Exposure-age record of Holocene ice sheet and ice shelf change in the northeast Antarctic Peninsula

摘要

This paper describes glacial-geologic observations and cosmogenic-nuclide exposure ages from ice-free areas adjacent to the Sj?gren, Boydell, and Drygalski Glaciers of the northeast Antarctic Peninsula. These provide a record of Holocene glacier and ice shelf change in this region. Early Holocene ice surface elevation near the present coastline was locally at least 500 m above present sea level, but our observations do not constrain the maximum thickness of Last Glacial Maximum (LGM) ice or the time at which it was attained. The boundary between frozen-based and wet-based ice reached a maximum elevation of 100-150 m above present sea level. The ice surface elevation decreased from 300-500 m elevation to near present sea level between 9 ka and ca 4 ka. Below 160 m elevation, we observed a bimodal distribution of apparent exposure ages in which a population of glacially transported clasts with mid-Holocene exposure ages coexists with another that has exposure ages of 100-600 years. We consider the most likely explanation for this to be i) complete deglaciation of currently ice-free areas, which presumably required the absence of ice shelves, at 3.5-4.5 ka, followed by ii) subsequent ice shelf formation and grounding line advance after ca 1.4 ka, and iii) complete re-exposure of the sites after ice shelf breakup and glacier surface lowering in recent decades. This explanation is consistent with marine sedimentary records indicating that ice shelves in the Prince Gustav Channel and Larsen A embayment were absent in the middle to late Holocene and were re-established within the last 2000 years.