T105 Neogene and Quaternary Biological Paleolimnology: In Memory of J. Platt Bradbury

Monday, 23 October 2006
1:30 PM - 5:30 PM

10BE DATES OF MORAINES IN EAST GREENLAND SUGGEST THAT THE LITTLE ICE AGE MOUNTAIN GLACIER ADVANCE WAS THE MOST EXTENSIVE GLACIAL ADVANCE DURING THE HOLOCENE EPOCH

Paper number: T105-12
Program: Technical Sessions
Time: 4:15 PM – 4:30 PM

Authors

Abstract

A discrepancy exists between paleotemperatures during the last glacial period recorded by Greenland ice cores and those derived from mid-latitude mountain glacier records. Paleotemperatures recorded by Greenland ice cores indicate a cooling of ~15°C during Younger Dryas cold event at the end of the last glacial period. Temperatures reconstructed based on mid-latitude mountain glacier extents indicate a cooling of less than ~3-4°C during the Younger Dryas. To explain this mismatch it is suggested that, during the last glacial period, mid-latitude glaciers predominantly were driven by summer temperature and the North Atlantic region was characterized by hyper-cold winters. To test this hypothesis, we are using cosmogenic nuclide dating to develop records of past mountain glacier extents in the Scoresby Sund region, East Greenland (~70-72° N, 20-30° W) for comparison with nearby ice core records.

Key results from a tributary glacier in Gurreholm Valley include 10Be dates as young as 300-800 years from boulders atop a moraine that is not weathered or covered with vegetation. It is interpreted that this moraine was deposited by a glacial advance during the Historical Period or Little Ice Age. In contrast, four 10Be dates on a distal, more vegetated and weathered moraine located just 50 m outside of the Little Ice Age moraine yield ages between ~10,800 and 12,500 years. It is interpreted that this moraine was deposited during the late-glacial period. The 10Be chronology and a lack of moraines or other deposits between the Little Ice Age and late-glacial age moraines imply that the Little Ice Age glacial advance was the most extensive mountain glacier advance during the Holocene Epoch.

This Little Ice Age advance was almost as extensive as the late-glacial age advance and likely overran moraines deposited by prior Holocene ice advances, such as one that may have occurred during the 8,200 year cold event. This preliminary result is compared to paleotemperature records from Greenland ice cores which indicate that the 8,200 year cold event was about 3-4° C colder than the Little Ice Age. The comparison suggests that perhaps the mismatch between Greenland ice cores and mountain glacier records persisted during the 8,200 yr event.