HR: 08:30h
AN: U21F-03 INVITED    [Abstracts]
TI: Neogene climate history of Antarctica: Initial results from the ANDRILL McMurdo Ice Shelf Project
AU: * Naish, T R
EM: t.naish@gns.cri.nz
AF: GNS Science, PO Box 30368, Lower Hutt, 2001, New Zealand
AU: * Naish, T R
EM: t.naish@gns.cri.nz
AF: Antarctic Research Centre, Victoria University of Wellington, Wellington, 1000, New Zealand
AB: The ANDRILL (ANtarctic geological DRILLing) Program successfully recovered a 1285m-long succession of cyclic glacial, glacimarine and marine sediment with interbedded volcanic deposits from beneath the McMurdo Ice Shelf (MIS), northwest part of the Ross Ice Shelf system. The MIS drillcore represents the longest and most complete (98 percent recovery) geological record from the Antarctic continental margin to date, and provides a key reference record of climate and ice sheet variability through the Neogene. Here we present the initial outcomes from the drilling with emphasis on the potential of the record for improving our knowledge of Antarctica's influence on, and response to global climate change. Repetitive vertical successions of facies imply at least 60 fluctuations, of Milankovitch-duration, between subglacial, ice-proximal and ice-distal open marine environments. These have been grouped into 3 main types of facies cycles that corresponds to glacial-interglacial variability during climatically-distinct periods: i) Cold polar climate dominated by grounded ice, but with retreat to ice shelf conditions during interglacials (Late Miocene, ~13-10 Ma & Pleistocene, ~1-0 Ma), ii) Warmer climate dominated by ice-shelf and open water conditions (hemipelagites), with occasional periods of grounded ice. (early-Late Miocene, ~9-6 Ma). iii) Warmer climate with extended periods experiencing open ocean conditions (pelagic diatomites) with periods of sub-ice shelf and grounded ice deposition (Pliocene, ~5-2 Ma). The ~90m-thick Early Pliocene (~4 Ma) interval of diatomite shows no apparent glacial cyclicity and represents an extended period of ice-free conditions indicative of a reduced WAIS. Late Pliocene (~2.6-2.2 Ma) glacial- interglacial cycles characterised by abrupt alternations between subglacial/ice-proximal facies and open marine diatomites imply significant WAIS volume fluctuations around the time of the early Northern Hemisphere glaciations. A ~4m-thick interval of diatomaceous mudstone deposited during MIS 31 represents an open Ross Sea with SSTs warmer than the Holocene. Intriguingly, the last million years, is characterized by a relatively stable, extensive grounded ice-sheet with marine terminus. Super-interglacials following the mid-Pleistocene climate transition produced ice shelf conditions like the present day.
UR: http://www.andrill.org
DE: 1105 Quaternary geochronology
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1637 Regional climate change
DE: 1641 Sea level change (1222, 1225, 4556)
SC: Union [U]
MN: 2007 Fall Meeting