Antarctica is ringed by ice shelves: enormous, glacier-fed slabs of floating ice that can stretch hundreds of kilometers outward from the coastline. In locations where these shelves experience substantial melting and refreezing, the compacted snow at the top can become impermeable enough to trap ponds of meltwater. As this fluid percolates slowly beneath the surface, it can expand existing cracks, helping to fracture ice shelves and ultimately—as in the case of the Larsen B ice shelf—hastening their collapse.
Weather station data suggest that there has been an increase in the amount of melting occurring across the Antarctic Peninsula since the mid-20th century, but the existing record of radar scatterometry data from NASA’s Quick Scatterometer (QuikSCAT) mission is from 1999 to 2009—too short to detect melt trends since the turn of the 21st century.
To extend this record, Bevan et al. turned to Advanced Scatterometer (ASCAT) radar data from the European Space Agency’s Meteorological Operational satellite (MetOp) mission, which launched in 2006. Because of differences in the time of day when the measurements were made, the two records had not previously been combined.
By comparing the results from the 2008–2009 season, the only season for which the two data sets overlap, the team determined that the QuikSCAT data collected in the morning agree most closely with the newer ASCAT data. The researchers then used these results to extend the duration of the melt record on Antarctica’s Larsen C ice shelf. The combined 18 years of results show the duration of annual melt across much of Larsen C decreased 1–2 days per year between 2000 and 2017, a finding the authors attribute to declining 21st century surface air temperatures across the Antarctic Peninsula.
A better understanding of how to interpret the ASCAT melt record and how this information compares with the older QuikSCAT results is particularly important since the MetOp mission is slated to continue until at least 2020. These results will help scientists continue to monitor the rate of surface melt on the Larsen C and other Antarctic ice shelves, with the ultimate aim of creating a record long enough to allow climatological changes to be identified. The melt observations may also be used to validate energy balance models to help clarify ice shelf melt processes and more accurately predict potential global sea level rise. (Earth and Space Science, https://doi.org/10.1029/2018EA000421, 2018)
—Terri Cook, Freelance Writer