Bering Sea ice extent is at most reduced state in last 5,500 years


Date:
September 2, 2020
Source:
University of Alaska Fairbanks
Summary:
Through the analysis of vegetation from a Bering Sea island,
researchers have determined that the extent of sea ice in the
region is lower than it's been for thousands of years.



FULL STORY ========================================================================== Through the analysis of vegetation from a Bering Sea island, researchers
have determined that the extent of sea ice in the region is lower than
it's been for thousands of years.


==========================================================================
A newly published paper in the journal Science Advances describes how a
peat core from St. Matthew Island is providing a look back in time. By analyzing the chemical composition of the core, which includes plant
remains from 5,500 years ago to the present, scientists can estimate
how sea ice in the region has changed during that time period.

"It's a small island in the middle of the Bering Sea, and it's essentially
been recording what's happening in the ocean and atmosphere around
it," said lead author Miriam Jones, a research geologist with the
U.S. Geological Survey.

Jones worked as a faculty researcher at the University of Alaska Fairbanks
when the project began in 2012.

The ancient sea ice record comes in the form of changes in the
relative amounts of two isotopes of the element oxygen -- oxygen-16 and oxygen-18. The ratio of those two isotopes changes depending on patterns
in the atmosphere and ocean, reflecting the different signatures that precipitation has around the globe.

More oxygen-18 makes for an isotopically "heavier" precipitation, more
oxygen- 16 makes precipitation "lighter." By analyzing data from a
model that tracks atmospheric movement using the isotopic signature of precipitation, the authors found that heavier precipitation originated
from the North Pacific, while lighter precipitation originated from
the Arctic.

A "heavy" ratio signals a seasonal pattern that causes the amount of
sea ice to decrease. A "light" ratio indicates a season with more sea
ice. That connection has been confirmed though sea ice satellite data
collected since 1979, and to a smaller extent, through the presence of
some microorganisms in previous core samples.

UAF's Alaska Stable Isotope Facility analyzed isotope ratios throughout
the peat layers, providing a time stamp for ice conditions that existed
through the millennia.

After reviewing the isotopic history, researchers determined that modern
ice conditions are at remarkably low levels.

"What we've seen most recently is unprecedented in the last 5,500 years,"
said Matthew Wooller, director of the Alaska Stable Isotope Facility and
a contributor to the paper. "We haven't seen anything like this in terms
of sea ice in the Bering Sea." Jones said the long-term findings also
affirm that reductions in Bering Sea ice are due to more than recent
higher temperatures associated with global warming.

Atmospheric and ocean currents, which are also affected by climate change,
play a larger role in the presence of sea ice.

"There's a lot more going on than simply warming temperatures,"
Jones said.

"We're seeing a shift in circulation patterns both in the ocean and
the atmosphere."

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


========================================================================== Journal Reference:
1. Miriam C. Jones, Max Berkelhammer, Katherine J. Keller, Kei
Yoshimura and
Matthew J. Wooller. High sensitivity of Bering Sea winter sea
ice to winter insolation and carbon dioxide over the last 5500
years. Science Advances, 2020 DOI: 10.1126/sciadv.aaz9588 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200902152143.htm

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