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1.
With accelerated melting of alpine glaciers, understanding the future state of the cryosphere is critical. Because the observational record of glacier response to climate change is short, palaeo‐records of glacier change are needed. Using proglacial lake sediments, which contain continuous and datable records of past glacier activity, we investigate Holocene glacier fluctuations on northeastern Baffin Island. Basal radiocarbon ages from three lakes constrain Laurentide Ice Sheet retreat by ca. 10.5 ka. High sedimentation rates (0.03 cm a?1) and continuous minerogenic sedimentation throughout the Holocene in proglacial lakes, in contrast to organic‐rich sediments and low sedimentation rates (0.005 cm a?1) in neighbouring non‐glacial lakes, suggest that glaciers may have persisted in proglacial lake catchments since regional deglaciation. The presence of varves and relatively high magnetic susceptibility from 10 to 6 ka and since 2 ka in one proglacial lake suggest minimum Holocene glacier extent ca. 6–2 ka. Moraine evidence and proglacial and threshold lake sediments indicate that the maximum Holocene glacier extent occurred during the Little Ice Age. The finding that glaciers likely persisted through the Holocene is surprising, given that regional proxy records reveal summer temperatures several degrees warmer than today, and may be due to shorter ablation seasons and greater accumulation‐season precipitation. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

2.
Examination of a sample of 150 fluted-point localities from southern Ontario, Canada in relation to datable features of Late Wisconsinan ice retreat discloses maximum possible ages for early Palaeo-Indian occupation and reveals selection of specific physiographic situations. General relationship to maximum ice-advance positions suggests occupation during the Two Creeks Interstade after Port Huron ice retreat about 12,300 yr B.P. Specific relationship to 14C-dated proglacial Great Lake strands favors occupation during the North Bay Interstade after Greatlakean ice retreat about 11,500 yr B.P. Locality frequency on Lake Algonquin strands suggests contemporaneity with the main stage of this lake about 11,500 to 10,400 yr B.P., with a small number of lake-plain localities indicating minor post-Algonquin persistence. Radiocarbon dates for fluted-point sites elsewhere in the glaciated northeast place occupation coeval with the southwestern Folsom fluted-point tradition of about 10,850 to 10,200 yr B.P. Locality situation in regions dominated by proglacial sediments, on lake-edge features adjacent to strand-dissecting tributaries, within major river valleys, implies selectivity reflecting primary adaptation. Fluted-point associations with caribou and elk remains suggest that “focal” adaptation to cervids, comparable to southwestern Folsom bison exploitation, might underlie the homogeneous nature and distribution of early Palaeo-Indian localities throughout the northeast.  相似文献   

3.
During and after deglaciation, Lake Vättern developed from a proglacial lake situated at the westernmost rim of the Baltic Ice Lake (BIL), into a brackish water body connecting the North Sea and the Baltic Sea, and finally into an isolated freshwater lake. Here we present geochemical and mineralogical data from a 70‐m composite sediment core recovered in southern Lake Vättern. Together with a radiocarbon age model of this core, we are able to delineate the character and timing of the different lake stages. In addition to a common mineralogical background signature seen throughout the sediment core, the proglacial sediments bear a calcite imprint representing ice‐sheet transported material from the limestone bedrock that borders the lake basin in the northeast. The proglacial fresh to brackish water transition is dated to 11 480±290 cal. a BP and is in close agreement with other regional chronologies. The brackish period lasted c. 300 years and was followed by a c. 1600 year freshwater period before the Vättern basin became isolated from the Initial Littorina Sea. Decreasing detrital input, increasing δ13C values and the appearance of diatoms in the upper 15 m of the sediment succession are interpreted as an overall increase in biological productivity. This mode of sedimentation continues until the present and is interpreted to mark the final isolation of the lake at 9530±50 cal. a BP. Consequently, the isolation of Lake Vättern was not an outcome of the Ancylus Lake regression, but rather because of ongoing continental uplift in the early Littorina period.  相似文献   

4.
We present results from three geophysical campaigns using high‐resolution sub‐bottom profiling to image sediments deposited in Loch Ness, Scotland. Sonar profiles show distinct packages of sediment, providing insight into the loch's deglacial history. A recessional moraine complex in the north of the loch indicates initial punctuated retreat. Subsequent retreat was rapid before stabilisation at Foyers Rise formed a large stillstand moraine. Here, the calving margin produced significant volumes of laminated sediments in a proglacial fjord‐like environment. Subsequent to this, ice retreated rapidly to the southern end of the loch, where it again deposited a sequence of proglacial laminated sediments. Sediment sequences were then disturbed by the deposition of a thick gravel layer and a large turbidite deposit as a result of a jökulhlaup from the Spean/Roy ice‐dammed lake. These sediments are overlain by a Holocene sheet drape. Data indicate: (i) a former tributary of the Moray Firth Ice Stream migrated back into Loch Ness as a major outlet glacier with a calving margin in a fjord‐like setting; (ii) there was significant sediment supply to the terminus of this outlet glacier in Loch Ness; and (iii) that jökulhlaups are important for sediment supply into proglacial fjord/lake environments and may compose >20% of proglacial sedimentary sequences. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

5.
It is important for both current monitoring and paleoenvironmental research conducted on proglacial lakes and their adjacent glaciers to clarify the hydrological processes operating on these lakes. However, in remote regions with limited accessibility it may be difficult to study hydrological processes by direct monitoring. In this study, we use measurements of stable isotopic compositions to trace the multiple water sources contributing to Ranwu Lake, a proglacial lake in south-eastern Tibet. Using stable isotopic data from precipitation, inflowing rivers and the lake water, a water and isotope mass balance modelling method was used to calculate the ratio of evaporation to input. Subsequently, using hydrological and climatic data for the outflow, the largest inflow and precipitation, other hydrological elements of the lake water balance were also calculated. The results demonstrate that the ratio of evaporation to inflow is as low as 0.009, the lowest value observed for the Tibetan Plateau, indicating that Ranwu Lake is a through-flow lake with a very short retention time. Glacial meltwater accounts for at least 55% of total runoff, the highest value observed for the Tibetan Plateau, indicating that the sediments of Ranwu Lake may have considerable potential for reconstructing variations in the activity of the local glaciers. Finally, we note that it may be inappropriate in this glacier-fed lake to use the intersection of the local meteoric water line with the lake water line for determining the isotopic composition of the input water, and this possibility must be carefully considered when stable isotope mass modelling is used in proglacial lakes.  相似文献   

6.
This article reports on an Early Saalian proglacial lake formed between the Scandinavian Ice Sheet and the front of the Sudeten Mountains, Poland. Sediments investigated at Mys?ów point to a transition from glacifluvial to glaciolacustrine environments. The bulk of the sediments was deposited in deep‐water Gilbert‐type deltas (A–E complexes). A delta plain (topset) gradually passes into a subaerial plateau and then a clastic shoreline and the subaquatic slope of a prograding delta (foreset). The glaciolacustrine lithofacies represent a number of lake‐basin environments, from marginal subaqueous slopes to distal parts of a subaqueous fan. Glaciolacustrine and glaciodeltaic deposits locally reach ?50–70 m in thickness. Analyses of A–E complexes indicate that the lake existed for more than 130 years and that its origin and evolution were closely connected with the ice front. This case study records lake sedimentation at an ice‐sheet margin with cohesionless gravity flows, turbidity currents, debris‐avalanching and, to a much lesser degree, parapelagic suspension fall‐out and ice‐raft dumping. In the initial stage, the lake extended more than 10 km to the south, and the deposition was relatively slow. In the second stage, recession of the ice sheet caused rapid growth of a delta. The third and ultimate stage coincided with the final glacial recession, with rapid deposition occurring only on the lake bottom. The model of the glaciolacustrine environment presented here may also be applicable to many other proglacial lakes in mountain areas.  相似文献   

7.
The transition from full glacial to interglacial conditions along the southern margin of the Laurentide ice sheet resulted in dramatic changes in landscapes and biotic habitats. Strata and landforms resulting from the Wisconsin Episode of glaciation in the area directly west of Lake Superior indicate a context for late Pleistocene biota (including human populations) connected to ice margins, proglacial lakes, and postglacial drainage systems. Late Glacial landscape features that have the potential for revealing the presence of Paleoindian artifacts include abandoned shorelines of proglacial lakes in the Superior and Agassiz basins and interior drainages on deglaciated terrains. The linkage between Late Pleistocene human populations and Rancholabrean fauna has yet to be demonstrated in the western Lake Superior region, although isolated remains of mammoth ( Mammuthus) have been documented, as well as fluted points assigned to Clovis, Folsom, and Holcombe‐like artifact forms. Agate Basin and Hell Gap (Plano‐type) artifacts also imply the presence of human groups in Late Glacial landscapes associated with the Agassiz and Superior basins. © 2007 Wiley Periodicals, Inc.  相似文献   

8.
High‐resolution loss‐on‐ignition analyses of lacustrine sediment cores from both proglacial and non‐glacial lakes in southern Norway have revealed a specific pattern characterised by a significant, two‐peaked reduction of the loss‐on‐ignition values in the basal half of the cores. In non‐glacier‐fed lakes, the loss‐on‐ignition variations are interpreted to reflect mainly lake productivity and hence variability in surface summer air temperature. Sediments deposited in proglacial lakes, however, reflect mainly the glacier activity in the lake catchment. Bulk AMS radiocarbon dates from the core sequences and the loss‐on‐ignition curve pattern suggest that this event correlates with the ‘8200 cal. yr BP event’ recorded in the GRIP and GISP2 Greenland ice‐cores, termed the Finse event in southern Norway. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

9.
Radiocarbon-dated sediment cores from the Champlain Valley (northeastern USA) contain stratigraphic and micropaleontologic evidence for multiple, high-magnitude, freshwater discharges from North American proglacial lakes to the North Atlantic. Of particular interest are two large, closely spaced outflows that entered the North Atlantic Ocean via the St. Lawrence estuary about 13,200–12,900 cal yr BP, near the beginning of the Younger Dryas cold event. We estimate from varve chronology, sedimentation rates and proglacial lake volumes that the duration of the first outflow was less than 1 yr and its discharge was approximately 0.1 Sv (1 Sverdrup = 106 m3 s−1). The second outflow lasted about a century with a sustained discharge sufficient to keep the Champlain Sea relatively fresh for its duration. According to climate models, both outflows may have had sufficient discharge, duration and timing to affect meridional ocean circulation and climate. In this report we compare the proglacial lake discharge record in the Champlain and St. Lawrence valleys to paleoclimate records from Greenland Ice cores and Cariaco Basin and discuss the two-step nature of the inception of the Younger Dryas.  相似文献   

10.
This study describes changes to the proglacial drainage network of Skaftafellsjökull, Iceland from 1998 to 2011. Proglacial landscapes are highly sensitive to glacier retreat, and the retreat of glaciers around the world has accelerated since the mid‐1990s. Skaftafellsjökull has retreated at an average rate of 53 m per year since 1999. From 1999 to 2003, the river incised and formed a sequence of now abandoned channels and fluvial terraces extending ～1 km downstream from the glacier. Retreat of the glacier from an over‐deepened ice‐contact slope meant that there was a positive correlation between the distance of glacier retreat and the amount of fluvial incision. Incision was episodic, occurring annually in response to drainage reactivation and reorganization. On an annual basis, the rate of retreat is moderately negatively correlated with the rate of incision. This is partly because the ice‐contact slope decreases away from the position of maximum glacier extent, and also because more sediment is released with faster retreat, counteracting the effect of retreat down an ice‐contact slope. From 2003 onwards, proximal terrace formation ceased, as a proglacial lake became established. Downstream of the lake outlet further incision deepened the channel, with most change occurring during a flood in 2006, where incision in the upstream confined reach was accompanied by downstream aggradation and terrace formation. These observations indicate that proglacial changes in response to glacier retreat are a result of the interactions of river channel incision and terrace formation, aggradation, lake development, and flooding, which together control river channel changes, sediment redistribution and sandur stratigraphy.  相似文献   

11.
Scdimentological studies of a small ice-contact proglacial lake at Briksdal. southwest Norway, have led to the discovery of two types of tubular traces developed on the surfaces of material collected in sediment traps. The traces are described and attributed, with certainty, to the burrowing activities of chironomid midge larvae.  相似文献   

12.
Livingstone, S. J., Ó Cofaigh, C., Evans, D. J. A. & Palmer, A. 2010: Sedimentary evidence for a major glacial oscillation and proglacial lake formation in the Solway Lowlands (Cumbria, UK) during Late Devensian deglaciation. Boreas, Vol. 39, pp. 505–527. 10.1111/j.1502‐3885.2010.00149.x. ISSN 0300‐9483. This paper is a sedimentological investigation of Late Devensian glacial deposits from the Solway Lowlands, northwest England, in the central sector of the last British–Irish Ice Sheet. In this region, laminated glaciolacustrine sediments occur, sandwiched between diamictons interpreted as subglacial tills. At one location the laminated sediments are interpreted as varves, and indicate the former presence of a proglacial lake. Correlation of these varves with other laminated sediments indicates that the glacial lake was at least 140 km2 in area and probably much larger. Extensive beds of sand, silt and gravel throughout the Solway Basin associated with the lake demonstrate ice‐free conditions over a large area. Based on the number of varves, the lake was in existence for at least 261 years. The stratigraphic sequence of varves bracketed by tills implies a major glacial oscillation prior to the Scottish Re‐advance (16.8 cal. ka BP). This oscillation is tentatively correlated with the Gosforth oscillation at c.19.5 cal. ka BP. Subsequent overriding of these glaciolacustrine sediments during a westward‐moving re‐advance demonstrates rapid ice loss and then gain within the Solway Lowlands from ice‐dispersal centres in the Lake District, Pennines and Southern Uplands. It is speculated that the existence of this and other lakes along the northeastern edge of the Irish Sea Basin would have influenced ice‐sheet dynamics.  相似文献   

13.
This paper describes a Geographical Information System (GIS)-based palaeogeographic reconstruction of the development of proglacial lakes formed during deglaciation in Estonia, and examines their common features and relations with the Baltic Ice Lake. Ice marginal positions, interpolated proglacial lake water levels and a digital terrain model were used to reconstruct the spatial distribution and bathymetry of the proglacial lakes. Our results suggest that the proglacial lakes formed a bay of the Baltic Ice Lake after the halt at the Pandivere-Neva ice margin about 13.3 cal. kyr BP. Shoreline reconstruction suggests that two major proglacial lake systems, one in eastern and the other in western Estonia, were connected via a strait and thus had identical water levels. The water budget calculations show that the strait was able to transfer a water volume several times greater than the melting glacier could produce. As this strait compensated for the water level difference between the two lake parts, the subsequent further merging in north Estonia did not result in catastrophic drainage, as has been proposed.  相似文献   

14.
Glacigenic sediments exposed in coastal cliffs cut through undulatory terrain fronting the Last Glacial Maximum laterofrontal moraine at Waterville on the Iveragh Peninsula, southwest Ireland, comprise three lithofacies. Lithofacies 1 and 2 consist of interdigitated, offlapping and superimposed ice‐proximal subaqueous outwash and stacked sequences of cohesionless and cohesive subaqueous debris flows, winnowed lag gravels and coarse‐grained suspension deposits. These are indicative of sedimentation in and around small grounding line fans that prograded from an oscillating glacier margin into a proglacial, interlobate lake. Lithofacies 3 comprises braided river deposits that have undergone significant syn‐sedimentary soft‐sediment deformation. Deposition was likely related to proglacial outwash activity and records the reduction of accommodation space for subaqueous sedimentation, either through the lowering of proglacial water levels or due to basin infilling. The stratigraphic architecture and sedimentology of the moraine at Waterville highlight the role of ice‐marginal depositional processes in the construction of morphostratigraphically significant ‘end moraine’ complexes in Great Britain and Ireland. Traditional ‘tills’ in these moraines are often crudely stratified diamictons and gravelly clinoforms deposited in ice‐proximal subaqueous and subaerial fans. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

15.
A sedimentological and geochemical study of the Lago Enol sequence (Cantabrian Mountains, northern Spain), together with detailed geomorphological mapping, provides a first record of glacier evolution and climate change over the last 40 ka in the Picos de Europa National Park. The Enol glacier retreated from its maximum extent prior to 40 ka BP as demonstrated by the onset of proglacial lacustrine sedimentation in two glaciated depressions: the Comella hollow to the north (before 40 ka BP) and the Lago Enol (before 38 ka BP). These results support previous evidence that the maximum extent of southern European glaciers occurred earlier than in northern Europe. Alternation of homogeneous and laminated proglacial sediments during the glacier retreat illustrate a dynamic glacial evolution during the Marine Isotope Stage (MIS) 3 (40–26 ka BP). A slight warming is detected at 26 ka ago with the change from proglacial sediments (in a lake located in contact to the glacier) to glaciolacustrine sedimentation (in a non‐contact or distal lake). Finally, the onset of organic‐rich sediments took place at 18 ka ago. This last transition occurred in two phases, similarly to the North Atlantic Last Termination, suggesting a link between North Atlantic Deep Water formation oscillations and palaeohydrological variability in the Cantabrian Mountains. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

16.
In the present paper the effects of rapid, high‐amplitude base‐level changes during the last glacial‐interglacial transition were studied for the Ain River in eastern France. During the Würm glacial maximum (MIS 2) rapid aggradation by deep‐water Gilbert‐type deltas and shallow‐water fan deltas occurred at the margins of a 20 to 50 m deep proglacial lake. A temporal high‐amplitude lake‐level fall of 60 m resulted in gravel deposition by forced‐regressive deltas, followed by rapid lake‐level rise and fine‐grained glaciolacustrine deposition. During the final deglaciation, a rapid base‐level fall of 40 m resulted in a complex fluvial response. Knickpoint formation and headward incision of the highstand deltas and concomitant deposition of gravel sheets by forced‐regressive deltas and braided systems occurred in several depocentres on the former glacial lake floor. Preservation of highstand and falling‐stage deposits and terrace formation in the incised valley depended on vertical incision and lateral channel migration. Terraces are well developed in the former lake‐floor depressions, whereas vertical incision was dominant in the higher lake‐floor areas. The Ain terrace staircase was likely formed by autogenic processes during a single allogenic base‐level fall. This case study possibly offers an analogue for the preservation of interglacial highstand coastal deltas during sea‐level fall at warm‐to‐cold climate transitions, although the rates of base‐level fall are different.  相似文献   

17.
The Charlevoix region, in southeastern Québec, is characterized by a dramatic landscape formed by the junction of the Laurentian Highlands, the Charlevoix Astrobleme and the St Lawrence Estuary. At the Last Glacial Maximum (LGM), the region was completely covered by the Laurentide Ice Sheet (LIS). The complex topography of the region was the stage of many of the major deglacial events of southern Quebec (e.g. Goldthwait Sea Invasion, St Lawrence Ice‐Stream, Saint‐Narcisse Episode). We present a detailed reconstruction of the pattern of retreat of the LIS in the Charlevoix region based on the interpretation of ice‐marginal features (e.g. moraines, fans) and glaciolacustrine landforms and deposits, two extensive field campaigns, and the interpretation of high‐resolution 3D digital aerial photographs and LiDAR data. Our results indicate five moraine complexes in the region: the Rochette, the Brûlée, the Sainte‐Anne, the Saint‐Narcisse and the Mars‐Batiscan complexes. Deltas, fans, fine‐grained sediments, littoral deposits, drainage breaches and deposits were used to identify 91 palaeo‐proglacial lakes. The identification of these lakes and their relation to moraine complexes enabled the reconstruction of six stages of lake development during the Charlevoix deglaciation. The development of proglacial lakes occurred in all types of terrain (highlands, lowlands, transitory levels above marine limit). We conclude that local topography had a decisive effect on promoting both moraine deposition and lake development. We suggest that similar topographical regions (hilly‐mountainous) that were affected by major ice‐margin stabilizations during glacial retreat should have experience small lakes dominating valleys and topographical lows.  相似文献   

18.
Paleogeographic reconstructions for the Samarovo, Taz, Murukta, and Sartan glaciations reveal the formation conditions of proglacial lakes dammed by ice in intermontane depressions and valleys of large rivers in eastern Transbaikalia. Middle-Late Pleistocene climate change is reconstructed using spore-pollen spectra from Pleistocene sediments in northern Transbaikalia. The age and lifetime of proglacial lakes are constrained by radiocarbon, thermoluminescence, and varve chronology of their bottom sediments in the periglacial zone. The lake levels remain recorded in sediments produced by deposition and erosion along the former lake shores, as well as in morphology and lithology variations of terminal moraines. A large proglacial lake, with a maximum level of 1020 m, occupied vast areas in Transbaikalia and its surroundings during the Samarovo glaciation. After the glaciers degraded, the Amur River system expanded into the area of closed lake basins in the southeastern Baikal region, including North China and Mongolia. The obtained results have implications for the Middle-Late Pleistocene history of lake deposition.  相似文献   

19.
Local glaciers and ice caps (GICs) comprise only ~5.4% of the total ice volume, but account for ~14–20% of the current ice loss in Greenland. The glacial history of GICs is not well constrained, however, and little is known about how they reacted to Holocene climate changes. Specifically, in North Greenland, there is limited knowledge about past GIC fluctuations and whether they survived the Holocene Thermal Maximum (HTM, ~8 to 5 ka). In this study, we use proglacial lake records to constrain the ice‐marginal fluctuations of three local ice caps in North Greenland including Flade Isblink, the largest ice cap in Greenland. Additionally, we have radiocarbon dated reworked marine molluscs in Little Ice Age (LIA) moraines adjacent to the Flade Isblink, which reveal when the ice cap was smaller than present. We found that outlet glaciers from Flade Isblink retreated inland of their present extent from ~9.4 to 0.2 cal. ka BP. The proglacial lake records, however, demonstrate that the lakes continued to receive glacial meltwater throughout the entire Holocene. This implies that GICs in Finderup Land survived the HTM. Our results are consistent with other observations from North Greenland but differ from locations in southern Greenland where all records show that the local ice caps at low and intermediate elevations disappeared completely during the HTM. We explain the north–south gradient in glacier response as a result of sensitivity to increased temperature and precipitation. While the increased temperatures during the HTM led to a complete melting of GICs in southern Greenland, GICs remained in North Greenland probably because the melting was counterbalanced by increased precipitation due to a reduction in Arctic sea‐ice extent and/or increased poleward moisture transport.  相似文献   

20.
Lake Vättern represents a critical region geographically and dynamically in the deglaciation of the Fennoscandian Ice Sheet. The outlet glacier that occupied the basin and its behaviour during ice‐sheet retreat were key to the development and drainage of the Baltic Ice Lake, dammed just west of the basin, yet its geometry, extent, thickness, margin dynamics, timing and sensitivity to regional retreat forcing are rather poorly known. The submerged sediment archives of Lake Vättern represent a missing component of the regional Swedish deglaciation history. Newly collected geophysical data, including high‐resolution multibeam bathymetry of the lake floor and seismic reflection profiles of southern Lake Vättern, are used here together with a unique 74‐m sediment record recently acquired by drill coring, and with onshore LiDAR‐based geomorphological analysis, to investigate the deglacial environments and dynamics in the basin and its terrestrial environs. Five stratigraphical units comprise a thick subglacial package attributed to the last glacial period (and probably earlier), and an overlying >120‐m deglacial sequence. Three distinct retreat–re‐advance episodes occurred in southern Lake Vättern between the initial deglaciation and the Younger Dryas. In the most recent of these, ice overrode proglacial lake sediments and re‐advanced from north of Visingsö to the southern reaches of the lake, where ice up to 400 m thick encroached on land in a lobate fashion, moulding crag‐and‐tail lineations and depositing till above earlier glacifluvial sediments. This event precedes the Younger Dryas, which our data reveal was probably restricted to north‐central sectors of the basin. These dynamics, and their position within the regional retreat chronology, indicate a highly active ice margin during deglaciation, with retreat rates on average 175 m a?1. The pronounced topography of the Vättern basin and its deep proglacial‐dammed lake are likely to have encouraged the dynamic behaviour of this major Fennoscandian outlet glacier.  相似文献   

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