Recent growth and sudden declines in Antarctic sea ice to be unique
changes since the early 20th century
Research paints a dramatic first-ever picture for weather and climate implications on the world's southernmost continent

Date:
January 10, 2022
Source:
Ohio University
Summary:
Researchers show that the increase of sea ice surrounding Antarctica
since 1979 is a unique feature of Antarctic climate since 1905 --
an observation that paints a dramatic first-ever picture for weather
and climate implications on the world's southernmost continent.



FULL STORY ==========================================================================
A study led by Ohio University researchers shows that the increase
of sea ice surrounding Antarctica since 1979 is a unique feature of
Antarctic climate since 1905 -- an observation that paints a dramatic first-ever picture for weather and climate implications on the world's southernmost continent.


==========================================================================
Dr. Ryan Fogt's study, published today in Nature Climate Change, is
the first to detail sea ice extent surrounding the entire continent
though all four seasons over the last century. Weather, especially winds
and temperatures, contribute to sea ice changes. Fogt is professor of
Geography in OHIO's College of Arts and Sciences.

Previous historical estimates of Antarctic sea ice before satellite measurements began around 1979 were obtained mostly through the lens
of a small number of weather stations across the vast continent,
human observation along the ice edges, and ice core and ocean sediment
samples. However, these estimates all have limitations -- most were only observing sea ice conditions in a small area or at a specific time of
the year.

But the OHIO study extends the reliable measurements from satellite
imagery since 1979 back through the 20th century using historical weather
data at places away from the Antarctic continent. At the heart of Fogt's statistical reconstruction model is the strong connection Antarctic sea
ice shares with regional and large-scale climate variability, captured
through a network of 30 long-term temperature and pressure observations
across the Southern Hemisphere.

This new study has nearly tripled the length of observed data about
the entire continent, instead of just a specific region, and provides
a year-round look, rather than an annual average.

"This reconstruction of Antarctic sea ice back through the 20th century
gives us detail not only for every season, but also for different regions around the whole of Antarctica. When we sum it up, it gives us the first complete estimate of total Antarctic sea ice extent -- how far away the
sea ice reaches from the continent -- back through the 20th century,"
Fogt said.

Regime Shift: Sea increases since 1979, and sudden declines From the new
data, the most impressive feature is what Fogt calls a regime shift. "The
short period provided from satellite measurements of Antarctic sea ice
is really unique. It's the only period since the beginning of the 20th
century where we see increases in total sea ice in all seasons," Fogt
said. "We have a statistically significant positive trend over that
satellite period.

Perhaps even more impressively, these increases since 1979 are juxtaposed
by long-term decreases in Antarctic sea ice throughout the early and
middle 20th century." Ice core records similarly confirm regional aspects
of the decrease in much of the 20th century.



==========================================================================
The satellite measurements start in 1979 at a time when sea ice had been decreasing throughout the first half of the 20th century. Fogt is very interested in the recent increases in sea ice and an anomaly in 2016
and 2017 when the sea ice suddenly decreased, only to rebound again by mid-2020. Sea ice conditions in early 2022 are once again below average
around Antarctica.

Unlike the portions of the West Antarctic Ice Sheet that are receding,
Fogt explains that the Antarctic sea ice is ice that is floating on the
ocean, and it melts and reforms as the seasons change. Since it floats
on the ocean, this melting and refreezing doesn't affect the sea level.

"2016 was a year that surprised all of us, really, because up until then
the ice around Antarctica had been increasing, even if slowly," Fogt
said. "And then 2016 came along and, boom, it suddenly dropped down, and
it was this big loss that we had never seen in the observation record,
and it stayed below average all the way up until mid-2020. And then
it kind of went back to normal, but only for a short time." Fogt said
that understanding what happened over the past 40 years in context of
the last century -- and how 2016 was different -- is a next step for
climate researchers. The data repository from Fogt's study is available
to other researchers at figshare (https://figshare.com/collections/ Antarctic_Sea_Ice_Reconstructions/5709767).

"These new Antarctic sea ice extent reconstructions continue to show
there are changes going on in our climate system that we hadn't previously observed in the context of almost 150 years. The causes of these changes
-- the decline in the 20th century, the increase after 1979, and the rapid decline in 2016 -- are all yet to be precisely determined. But what we're seeing is something pretty dramatic going on recently," he said. "Our new
data set has a lot of potential to really expand our understanding of what causes the Antarctic sea ice to change over much longer timescales. And
that's the work that we and the scientific community will have to start
doing now." Fogt conducted fieldwork in Antarctica early in his career
and said he knew in graduate school that he wanted to spend his life researching the continent. And he does love penguins.

"I mentioned there's no impact on sea level rise with sea ice. Why
then are we concerned about sea ice around Antarctica? Well, for one,
it affects ecosystems. Penguins and seals in Antarctica are like the
polar bears in the Arctic. They are critically dependent on how much
sea ice there is. The ocean circulation, including the formation of
dense water that can sink to the ocean floor, is also related to sea
ice variations. Changes in the ocean around Antarctica can have global implications," Fogt said.

Fogt's paper, "A Regime Shift in Seasonal Total Antarctic Sea Ice Extent
in the 20th Century," was co-authored by Ohio University alumna Amanda Sleinkofer, who earned an M.S. in Geography from the College of Arts and Sciences in 2021 and worked on the project for her thesis. Additional co-authors are Marilyn Raphael and Mark Handcock from the University of California-Los Angeles. The project is a collaborative effort between
Ohio University and UCLA funded by the National Science Foundation Office
of Polar Programs.

========================================================================== Story Source: Materials provided by Ohio_University. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Ryan L. Fogt, Amanda M. Sleinkofer, Marilyn N. Raphael, Mark
S. Handcock.

A regime shift in seasonal total Antarctic sea ice extent
in the twentieth century. Nature Climate Change, 2022; DOI:
10.1038/s41558-021- 01254-9 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220110114135.htm
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