Rising temperatures and the decline in sea ice around Antarctica are leading to increased evaporation resulting in more snow falling over the Antarctic ice sheet and thus partially offsetting the contribution to sea level rise.
A research team from Pennsylvania State University analyzed the relationships between sea ice concentration, evaporation and the mass of the ice sheet in West Antarctica and found that when there is less sea ice cover, more moisture is released into the atmosphere via the ice-free sea surface of the Amundsen Sea. When this moist air meets the colder edges of the ice sheet, it condenses and leads to heavier snowfall over the West Antarctic Ice Sheet, which at least partially compensates for the mass loss due to warming, the researchers report in Geophysical Research Letters in September this year.
Luke Trusel, assistant professor of geography at Pennsylvania State University and co-author of the study, points out that including the additional snowfall in the climate models can improve the prediction of various factors, such as sea level rise.
“For a place like Antarctica, which is just massive, the amount of snow falling on top of the ice sheet is as important or even more important than other processes like meltwater or ice breaking off,” Trusel said in a university press release. “We’re tracking both snowfall and melt to understand both ends of the equation — what takes from sea level and what gets returned to the ocean. We want to know how those factors are impacting the ice sheets.”
Global sea levels depend crucially on how the volume of the Antarctic ice sheet changes, which stores around 60 percent of the Earth’s total fresh water. Snowfall plays an important role in this, depending mainly on evaporation from the Southern Ocean, which in turn is largely controlled by sea ice.
“Sea ice is significant,” says Jessica Kromer, a doctoral candidate at Penn State University and lead author of the study. “It reflects sunlight, aids in cooling the planet and influences interactions between the atmosphere and ocean, including oceanic evaporation. We found that precipitation varies so much year to year. In some years, precipitation can take away from sea level or lessen the impact of the ice discharged from the sheets.”
The evaluation of the satellite observations and climate data also revealed a feedback loop between sea ice and the water vapour in the atmosphere. The higher moisture in the atmosphere with lower sea ice cover causes an increased greenhouse effect locally, which leads to increased downward long-wave radiation, which in turn reduces the sea ice cover one month later.
“While Arctic sea ice has been rapidly declining over the satellite record, the Antarctic experienced a slight increase until 2015, followed by a sharp decline in 2016,” Kromer said. “In 2022, we witnessed a new record low, and this year’s levels are even lower, significantly below previous observations. These recent rapid changes in Antarctic sea ice highlight the urgency of understanding their causes and their potential impact on the Antarctic ice sheet.”
The researchers assume that the correlation between sea ice and heavier snowfall over the ice sheet applies not only to West Antarctica, but to the entire continent. “Increased snowfall in Antarctica might slow the sea level rise, but it’s essential to recognize that the ice sheet will continue to contribute to rising sea levels,” Trusel said. However, according to him, more accurate predictions require improvements to current climate models, particularly in representing sea ice dynamics.
The research team was unable to investigate the effects of the increased snowfall on the penguin colonies as part of the study. However, unusually heavy snowfall could impact the breeding success of Adélie and Emperor penguins.
Julia Hager, PolarJournal
Link to the study Jessica D. Kromer, Luke D. Trusel. Identifying the Impacts of Sea Ice Variability on the Climate and Surface Mass Balance of West Antarctica. Geophysical Research Letters, 2023; 50 (18) DOI: 10.1029/2023GL104436
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