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| Titel |
The timing of post-LGM ice-sheet retreat in West Antarctica: An integrated palaeomagnetic and radiocarbon approach |
| VerfasserIn |
Claus-Dieter Hillenbrand, Steven G. Moreton, Barbara Maher, Julian A. Dowdeswell, Jeffrey Evans, Monika Korte, Gerhard Kuhn, Rob Larter, Colm Ó. Cofaigh, James A. Smith |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250036305
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| Zusammenfassung |
| The timing of the grounding-line retreat of marine-based ice sheets from the Antarctic shelf
after the last glacial maximum (LGM) is not well constrained. Most of the published
deglaciation ages are AMS 14C dates obtained from the acid-insoluble fraction of the bulk
organic matter (AIO) or from calcareous (micro-)fossils in biogenic glaciomarine sediments
recovered with cores. Actually, these dates provide ages for the post-LGM onset of seasonal
open-marine conditions on the Antarctic shelf, and thus only minimum ages for ice-sheet
retreat. Moreover, the AIO dates suffer from a variable down-core contamination with
reworked, fossil organic material (which especially affects sediments deposited in the
vicinity of an ice-sheet grounding-line), while calcareous (micro-)fossils are often
absent from Antarctic shelf sediments. If calcareous material is present in cores, it
often occurs at a stratigraphic level significantly younger than the grounding-line
retreat.
Over the last decade, progress in more precise dating of Antarctic ice-sheet retreat since
the LGM has been made by i) correlating the palaeomagnetic intensity records of post-LGM
sedimentary sequences with global or regional reference curves and ii) compound-specific
AMS 14C dating of organic matter in sediments deposited subsequent to grounding-line
retreat. Here we present the initial results of our attempt to obtain more reliable chronologies
for the retreat of marine-based ice streams that drained the Antarctic Peninsula Ice Sheet and
the West Antarctic Ice Sheet at the LGM. We measured the palaeomagnetic intensity records
of selected sediment cores recovered from glacial troughs that were eroded by the
palaeo-ice streams into the West Antarctic shelf. In addition, we AMS 14C dated the
AIO in the sediments deposited subsequent to grounding-line retreat by sample
combustion at a relatively low temperature of 300 Ë C. The hypothesis underlying sample
combustion at this low temperature step is that younger, more labile carbon, which we
assume to be more representative of the organic material that was recently alive at
the time of sediment deposition, will pyrolise at a lower temperature than more
recalcitrant fossil carbon that was transported and reworked at the base of the ice
streams. We will compare the chronological results obtained from the two dating
techniques, highlight their specific advantages and shortfalls, and present time lines of
post-LGM grounding-line retreat for individual West Antarctic palaeo-ice streams. |
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