Smith Lecture: Drilling Deep Beneath Antarctic Ice to Reveal Past and Future Climate Changes
The ANDRILL (ANtarctic geological DRILLing) Program cored a >2,300 m-thick sedimentary record of environmental conditions spanning the last 20 million years from the continental shelf of the Ross Sea, Antarctica during two drilling campaigns in 2006 and 2007. Integrated data and modeling studies suggest that marine margins of Antarctica’s ice sheets retreated to the coast repeatedly during the early Pliocene and mid-Miocene when atmospheric CO2 concentrations were >400 ppm. Ice sheets only advanced across the continental shelf when CO2 decreased below 400 ppm. These outcomes support hypotheses for the existence of CO2 thresholds in the climate system. For its next drilling campaign ANDRILL seeks to examine Antarctic ice sheet behavior by recovering a rock record from a prior interval of geologic time when CO2 concentrations were much higher, and approached values projected for the next century. Oligocene and older Paleogene strata at two sites on Coulman High beneath the Ross Ice Shelf will reveal past physical and biological conditions in the Ross Sea and provide new constraints on ice sheet response to climate change forced by high atmospheric CO2. Ice volume estimates from ice sheet models using BEDMAP2 boundary conditions suggest that ocean-driven melt of marine-based sectors of Antarctica’s ice sheets could contribute up to 22 meters to future global sea level rise. Geological records of sea level and proxy-based reconstructions of atmospheric CO2 indicate that sea level was up to 22 meters higher than present when CO2 concentrations last exceeded 400 ppm. These results suggest that Earth’s marine-based ice sheets are vulnerable to atmospheric CO2 concentrations above preindustrial levels. Direct evidence of ice sheet dynamics under relevant CO2 concentrations are required to test these model-derived inferences.