Abstract
Abstract. Along with record-breaking summer air temperatures at an Antarctic Peninsula meteorological station in February 2020, the Larsen C ice shelf experienced an exceptionally long and extensive 2019/2020 melt season. We use a 40-year time series of passive and scatterometer satellite microwave data, which are sensitive to the presence of liquid water in the snow pack, to reveal that the extent and duration of melt observed on the ice shelf in the austral summer of 2019/2020 was the greatest on record. We find that unusual perturbations to Southern Hemisphere modes of atmospheric flow, including a persistently positive Indian Ocean Dipole in the spring and a very rare Southern Hemisphere sudden stratospheric warming in September 2019, preceded the exceptionally warm Antarctic Peninsula summer. It is likely that teleconnections between the tropics and southern high latitudes were able to bring sufficient heat via the atmosphere and ocean to the Antarctic Peninsula to drive the extreme Larsen C Ice Shelf melt. The record-breaking melt of 2019/2020 brought to an end the trend of decreasing melt that had begun in 1999/2000, will reinitiate earlier thinning of the ice shelf by depletion of the firn air content, and probably affected a much greater region than Larsen C Ice Shelf.
Highlights
Surface melt and ponding on Antarctic Peninsula (AP) ice shelves has been linked to firn densification (Holland et al, 2011), surface lowering (Paolo et al, 2015), hydrofracture (Banwell et al, 2013), and eventual collapse (Scambos et al, 2000; van den Broeke, 2005)
Comparing the maps of melt on LCIS (Fig. 2) we can see that the 2017/2018 melt based on Level 1 ASCAT data (Fig. 2b) compares well with the scatterometer image reconstruction (SIR) data (Fig. 2a)
Melt distribution follows the typical pattern of enhanced melt in the inlets close to the mountains superimposed on a general south-tonorth gradient of increasing melt (Bevan et al, 2018, Figs. 6, and A1)
Summary
Surface melt and ponding on Antarctic Peninsula (AP) ice shelves has been linked to firn densification (Holland et al, 2011), surface lowering (Paolo et al, 2015), hydrofracture (Banwell et al, 2013), and eventual collapse (Scambos et al, 2000; van den Broeke, 2005). Larsen C Ice. Shelf (LCIS, Fig. 1) is the largest remaining ice shelf on the AP, and surface melt and ponding have led to surface lowering, concentrated in the inlets and the northern parts of the shelf, and to the formation of a large subsurface mass of ice (Hubbard et al, 2016). Removal of ice shelves has consequences other than sea-level rise with potential impacts on ocean circulation and biodiversity (Siegert et al, 2019)
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