PP24A-05
Antarctic Ice Sheet Sensitivity to Atmospheric CO2 Variations During the Early to Mid-Miocene
Tuesday, 15 December 2015: 17:00
2012 (Moscone West)
Richard H Levy, GNS Science, Lower Hutt, New Zealand, David M Harwood, University of Nebraska Lincoln, Lincoln, NE, United States, Fabio Florindo, National Institute of Geophysics and Volcanology, Rome, Italy, Francesca Sangiorgi, Utrecht University, Utrecht, Netherlands, Robert Eagle, University of California Los Angeles, Los Angeles, CA, United States, Hilmar von Eynatten, Geoscience Center Göttingen (GZG), Sedimentology & Environmental Geology, Göttingen, Germany, Edward Gasson, University of Massachusetts Amherst, Amherst, MA, United States, Gerhard Kuhn, Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Bremerhaven, Bremerhaven, Germany and Aradhna Tripati, UCLA, Los Angeles, CA, United States
Abstract:
The Early to mid-Miocene (23 to 14 million years ago) is a compelling interval to study Antarctic ice sheet sensitivity to changes in atmospheric CO2 as oceanic and atmospheric circulation patterns in the southern hemisphere were broadly similar to present and reconstructed atmospheric CO2 concentrations were analogous to those projected for the next several decades. This time interval includes the Miocene Climatic Optimum (MCO), a period of global warmth during which average surface temperatures were 3 to 4°C higher than today. Miocene sediments in the AND-2A drill core from the Western Ross Sea, Antarctica provide direct information regarding ice sheet variability through this key time interval and offer insight into the potential Antarctic contribution to future sea level rise. A multi-proxy dataset derived from AND-2A identifies four distinct environmental “motifs” based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of marine-based ice across the Ross Sea. They all correlate with major positive shifts in benthic oxygen isotope records and episodes of sea-level fall, and generally coincide with intervals when atmospheric CO2 concentrations were below current levels (~400 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for significant ice mass loss during episodes of high (>400 ppm) atmospheric CO2. These results suggest that polar climate and the Antarctic Ice Sheet (AIS) were highly sensitive to relatively small changes in CO2 during the early to mid-Miocene, which is supported by numerical ice sheet and climate modelling.
