As a result, individual exposure ages can vary widely across a single landform (e.g. In glacial settings, cold-based, non-erosive glacier ice may fail to remove inventories of inherited nuclides in glacially transported material. The preservation of cosmogenic nuclides that accumulated during periods of prior exposure but were not subsequently removed by erosion or radioactive decay, complicates interpretation of exposure, erosion, and burial ages used for a variety of geomorphological applications. Slowing of grounding-line retreat in the late Holocene may have been due to the effects of increased accumulation and falling local sea level, suggesting that these factors may be important in controlling the extent of the Antarctic Ice Sheet. Rather, recession was delayed significantly relative to the global deglaciation. The timing of grounding-line retreat does not correspond closely with the largest post-LGM changes in global sea level or ocean temperature. My data show that this was followed by a more gradual period of retreat in the late Holocene, with possible stabilization of the grounding line shortly after ~3000 yrs BP when it retreated to near its current position on the Siple Coast in the vicinity of Mercer Ice Stream. Prior studies show that the deglaciation was marked by an initial period of rapid retreat, indicative of instability in this sector of the AIS. My results indicate that the Ross Sea grounding line retreated southeastward past Liv Glacier by ~4,200 yrs BP and past Amundsen Glacier by 2,900 yrs BP. This chronology comes from radiocarbon dates of algae that lived in former ice-marginal ponds dammed by the ice sheet. My goal was to document these deposits and produce a chronology for the last stages of the most recent ice retreat.
Thinning during the last deglaciation left drift on nunataks along the Ross Sea coast. I carried out fieldwork at Amundsen and Liv Glaciers, outlet glaciers of the East Antarctic Ice Sheet that drain through the Transantarctic Mountains to the Ross Ice Shelf. Here, I examine how the marine portions of the ice sheet responded to the major warming that occurred at the end of the last ice age. Documenting the timing and nature of this deglaciation is crucial to understand the mechanisms behind ice-sheet behavior. This study focuses on a major unanswered question - namely, the cause of Antarctic Ice Sheet retreat following the last glaciation. Examination of past ice-sheet behavior during periods of warming climate can afford insight useful for predicting future sea-level rise. The Antarctic Ice Sheet contains ~58 m of global sea-level equivalent and thus its future behavior under global warming is of pressing concern. If correct, this hypothesis implies that the grounding line could continue to recede into the interior reservoir of the West Antarctic Ice Sheet. Ice retreat, once set in motion, continued in the absence of sea-level forcing.
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. 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. 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 65 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. 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.
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. More than 250 radiocarbon dates of lacustrine algae and marine shells afford a chronology for Ross Sea drift in eastern Taylor Valley.
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