"Antarctica is a vast and isolated continent and these results show that we can monitor and understand what is happening there using satellite-based tools," team leader Marco Tedesco of the University of Maryland in Baltimore County and the NASA Goddard Space Flight Centre, told environmentalresearchweb. "Antarctica contains 90% of Earth's fresh water, which means it plays an important role in a sea-level rise scenario."
The researchers analysed data collected from 1987 to 2006 and found that snow is melting as far inland as 700 km from the Antarctic coast and as high as 2 km above sea level in the Transantarctic mountains. The team also discovered that snow-melt is increasing on the Ross Ice Shelf.
The results were obtained by analysing microwave data at 19.35 GHz, or the so-called brightness temperature, measured by the Special Sensor Microwave Imaging Radiometer on board the Defense Meteorological Satellite Program. The sensors fly over Antarctica and measure the electromagnetic radiation emitted naturally by snow and ice at microwave frequencies.
"Microwaves allow us to study melting occurring either on the surface or below it because they have the property of also being sensitive to sub-surface processes," explains Tedesco. "This is a major difference when compared to visible or infrared data, which only give us information regarding the surface. Moreover, microwave data do not need solar illumination to be acquired and can 'see through' clouds, providing us with data in all-weather conditions – and during both the day and night."
In their study, Tedesco and colleagues considered "persisting melting" – that is, melting that occurs for at least three days or for one consecutive day and night. "This means that we excluded sporadic melting events that might not considerably affect surface or sub-surface processes," he said.
Microwaves are also sensitive to the presence of liquid water within the snowpack. When snow is dry, the brightness temperature is very low, but when there is liquid water (either on the surface or below it) this temperature jumps up and melting snow can be detected. Although there are other factors that can increase brightness temperature, none increase it so fast as the appearance of liquid water, says Tedesco.
Increased ice melt on the Ross Ice Shelf is particularly worrying because the melt water eventually fills small cracks in the shelf. The liquid water puts pressure on these cracks, causing larger fractures in the ice shelf.
Tedesco says that snow melting is strongly connected to surface temperature change, so warmer temperatures are likely to be responsible for the observations. The results also support related research that showed a direct link between changes in near-surface air temperatures and snow melting in Antarctica.
The team now plans to evaluate its results and compare them to climate models to understand the mass balance of the Antarctica ice sheet and its contribution to rises in sea levels. "We will also continue to monitor ice melting on the continent using a near-real time framework in which satellite data are analysed within 24 hours of their acquisition to detect extreme melting events and evaluate the trend of the melting season as it goes on," adds Tedesco.
The researchers published their results in Geophysical Research Letters.