EXPOSURE DATING AND ANTARCTIC GLACIAL HISTORY

Exposure dating in Antarctica, which began shortly after the first terrestrial cosmogenic nuclide measurements, has contributed greatly to our knowledge of the glacial history of the continent. Initially the method promised applicability to every rock and rock type, to sites not datable with carbon-14, and, given low rates of Antarctic rock weathering, the possibility of multi-million-year chronologies. Nearly three decades of experience have sobered expectations – moraine degradation, periglacial disturbance and recycling of rocks from the deposits of one glaciation to the next – demand careful attention, and the method still relies on nuclide production-rate calibrations from sites outside Antarctica. Nevertheless, exposure-dating chronologies are now widespread, cover most sectors of both the East and West Antarctic Ice Sheets, and underpin recent high-resolution numerical models of the ice sheet through the last glacial period.

Exposure ages from across Antarctica have revealed: (i) A complex history of asynchronous advance and retreat of ice in East and West Antarctica, and along the Antarctic Peninsula. (ii) Culmination of Antarctic ice volume thousands of years after the northern hemisphere ice sheets. (iii) Deglaciation persisting into the late Holocene at many sites, making Antarctica an important source of Holocene sea-level rise. (iv) Episodes of rapid glacier and ice-sheet thinning at sites on the Amundsen Sea, Marie Byrd Land and southern Ross Sea coasts which removed hundreds of meters of ice on millennial timescales; these events may be the best available analogs for rates of ice-sheet collapse envisaged in some future climate scenarios.

Low erosion beneath much of the ice sheet leads to long-term bedrock preservation. This complicates the use of bedrock for dating recent glaciation, but leads to records of cumulative ice-cover and exposure over millions of years, that can be interpreted with data from radionuclides with different half-lives. Bedrock preservation beneath the ice sheet also opens up the possibility of subglacial drilling for previously-exposed rock. Cosmogenic nuclide data from such material could be used to determine ice sheet extent during interglacial periods warmer than the present, and the vulnerability of the ice sheet to future climate change.