Deglaciation of the Northeast Greenland ice stream and interaction with ocean circulation

Abstract

<p>Large sections of the Greenland Ice Sheet (GrIS) drain directly to the ocean through tidewater glaciers and are, therefore, sensitive to changes in ocean circulation through time. Recent research has identified the dynamic response of many tidewater glaciers draining the GrIS showing thinning, flow acceleration and, in many cases, the break-up and retreat of fringing ice shelves and calving margins. This instability has been linked to incursion of relatively warm Atlantic Water as well as increased air temperatures and sea-ice loss.</p><p>The Northeast Greenland Ice Stream (NEGIS) is one of the largest ice streams draining approximately 15% of the GrIS with a sea level equivalent of ~ 1.4 m. Recent observations have identified ice shelf loss and grounding line retreat of Zachariae Isstrom, the southern arm of the NEGIS, post 2010 suggesting this sector of the GrIS might be starting to respond to climate forcing. The primary aim of the ‘NEGIS’ project is to reconstruct the history of NEGIS since the Last Glacial Maximum (LGM) to improve our understanding of the interaction between NEGIS and climate (specifically ocean circulation). A series of sediment cores were collected along with bathymetric and sub-bottom profiler data concentrating on the Westwind and Norske Trough systems, two cross-shelf troughs originating from the present day margin of NEGIS. The data were collected through collaboration with the Alfred Wegener Institute as part of the GRIFF project supported by two cruises of the RV Polarstern in 2016 and 2017.</p><p>This presentation will focus on the deglaciation and palaeoceanographic evolution of the inner section of Norske Trough (inner continental shelf) investigating the interaction between ocean circulation and the dynamics of the tidewater margins of NEGIS. We present multiproxy results from a spliced box core and 10 m long gravity core collected from the same location covering the last 11,000 cal years. We use the benthic foraminiferal fauna and stable isotope signature to investigate variability in ocean circulation, specifically the relative strength of the Atlantic Water inflow along Norske Trough to the present day ice margin. We also investigate surface water conditions (including sea ice concentration) based on diatoms, dinoflagellates, IP<sub>25</sub> and planktic foraminiferal stable isotopes. Our benthic foraminiferal assemblages record the variability in strength of Atlantic Water flow since deglaciation indicating relatively strong Atlantic Water flux during deglaciation reaching a peak during the early Holocene. Surface water proxies indicate variability in meltwater flux and sea ice concentration from the early Holocene. These results provide the first evidence for a variable ocean circulation with the potential to influence ice margin dynamics during deglaciation and through the Holocene.</p>