Ground beneath Thwaites Glacier mapped

Date:
May 31, 2023
Source:
British Antarctic Survey
Summary:
The ground beneath Antarctica's most vulnerable glacier has
now been mapped, helping scientists to better understand how
it is being affected by climate change. Analysis of the geology
below the Thwaites Glacier in West Antarctica shows there is less
sedimentary rock than expected -- a finding that could affect how
the ice slides and melts in the coming decades.


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FULL STORY ==========================================================================
The ground beneath Antarctica's most vulnerable glacier has been mapped
for the first time, helping scientists to better understand how it is
being affected by climate change. Analysis of the geology below the
Thwaites Glacier in West Antarctica shows there is less sedimentary
rock than expected -- a finding that could affect how the ice slides
and melts in the coming decades.

"Sediments allow faster flow, like sliding on mud," says Dr Tom Jordan,
a geophysicist with the British Antarctic Survey (BAS), who led the
study. "Now we have a map of where the slippery sediments are, we can
better predict how the glacier will behave in future as it retreats."
The distribution of sedimentary rocks beneath the Thwaites glacier is
included in a new map of the geology of the region produced by the BAS researchers and published in the journal Science Advances. The findings
are important because the glacier, which is the size of Great Britain
or the US state of Florida, is one of the fastest changing ice-ocean
systems in Antarctica.

The Thwaites glacier's grounding zone -- the point where it meets the
seafloor -- has retreated 14 km since the late 1990s. Much of the ice
sheet is below sea level and susceptible to rapid, irreversible ice loss
that could raise global sea-level by over half a metre within centuries.

The new analysis is based on airborne surveys using aircraft equipped
with radar which can see through the ice to the rocks below, as well
as sensors which can map minute variations in gravity and magnetism
hundreds to thousands of metres below the ground and seabed on which
the glacier rests.

The researchers then use these multiple data sources to compile a 3D
picture of features, including the type and extent of different rocks.

Jordan says: "The integrated nature of the airborne surveys was one of the
keys to this research. Each sensor on the aircraft provided an important
but incomplete part of the picture, but by bringing them all together we
could provide the detailed map of the underlying geology." In doing so,
the study effectively turns back the geological clock to examine what
happened when New Zealand was ripped away from Antarctica about 100
million years ago -- long before the Thwaites glacier was formed.

Because the base of Thwaites Glacier lies far below sea level, researchers
had expected that thick sediments would have been deposited there over the subsequent millions of years Similar analysis has been done on some other Antarctic glaciers, showing that these other systems were predominantly underlain by thick sediments.

But the aircraft data suggests that only about a fifth of the ground
below the glacier is sedimentary rock. These lie in a series of basins
between 80 and 200 km long and about 30 km wide.

The rest is made up of other types of geological bodies, including granite peaks and other hard rocks. The scientists think that these sedimentary
basins were once much larger, but they have been ground down to the
bedrock by movement of the glacier.

It's not yet clear how this new knowledge of the subglacial geology
will affect estimates of ice flow and loss from Thwaites and other
glaciers. The study does show that the geological landscape has a direct control on the basal shear stress, which influences how fast ice can
flow into the ocean. Members of the research team will now carry out
more detailed studies of these processes.

Modellers may also be able to use the new data to make more reliable projections of future ice loss.

Jordan says: "We hope that by showing the detailed geology, and how it correlates with the basal friction, future models of glacial retreat
will have lower uncertainty, as the controls of the basal processes
will be better understood." He adds: "No single scientific study
could ever match she scale and challenge of climate change. But it
is the incremental building of all the individual scientific studies
like this that allows us to understand and tackle that challenge."
Glaciologist Dr Sarah Thompson, co-author on the paper, said: "The
integrated approach used in this study has significant potential for
successful application elsewhere in Antarctica, enabling us to explore
other potentially vulnerable regions where current knowledge is sparse."
* RELATED_TOPICS
o Earth_&_Climate
# Global_Warming # Snow_and_Avalanches # Ice_Ages
# Oceanography # Climate # Geography # Geology #
Environmental_Awareness
* RELATED_TERMS
o Ice_shelf o Glacier o Paleoclimatology o Antarctic_ice_sheet
o Temperature_record_of_the_past_1000_years o Antarctica o
Metamorphic_rock o Global_warming

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


========================================================================== Journal Reference:
1. Tom A. Jordan, Sarah Thompson, Bernd Kulessa, Fausto Ferraccioli.

Geological sketch map and implications for ice flow of Thwaites
Glacier, West Antarctica, from integrated aerogeophysical
observations. Science Advances, 2023; 9 (22) DOI:
10.1126/sciadv.adf2639 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/05/230531145123.htm

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