Antarctic Paleoclimate and Ice Sheet Behavior During the Early and Middle Miocene: Results from the ANDRILL AND-2A Drillcore
Abstract
The AND-2A drillcore records a near-continuous history of variability in climate and ice sheet behavior during the early Miocene to early middle Miocene, including a sustained warm interval recognized in global deep-sea geochemical records as the Mid-Miocene Climatic Optimum. This expanded sedimentary archive (1138 m-long; 98% recovery) was obtained from a proximal shelf setting in McMurdo Sound. It preserves a record of the pace and scale of climate and ice sheet variation, and allows for the evaluation of climate sensitivity through data and numerical modeling integration. Stratigraphic sequences and facies interpretations reveal a cyclical history of climate changes, glacial advance and retreat cycles, and water-depth variation. Substantial environmental variability is evident in the more than 60 sedimentary sequences. The glacial regime varied from sub-polar with significant meltwater through proximal and distal high-latitude temperate glacial conditions with abundant meltwater. The AND-2A drillcore was deposited in the subsiding Victoria Land Basin, during a period of relatively steady thermal subsidence, on the coastal plain and continental shelf seaward of the rising Transantarctic Mountains. A well-developed chronostratigraphic framework developed through integrated diatom biostratigraphy, magnetostratigraphy, Sr isotope geochemistry, and radiometric dating of volcanic materials, allows for the comparison of events recognized in this drillcore with events identified in distal proxy records from deep-sea stable isotope studies, and in sea-level reconstructions based on continental shelf sequence stratigraphy. Three ‘key’ scientific themes provide a framework for describing and analysing the character of climate and ice sheet history in this region: (1) the transition from an early Miocene transient glaciation abruptly into interglacial conditions (interval ~1100 to 1000 mbsf); (2) a sustained period of reduced ice sheet influence at the drill site during the early Miocene (~790 to 900 mbsf) and may be due to limited influence of predicted ice sheet modulation by orbital forcing for a period of nearly 1 m.y.; and (3) Antarctic Ice Sheet behavior during the Mid-Miocene Climatic Optimum. These changes provide insight into the mechanics that control the global climate system, and will help assess how Antarctic events are recorded in distal proxy records. The best dated intervals suggest frequencies consistent with orbital control on the sedimentary cycles/sequences (precession and obliquity). The ages of lithofacies changes and disconformities in the AND-2A drillcore correspond with large-scale global isotope events and patterns of mid-Cenozoic eustatic variation.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.C54A..06H
- Keywords:
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- 0726 CRYOSPHERE / Ice sheets;
- 1621 GLOBAL CHANGE / Cryospheric change;
- 3036 MARINE GEOLOGY AND GEOPHYSICS / Ocean drilling;
- 4926 PALEOCEANOGRAPHY / Glacial