Solar energy explains rapid annual retreat of Southern Ocean sea ice

Solar energy explains rapid annual retreat of Southern Ocean sea ice

In the Southern Ocean, the sea ice cover around Antarctica gradually expands during the mostly sunless months from March to October. But then, as the sunlight returned, it receded at a faster rate, most notably around December, when Antarctica experienced persistent sunlight. This pattern has been consistent for a long time, unlike other sea ice conditions, which can vary widely from year to year.

New research in the journal natural geosciences This asymmetry is explained: it turns out to obey a simple set of conditions.

“Despite puzzling long-term trends and large year-to-year variability in Antarctic sea ice, seasonal cycles are indeed consistent, always showing rapid retreat relative to slow growth,” said the lead author. Leti Roch, who conducted the research as a postdoctoral researcher at the University of Washington. “I was surprised that the rapid seasonal retreat of Antarctic sea ice could be explained by such a simple mechanism, considering how complex our climate system is,” said Roach, now a research scientist at the institute. NASA Goddard Institute for Space Studies and Columbia University Center for Climate System Research.

During the dark months in the southern hemisphere, the total ice area of ​​the ocean can increase by more than six times, making it larger than the land area of ​​Russia.Previous research has explored whether wind pattern Or warmer waters could be responsible for the quicker fall. Just as hot summer days reach their greatest high temperature conditions in the late afternoon, the Antarctic summer’s melting power peaks in the midsummer south, accelerating warming and sea ice loss, new research shows. Changes in temperature and sea ice were slower for the rest of the year.

The researchers looked at global climate models and found that they reproduced the faster retreat of Antarctic sea ice. They then built a simple physics-based model to show that the ice’s rapid decline is due to seasonal patterns of incoming solar radiation.

While the annual rhythm of ice formation and retreat is consistent, the overall extent of the Antarctic ice sheet has inexplicably fluctuated up and down in recent decades, despite global warming. This is in stark contrast to the Arctic Ocean, which has more similar ice advance and retreat seasons, but has seen overall ice cap decline as global warming since the 1970s. Researchers are still working to understand the polar inconsistencies and better represent them in climate models.

“Our results show that the seasonal cycle of Antarctic sea ice can be explained by very simple physics,” Roach said. “In terms of seasonal cycles, Antarctic sea ice is behaving in line with our expectations. [It] is the more mysterious arctic seasonal cycle. “

Researchers are now exploring why Arctic sea ice does not follow Antarctic patterns, but instead grows slightly faster than it recedes over the ocean each year. Because of the simple geography of Antarctica, where the polar continent is surrounded by oceans, this aspect of its sea ice may be more straightforward, Roach said.

“We know that the Southern Ocean plays an important role in Earth’s climate. Being able to explain this key feature of Antarctic sea ice that the standard textbooks miss, and showing that models reproduce it correctly, is a step toward understanding this system and predicting future changes. a step forward,” said the co-authors. Cecilia Beatsprofessor of atmospheric sciences at the University of Washington.

Other co-authors of the study are Edward Blanchard-Wrigglesworth of the University of Washington; Ian Eisenman of the Scripps Institution of Oceanography; and Till Wagner of the University of Wisconsin-Madison. The research work was funded by the National Science Foundation, the National Oceanic and Atmospheric Administration and the British Scientific Council for Antarctic Research.