Reconstructing ice sheet and alpine glacier margins during the early Holocene on Nuussuaq in central West Greenland
Cronauer, Sandra L.
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Comparison of past ice sheet margin and alpine glacier reconstructions to paleoclimate records can offer insight into the dominant forcing mechanisms that determine glacial response to changes in climate. Previous research on a major ice stream in central West Greenland reveals that the Greenland Ice Sheet (GrIS) responded to abrupt centennial-scale cold periods at ~9.3 and ~8.2 ka. The aim of this thesis is to determine whether or not alpine glaciers and a land-terminating ice sheet margin on the peninsula of Nuussuaq in central West Greenland also responded to abrupt climate changes in the early Holocene. To this end, I reconstructed ice sheet and alpine glacier histories on Nuussuaq using cosmogenic 10 Be surface exposure dating (herein 10 Be dating) and lake sediment analysis. Neither the ice margin nor alpine glacier chronologies indicate a response to abrupt climate change at 9.3 ka or 8.2 ka. I found that the Drygalski Moraines are early Holocene in age, with mean moraine ages of 8.6 ± 0.4 ka (n=2), 8.5 ± 0.2 ka (n=3), and 7.6 ± 0.1 ka (n=2) from outer to inner. The moraine chronology, combined with radiocarbon dated lake sediment stratigraphy from an adjacent proglacial lake, reveal that the ice margin remained within about one kilometer of its present position from ~9.9 to 5.4 ka. This evidence for ice sheet stability during the first half of the Holocene, followed by minimum ice extent between ~5.4 and 0.6 ka, contrasts with many records of early Holocene warmth during the Holocene maximum of Northern Hemisphere summer insolation. This period of ice margin stability may relate to adjacent ocean temperatures, which did not increase until the middle Holocene. A 10 Be chronology of moraines deposited by a nearby alpine glacier reveals glacier stability at 10.5 ± 0.3 ka, during the Preboreal period. Moraine deposition at this time is potentially due to increased moisture availability as the GrIS retreated and sea ice declined. The alpine glacier chronology also fits well within an emerging pattern of alpine glacier advance during the Preboreal period on East and West Greenland. The results presented in this thesis suggest that GrIS and alpine glacier margin response to changes in climate is complex, and that detailed chronologies from moraines on Greenland can shed light on the intricate processes that link glaciers and climate.