Interannual variations in meltwater input to the Southern Ocean from Antarctic ice shelves

Abstract

Ocean-driven basal melting of Antarctica's floating ice shelves accounts for about half of their mass loss in steady state, where gains in ice-shelf mass are balanced by losses. Ice-shelf thickness changes driven by varying basal melt rates modulate mass loss from the grounded ice sheet and its contribution to sea level, and the changing meltwater fluxes influence climate processes in the Southern Ocean. Existing continent-wide melt-rate datasets have no temporal variability, introducing uncertainties in sea level and climate projections. Here, we combine surface height data from satellite radar altimeters with satellite-derived ice velocities and a new model of firn-layer evolution to generate a high-resolution map of time-averaged (2010-2018) basal melt rates and time series (1994-2018) of meltwater fluxes for most ice shelves. Total basal meltwater flux in 1994 (1,090 ± 150 Gt yr-1) was similar to the steady-state value (1,100 ± 60 Gt yr-1), but increased to 1,570 ± 140 Gt yr-1 in 2009, followed by a decline to 1,160 ± 150 Gt yr-1 in 2018. For the four largest 'cold-water' ice shelves, we partition meltwater fluxes into deep and shallow sources to reveal distinct signatures of temporal variability, providing insights into climate forcing of basal melting and the impact of this melting on the Southern Ocean.

Forty-year Simulations of Firn Processes over the Greenland and Antarctic Ice Sheets

“…We then describe our selected climate forcing from NASA's Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) used in our simulations. Finally, we discuss the differences between GSFC-FDMv1 and v0, the latter of which was used in Smith et al (2020) and Adusumilli et al (2020).…”

32-year record-high surface melt in 2019/2020 on north George VI Ice Shelf, Antarctic Peninsula

“…However, as these surface lakes have generally been observed to refreeze on the ice-shelf surface at the end of each austral summer, with to date, no evidence of meltwater drainage into moulins, limited mass is lost through surface melting. Instead, mass has been mostly lost due to high basal melt rates (Adusumilli et al, 2020), attributed to the warm Circumpolar Deep Water (CDW) current that extends under the entire length of the GVIIS (Holland et al, 2010;Pritchard et al, 2012), though rates of basal melting are greatest at the southern end of the GVIIS (Adusumilli et al, 2020;Smith et al 2020). These high basal melt rates have resulted in sustained thinning rates (Pritchard et al 2012), which together with frontal calving (Pearson and Rose, 1983;Reynolds and Hambrey, 1988), have contributed to the ice shelf's negative net mass balance since at least 2003 (Rignot et al 2013;Paolo et al, 2015).…”

Review Article: Earth's ice imbalance

“…To compute trends in the volume of Antarctic ice shelves associated with changes in their extent, we combined satellitebased records of their thickness (Fretwell et al, 2013) and area change (Cook and Vaughan, 2010) over time, adjusted for changes in thickness where they have been recorded (Adusumilli et al, 2020). We restrict this calculation to ice shelves where a record of progressive retreat has been well-established ( Fig.…”

“…CC BY 4.0 License. uncertainty, between 1994 and 2020 (Adusumilli et al, 2020). The altimeter range measurements were first adjusted for changes in ocean surface height, including contributions due to the geoid, mean dynamic topography, ocean tide, ocean load tide, atmospheric pressure, and sea-level rise.…”

“…grounded ice upstream (Weertman, 1974), and have been a persistent element of the climate system throughout the Holocene period (Domack et al, 2005). There are over 343 documented ice shelves around Antarctica (SCAR, 2020) containing an estimated 380 thousand km 3 of ice (Fretwell et al, 2013), and fluctuations in their volume occur as a result of changes in their extent (Cook and Vaughan, 2010) and thickness (Adusumilli et al, 2020). Mountain glacier ice moderates global sealevel and regional hydrology (Huss and Hock, 2018), impacting on local communities who rely on it as a source of freshwater (Immerzeel et al, 2020).…”