Publication Date

April 2016

Advisor(s)

Suzanne O'Connell

Major

Earth and Environmental Sciences

Language

English (United States)

Abstract

As climate change intensifies and the world begins to feel its impacts, scientists are looking to past climatically similar periods to understand how our planet will respond. During the Pliocene Epoch (5.33-2.58 millions of years ago), the West Antarctic Ice Sheet (WAIS) nearly de-glaciated under peak CO2 concentrations of ~400 ppm (Fedorov et al., 2013) and global average temperatures 2-3°C warmer than pre-industrial values (Yamane et al., 2015). The sensitivity of the WAIS to CO2 and ocean temperature fluctuations on orbital timescales is well established (DeConto & Pollard, 2003; Naish et al., 2009). A more controversial question is how sensitive the East Antarctic Ice Sheet (EAIS) is to similar forcings. To address this question, we analyze sedimentological changes in Antarctic Weddell Sea ODP Site 697 marine cores deposited 3.8-3.0 Ma for cyclicities in ice sheet dynamics and bottom water fluctuations. Spectral analysis of fine fraction mineral assemblages identifies smectite, illite, chert, chalcedony, SiO2, garnet and feldspar. Continuous detrital smectite deposition points to high Antarctic Bottom Water (AABW) circulation through the Jane Basin 3.8 to 3.0 Ma. Varimax-rotated principal component analysis and wavelet analysis of elemental count ratios suggest Jane Basin sediment deposition transitioned from a dominant eccentricity forcing with obliquity inputs to a dominant precession forcing modulated by eccentricity at ~3.3 Ma. Derived linear sedimentation rates slow from ~6.3 cm/kyr between 3.78 and 3.21 Ma to 4.74 cm/kyr between 3.14 and 3.03 Ma. These findings indicate that EAIS and WAIS behavior as moderated by an eccentricity and obliquity forcing during Pliocene peak warming and a precession forcing during cooler conditions after ~3.3 Ma.

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