Fig 1.
A: Automatic weather station S5 along the K-transect in the lower ablation zone of the south-western GrIS in September 2014 (67°06’N, 50°07’W, ~500 m asl, credit Christian Steger, IMAU) [19] and B: meteorological measurement site of Neumayer base in austral summer 2004/05, situated on the Ekström ice shelf in East Antarctica (70°39’S, 8°15’W, ~50 m asl, credit Bernd Loose, Alfred-Wegener-Institut für Polar- und Meeresforschung) [20]. Both stations are situated near the ice sheet margin, which for the GrIS in this sector is land-terminating, whereas it is marine terminating at Neumayer.
Fig 2.
Definitions of ice sheet mass balance (MB), surface mass balance (SMB) and liquid water balance, all ice-sheet integrated mass fluxes expressed in gigatonnes per year (Gt yr-1).
‘Basal mass balance’ refers to ablation at the ice-bedrock interface. ‘Erosion’ refers to removal of snow by wind, ‘Retention’ to the irreducible water content of porous snow. Note that the definition of SMB used here includes processes in the firn layer, and is formally referred to as ‘climatic mass balance’ [64]. Surface Energy Balance (SEB) is defined locally and expressed in watts per square metre (W m-2). SEB symbols are explained in the main text. Adapted from [65].
Fig 3.
Time series of hourly average near-surface air temperature (T2m), surface temperature (Ts) and 10 m wind speed (V10m) (left axis) and SEB components (right axis) at (a) S5 along the K-transect in the south-western GrIS and (b) at Neumayer station on the Ekström ice shelf, East Antarctic ice sheet. Negative/positive SEB values indicate surface energy losses/gains. Station locations are indicated in Fig 4, images of the measurement sites in Fig 1.
Fig 4.
Modelled average (1991–2020) annual melt on the GrIS (left, 0,05 latitudinal degree or ~5.5 km resolution) and the AIS (right, 0.25 latitudinal degree or ~27 km resolution) from the polar regional climate model RACMO2.3p2. Continuous black lines indicate grounded ice sheet margin or coastlines. Yellow dots indicate locations of AWS S5 (Greenland) and Neumayer base (Antarctica). Note the nonlinear melt scale. Made with Natural Earth (Public Domain, https://www.naturalearthdata.com/about/terms-of-use/).
Fig 5.
Timeseries of RACMO2.3p2 annual melt totals over the contiguous GrIS (red) and AIS including ice shelves (blue).
Solid lines represent hindcast using ERA forcing, dashed lines represent forcing from the earth system model CESM2 for the historical period (up to 2014) and for a high-warming, fossil-fuelled development scenario SSP5-8.5 (until 2100). Orange triangles are satellite-based melt estimates, coloured bands indicate 1961–1990 (GrIS) and 1979–1990 (AIS) range (average +/- one standard deviation).