Greenland in a warmer climate: What controls the advance & retreat of the NE Greenland Ice Stream

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Over the past decade the Greenland ice sheet has thinned at an accelerating rate and is currently the largest single contributor to global sea-level rise. Understanding the likely rate and magnitude of future change matters because accurate projections of sea-level rise are necessary if governments are to plan for the future in a warming world and develop sustainable coastal defence strategies.A significant portion of Greenland's contribution to sea-level rise has been associated with the speed-up and melting of an increased number of fast-flowing outlet glaciers. Rapid thinning of these glaciers has coincided with increases in air and ocean temperatures, suggesting that they are sensitive and responsive to these parameters. However, although various mechanisms related to atmospheric and oceanic forcing have been proposed to explain the recent thinning, there exist large uncertainties in the relative importance of and interplay between each of these and the ice sheet response to them over longer timescales. Without this crucial information output from the current generation of ice sheet models has limitations and there is potential for significant errors in sea-level rise projections.This research will directly address this critical gap in our understanding by reconstructing the past behaviour of the Northeast Greenland Ice Stream (NEGIS) over the past 10,000 years. NEGIS is of particular interest because recent studies show that this cold, High Arctic region of the ice sheet has started to undergo sustained thinning after more than 25 years of relative stability. This has raised concerns that rapid inland retreat is already underway and could lead to drawdown of the NEGIS catchment. Complete collapse of its drainage basin would raise sea-level by ~1.4 m (equivalent to the combined Pine Island-Thwaites catchment in Antarctica) posing a major hazard for coastal populations. NEGIS provides an unparalleled opportunity to investigate the response of an ice stream to past change (oceanic and atmospheric warming), because there is evidence that it underwent dramatic retreat (and then advance) during the Holocene Thermal Maximum (a period of increased air temperatures analogous to that predicted for late 21st century). To achieve this we have assembled an experienced team who will generate a detailed record of changes in NEGIS geometry, and the contemporaneous atmospheric, oceanic and relative sea level changes. We will reconstruct ice stream configuration (thickness, extent) from marine and terrestrial data, and produce high-resolution records of oceanic and atmospheric temperatures and relative sea level. Using a state-of-the-art ice sheet model (BISICLES), these data will be used to test the sensitivity of the ice stream to different forcing mechanisms at 100-1000 year timescales. Our chosen timescale will allow us to differentiate short term 'noise' from long term trends, something that has been recognised as a potential issue, which is not possible from investigations of contemporary margin fluctuations derived from a few decades of instrumental records. Ultimately our project will deliver significant improvements in our understanding of the sensitivity of the ice sheet to various forcing mechanisms that will help to underpin sea-level rise projections, shape policy on coastal defence and protect future generations.The project has significant added value in that we will work within a funded European programme 'Greenland Ice Sheet/Ocean Interaction and Fram Strait Fluxes' and has confirmed funded logistical support through the Alfred Wegener Institute, Germany and a 50 day cruise on the RV Polarstern (2016) to this remote area.