Solar energy explains fast yearly retreat of Antarctica's sea ice

Date:
March 28, 2022
Source:
University of Washington
Summary:
Sea ice around Antarctica retreats more quickly than it advances,
an asymmetry that has been a puzzle. New analysis shows that the
Southern Hemisphere is following simple rules of physics, as peak
midsummer sun causes rapid changes. In this respect, it seems,
it's Arctic sea ice that is more mysterious.



FULL STORY ==========================================================================
In the Southern Hemisphere, the ice cover around Antarctica gradually
expands from March to October each year. During this time the total
ice area increases by 6 times to become larger than Russia. The sea
ice then retreats at a faster pace, most dramatically around December,
when Antarctica experiences constant daylight.


==========================================================================
New research led by the University of Washington explains why the ice
retreats so quickly: Unlike other aspects of its behavior, Antarctic
sea ice is just following simple rules of physics.

The study was published March 28 in Nature Geoscience.

"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 lead author Lettie Roach, who conducted the study as a postdoctoral researcher at the UW and is now research scientist at NASA and 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 explored whether wind
patterns or warm ocean waters might be responsible for the asymmetry
in Antarctica's seasonal sea ice cycle. But the new study shows that,
just like a hot summer day reaches its maximum sizzling conditions in
late afternoon, an Antarctic summer hits peak melting power in midsummer, accelerating warming and sea ice loss, with slower changes in temperature
and sea ice when solar input is low during the rest of the year.

The researchers investigated global climate models and found they
reproduced the quicker retreat of Antarctic sea ice. They then built
a simple physics- based model to show that the reason is the seasonal
pattern of incoming solar radiation.

At the North Pole, Arctic ice cover has gradually decreased since the
1970s with global warming. Antarctic ice cover, however, has seesawed
over recent decades. Researchers are still working to understand sea
ice around the South Pole and better represent it in climate models.

"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," Roach said. "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." The researchers are now exploring why Arctic sea ice
doesn't follow this pattern, instead each year growing slightly faster
over the Arctic Ocean than it retreats. Because Antarctica's geography
is simple, with a polar continent surrounded by ocean, this aspect of
its sea ice may be more straightforward, Roach said.

"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," said co- author Cecilia Bitz, a UW professor
of atmospheric sciences.

Other co-authors are; Edward Blanchard-Wrigglesworth, a UW research
assistant professor in atmospheric sciences; Ian Eisenman at Scripps Institution of Oceanography; and Till Wagner at the University of Wisconsin-Madison. Roach is currently a research scientist with the NASA Goddard Institute for Space Studies. This work was funded by the National Science Foundation, the National Oceanic and Atmospheric Administration
and the U.K.-based Scientific Committee on Antarctic Research.


========================================================================== Story Source: Materials provided by University_of_Washington. Original
written by Hannah Hickey. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. L. A. Roach, I. Eisenman, T. J. W. Wagner,
E. Blanchard-Wrigglesworth, C.

M. Bitz. Asymmetry in the seasonal cycle of Antarctic sea
ice driven by insolation. Nature Geoscience, 2022; DOI:
10.1038/s41561-022-00913-6 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220328112307.htm

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