Expedition to Antarctica’s glaciers

by    DiveSSI    13th February 2017
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Detail of an iceberg near Pine (c) Jan Grobys
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Table iceberg near Pine Island (c) Jan Grobys
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Table iceberg and shelf ice near Pine Island (c) Jan Grobys
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Aerial picture of Pine Island Bay (c) Karsten Gohl

Research will improve forecasts for global sea levels

How has alternating warm and cold time periods affected the West
Antarctic Ice Sheet? What does this mean for present and future sea
levels? In a bid to find the answers to these questions, fifty
researchers from the Alfred Wegener Institute (AWI) are currently on
their way to the Amundsen Sea, having departed from Punta Arenas
(Chile) on February 6th.

Cracks in the Antarctic's Larsen Ice Shelf and Brunt Ice Shelf (where
the UK's Halley Research Station is located) are under observation. The
loss of ice mass is faster in the continent's Pacific sector than the
Atlantic sector.

The scientists, travelling on board the research
vessel Polarstern, are currently headed for the Pacific sector to
investigate changes in the ice sheet and how they have contributed to
sea-level changes in the past. In doing so, they hope to improve on the
forecast of future changes.

The sea level has risen by 19 centimetres between 1901 and 2010. By the
end of this century, the projections have indicated a rise of 26 to 82
centimetres; this amount is still contains some uncertainty though,
with the latest models showing a possible rise by an additional metre.
Such predictions are essential as they serve as the foundation for
adapting to and minimising climate change impact, for example, through
coastal protection measures.

Although present computer models can work out the relationship between
ice and the ocean, there is currently no such data for the West
Antarctic Ice Sheet.

“That’s exactly
why we want to explore how the ice sheet has advanced and retreated in
the past, including the spatial and chronological variability and the
rate,” said AWI's Dr Karsten Gohl, the expedition's chief scientist.

“Particularly in the Amundsen Sea
region, we’ve observed an unusually rapid retreat over the past few
decades, which many believe to be the first step in a complete collapse
of the West Antarctic Ice Sheet,” he added.

Located in the Pacific sector of the Antarctic, the Amundsen Sea is
situated where two big glaciers (Pine Island Glacier and Thwaites
Glacier) discharge into the ocean, transporting a huge mass of ice from
the West Antarctic Ice Sheet.

For the West Antarctic Ice Sheet, a
large portion of its base is on the continent below sea level. Today,
as the comparatively warm seawater circulates over the continental
shelf of the Amundsen Sea, tangible reactions are produced in both the
grounding zone of the continental ice and the floating ice shelf.  As
the ocean gets warmer, the ice shelf starts to melt from below and the
grounding zone moves farther inland.  This causes the glaciers to
retreat, resulting in a situation in which where there was once an ice
sheet hundreds of metres thick, there is now only open water covered by
a thin sheet of seasonal sea-ice.

For geoscientists, such changes in ice sheet movement allow them to use
sediment cores from the ice-free continental shelf to find out when in
Earth's history and to what extent the Amundsen Sea was covered with
ice or was ice-free.  They do this by examining the remains of
single-celled algae (foraminifera and diatoms) which sink to the
seafloor as sediment upon death.

For the first time, the seafloor drill rig MARUM-MeBo70
from University of Bremen’s Center for Marine Environmental Sciences
(MARUM) will be used in the Antarctic. It can drill sediment cores of
up to 70 metres long. Subsequent analysis of the cores, such as the
determination of the species and ages of the fossil algae, is expected
to yield information about past water temperatures and the history of
ice cover in the Amundsen Sea.

“We plan to collect samples from
epochs of the Earth’s history with similar climatic conditions to those
we expect to see in the next 100 to 200 years,” said Dr Gohl. As
such, one of the drill targets is the last interglacial before the
current one, which was about 125,000 years ago.

The Pliocene is also of
interest to the research team. Three to five million years ago, the
temperature was two to three degrees higher than it was just before the
Industrial Revolution, and the carbon dioxide concentration in the
atmosphere (at 400 parts per million) was roughly similar to what it is
today.

For more information see here.

Written by
DiveSSI
Date
13th February 2017
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