East Antarctica’s past and future

Most attention to sea-level rise from the melting of Antarctic ice has focused on the glaciers of West Antarctica, which are in a precarious state (see Physics Today, July 2014, page 10 ). The larger, thicker East Antarctic ice sheet is more secure. But evidence has been accumulating that it, too, may be in danger from anthropogenic climate change.

To predict how glaciers will respond to the warming ocean and atmosphere in the future, modelers are helped by the geologic record of how the ice behaved in the warm climates of the ancient past. Antarctica’s vastness, however, means that the known record is far from complete: Much of the East Antarctic coast has never even been visited by a research vessel.

Four years ago, Sean Gulick (University of Texas at Austin), Amelia Shevenell (University of South Florida in St. Petersburg), and their colleagues undertook the first foray into one of those previously unexplored areas: the waters off the coast of the Aurora Subglacial Basin (ASB), near the Totten Glacier, which aerial measurements had shown to be losing mass faster than anywhere else in East Antarctica. They’ve now analyzed their results.

By acoustically probing the seafloor and the rock below it from the back of the icebreaker shown here, the researchers uncovered the history of ice on the continental shelf. Between the first formation of Antarctic ice and the stabilization of today’s polar ice cap, the ASB spent tens of millions of years advancing and retreating hundreds of kilometers in response to changes in climate. To pin down the timeline, the researchers scooped up sediment samples and looked at which microfossil species were present in each layer. The dynamic period, they concluded, began more than 35 million years ago and ended around 5 million to 7 million years ago. During much of that time, the atmospheric carbon dioxide concentration was close to what it is today, and the global average temperature was at a level it may reach again by the end of this century. (S. P. S. Gulick et al., Nature 552, 225, 2017 . Photo by Sean Gulick.)