (H-1) off Hudson Strait, dated at 14.5 ka, but it is coeval with the pronounced warming seen in GISP2 records from the Greenland Ice Sheet during interstadial #1. We hypothesize that BBDC episodes are coeval with major interstadial δ18O peaks from GISP2 and other Greenland ice core records and are caused by or associated with the advection of Atlantic Water into Baffin Bay (cf. Hiscott et al., 1989) and the subsequent rapid retreat of ice streams in the northern approaches to Baffin Bay.  相似文献   

2.
Eight Labrador Sea piston cores with faunal and ash-zone stratigraphies correlated to deep-sea oxygen isotope stages were used to compute Labrador Sea terrigenous sand input rates (mg/cm2/1000 years) during the last 100,000 years. Sources of the sand in Labrador Sea cores are likely to be ice-rafting, turbid glacial meltwater inflow or deflation and wind erosion of unvegetated landscapes in the wake of retreating continental ice sheets. High levels of sand input to the Labrador Sea are therefore undoubtedly glacier-related while low levels of sand input are not. Comparison of the history of Labrador Sea sand input with the chronology of glacial and non-glacial events on Baffin Island reveals that the era of highest sand input rates, the isotopic stage 5a/4 transition, closely coincided with an episode of early Foxe glacier advance to tidewater (Ayr Lake Stade) along the outer coast of Baffin Island ca. 80,000 B.P. to 60,000 B.P. The period of lowest Labrador Sea sand input rates, late isotopic stage 3 to the present, largely corresponds to a major disconformity in the raised marine and glacigenic sediments on Baffin Island, but includes also the late Foxe/early Holocene Cockburn glacial advance (which did not reach the outer coast of the island) and the modern glacial minimum. Labrador Sea and central-subpolar North Atlantic sand input histories are reciprocally related over the last 80,000 years. Accelerated sand input in the Labrador Sea during times of reduced sand input in the North Atlantic implies: (1) major early Wisconsin glacier expansion in the circum Labrador Sea/Baffin Bay region and/or; (2) a surface circulation pattern in the North Atlantic which inhibited iceberg melting there while delivering icebergs and relatively warm surface water into the Labrador Sea. Conversely, reduced sand input in the Labrador Sea during times of accelerated sand input in the North Atlantic implies: (1) late Wisconsin glacier recession in the circum Labrador Sea/Baffin Bay region and/or; (2) a circulation pattern which carries icebergs southward and eastward away from the Labrador Sea. These implications are discussed in the light of paleoceanographic evidence for three periods - 80,000 B.P. to 57,000 B.P.; 25,000 B.P. to 13,000 B.P.; and 13,000 B.P. to 9800 B.P  相似文献   

3.
Along the West Greenland continental margin adjoining Baffin Bay, bathymetric data show a series of large submarine fans located at the mouths of cross‐shelf troughs. One of these fans, termed here ‘Uummannaq Fan’, is a trough‐mouth fan built largely by debris delivered from a fast‐flowing outlet of the Greenland Ice Sheet during past glacial maxima. Cores from this fan provide the first information on glacimarine sedimentary facies within a major West Greenland trough‐mouth fan and on the nature of Late Weichselian–Holocene glacigenic sediment delivery to this region of the Baffin Bay margin. Glacigenic debris flows deposited on the upper slope and extending to at least 1800 m water depth in front of the trough‐mouth are related to the remobilization of subglacial debris that was delivered onto the upper slope at times when an ice stream was positioned at the shelf edge. In contrast, sedimentary facies from the northern sector of the fan are characterized by hemipelagic and ice‐rafted sediments and turbidites; glacigenic debris flows are notably absent in cores from this region. Quantitative X‐ray diffraction studies of the <2‐mm sediment fraction indicate that the bulk of the sediment in the fan is derived from Uummannaq Trough but there are distinct intervals when sediment from northern Baffin Bay sources dominates, especially on the northern limit of the fan. These data demonstrate considerable variation in the nature of sediment delivery across the Uummannaq Fan when the Greenland Ice Sheet was at the shelf edge. They highlight the variability of glacimarine depositional processes operating on trough‐mouth fans on high‐latitude continental margins during the last glacial maximum and indicate that glacigenic debris flows are just one of a number of mechanisms by which such large depocentres form. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

4.
Calculations based on temperature-corrected oxygen-isotope ratios from deep-sea cores yield a glacioeustatic sea-level fall in excess of 50 m during the first 10,000 yr of the last glaciation, and generally support the local regression of about 70 m inferred from tectonically rising New Guinea beaches. We propose that this rapid glacial buildup depended on high-latitude cooling, and large increases of high-latitude regional winter precipitation in the Laurentide and the Fennoscandian-Barents Sea areas, and that these factors were caused by a critical alteration of North Atlantic Drift currents and their associated subpolar atmospheric circulation. In support of this, faunal data from northeast North Atlantic deep-sea cores show that the glacial buildup was accompanied by a sudden loss of most of the North Atlantic Drift from the Greenland-Norwegian Sea, a factor favoring reduced heat input into the higher latitudes. Subpolar mollusk and foraminifera fauna from elevated marine deposits on the Baffin Island coast, and northwest North Atlantic core data suggest a continuation or an associated restoration of subpolar water west of Greenland as far north as Baffin Bay, a factor favoring precipitation in the northeast Canadian region. Heat transport and atmospheric circulation considerations suggest that the loss of the northeast North Atlantic Drift was itself a major instrument of high-latitude climate change, and probably marked the initiation of major new ice-sheet growth.  相似文献   

5.
Lichen diameters and radiocarbon dates from the western and southern margins of the Barnes Ice Cap yield a growth curve similar to that from southeastern Baffin Island. As a consequence, the moraine chronology of the northern and western Barnes Ice Cap needs revision, as does the chronology of the large proglacial lakes that existed north of the present Barnes Ice Cap. The revised chronology indicates that moraines were formed along the western margin of the Barnes Ice Cap during the following intervals: (1) less than 100 years ago; (2) 400–500 B.P.; (3) ca. 750 B.P.; (4) ca. 1000 B.P.; (5) ca. 1600 B.P.; (6) ca. 2100 B.P.; and (7) 2800 to 3100 B.P. As the western margin of the Barnes Ice Cap retreated, punctuated by stillstands and readvances, the northern margin of the Barnes Ice Cap lay athwart a series of westerly draining valleys, and a complex of proglacial lakes were dammed between the ice margin and the height of land. This sequence is traced by means of well-developed shorelines, lacustrine deltas, and spillways; specific lake levels are dated by lichenometry.
The Barnes Ice Cap moraine sequence is more complex than other Neoglacial records fringing mountain glaciers in Colorado, Alaska and Lappland. However, the chronology for the western Barnes Ice Cap closely resembles independent moraine chronology of mountain glaciers in Cumberland Peninsula, Baffin Island, and thus indicates that the difference between the Baffin Island climatic record and the general Neoglacial/Holocene climatic record (Denton & Karlén, Quaternary Research 7 , 1977) is real. Comparison of specific data from Swedish Lappland and Baffin Island shows substantial agreement. Although Neoglacial records may be globally synchronous, the case for a 2500 year periodicity of glacial fluctuations is not proven: a 300 to 600 year return interval is suggested for the period between 0 and 3000 B.P.  相似文献   

6.
孟加拉湾由于陆源物质大量输入产生稀释效应,使碳酸盐含量表现为冰期时减小、间冰期时增大的“大西洋型”旋回。通过对该区四支活塞岩芯的有孔虫溶解指数、浮游有孔虫沉积通量、CaCO3 沉积通量和 >16 0 μm粗组分沉积通量的分析发现,研究区碳酸盐溶解作用强烈,表现出冰期减弱而间冰期增强的总趋势,且溶解作用滞后于浮游有孔虫壳的氧同位素旋回,尤以氧同位素 4、5期的高溶解度情况与印度洋和太平洋氧同位素 5期晚期至 4期为CaCO3溶解高峰一致。因此,孟加拉湾地区的CaCO3 旋回是大西洋型稀释作用与太平洋型溶解作用两者叠加的产物.  相似文献   

7.
Marine, fluvial and glacigene sediments exposed in coastal cliffs and stream-cut sections in East Greenland between latitudes 69° and 78° N display a record of Quaternary climatic and environmental change going back to pre-Saalian times (> 240 ka), but with main emphasis on the last interglacial/glacial cycle. The stratigraphical scheme is based on studies on the Jameson Land peninsula, and contains five glacial stages and stades with the Greenland ice sheet or its outlets reaching the outer coasts. Individual sites are correlated and dated by a combination of biostratigraphy, luminescence dating, amino acid analyses, as well as 14C- and uranium series dating. The pre-Weichselian Lollandselv and Scoresby Sund glaciations were the most extensive. During the Weichselian the Inland Ice margin in this part of East Greenland was apparently very stable. The Aucellaelv, Jyllandselv and Flakkerhuk stades mark the advance and subsequent retreat of outlet glaciers from the Inland Ice which advanced through the wide Scoresby Sund basin and reached the inner shelf. In-between the glacier advances, three interglacial or interstadial periods have been recognized. During the Langelandselv interglacia-tion (≅ Eemian) the advection of warm Atlantic water was higher than during the Holocene, and the terrestrial flora and insect faunas show that summer temperatures were 3–4°C higher than during the Holocene optimum. There is no unambiguous evidence for cooling in the sediments from this interval. Later, in isotope stage 5, there were apparently two ice-free periods. During the Hugin Sø interstade, stable Polar water dominated Scoresby Sund, and the terrestrial flora suggests summer temperatures 2° -3° lower than the present. The marine and fluvial sediments from the second ice-free period, the Mønselv interstade, are devoid of organic remains.  相似文献   

8.
For the past half-century, reconstructions of North American ice cover during the Last Glacial Maximum have shown ice-free land distal to the Laurentide Ice Sheet, primarily on Melville and Banks islands in the western Canadian Arctic Archipelago. Both islands reputedly preserve at the surface multiple Laurentide till sheets, together with associated marine and lacustrine deposits, recording as many as three pre-Late Wisconsinan glaciations. The northwest corner of Banks Island was purportedly never glaciated and is trimmed by the oldest and most extensive glaciation (Banks Glaciation) considered to be of Matuyama age (>780 ka BP). Inside the limit of Banks Glaciation, younger till sheets are ascribed to the Thomsen Glaciation (pre-Sangamonian) and the Amundsen Glaciation (Early Wisconsinan Stade). The view that the western Canadian Arctic Archipelago remained largely ice-free during the Late Wisconsinan is reinforced by a recent report of two woolly mammoth fragments collected on Banks and Melville islands, both dated to ～22 ka BP. These dates imply that these islands constitute the northeast extremity of Beringia.A fundamental revision of this model is now warranted based on widespread fieldwork across the adjacent coastlines of Banks and Melville islands, including new dating of glacial and marine landforms and sediments. On Dundas Peninsula, southern Melville Island, AMS 14C dates on ice-transported marine molluscs within the most extensive Laurentide till yield ages of 25–49 ka BP. These dates require that Late Wisconsinan ice advanced northwestward from Visount Melville Sound, excavating fauna spanning Marine Isotope Stage 3. Laurentide ice that crossed Dundas Peninsula (300 m asl) coalesced with Melville Island ice occupying Liddon Gulf. Coalescent Laurentide and Melville ice continued to advance westward through M'Clure Strait depositing granite erratics at ≥235 m asl that require grounded ice in M'Clure Strait, as do streamlined bedforms on the channel floor. Deglaciation is recorded by widespread meltwater channels that show both the initial separation of Laurentide and Melvile ice, and the successive retreat of Laurentide ice southward across Dundas Peninsula into Viscount Melville Sound. Sedimentation from these channels deposited deltas marking deglacial marine limit. Forty dates on shells collected from associated glaciomarine rhythmites record near-synchronous ice retreat from M'Clure Strait and Dundas Peninsula to north-central Victoria Island ～11.5 ka BP. Along the adjacent coast of Banks Island, deglacial shorelines also record the retreat of Laurentide ice both eastward through M'Clure Strait and southward into the island's interior. The elevation and age (～11.5 ka BP) of deglacial marine limit there is fully compatible with the record of ice retreat on Melville Island. The last retreat of ice from Mercy Bay (northern Banks Island), previously assigned to northward retreat into M'Clure Strait during the Early Wisconsinan, is contradicted by geomorphic evidence for southward retreat into the island's interior during the Late Wisconsinan. This revision of the pattern and age of ice retreat across northern Banks Island results in a significant simplification of the previous Quaternary model. Our observations support the amalgamation of multiple till sheets – previously assigned to at least three pre-Late Wisconsinan glaciations – into the Late Wisconsinan. This revision also removes their formally named marine transgressions and proglacial lakes for which evidence is lacking. Erratics were also widely observed armouring meltwater channels originating on the previously proposed never-glaciated landscape. An extensive Late Wisconsinan Laurentide Ice Sheet across the western Canadian Arctic is compatible with similar evidence for extensive Laurentide ice entering the Richardson Mountains (Yukon) farther south and with the Innuitian Ice Sheet to the north. Widespread Late Wisconsinan ice, in a region previously thought to be too arid to sustain it, has important implications for paleoclimate, ice sheet modelling, Arctic Ocean ice and sediment delivery, and clarifying the northeast limit of Beringia.  相似文献   

9.
Previous interpretations of Labrador Sea and Baffin Bay sediment cores were hampered by failure to recognize that the presence of small (62–149 μm) specimens of 'subpolar' planktic foraminifera in high-latitude marine sediments is primarily a function of the geochemistry of the water column and/or sediments rather than an indicator of environmental conditions in overlying surface waters. Assuming this rationale is correct, foraminiferal data from core HU75–42 indicate that surface conditions in the Labrador Sea were characterized by polar waters, with probable year-round sea-ice cover, throughout most of the period from isotope stage 5a to Termination I. The single exception to this sustained cold history for the eastern Labrador Sea was a transient pulse that apparently brought relatively warm, subpolar waters to the eastern Labrador Sea for a short (probably < 600 years) interval at the isotope stage 5a/4 transition.  相似文献   

10.
Nioghalvfjerdsfjorden in North-East Greenland is at present covered by a floating glacier. Raised marine deposits in the surrounding area contain shells of marine molluscs, bones of marine mammals and pieces of driftwood. A fairly systematic sampling of such material has been conducted, followed by extensive radiocarbon dating. We suggest that the Greenland ice sheet extended onto the shelf offshore North-East Greenland during isotope stage 2, perhaps even reaching the shelf break. During the subsequent recession of the ice sheet, the entrance of Nioghalvfjerdsfjorden had become ice-free by 9.7 cal. ka BP. The recession culminated between 7.7 and 4.5 cal. ka BP, during which time the fjord was glacier-free along its entire 80 km length. No dates younger than 4.5 cal. ka BP are available on marine material from the fjord, and it seems probable that the fjord has been continuously covered by the floating glacier since this time. The maximum glaciation was attained around AD 1900, after which thinning and recession took place. The marine limit increases from c. 40 m above sea level near the present margin of the Inland Ice to c. 65 m above sea level at the outer coast. These figures fit into the regional pattern of the marine limit for areas both to the south and north. The marine fauna comprise two bivalves, Macoma calcarea and Serripes groenlandicus, that may represent a southern element present during the Holocene temperature optimum. Remains of three taxa of southern extralimital terrestrial and limnic plants were dated to 5.1 cal. ka BP, and remains of another extralimital plant were dated to 8.8 and 8.5 cal. ka BP. The known Holocene time ranges of the willow Salix arctica and the lemming Dicrostonyx torquatus have been extended back to 8.8 and 6.4 cal. ka BP, respectively, providing minimum dates for their immigration to Greenland.  相似文献   

11.
西藏东南部末次冰期早阶段冰川作用及其古气候意义   总被引：1，自引：1，他引：0  
西藏东南部的“古乡冰期”和“白玉冰期”是划分中国第四纪冰期的蓝本。其中,白玉冰期即末次冰期,分为早阶段和晚阶段,相对应的冰川沉积广泛分布于本区的波堆藏布谷地。已有的冰川数值年代结果显示,末次冰期晚阶段的冰川作用发生于海洋氧同位素阶段（MIS）2。然而,关于早阶段的冰进记录,目前却未有确切的年代学证据,此次冰川作用究竟发生于MIS 4还是MIS 3,是一个悬而未决的问题。在前人研究及野外地貌调查的基础上,运用光释光测年手段对波堆藏布谷地疑似形成于末次冰期早阶段的冰碛垄进行测年,年代结果介于（56.4±4.2）~（65.9±3.9） ka之间,相当于MIS 4。藏东南地区MIS 4冰期冰川作用年代与青藏高原及其周边山地具有可比性,表明该阶段冰川作用发生的普遍性。通过对比北半球低纬度地区夏季太阳辐射及亚洲季风区古气温与古降水指标记录,认为藏东南地区MIS 4冰期冰川作用可能是对北半球低纬度地区夏季太阳辐射减弱及气温下降的响应,与季风降水无关。  相似文献   

12.
During the last glacial stage, Washington Land in western North Greenland was probably completely inundated by the Greenland Ice Sheet. The oldest shell dates from raised marine deposits that provide minimum ages for the last deglaciation are 9300 cal. yr BP (northern Washington Land) and 7600 cal. yr BP (SW Washington Land). These dates indicate that Washington Land, which borders the central part of Nares Strait separating Greenland from Ellesmere Island in Canada, did not become free of glacier ice until well into the Holocene. The elevation of the marine limit falls from 110 m a.s.l. in the north to 60 m a.s.l. in the southwest. The recession was followed by readvance of glaciers in the late Holocene, and the youngest shell date from Neoglacial lateral moraines north of Humboldt Gletscher is 600 cal. yr BP. Since the Neoglacial maximum, probably around 100 years ago, glaciers have receded. The Holocene marine assemblages comprise a few southern extralimital records, notably of Chlamys islandica dated to 7300 cal. yr BP. Musk ox and reindeer disappeared from Washington Land recently, perhaps in connection with the cold period that culminated about 100 years ago.  相似文献   

13.
夏特河源于天山最大现代冰川作用中心托木尔—汗腾格里峰的东北坡,流域内保存有形态较为清晰的四套冰川沉积。这些地形记录了夏特河流域的古冰川变化,对它们进行研究可获得该地晚第四纪以来的冰川时空演化规律。在第三套冰碛夹层中的砂质透镜体里采集了5个OSL年代学样品,应用单片再生（SAR）测年技术测得它们的年龄为（13.3±0.8）~（20.1±1.3） ka。基于测年结果、各套冰碛距现代冰川的远近、冰碛垄的完整程度、冰碛物的风化胶结状况及接触关系,并参阅托木尔—汗腾格里峰南坡与东南坡以及东、中、西段天山其他流域的年代学资料,可初步得出：第一套和第二套冰碛分别沉积于小冰期和新冰期;第三套冰碛形成于末次盛冰期及随后的冰消期,可对应于海洋氧同位素阶段（MIS） 2;保存在河口的第四套冰川沉积及与其相关联的宽阔且长达数十千米的“U”形谷共同指示,它应形成于冰川规模较大的倒数第二次冰期,时间上可对应于MIS 6。  相似文献   

14.
Core HU97048‐007PC was recovered from the continental Labrador Sea slope at a water depth of 945 m, 250 km seaward from the mouth of Cumberland Sound, and 400 km north of Hudson Strait. Cumberland Sound is a structural trough partly floored by Cretaceous mudstones and Paleozoic carbonates. The record extends from ～10 to 58 ka. On‐board logging revealed a complex series of lithofacies, including buff‐colored detrital carbonate‐rich sediments [Heinrich (H)‐events] frequently bracketed by black facies. We investigate the provenance of these facies using quantitative X‐ray diffraction on drill‐core samples from Paleozoic and Cretaceous bedrock from the SE Baffin Island Shelf, and on the < 2‐mm sediment fraction in a transect of five cores from Cumberland Sound to the NW Labrador Sea. A sediment unmixing program was used to discriminate between sediment sources, which included dolomite‐rich sediments from Baffin Bay, calcite‐rich sediments from Hudson Strait and discrete sources from Cumberland Sound. Results indicated that the bulk of the sediment was derived from Cumberland Sound, but Baffin Bay contributed to sediments coeval with H‐0 (Younger Dryas), whereas Hudson Strait was the source during H‐events 1–4. Contributions from the Cretaceous outcrops within Cumberland Sound bracket H‐events, thus both leading and lagging Hudson Strait‐sourced H‐events. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

15.
Holocene climatic and paleoceanographic development of the SE Greenland Shelf is studied from cores MD99-2317 and MD99-2322, at sites north and south of the Denmark Strait, respectively. Lithofacies, IRD counts, calcium carbonate percentages, benthic and planktic foraminiferal assemblages and oxygen isotope analyses, and summer SSTs reveal significant climate variations in the Holocene driven by declining solar insolation and its interaction with waning continental ice sheets, and changing atmospheric pressure patterns. Large changes in the East Greenland and Irminger Currents and the Greenland Ice Sheet are manifested as a 4-part division of the Holocene. An early Holocene cold interval dominated by melting of the Greenland Ice Sheet and Polar Front retreat extends from 11.8 to 9.5 cal kyr BP. A cold interval from 9.5 to 8.1 cal kyr BP involved episodic cooling of the Irminger Current resulting from the last phases of Laurentide Ice Sheet deglaciation and delayed the Holocene optimum off East Greenland by 3 kyr relative to peak summer solar insolation, which likely helped to limit the early Holocene melting of the Greenland Ice Sheet. The period 8.1–3.5 cal kyr BP represents a climatic optimum interval of maximum Greenland Ice Sheet retreat and strong Irminger Current inflow to the Denmark Strait. Between 6.8 and 3.5 cal kyr BP, the Irminger Current penetrated further North into the Nordic Seas than has been observed in recent decades. This signal is consistent with diminished northerly winds, a weaker Greenland High and contracted subpolar gyre. By 5 cal kyr BP, periods of increased Polar Water and decreasing salinity in the Irminger Current suggest a transition toward expansion of the subpolar gyre and increased Polar Water in the EGC. The Neoglacial interval from 3.5 to 0.2 cal kyr BP was cold and variable with increased freshwater forcing from the Arctic Ocean, advance of the Greenland Ice Sheet and southward advance of the Polar Front. Enhanced northerly winds and a strengthened Greenland High are consistent with thicker and more extensive Polar Water and greatly diminished northward advection of Irminger Current in the Denmark Strait.  相似文献   

16.
Macrofossil plant and insect remains from nearshore marine sediments in Jameson Land, central East Greenland show that the land biotas of the last interglacial stage, the Langelandselv stage, were more diverse than those of the Holocene. Rich dwarf shrub heaths with a diverse assemblage of ericaceous plants occupied low land areas with copses of Betula pubescens on sheltered sites. Many southern extra-limital species were present, and the mean summer temperature was c . 5°C higher than today. The subarctic bioclimatic zone was displaced from southernmost Greenland/Iceland to central East Greenland. The diverse beetle fauna was of palaearctic affinity and strikingly different from the Plio-Pleistocene and the Holocene Greenlandic beetle faunas. A few fossil assemblages from the Hugin Sø Interstade, which is correlated with oxygen isotope stage 5c (early last glacial stage), point to poor, perhaps entirely herbaceous vegetation with a mean summer temperature that was perhaps 3 4°C lower than today.  相似文献   

17.
The extent of glacier ice in the Canadian High Arctic during the Last Glacial Maximum (LGM) has been debated for decades. One school proposed a regional Innuitian Ice Sheet whereas another proposed a smaller, non-contiguous Franklin Ice Complex. Research throughout western Nares Strait supports coalescent Innuitian and Greenland ice during the LGM, based on widespread glacial and marine deposits dated by 14C and amino acid analyses. This coalescence likely promoted a vigorous regional ice flow westward across Ellesmere Island to Eureka Sound. Post-glacial emergence in Eureka Sound suggests a former ice thickness at least as great as that in Nares Strait (≥ 1 km). Recently, independent field studies elsewhere in the High Arctic also support an Innuitian Ice Sheet during the LGM. Collectively, these studies resolve a long-standing debate, and initiate new opportunities concerning the reconstruction of high-latitude palaeoenvironmental and palaeoclimatic change. © 1998 John Wiley & Sons, Ltd.  相似文献   

18.
《Quaternary Science Reviews》1999,18(8-9):993-1019
Outcrops bearing stained, striated facets indicative of north–northeastward moving ice, truncated by unstained, striated facets indicative of various younger flows occur in the Caniapiscau area of north–central Quebec. This is the first report of differential staining of striated facets in the region. We propose that the staining occurred in an ice-free interval of probable interglacial age. This early ice flow probably occurred during ice retreat toward the Quebec highlands. Ice flow and glacial transport data from the southern Hudson Bay and James Bay basins indicate that the next major regional ice flow was toward the northwest and resulted from the expansion of an Early Wisconsinan glacier in the Quebec highlands. The northern part of this flow was diverted northwestward through Hudson Bay, and the southern part southwestward across James Bay, following a progressive counterclockwise rotation of flow. A zone of intersection (ZI) of two major glacier bedform systems, often referred to as the horseshoe-shaped Labrador Ice Divide, represents the head of a large northward convergent ice-flow system that extended to Ungava Bay and beyond. The Ungava flow propagated southward and captured the head of the opposing flow from an outflow centre located east of Caniaspiscau reservoir. We propose that this capture event correlates with the Gold Cove Advance in Ungava Bay and on Baffin Island at about 9900 14C yr BP. It is the largest advance of Quebec-Labrador ice yet proposed for the region. This correlation is based on the relative ice-flow chronology, accommodation of glacial lakes Naskaupi and McLean in the deglaciation sequence, the constraints placed on Last Glacial Maximum (LGM) ice configuration by the postglacial uplift pattern and events in the deep-sea record. Therefore, the Ungava ice-flow pattern is not a relict pre-Wisconsinan glacial landscape as recently proposed.  相似文献   

19.
In this study, we present new information on the glacial history of the Greenland Ice Sheet (GrIS) and a local ice cap in Qaanaaq, northwest Greenland. We use geomorphological mapping, 10Be exposure dating of boulders, analysis of lake cores, and 14C dating of reworked marine molluscs and subfossil plants to constrain the glacial history. Our 14C ages of reworked marine molluscs reveal that the ice extent in the area was at or behind its present‐day position from 42.2 ± 0.4 to 30.6 ± 0.3k cal a BP after which the GrIS expanded to its maximum position during the Last Glacial Maximum. We find evidence of early ice retreat in the deep fjord (Inglefield Bredning) at 11.9 ± 0.6 ka whereas the Taserssuit Valley was deglaciated ~4 ka later at 7.8 ± 0.1k cal a BP. A proglacial lake record suggests that the local ice cap survived the Holocene Thermal Maximum but moss kill‐dates reveal that it was smaller than present for a period of time before 3.3 ± 0.1k until 0.9 ± 0.1k cal a BP, following which the ice in the area expanded towards its Little Ice Age extent. Copyright © 2019 John Wiley & Sons, Ltd.  相似文献   

20.
The loess series at St. Pierre-les-Elbeuf and St. Sauflieu are key successions for the western European Quaternary stratigraphy. The present study proposes a detailed record of the last interglacial-glacial climatic cycle at St. Pierre and its integration into the synthetic pedosedimentary record of north-western France using detailed correlations with the type sections of St. Sauflieu and Achenheim. Finally, comparisons with the marine isotope, Greenland GRIP chronologies and dust records are proposed. At St. Pierre, the pedostratigraphic and sedimentological analyses (total iron, organic matter, carbonate, grain size), in association with low field magnetic susceptibility measurements, demonstrate that this loess succession records the major climatic events of the Upper Pleistocene. The basal soil complex at St. Pierre is similar to those from the main successions of North (St. Sauflieu) or Northeast France (Achenheim). It shows a Bt horizon of brown leached soil, a deeply reworked grey forest soil and two isohumic steppe soils separated by a non-calcareous loess layer. This loess level corresponds to the first aeolian event clearly observed in the succession and can be correlated with Marker II of the Central European stratigraphy located around the marine isotope stage (MIS) 5/4 boundary. The main aeolian sedimentation starts after the soil complex and ends with the top soil (brown leached soil). Finally, a good parallel is observed between the strongest peaks of the dust records of the ice cores and the main period of loess deposition in St Pierre-lès-Elbeuf occurring during MIS 2.  相似文献   

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