Rapid sea ice retreat can be explained with simple physics

In Antarctica, the ice cover gradually expands from March to October each year, increasing six-fold. Afterwards, the ice retreats at a very fast pace, most dramatically in December, when there is constant daylight. Although this pattern has puzzled scientists for years, a new study led by the University of Washington (UW) has found that, unlike other aspects of its behavior, in this case Antarctic sea ice is just following basic rules of physics.    

“In spite of the puzzling longer-term trends and the large year-to-year variations in Antarctic sea ice, the seasonal cycle is really consistent, always showing this fast retreat relative to slow growth,” said study lead author Lettie Roach, a former postdoctoral fellow at UW and currently a polar climate scientist at Columbia University. “Given how complex our climate system is, I was surprised that the rapid seasonal retreat of Antarctic sea ice could be explained with such a simple mechanism.”

Previous studies have argued that wind patterns and warm ocean waters may be responsible for the asymmetry in Antarctica’s seasonal sea ice cycle. However, Dr. Roach and her colleagues have shown that, similarly to a hot summer day that reaches its maximum temperatures in late afternoon, an Antarctic summer hits peak melting power in midsummer, greatly accelerating ice loss, while exhibiting less changes in temperature and ice levels when solar input is low during the rest of the year.

“I think because we usually expect Antarctic sea ice to be puzzling, previous studies assumed that the rapid seasonal retreat of Antarctic sea ice was also unexpected – in contrast to the Arctic, where the seasons of ice advance and retreat are more similar,” explained Roach. 

“Our results show that the seasonal cycle in Antarctic sea ice can be explained using very simple physics. In terms of the seasonal cycle, Antarctic sea ice is behaving as we should expect, and it is the Arctic seasonal cycle that is more mysterious.” According to Dr. Roach, since Antarctica’s geography is simple, with a polar continent surrounded by ocean, this aspect of its sea ice is more straightforward.

“We know the Southern Ocean plays an important role in Earth’s climate. Being able to explain this key feature of Antarctic sea ice that standard textbooks have had wrong, and showing that the models are reproducing it correctly, is a step toward understanding this system and predicting future changes,” concluded study co-author Cecilia Bitz, a professor of Atmospheric Sciences at UW.

The study is published in the journal Nature Geoscience.

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By Andrei Ionescu, Earth.com Staff Writer