Antarctic ice sheet sensitivity to atmospheric CO₂ variations in the early to mid-Miocene

• Published in: Proceedings of the National Academy of Sciences - PNAS 2016-03, Vol.113 (13), p.3453-3458
• Main Authors: Levy, Richard, Harwood, David, Florindo, Fabio, Sangiorgi, Francesca, Tripati, Robert, von Eynatten, Hilmar, Gasson, Edward, Kuhn, Gerhard, Tripati, Aradhna, DeConto, Robert, Fielding, Christopher, Field, Brad, Golledge, Nicholas, McKay, Robert, Naish, Timothy, Olney, Matthew, Pollard, David, Schouten, Stefan, Talarico, Franco, Warny, Sophie, Willmott, Veronica, Acton, Gary, Panter, Kurt, Paulsen, Timothy, Taviani, Marco
• Format: Article
• Language: English
• Subjects: Physical Sciences
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1516030113

Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23–14 Mya) is a compelling interval to study as global temperatures and atmospheric CO₂ concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3–4 °C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core 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 grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO₂ concentrations were at or below preindustrial levels (∼280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (∼500 ppm) atmospheric CO₂. These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO₂ during the early to mid-Miocene.