EIGHT MILLION YEARS OF LAND-BASED ANTARCTIC ICE SHEET STABILITY RECORDED BY IN SITU 10BE FROM THE ANDRILL-1B CORE

The response of the East Antarctic Ice Sheet (EAIS) to Pliocene warmth provides a critical way to gauge its stability in the face of future climate change, but is relatively uncertain. For instance, mid-Pliocene sea level estimates range from <10 m to >30 m, and cosmogenic nuclide and sedimentological studies from the Transantarctic Mountains imply extreme landscape stability over the last several Myr whereas several ocean records suggest orbital-scale instability of at least marine-based sectors of the ice sheet. The AND-1B marine sediment core drilled beneath the Ross Ice Shelf contains a remarkably complete late Cenozoic sequence of glacial diamictons sourced from the adjacent EAIS, intercalated with open-water sediments likely associated with marine-based collapse of the West Antarctic Ice Sheet (Naish et al., 2009; Pollard and DeConto, 2009). We measured concentrations of in situ ¹⁰Be – produced only when ice cover is reduced and the landscape is exposed – in eight samples of glacially-derived quartz sand from AND-1B spanning parts of the last 8 Myr. Decay-corrected concentrations are low and show a long-term decline from ~13,000 to 1000 atoms per gram over the record. These low values and the monotonic trend suggest that land-based ice sheet sectors have experienced little, if any, exposure during the past 8 Myr; the ¹⁰Be concentrations we measured are equivalent to only centuries or a few kyr of surface exposure. Perhaps more likely, the small quantities of ¹⁰Be were produced prior to the establishment of a full EAIS in the mid-Miocene, and reflect deeply-exhumed and thus ¹⁰Be-poor material that has been radioactively decaying beneath near-continuous ice sheet cover. In either case, these results strongly suggest that land-based portions of the EAIS draining into the Ross Embayment have been stable over the range of climatic conditions experienced during the late Cenozoic and exhibited, at most, short-lived ice margin responses to Pliocene warmth.