Abstract
Abstract. The Northeast Greenland Ice Stream (NEGIS) has been suffering a significant ice mass loss during the last decades. This is partly due to increasing oceanic temperatures in the subpolar North Atlantic, which enhance submarine basal melting and mass discharge. This demonstrates the high sensitivity of this region to oceanic changes. In addition, a recent study suggested that the NEGIS grounding line was 20–40 km behind its present-day location for 15 ka during Marine Isotope Stage (MIS) 3. This is in contrast with Greenland temperature records indicating cold atmospheric conditions at that time, expected to favour ice-sheet expansion. To explain this anomalous retreat a combination of atmospheric and external forcings has been invoked. Yet, as the ocean is found to be a primary driver of the ongoing retreat of the NEGIS glaciers, the effect of past oceanic changes in their paleo evolution cannot be ruled out and should be explored in detail. Here we investigate the sensitivity of the NEGIS to the oceanic forcing during the last glacial period using a three-dimensional hybrid ice-sheet–shelf model. We find that a sufficiently high oceanic forcing could account for a NEGIS ice-margin retreat of several tens of kilometres, potentially explaining the recently proposed NEGIS grounding-line retreat during Marine Isotope Stage 3.
Highlights
The Northeast Greenland Ice Stream (NEGIS) is the largest ice stream in the Greenland Ice Sheet (GrIS), extending more than 600 km inland (Joughin et al, 2001) and discharging 12 % of the whole ice sheet through three outlet glaciers (Rignot and Mouginot, 2012): Nioghalvfjerdsfjord Gletscher (79N), Zachariae Isstrøm (ZI), and Storstrømmen Gletscher (SG), which today is a surging glacier
During Marine Isotope Stage (MIS)-3, the ice-margin position gradually advances towards its maximum glacial extent, which is reached at about 20 ka (LGM), when the ice sheet becomes grounded at a mean distance of 40 km from the shelf break, reducing the area of the floating ice shelf in the region (Fig. 4a–e)
We have studied the sensitivity of the NEGIS ice margin to oceanic forcing during the last glacial period
Summary
The Northeast Greenland Ice Stream (NEGIS) is the largest ice stream in the Greenland Ice Sheet (GrIS), extending more than 600 km inland (Joughin et al, 2001) and discharging 12 % of the whole ice sheet through three outlet glaciers (Rignot and Mouginot, 2012): Nioghalvfjerdsfjord Gletscher (79N), Zachariae Isstrøm (ZI), and Storstrømmen Gletscher (SG), which today is a surging glacier. Enhanced stability of 79N has been recently tested under various future warming scenarios by another modelling study (Choi et al, 2017), suggesting that it may be related to the presence of pinning points (such as ice rises) near the calving front Ice loss from these two marine-terminating glaciers is thought to be partly related to the increasing temperature of North Atlantic waters (Khan et al, 2014; Mouginot et al, 2015), which increases the oceanic heat flux and accelerates the submarine melting (Mayer et al, 2018). 79N has been suggested to be more resistant to increasing basal and frontal
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