Reconstruction of Koettlitz Glacier, Southern McMurdo Sound, Antarctica, During the Last Glacial Maximum and Termination
Accurate reconstructions of the Antarctic Ice Sheet (AIS) are important for evaluating past, present, and future sea-level change. Insight into future changes of the AIS and its tolerances to various climate variables can come from investigation of its past behavior. During the last glacial maximum...
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DigitalCommons@UMaine
2020
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| Online Access: | https://digitalcommons.library.umaine.edu/etd/3318 https://digitalcommons.library.umaine.edu/cgi/viewcontent.cgi?article=4396&context=etd |
| Summary: | Accurate reconstructions of the Antarctic Ice Sheet (AIS) are important for evaluating past, present, and future sea-level change. Insight into future changes of the AIS and its tolerances to various climate variables can come from investigation of its past behavior. During the last glacial maximum (LGM), ice grounded in the Ross Sea, reaching close to the continental shelf edge. One hypothesis is that this event was caused largely by changing sea level that led to widespread grounding of floating portions of the ice sheet. This grounding buttressed the inflowing East Antarctic outlet glaciers and caused thickening on the lower reaches of these glaciers; interior ice remained the same or even thinned because of reduced accumulation. The Holocene was characterized by rapid recession of marine portions and possible thickening of interior ice and growth of local glaciers in response to accumulation increase. In contrast, an alternate hypothesis is that expansion of grounded Ross Sea ice was due to growth of local glaciers and East Antarctic outlets. These glaciers are thought to have receded to their present positions in the Holocene despite relatively high accumulation. These hypotheses have very different implications for the future of the ice sheet under global warming. Koettlitz Glacier, a large local glacier, flows from the Royal Society Range into McMurdo Sound (78°S, 163°E) and is ideal for testing these two hypotheses. Competing hypotheses as to how this glacier behaved during the LGM range from minor recession to significant expansion. Today, Koettlitz Glacier blocks the mouth of ice-free Pyramid Trough. However, based on surficial mapping, I infer that grounded Ross Sea ice blocked the valley mouth at the LGM. Radiocarbon dates of subfossil lacustrine algae from a lake dammed in Pyramid Trough by the Ross Sea ice date to 11-23 ka, suggesting the ice dam existed throughout that time period. The stratigraphic position and geometry of moraines indicates that Koettlitz Glacier was smaller at the LGM than it ... |
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