Abstract

“The part of the West Antarctic Ice Sheet that drains into the Amundsen Sea is currently thinning at such a rate that it contributes nearly 10% of the observed rise in global mean sea level. Acceleration of the outlet glaciers means that the sea level contribution has grown over the past decades, while the likely future contribution remains a key unknown. The synchronous response of several independent glaciers, coupled with the observation that thinning is most rapid at their downstream ends, where the ice goes afloat, is generally taken as an indicator that the changes are being forced by the ocean. On Pine Island Glacier (PIG), in particular, the signatures of acceleration, thinning and inland retreat of the grounding line, where the ice goes afloat, have been almost monotonic in the admittedly short and patchy observational record. Understanding the causes of these changes and their relationship to climate variability is imperative if we are to make quantitative estimates of sea level into the future. Observations made since the mid-1990s on the Amundsen Sea continental shelf have revealed that the deep troughs, carved by previous glacial advances, are flooded by almost unmodified Circumpolar Deep Water (CDW) with temperatures around 3-4°C above the freezing point, and that this water mass drives rapid melting of the floating ice. This talk summarises the results of recent work, including both observations made by an Autonomous Underwater Vehicle beneath the floating tongue of PIG and numerical modelling of ocean circulation in the Amundsen Sea. The results give us important insight into the processes that could cause variability of CDW inflows and how the impact of such variability on PIG would have been influenced by the seabed topography beneath the floating glacier tongue.”

This lecture is held jointly with the Cambridge Philosophical Society