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| Titel |
Improving the timing of middle Holocene retreat and late Holocene advance of Jakobshavn Isbrae, Greenland |
| VerfasserIn |
J. P. Briner, H. A. Stewart, N. E. Young, B. Csatho, Y. Axford |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250026061
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| Zusammenfassung |
| The Greenland Ice Sheet is undergoing dramatic change. How the ice sheet continues to
respond to climate change has important ramifications for global climate and sea level rise,
but the observation-based record of ice sheet change is extremely short. We use
glacial-geologic techniques to determine the behavior of the Greenland Ice Sheet over longer
timescales. In particular, we focus on the Holocene history of Jakobshavn Isbrae, one of the
key ice streams on Greenland that is responsible for disproportionate mass loss of
the Greenland Ice Sheet. Radiocarbon ages from basal lake sediments and 10Be
exposure ages of bedrock spanning from the present ice margin to Disko Bugt, ~50 km
west, reveal rapid deglaciation between ~8 and ~7 ka. After ~7 ka, the ice margin
continued to retreat inland behind its present position. Although it is difficult to
reconstruct how far inland the ice margin retreated, the Little Ice Age advance reworked
marine bivalves that date from 2.2 to 6.1 ka (Weidick and Bennike, 2007). The
bivalve ages indicate that the ice margin was behind its Little Ice Age position
between ~6 and ~2 ka, and that its Neoglacial advance post-dates ~2 ka. We improve
the timing of the Neoglacial advance of Jakobshavn Isbrae by collecting sediment
cores from lakes that are beyond the Little Ice Age margin but close enough to
receive ice sheet meltwater during the Little Ice Age advance. The sediments in
these “threshold” lakes contain distinct units of varved sediments (representing
a proglacial environment) that sharply overlie gyttja (representing a non-glacial
environment). Four radiocarbon ages of the sedimentary contacts from three different
lake sites range from 530±10 to 370±60 cal yr BP (1410-1640 AD), and reveal
when Jakobshavn Isbrae neared its maximum Little Ice Age margin. Furthermore,
the lake sediments reveal that between early Holocene deglaciation and the Little
Ice Age, Jakobshavn Isbrae never spilled into these lake basins, indicating that
the Little Ice Age was the most extensive position of this sector of the Greenland
Ice Sheet since deglaciation. Future work will be focused on generating climate
reconstructions from lake sediments and microfossils (chironomids), and subsequently
drawing links between past climate change and corresponding glacier response. |
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