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1.
The overall pattern of deglaciation of the southern part of the Scandinavian Ice Sheet has been considered established, although details of the chronology and ice sheet dynamics are less well known. Even less is known for the south Swedish Upland because the area was deglaciated mostly by stagnation. Within this area lies the conspicuous Vimmerby moraine, for which we have used the terrestrial cosmogenic nuclide (10Be) exposure dating technique to derive the exposure age of six glacially transported boulders. The six 10Be cosmogenic ages are internally consistent, ranging from 14.9 ± 1.5 to 12.4 ± 1.3 ka with a mean of 13.6 ±0.9 ka. Adjusting for the effects of surface erosion, snow burial and glacio-isostatic rebound causes the mean age to increase only by c. 6% to c. 14.4± 0.9 ka. The 10Be derived age for the Vimmerby moraine is in agreement with previous estimates forthe timing of deglaciation based on radiocarbon dating and varve chronology. This result shows promise for further terrestrial cosmogenic nuclide exposure studies in southern Sweden.  相似文献   

2.
Owing to increased winter balances especially since AD 1988/89, almost all valley outlet glaciers of Jostedalsbreen in western Norway are experiencing the largest advance since that of the early 18th century, the regional "Little Ice Age" maximum. Brigsdalsbreen advanced 441 m between 1987 and 1997. By the end of this period, the glacier had reached the outlet of the proglacial lake Brigsdalsvatnet, ploughing into unfrozen, fine-grained, water-soaked glaciolimnic sediments from the lake bottom and forming frontal moraines. These moraines are characterised by a lack of internal structures and preferred fabric. Owing to the strong advance, the moraine morphology is constantly changing, leaving only temporary moraine ridges.
Observations made along the glacier front suggest that the formation of these moraines can best be described as "bulldozed moraines", since the term push moraine, commonly associated with advancing glaciers, should be restricted to permafront environments. Different processes involved in moraine formation at frontal and lateral glacier margins result from variations in proglacial sediment properties, microrelief and glacier dynamics. Among these processes, large boulders left in the proglacial areas are pushed forward, forming pressure ridges on the distal side. Some of the largest boulders ( c . 80–120 m3) are overturned or rotated by the glacier.  相似文献   

3.
ABSTRACT. Initial cosmogenic 10Be results from a former ice limit in Torres del Paine indicate a shortlived stillstand or readvance of Patagonian ice culminating at 12–15 kyr BP with a mean age of 13.2 ± 0.8 kyr BP. The glacier extended some 40 km beyond the present ice margin and was within 15 km of the presumed Last Glacial Maximum limits. The timing of the glacier stage spans the cooling event recorded in Antarctic ice cores, termed the Antarctic Cold Reversal (14.5–12.9 kyr BP). This result implies that glaciers at these latitudes were out of phase with those in the northern hemisphere; instead they mirrored the climate structure of Antarctica during the last glacial to interglacial transition.  相似文献   

4.
ABSTRACT. Glacier fluctuations in the Strait of Magellan tell of the climatic changes that affected southern latitudes at c. 53–55°S during the Last Glacial Maximum (LGM) and Late-glacial/Holocene transition. Here we present a revised chronology based on cosmogenic isotope analysis, 14C assays, amino acid racemisation and tephrochronology. We unpick the effect of bedrock-derived lignite which has affected many 14C dates in the past and synthesise new and revised dates that constrain five glacier advances (A to E). Advance A is prior to the LGM. LGM is represented by Advance B that reached and largely formed the arcuate peninsula Juan Mazia. Carbon-14and 10Be dating show it occurred after 31 250 cal yrs BP and culminated at 25 200–23 100 cal yrs BP and was then followed by the slightly less extensive advance C sometime before 22 400–20 300 cal yrs BP. This pattern of an early maximum is found elsewhere in South America and more widely. Stage D, considerably less extensive, culminated sometime before 17 700–17 600 cal yrs BP and was followed by rapid and widespread glacier retreat. Advance E, which dammed a lake, spanned 15 500–11770 cal yrs BP. This latter advance overlaps the Bølling-Allerød interstadials and the glacier retreat occurs during the peak of the Younger Dryas stadial in the northern hemisphere. However, the stage E advance coincides with the Antarctic Cold Reversal (c. 14800–12700 cal yrs BP) and may indicate that some millennial-scale climatic fluctuations in the Late-glacial period are out of phase between the northern and southern hemispheres.  相似文献   

5.
The deglaciation history of Balsfjord, northern Norway, and post-glacial mass movement events were investigated. Radiocarbon dates indicate that the Balsfjord glacier retreated from the Tromsø–Lyngen moraines about 10.4 14C Ky BP. Between ca. 10.3 14C Ky BP and 9.9 14C Ky BP, deposition of a distinct end moraine–the Skjevelnes moraine–in the central part of Balsfjord occurred. The transition from glacimarine to open marine sedimentary environment took place before 9.6 14C Ky BP. Between ca. 9.5 14C Ky BP and 8.4 14C Ky BP, at least one local and three regional mass movement events occurred. After this period, no gravity flow activity is preserved in the cores. The high frequency of mass movements in the early post-glacial period is presumed to be due to fast sea level changes and/or tectonic activity induced by rapid isostatic uplift.  相似文献   

6.
Moraine ridges are commonly used to identify past glacier ice margins and so infer glacier mass balance changes in response to climatic variability. However, differences in the form of past ice margins and post-depositional modification of moraine surfaces can complicate these geomorphic records. As a result, simple relationships, such as distance from current ice margin, or linear alignments, may not necessarily indicate moraines deposited contemporaneously. These disturbances can also modify the size distribution of lichen populations, providing a distinctive signature for surfaces with similar histories and a means of identifying contemporaneous moraine surfaces. In this paper, statistical analysis of lichen size distributions is used to identify moraine surfaces with similar histories from complex suites of Little Ice Age moraine fragments in the proglacial areas of Skálafellsjökull (including Sultartungnajökull) and Heinabergsjökull, southeast Iceland. The analysis is based on a novel use of the goodness-of-fit statistic, Watson's U2 which provides a measure of 'closeness' between two sample distributions. Moraine fragments with similar histories are identified using cluster analysis of the U2 closeness values. The spatial pattern of the clustered moraines suggests three distinct phases of moraine deposition at Skálafellsjökull and Heinabergsjökull, four phases at Sultartungnajökull and a digitate planform margin at Heinabergsjökull. These spatial patterns are corroborated with tephrochronology. The success of the U2 statistical analysis in identifying surfaces with similar histories using lichen size distributions suggests that the technique may be useful in augmenting lichenometric surface dating as well as differentiating between other surfaces that support lichen populations, such as rock avalanche deposits.  相似文献   

7.
207Pb/206Pb single-grain zircon, 40Ar/39Ar single-grain hornblende and biotite, and 40Ar/39Ar bulk-sample muscovite and biotite ages from the Nelshoogte trondhjemite pluton located in eastern Transvaal, South Africa, show that this granitoid had a protracted thermal history spanning 3213±4  Ma to about 3000  Ma. Whole-rock 40Ar/39Ar ages from cross-cutting dolerite dykes indicate that these were intruded at about 1900  Ma. There is no evidence of this or other, later events significantly affecting the argon systematics of the minerals from the pluton dated by the 40Ar/39Ar method.
  The pluton has a well-defined palaeomagnetic pole which is dated at 3179±18 (2 σ ) Ma by 40Ar/39Ar dating of hornblende. This pole (18°N, 310°E, A 95=9°) yields a palaeolatitude of 0°, significantly different from other Archaean poles from the Kaapvaal Craton. The palaeolatitude difference implies that there was significant apparent polar wander during the Archaean. A second, overprinting magnetization seen in the pluton is also seen in the lower-Proterozoic dolerite dykes, and is consistent with other lower-Proterozoic (2150–1950  Ma) poles for southern Africa.  相似文献   

8.
An 8 m long carcass of a bowhead whale ( Balaena mysticetus ) melted out from remnant glacier ice in the lateral moraine of the Jemelianovbreen glacier in August 1996. Folded and sheared sediment bands in the ice suggest that the whale was incorporated during an advance of the glacier. The whale's longitudinal axis was oriented parallel to the direction of the ice-flow, with the thinnest posterior part dipping upflow. The posterior section was best preserved with muscles and blubber, although the entire skin surface was strongly decomposed and only a thick fibrous surface was left of the blubber. The abdominal wall was holed, most likely by marine organisms, and partly filled with a compacted mixture of well-sorted gravelly beach sediments and fat. the whale seems to have been incorporated into the glacier together with glaciomarine sediments and carried by the flowing ice to an altitude of ca. 15 m. Jemelianovbreen is a tidewater glacier with two known surge-episodes. The first and most extensive of these occurred ca. 1900 AD and reached ca. 7 km outside the present coast-line. Radiocarbon dating of a fragment of a caudal vertebra yielded 345 ± 40 14C years BP (1535-1660 cal. AD), suggesting that the whale lived some time during the last part of the cold period known as the Little Ice Age.  相似文献   

9.
Interhemispheric Linkage of Paleoclimate During the Last Glaciation   总被引：4，自引：0，他引：4  
Combined glacial geologic and palynologic data from the southern Lake District, Seno Reloncaví, and Isla Grande de Chiloé in middle latitudes (40°35’–42°25’S) of the Southern Hemisphere Andes suggest (1) that full-glacial or near-full-glacial climate conditions persisted from about 29,400 to 14,550 14C yr BP in late Llanquihue time, (2) that within this late Llanquihue interval mean summer temperature was depressed 6°–8°C compared to modern values during major glacier advances into the outer moraine belt at 29,400, 26,760, 22,295–22,570, and 14,550–14,805 14C yr BP , (3) that summer temperature depression was as great during early Llanquihue as during late Llanquihue time, (4) that climate deteriorated from warmer conditions during the early part to colder conditions during the later part of middle Llanquihue time, (5) that superimposed on long-term climate deterioration are Gramineae peaks on Isla Grande de Chiloé that represent cooling at 44,520–47,110 14C yr BP (T-11), 32,105–35,764 14C yr BP (T-9), 24,895–26,019 14C yr BP (T-7), 21,430–22,774 14C yr BP (T-5), and 13,040–15,200 14C yr BP (T-3), (6) that the initial phase of the glacial/interglacial transition of the last termination involved at least two major steps, one beginning at 14,600 14C yr BP and another at 12,700–13,000 14 C yr BP , and (7) that a late-glacial climate reversal of ≥2–3° C set in close to 12,200 14C yr BP , after an interval of near-interglacial warmth, and continued into Younger Dryas time. The late-glacial climate signal from the southern Chilean Lake District ties into that from proglacial Lago Mascardi in the nearby Argentine Andes, which shows rapid ice recession peaking at 12,400 14C yr BP , followed by a reversal of trend that culminated in Younger-Dryas-age glacier readvance at 11,400–10,200 14C yr BP . Many full- and late-glacial climate shifts in the southern Lake District match those from New Zealand at nearly the same Southern Hemisphere middle latitudes. At the last glacial maximum (LGM), snowline lowering relative to present-day values was nearly the same in the Southern Alps (875 m) and the Chilean Andes (1000 m). Particularly noteworthy are the new Younger-Dryas-age exposure dates of the Lake Misery moraines in Arthur's Pass in the Southern Alps. Moreover, pollen records from the Waikato lowlands on North Island show that a major vegetation shift at close to 14,700 14C yr BP marked the beginning of the last glacial/interglacial transition (Newnham et al. 1989). The synchronous and nearly uniform lowering of snowlines in Southern Hemisphere middle-latitude mountains compared with Northern Hemisphere values suggests global cooling of about the same magnitude in both hemispheres at the LGM. When compared with paleoclimate records from the North Atlantic region, the middle-latitude Southern Hemisphere terrestrial data imply interhemispheric symmetry of the structure and timing of the last glacial/interglacial transition. In both regions atmospheric warming pulses are implicated near the beginning of Oldest Dryas time (～14,600 14C yr BP) and near the Oldest Dryas/Bölling transition (～12,700–13,000 14 C yr BP ). The second of these warming pulses was coincident with resumption of North Atlantic thermohaline circulation similar to that of the modern mode, with strong formation of Lower North Atlantic Deep Water in the Nordic Seas. In both regions, the maximum Bölling-age warmth was achieved at 12,200–12,500 14 C yr BP , and was followed by a reversal in climate trend. In the North Atlantic region, and possibly in middle latitudes of the Southern Hemisphere, this reversal culminated in a Younger-Dryas-age cold pulse. Although changes in ocean circulation can redistribute heat between the hemispheres, they cannot alone account either for the synchronous planetary cooling of the LGM or for the synchronous interhemispheric warming steps of the abrupt glacial-to-interglacial transition. Instead, the dominant interhemispheric climate linkage must feature a global atmospheric signal. The most likely source of this signal is a change in the greenhouse content of the atmosphere. We speculate that the Oldest Dryas warming pulse originated from an increase in atmospheric water-vapor production by half-precession forcing in the tropics. The major thermohaline switch near the Oldest Dryas/Bölling transition then couldhave triggered another increase in tropical water-vapor production to near-interglacial values.  相似文献   

10.
Recent advances in the use of the environmental radionuclides caesium–137 and unsupported lead–210 to quantify medium– and longer–term rates of erosion and sediment accumulation have proved of considerable value in catchment sediment budget investigations. However, there remains a need to explore the potential for using other shorter–lived radionuclides to provide evidence of sediment mobilisation, transport and storage over shorter timescales and particularly for individual events. This contribution reports the results of a study aimed at exploring the potential for using beryllium–7 (7Be, t ½= 53.3 days) to meet this requirement. The study investigated the use of 7Be as a sediment tracer in three key components of the sediment budget, namely, soil erosion and sediment mobilisation from slopes, the transport, storage and remobilisation of fine sediment in river channels and overbank deposition on river floodplains. The results presented clearly demonstrate the potential for using 7Be to obtain information on short–term and event–based sediment redistribution rates for use in catchment sediment budget investigations.  相似文献   

11.
A Soil Chronosequence from Neoglacial Moraines in Western Norway   总被引：1，自引：0，他引：1  
A soil chronosequence is presented based upon podzols developed on Holocene moraine crests in the Jardalen cirque complex, western Norway. Simple and inexpensive field and laboratory tests provide information on soil depth development, pH changes, silt/clay translocation and B-horizon reddening and thickness with age. Chronological control on historical moraine ages is provided by lichenometric dates, which support a 5 cm/100 year soil development rate for the first 700 years of pedogenesis. This initial rapid depth development tails off to a maximum rate of 0.06 cm/100 years between c . 1.5 ka and 10 ka BP based upon a Preboreal/Younger Dryas age for the oldest moraines and associated soils in the Jardalen cirque.  相似文献   

12.
ABSTRACT. We examine the deglaciation of the eastern flank of the North Patagonian Icefield between latitudes 46° and 48°S in an attempt to link the chronology of the Last Glacial Maximum moraines and those close to present-day outlet glaciers. The main features of the area are three shorelines created by ice-dammed lakes that drained eastwards to the Atlantic. On the basis of 16 14C and exposure age dates we conclude that there was rapid glacier retreat at 15–16 ka (calendar ages) that saw glaciers retreat 90–125 km to within 20 km of their present margins. There followed a phase of glacier and lake stability at 13.6–12.8 ka. The final stage of deglaciation occurred at c. 12.8 ka, a time when the lake suddenly drained, discharging nearly 2000 km3 to the Pacific Ocean. This latter event marks the final separation of the North and South Patagonian Icefields. The timing of the onset of deglaciation and its stepped nature are similar to elsewhere in Patagonia and the northern hemisphere. However, the phase of lake stability, coinciding with the Antarctic Cold Reversal and ending during the Younger Dryas interval, mirrors climatic trends as recorded in Antarctic ice cores. The implication is that late-glacial changes in southern Patagonia were under the influence of the Antarctic realm and out of phase with those of the northern hemisphere.  相似文献   

13.
《Geomorphology》1995,14(2):149-156
We have used cosmogenic 36Cl surface exposure dating to determine apparent construction ages of late Pleistocene moraines in the Sierra Nevada, the White Mountains, and the Wind River Range, all in the western United States. The inferred glacial chronologies from the various localities all exhibit certain characteristics: (1) Local records are fragmentary and deposits of some glacial advances are always missing; no location has deposits of all glaciations and no glacial advance is recorded at all locations. This is due either to unfavorable conditions for glacier development at some times or to obliteration of earlier deposits by later, more extensive glaciers. (2) Most moraines have young apparent exposure ages, with only a few older than the last glacial cycle. This may be due to young true ages of these deposits, erosion of moraine surfaces, or obliterative overlap and covering of older deposits by younger ones. (3) Many deposits that were previously correlated (e.g., based on their stratigraphic positions) are not correlative; they may represent different stades and, sometimes, even different glaciations. Similarly, some previously uncorrelated deposits have the same exposure ages and may be correlative. (4) Clusters of several distinct moraines of nearly the same age are present at most locations. These clusters suggest that alpine moraines are formed during short deposition episodes that last between several hundred and several thousand years.  相似文献   

14.
We measured in situ 10Be, 26Al and36Cl on glacial deposits as old as 1.1 Myr in the southernmost part of Patagonia and on northern Tierra del Fuego to understand boulder and moraine and, by inference, landscape changes. Nuclide concentrations indicate that surface boulders have been exposed for far less time than the ages of moraines they sit upon. The moraine ages are themselves constrained by previously obtained 40Ar/39Ar ages on interbedded lava flows or U-series and amino acid measurements on related (non-glacial) marine deposits. We suggest that a combination of boulder erosion and their exhumation from the moraine matrix could cause the erratics to have a large age variance and often short exposure histories, despite the fact that some moraine landforms are demonstrably 1 Myr old. We hypothesize that fast or episodic rates of landscape change occurred during glacial times or near the sea during interglacials. Comparison with boulder erosion rates and exhumation histories derived for the middle latitudes of semi-arid Patagonia imply different geomorphic processes operating in southernmost South America. We infer a faster rate of landscape degradation towards the higher latitudes where conditions have been colder and wetter.  相似文献   

15.
Summary. Twenty-two plateau ages obtained by the 40Ar/39Ar step-heating method span most of the time of formation of eastern Iceland. With one exception the dates are consistent with the stratigraphy, the exception having a very unusual argon release pattern. It is concluded that the 40Ar/39Ar step-heating method can give correct dates on hydrothermally altered samples the total fusion ages of which are not correct; however, it is not possible to conclude from the results obtained that the method is inherently more accurate than the conventional method using carefully selected samples.
Though it is known from geological evidence that minor irregularities of spreading have occurred the results show that, within the resolution of the dates, spreading has been steady and symmetrical; in particular, neither a large eastward jump nor repetitive westward jumps can have occurred. The average half spreading rate for the period 2Myr to 12 Myr ago was 0.78 ± 0.16 cm yr-1.  相似文献   

16.
Global Positioning System (GPS) data are analysed from three permanent sites, two in the Western Alps (Grasse, France, and Zimmerwald, Switzerland) and the third in the Po Basin (Torino, Italy), for the 2.5-year period from 1 January 1996 to 1 July 1998. An analysis of the stochastic properties of the position time series reveals a significant amount of spatially and temporally correlated noise, which best fits a model combining white noise and flicker noise. The coloured noise is drastically reduced by spatially filtering the time series, suggesting that it is not due to site-specific effects such as monument motion, but rather to noise sources common to the three sites, such as reference frame, satellite orbit or Earth orientation errors. We find velocity uncertainties (95 per cent confidence interval) of 2.7  mm  yr−1 at GRAS, 2.3  mm  yr−1 at ZIMM, and 2.9  mm  yr−1 at TORI. The residual velocity in the Eurasian reference frame is statistically greater than zero at ZIMM only, with 2.4 ± 2.3  mm  yr−1 of motion in a NW direction. These uncertainties place an upper bound on the expected deformation in the Western Alps. Velocities relative to stable Eurasia do not exceed 3  mm  yr−1, corresponding to a maximum strain rate of 0.03  μstrain  yr−1 over the GRAS–TORI–ZIMM triangle.  相似文献   

17.
青藏高原东部当子沟末次冰期冰川演化光释光测年   总被引：1，自引：0，他引：1  
青藏高原东部横断山脉沙鲁里山北支雀儿山北麓的当子沟, 保留了4 组末次冰期冰碛垄, 每组冰碛垄由若干道小冰碛垄组成, 是末次冰期多次冰川波动的理想地貌证据。为恢复该地末次冰期冰川演化历史, 从这4 组冰碛垄中采集了7 个光释光测年样品进行年代测定。等效剂量采用单片再生法(SAR)和标准生长曲线法(SGC)进行测试。年代结果显示:第1~3 组冰碛垄形成于22.4-16.5 ka BP, 属深海氧同位素2 阶段(MIS-2), 大致与全球末次盛冰期(LGM)相当。第4 组冰碛垄形成于MIS-3。MIS-3 冰川规模大于MIS-2。第1~3 组9 道次一级小冰碛垄表明, 约在22.4-16.5 ka BP期间当子沟冰川经历了9 次小波动。冰川在稍早于22.4 ka BP达到MIS-2 的最大范围, 此后规模在波动中逐渐萎缩, 可能是冰川对MIS-2 后期太阳辐射增强、气温回升的响应。最里侧冰碛垄形成于16.5 kaBP, 可能标志着该地冰消期的开始。此后, 当子沟冰川大幅快速退缩。冰川融水在最里侧冰碛垄里侧低洼谷地汇集并被阻塞形成当子错。  相似文献   

18.
The European Alps are a mountain belt that is characterized by a series of discrete orogenic events, which have long been recognized. Despite the inherent episodic nature of orogenic evolution, the Alps have been continuously exhumed, mainly by erosion, but also by normal faulting. Since continental collision started in the late Eocene/Early Oligocene evidence for ongoing erosional exhumation has been preserved in synorogenic sediments that accumulated in basins adjacent to the pro- and retro-side of this double-vergent mountain belt. This long-term erosion record can be used to determine exhumation rates. Lag-times calculated from fission-track (FT) ages of detrital zircon from synorogenic sediments are fairly constant for the European Alps since the Oligocene–Late Miocene. Although the fast exhuming areas were unroofed at rates of 0.4–0.7 km Myr−1, the overall average exhumation rate is between 0.2 and 0.3 km Myr−1 on a regional scale. The detrital and bedrock zircon FT data of the Alps do not detect the increase in erosion rates since the Pliocene over the past ∼5 Myr, as shown elsewhere. This increase cannot be detected yet with the detrital zircon FT method because not enough rock has been removed to widely expose zircons with Pliocene or younger cooling ages in the Alps. Long term (30 Myr) exhumation rates appear to have been approximately constant when averaged over a sliding time window of about 8 Myr, or depth window of 5 to 10 km (ZFT closure depths); shorter-term fluctuations are not identified using this method.  相似文献   

19.
The lack of radiocarbon ages and correlated varve sequences in southeastern New England has left the deglacial chronology of the region poorly constrained. A 265-year varve series from Glacial Lake Narragansett was constructed from eight continuous sediment cores collected from the Providence River, Narragansett Bay, Rhode Island. This varve series could not be correlated with either the North American Varve Chronology or other varve sequences from southern New England or southeastern New York. The uncorrelated varve sequences presented here represent the minimum time of deposition within the northern segment of Glacial Lake Narragansett. These sequences, used in conjunction with the calibrated North American Varve Chronology and cosmogenic exposure ages from recessional end moraines, provide minimum (>19,400 cal BP) and maximum (<20,500 cal BP) ages for Glacial Lake Narragansett. Correlations with the updated Greenland (NGRIP and GRIP) ice core records suggest that cold periods associated with moraine formation are 200–250 years older than the cosmogenic exposure ages. Whereas many studies refer to the last glacial maximum occurring from 20,000 to 18,000 cal BP, the constrained age of Glacial Lake Narragansett suggests that at least for the southeastern portion of the Laurentide Ice Sheet, deglaciation was well underway by this time.  相似文献   

20.
More than 250 radiocarbon dates of lacustrine algae and marine shells afford a chronology for Ross Sea drift in eastern Taylor Valley. Dates of algae that lived in ice-dammed Glacial Lake Washburn show that grounded Ross Sea ice blocked the mouth of Taylor Valley between 8340 and 23,800 14C yr bp . Ross Sea ice was at its maximum position at the Hjorth Hill moraine between 12,700 and 14,600 14C yr bp and was within 500m distance of this position as late as 10,794 14C yr bp . The implication is that the flow line of the Ross Sea ice sheet which extended around northern Ross Island and across McMurdo Sound to Taylor Valley must have remained intact, and hence that a grounded ice sheet must have existed east of Ross Island as late as 8340 14C yr bp . Evidence from ice-dammed lakes in Taylor Valley and from shells from McMurdo Sound suggests grounding-line retreat from the vicinity of Ross Island between 6500 and 8340 14C yr bp . If this is correct, then most recession to the present-day grounding line on the Siple Coast took place subsequently in the absence of significant deglacial sea-level rise. Rising sea level may have triggered internal mechanisms within the ice sheet that led to retreat, but did not in itself drive continued ice-sheet recession. Ice retreat, once set in motion, continued in the absence of sea-level forcing. If correct, this hypothesis implies that the grounding line could continue to recede into the interior reservoir of the West Antarctic Ice Sheet.  相似文献   

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