Antarctic ice shelves are the floating extensions of glaciers that cover most of the Antarctic continent.
They play a crucial role in regulating the ice sheet mass balance and sea level rise, as they act as buttresses that slow down the flow of ice from the interior to the ocean.
However, ice shelves are also vulnerable to melting from both above and below, due to changes in atmospheric and oceanic conditions.
Melting can weaken the ice shelves and make them prone to collapse, as seen in the Larsen A and B ice shelves on the Antarctic Peninsula in 1995 and 2002.
A new study, published in Geophysical Research Letters, has assessed how surface melt rates of Antarctic ice shelves have changed over the past four decades, from 1980 to 2021.
The study was led by Alison Banwell, a glaciologist at the Cooperative Institute for Research in Environmental Sciences (CIRES), a partnership between the University of Colorado Boulder and the U.S. National Oceanic and Atmospheric Administration.
How surface melt rates were measured
JOHAN ORDONEZ/AFP via Getty Images
The researchers used two types of satellite data to measure surface melt rates of Antarctic ice shelves: passive microwave data and active microwave data, as per Phys.org.
Passive microwave data measure the brightness temperature of the surface, which changes when ice melts and refreezes.
Active microwave data measure the backscatter coefficient of the surface, which reflects how rough or smooth it is.
Melting and refreezing can alter the surface roughness by forming ponds, cracks, or ice crusts.
The researchers combined the satellite data with a numerical model called SNOWPACK, which simulates the physical processes that affect snow and firn (compacted snow) on ice shelves.
The model accounts for factors such as air temperature, humidity, wind speed, solar radiation, and precipitation, and it also estimates how much meltwater percolates into the firn layer or runs off into the ocean.
The researchers calculated the number of melt days per year for each ice shelf, defined as days when at least one of the satellite data sources or the model indicated melting.
They also calculated the total melt volume per year for each ice shelf, based on the model output.
The results showed that Antarctic ice shelves overall have experienced only minor changes in surface melt rates over the past four decades, as per Eurekalert.
The average number of melt days per year across all ice shelves was about 15, with no significant trend over time.
The average total melt volume per year across all ice shelves was about 71 cubic kilometers, with a slight but significant decrease over time.
However, some regional variations were observed.
The ice shelves on the Antarctic Peninsula had higher melt rates than those in East Antarctica or West Antarctica, reflecting their warmer climate and lower elevation.
The Peninsula ice shelves also showed more interannual variability in melt rates, with some exceptionally high melt seasons in recent years, such as 2019 to 2020.
The researchers attributed this variability to changes in atmospheric circulation patterns that affect temperature, precipitation, and cloud cover.
The researchers also compared their results with previous studies that used different methods or data sources to estimate surface melt rates of Antarctic ice shelves.
They found good agreement among most studies, except for some discrepancies in East Antarctica due to differences in satellite resolution or model assumptions.
The researchers concluded that surface melt rates of Antarctic ice shelves have been relatively stable since 1980, despite increasing air temperatures and greenhouse gas concentrations.
They suggested that this stability may be due to compensating effects of other factors, such as increased snowfall or cloud cover that reduce solar radiation and melting.
