The formation of the West Antarctic Ice Sheet was very different than previously believed
AWI experts confirm the delayed spread of the ice sheet 35 million years
ago

Date:
February 21, 2022
Source:
Alfred Wegener Institute, Helmholtz Centre for Polar and Marine
Research
Summary:
Roughly 35 million years ago, Earth cooled rapidly. At roughly
the same time, the Drake Passage formed between South America
and the Antarctic, paving the way for the Antarctic Circumpolar
Current. Thanks to these two factors, Antarctica was soon completely
covered in ice. This massive glaciation was delayed in at least
one region.



FULL STORY ========================================================================== Roughly 35 million years ago, Earth cooled rapidly. At roughly the same
time, the Drake Passage formed between South America and the Antarctic,
paving the way for the Antarctic Circumpolar Current. Thanks to these
two factors, Antarctica was soon completely covered in ice. As a study
from the Alfred Wegener Institute now shows, this massive glaciation was delayed in at least one region. This new piece of the puzzle concerning
the early history of the West Antarctic Ice Sheet could help to predict
its unstable future. The study was just released in the Nature journal Communications Earth & Environment.


==========================================================================
For climate researchers, the West Antarctic has been in the spotlight
for years. Here, the West Antarctic Ice Sheet lying atop the continent stretches to the adjacent Amundsen Sea. Near the coast, the ice is
still in direct contact with the soil; farther toward the open sea,
it floats. Because climate change progressively warms the seawater, the
latter is increasingly eroding the ice shelf from below. The grounding
line -the last point at which the ice still rests on the ground -moves
farther and farther inland. Due to meltwater and calving icebergs, the
Thwaites Glacier, which flows into the Amundsen Sea, now loses twice
as much ice as 30 years ago. If the West Antarctic Ice Sheet were to
collapse entirely, global sea levels would rise by more than three metres.

"The stability of the West Antarctic Ice Sheet is critical to the future development of the global sea level," says the study's first author,
Gabriele Uenzelmann-Neben from the Alfred Wegener Institute, Helmholtz
Centre for Polar and Marine Research (AWI). "Accordingly, researchers
around the world are working to predict the future behaviour of the ice
in a warmer world using numerical simulation. The more we know about
the history of the West Antarctic Ice Sheet, the more accurate we can
make these models. Its more recent history is well-documented, but we
still know very little about its earlier years - - particularly the
formation phase. Our study delivers an important piece of the puzzle."
In the course of two research cruises on board the Polarstern, the
Geophysicist and her team investigated sediments in the vicinity of Pine
Island Trough, a channel-like furrow in the seafloor of the shallow
part of the Amundsen Sea that stretches from north to south and leads
directly toward the western coast of Antarctica. To collect data, the
AWI team relied on the tried and proven reflection seismology method:
the Polarstern towed a 3,000-metre-long measuring cable -- or streamer
-- behind her. The streamer is equipped with hydrophones that utilise
a total of 240 measuring channels. During survey cruises, an airgun is
used to produce seismic pulses behind the ship. These pulses penetrate
the seafloor and are reflected back at geological boundaries -- e.g.

between the sediment and hard rock -- which is recorded by the streamer's hydrophones. Based on the different travel times for the waves and the respective positions of the individual channels, the internal structure
of the seafloor can be mapped.

The measurement data revealed a large sediment body, a sediment drift,
on the eastern flank of Pine Island Trough, one with no counterpart on
its western side. "Because of the Coriolis effect produced by Earth's
rotation, this asymmetrical deposition of a sediment drift on the trough's eastern side but not the western one can only have been produced by a deep-water current that flowed toward the coast from north to south,"
says Uenzelmann-Neben. "In order for that to occur, the ocean circulation
at the time of the deposition had to be similar to today's conditions,
that is, the prevailing westerlies and the Antarctic Circumpolar Current
had to have been located far to the south. And similar to today, the
deep water upwelled through the trough must have been comparatively
warm." Additional study of pollen from sediment cores gathered near
the trough indicate that the base of the sediment drift was formed
roughly 34 to 36 million years ago. At precisely the same time --
the Eocene-Oligocene boundary -- temperatures plummeted around the
globe, and the Antarctic continent became covered in ice. "Our study
offers compelling evidence that at the time of the great glaciation,
warmer deep water upwelled near the Amundsen Sea shelf and delayed the
West Antarctic Ice Sheet's expansion to the sea," the AWI Geophysicist explains. "This important and unexpected finding emphasises the tremendous importance that ocean currents had even during the formation phase of
the West Antarctic Ice Sheet and continue to have today. Armed with
this additional knowledge concerning the ice sheet's earliest phase,
forecasts on its future stability and ice retreat can now be improved." ========================================================================== Story Source: Materials provided by Alfred_Wegener_Institute,_Helmholtz_Centre_for_Polar_and
Marine_Research. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Gabriele Uenzelmann-Neben, Karsten Gohl, Katharina Hochmuth, Ulrich
Salzmann, Robert D. Larter, Claus-Dieter Hillenbrand, Johann
P. Klages, V. Afanasyeva, J. E. Arndt, T. Bickert, S. M. Bohaty,
R. Dziadek, B.

Ebermann, W. Ehrmann, O. Esper, T. Frederichs, T. Freudenthal, C.

Gebhardt, K. Ku"ssner, G. Kuhn, Y. Najman, H. Pa"like, F. Riefstahl,
T.

Ronge, M. Scheinert, P. Simoes Pereira, J. A. Smith, C. Spiegel,
T. Van de Flierdt, M. Zundel. Deep water inflow slowed offshore
expansion of the West Antarctic Ice Sheet at the Eocene-Oligocene
transition.

Communications Earth & Environment, 2022; 3 (1) DOI:
10.1038/s43247-022- 00369-x ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220221085738.htm

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