3000+ billion tons of ice lost from Antarctic Ice Sheet over 25 years


Date:
March 21, 2023
Source:
University of Leeds
Summary:
Scientists have calculated that the fastest changing Antarctic
region?- ?the Amundsen Sea Embayment?-?has lost more than 3,000
billion tonnes of ice over a 25-year?period.??

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FULL STORY ========================================================================== Scientists have calculated that the fastest changing Antarctic
region -  the Amundsen Sea Embayment - has
lost more than 3,000 billion tonnes of ice over a 25-year period.  

==========================================================================
If all the lost ice was piled on London, it would stand over 2 km tall - or 7.4 times the height of the Shard. If it
were to cover Manhattan, it would stand at 61 km - or 137 Empire
State Buildings placed on top of one another.  Twenty major glaciers form the Amundsen Sea Embayment in West Antarctica, which
is more than four times the size of the UK, and they play a key
role in contributing to the level of the world's oceans.    So much water is held in the snow and ice, that if it were to
all to drain into the sea, global sea levels could increase by more
than one metre.   The research, led by Dr Benjamin
Davison at the University of Leeds, calculated the "mass balance"
of the Amundsen Sea Embayment. This describes the balance between mass
of snow and ice gain due to snowfall and mass lost through calving,
where icebergs form at the end of a glacier and drift out to sea.

When calving happens faster than the ice is replaced by snowfall, then
the Embayment loses mass overall and contributes to global sea level rise.

Similarly, when snowfall supply drops, the Embayment can lose mass
overall and contribute to sea level rise.

The results show that West Antarctica saw a net decline of 3,331
billion tonnes of ice between 1996 and 2021, contributing over nine millimetres to global sea levels.  Changes in
ocean temperature and currents are thought to have been the most important factors driving the loss of ice.  Dr Davison, a Research
Fellow at the Institute for Climate and Atmospheric Science at Leeds,
said: "The 20 glaciers in West Antarctica have lost an awful lot of ice over the last quarter of a century and there
is no sign that the process is going to reverse anytime soon although
there were periods where the rate of mass loss did ease slightly.  "Scientists are monitoring what is happening in the Amundsen
Sea Embayment because of the crucial role it plays in
sea-level rise.

If ocean levels were to rise significantly in future years, there are communities around the world who would experience extreme flooding."  The research has been published in the scientific
journal Nature Communications.

Extreme snowfall events Using climate models that show how
air currents move around the world, the scientists identified that
the Amundsen Sea Embayment had experienced several extreme
snowfall events over the 25-year study period.  These
would have resulted in periods of heavy snowfall and periods of very little snowfall or a "snow drought."   The researchers
factored these extreme events into their calculations.

Surprisingly, they found that these events contributed up
to half of the ice change at certain times, and therefore played a
key role in the contribution the Amundsen Sea Embayment was making to sea level rise during certain time periods.  
For example, between 2009 and 2013, the models revealed a period
of a persistant snow drought. The lack of snowfall starved the ice
sheet and caused it to lose ice, therefore contributing about 25%
more to sea level rise than in years of average snowfall. 
In contrast, during the winters of 2019 and 2020 there
was very heavy snowfall. The scientists estimated that
this heavy snowfall mitigated the sea level contribution from the
Amundsen Sea Embayment, reducing it to about half of what it would have
been in an average year.   Dr Davison said:
"Changes in ocean temperature and circulation appear to be driving
the long-term, large-scale changes in West Antarctica ice sheet mass.  We absolutely need to research those more because
they are likely to control the overall sea level contribution from
West Antarctica.   "However, we were really surprised to
see just how much periods of extremely low or high snowfall could
affect the ice sheet over two to five-year periods - - so much so
that we think they could play an important, albeit secondary role, in controlling rates of West Antarctic ice loss."  Dr Pierre Dutrieux,
a scientist at the British Antarctic Survey and co-author of the study, added: "Ocean temperature changes and glacial dynamics appear
strongly connected in this part of the world, but this work highlights
the large variability and unexpected processes by which snowfall also
plays a direct role in modulating glacier mass." New glacier named The
ice loss from the region over the past 25 years has seen
the retreat of the Pine Island Glacier,  also known as PIG.

As it retreated, one of its tributary glaciers became
detached from the main glacier and rapidly accelerated. As a result, the tributary glacier has now been named
by the UK Antarctic Place-names Committee, Piglet Glacier, so
that it can be unambiguously located and identified by
future studies.   Dr Anna Hogg, one of the authors
of the paper and Associate Professor at the Institute of Climate
and Atmospheric Science at Leeds, said: "As well as shedding
new light on the role of extreme snowfall variability on ice sheet
mass changes, this research also provides new estimates of
how quickly this important region of Antarctica is contributing to
sea level rise.   "Satellite observations have showed that the newly named Piglet Glacier accelerated its ice speed by
40%, as the larger PIG retreated to its smallest extent since
records began."   Satellites such as the Copernicus Sentinel-1 satellite, which uses sensors that 'see'
through cloud even during the long Polar night, have transformed our
ability to monitor remote regions. It is essential to have frequent measurements of change in ice speed and iceberg calving,
so that we can monitor the incredibly rapid change taking place
in Antarctica. 
* RELATED_TOPICS
o Earth_&_Climate
# Global_Warming # Snow_and_Avalanches # Climate #
Ice_Ages
o Fossils_&_Ruins
# Early_Climate # Ancient_DNA # Evolution # Fossils
* RELATED_TERMS
o Ice_sheet o Paleoclimatology o Ice_age o Greenland_ice_sheet
o Larsen_Ice_Shelf o Antarctic_krill o Antarctic_ice_sheet
o Sea_level

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


========================================================================== Journal Reference:
1. Benjamin J. Davison, Anna E. Hogg, Richard Rigby, Sanne Veldhuijsen,
Jan
Melchior van Wessem, Michiel R. van den Broeke, Paul R. Holland,
Heather L. Selley, Pierre Dutrieux. Sea level rise from
West Antarctic mass loss significantly modified by large
snowfall anomalies. Nature Communications, 2023; 14 (1) DOI:
10.1038/s41467-023-36990-3 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/03/230321112644.htm

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