[Vision2020] Sudden onset of ice loss in Antarctica so large it affects Earth's gravity field

[Ted Moffett]

http://www.sciencedaily.com/releases/2015/05/150521143926.htm

May 21, 2015

A group of scientists, led by a team from the University of Bristol, UK has
observed a sudden increase of ice loss in a previously stable region of
Antarctica. The research is published today in *Science*.

Using measurements of the elevation of the Antarctic ice sheet made by a
suite of satellites, the researchers found that the Southern Antarctic
Peninsula showed no signs of change up to 2009. Around 2009, multiple
glaciers along a vast coastal expanse, measuring some 750km in length,
suddenly started to shed ice into the ocean at a nearly constant rate of 60
cubic km, or about 55 trillion litres of water, each year.

This makes the region the second largest contributor to sea level rise in
Antarctica and the ice loss shows no sign of waning.

Dr Bert Wouters, a Marie Curie Fellow at the University of Bristol, who
lead the study said: "To date, the glaciers added roughly 300 cubic km of
water to the ocean. That's the equivalent of the volume of nearly 350,000
Empire State Buildings combined."

The changes were observed using the CryoSat-2 satellite, a mission of the
European Space Agency dedicated to remote-sensing of ice. From an altitude
of about 700km, the satellite sends a radar pulse to Earth, which is
reflected by the ice and subsequently received back at the satellite. From
the time the pulse takes to travel, the elevation of the ice surface can
retrieved with incredible accuracy. By analysing roughly 5 years of the
data, the researchers found that the ice surface of some of the glaciers is
currently going down by as much as 4m each year.

The ice loss in the region is so large that it causes small changes in the
gravity field of the Earth, which can be detected by another satellite
mission, the Gravity Recovery and Climate Experiment (GRACE).

"The fact that so many glaciers in such a large region suddenly started to
lose ice came as a surprise to us," continued Dr Wouters. "It shows a very
fast response of the ice sheet: in just a few years the dynamic regime
completely shifted."

Data from an Antarctic climate model shows that the sudden change cannot be
explained by changes in snowfall or air temperature. Instead, the team
attributes the rapid ice loss to warming oceans.

Many of the glaciers in the region feed into ice shelves that float on the
surface of the ocean. They act as a buttress to the ice resting on bedrock
inland, slowing down the flow of the glaciers into the ocean. The westerly
winds that encircle Antarctica have become more vigorous in recent decades,
in response to climate warming and ozone depletion. The stronger winds push
warm waters from the Southern Ocean poleward, where they eat away at the
glaciers and floating ice shelves from below.

Ice shelves in the region have lost almost one-fifth of their thickness in
the last two decades, thereby reducing the resisting force on the glaciers.
A key concern is that much of the ice of the Southern Antarctic Peninsula
is grounded on bedrock below sea level, which gets deeper inland. This
means that even if the glaciers retreat, the warm water will chase them
inland and melt them even more.

Dr Wouters said: "It appears that sometime around 2009, the ice shelf
thinning and the subsurface melting of the glaciers passed a critical
threshold which triggered the sudden ice loss. However, compared to other
regions in Antarctica, the Southern Peninsula is rather understudied,
exactly because it did not show any changes in the past, ironically.

"To pinpoint the cause of the changes, more data need to be collected. A
detailed knowledge of the geometry of the local ice shelves, the ocean
floor topography, ice sheet thickness and glacier flow speeds are crucial
to tell how much longer the thinning will continue."
------------------------------

*Story Source:*

The above story is based on materials
<http://www.bristol.ac.uk/news/2015/may/ice-loss-in-antarctica.html>
provided by *University of Bristol* <http://www.bristol.ac.uk/>. *Note:
Materials may be edited for content and length.*
------------------------------

*Journal Reference*:

   1. B. Wouters, A. Martin-Español, V. Helm, T. Flament, J. M. Van Wessem,
   S. R. M. Ligtenberg, M. R. Van Den Broeke, J. L. Bamber. *Dynamic
   thinning of glaciers on the Southern Antarctic Peninsula*. *Science*,
   2015 DOI: 10.1126/science.aaa5727
   <http://dx.doi.org/10.1126/science.aaa5727>

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Vision2020 Post: Ted Moffett
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