New observations from ICESat-2 show remarkable Arctic sea ice thinning
in just three years

Date:
March 10, 2022
Source:
American Geophysical Union
Summary:
Over the past two decades, the Arctic has lost about one-third
of its winter sea ice volume, largely due to a decline in sea ice
that persists over several years, called multiyear ice, according
to a new study. The study also found sea ice is likely thinner
than previous estimates.

Seasonal sea ice, which melts completely each summer rather than
accumulating over years, is replacing thicker, multiyear ice and
driving sea ice thinning trends, according to the new research.



FULL STORY ==========================================================================
Over the past two decades, the Arctic has lost about one-third of its
winter sea ice volume, largely due to a decline in sea ice that persists
over several years, called multiyear ice, according to a new study. The
study also found sea ice is likely thinner than previous estimates.


========================================================================== Seasonal sea ice, which melts completely each summer rather than
accumulating over years, is replacing thicker, multiyear ice and driving
sea ice thinning trends, according to the new research.

Arctic sea ice snow depth is estimated, for the first time, from a
combination of lidar (ICESat-2) and radar (CryoSat-2) data. Using these estimates of snow depth and the height of sea ice exposed above water,
the study found multiyear Arctic sea ice has lost 16% of its winter
volume, or approximately half a meter (about 1.5 feet) of thickness,
in the three years since the launch of ICESat-2.

The study was published in the AGU journal Geophysical Research Letters,
which publishes short-format, high-impact papers with implications that
span the Earth and space sciences.

"We weren't really expecting to see this decline, for the ice to be this
much thinner in just three short years," said lead study author Sahra
Kacimi, a polar scientist at the California Institute of Technology's
Jet Propulsion Laboratory.

Scientists make satellite estimates of sea-ice thickness using snow
depth and the height of the floating ice above the sea surface. Snow
can weigh ice down, changing how ice floats in the ocean. The new study compared ice thickness using new snow depths from satellite radar and
lidar to previous ice thickness and snow depth estimates from climate
records. The researchers found using climatology-based estimates of
snow depth can result in overestimating sea-ice thickness by up to 20%,
or up to 0.2 meters (0.7 feet).

"Arctic snow depth, sea ice thickness and volume are three very
challenging measurements to obtain," said Ron Kwok, a polar scientist at
the University of Washington's Applied Physics Laboratory who co-authored
the new study. "The key takeaway for me is the remarkable loss of Arctic
winter sea ice volume -- one- third of the winter ice volume lost over
just 18 years -- that accompanied a widely reported loss of old, thick
Arctic sea ice and decline in end-of-summer ice extent." "This is the
first time anyone has several years' worth of data from the difference
between lidar and radar data for snow depth," said Robbie Mallett, a
polar ice researcher at University College London who was not involved in
the study. "It's a really useful update on how ICESat-2 is performing."
The study used an 18-year record of sea-ice observations from ICESat and
the newer ICESat-2 and CryoSat-2 satellites to capture monthly changes
in Arctic sea-ice thickness and volume, to provide context for sea ice thickness estimates from 2018 to 2021. The 18-year record showed a loss
of about 6,000 cubic kilometers of winter ice volume, largely driven by
the switch from predominantly multiyear ice to thinner, seasonal sea ice.

Older, multiyear ice tends to be thicker and therefore more resistant
to melting. As that "reservoir" of old Arctic sea ice is depleted and
seasonal ice becomes the norm, the overall thickness and volume of
Arctic sea ice is expected to decline. "Current models predict that by
the mid-century we can expect ice-free summers in the Arctic, when the
older ice, thick enough to survive the melt season is gone," Kacimi said.

"This is really old ice we're losing at quite a frightening rate,"
Mallett said.


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


========================================================================== Journal Reference:
1. Sahra Kacimi, Ron Kwok. Arctic snow depth, ice thickness and
volume from
ICESat‐2 and CryoSat‐2: 2018‐2021. Geophysical
Research Letters, 2022; DOI: 10.1029/2021GL097448 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220310143725.htm

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