Abstract
Increasing ocean and air temperatures have contributed to the removal of floating ice shelves from several Greenland outlet glaciers; however, the specific contribution of these external forcings remains poorly understood. Here we use atmospheric, oceanographic, and glaciological time series data from the ice shelf of Petermann Gletscher, NW Greenland to quantify the forcing of the ocean and atmosphere on the ice shelf at a site ~16 km from the grounding line within a large sub-ice-shelf channel. Basal melt rates here indicate a strong seasonality, rising from a winter mean of 2 m yr-1 to a maximum of 80 m yr-1 during the summer melt season. This increase in basal melt rates confirms the direct link between summer atmospheric warming around Greenland and enhanced ocean-forced melting of its remaining ice shelves. We attribute this enhanced melting to increased discharge of subglacial runoff into the ocean at the grounding line, which strengthens under-ice currents and drives a greater ocean heat flux toward the ice base.
Highlights
Over the past 20 years increasing ocean and air temperatures caused many of Greenland’s outlet glaciers to retreat (Rignot and Kanagaratnam, 2006)
Air temperatures persisted below freezing and the ocean adjacent to Petermann Gletscher Ice Shelf (PGIS) was largely covered with sea ice (Figs 3a, b)
Failure of the PG 16 Autonomous phase-sensitive Radio-Echo Sounder (ApRES) Iridium datalink on 2 May 2017 prevented acquisition of basal melt measurements during the 2017 summer when air temperatures exceeded 0°C and the sea ice retreated once again (Fig. 3)
Summary
Over the past 20 years increasing ocean and air temperatures caused many of Greenland’s outlet glaciers to retreat (Rignot and Kanagaratnam, 2006). For some of the glaciers, this retreat began with the loss of their floating ice shelf, continued inland This occurred most recently to major outlet glaciers Jakobshavn Isbrae (Holland and others, 2008) and Zachariae Isstrom (Mouginot and others, 2015). Several recent studies reveal that ongoing focused melting in channels can lead to ‘non steady-state’ thinning in already relatively thin regions of ice shelves (Alley and others, 2016; Marsh and others, 2016; Gourmelen and others, 2017). This structurally weakens the ice shelves, promotes fracturing and calving, and reduces their buttressing capabilities (Vaughan and 8 others, 2012; Dow and others, 2018). It has been suggested that while channels concentrate melting locally, they serve to reduce the mean basal melt rate of the ice shelf as a whole (Gladish and others, 2012)
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