Research sheds new light on the role of sea ice in controlling
atmospheric carbon levels

Date:
June 22, 2020
Source:
University of Exeter
Summary:
A new study has highlighted the crucial role that sea ice across
the Southern Ocean played in controlling atmospheric carbon dioxide
levels during times of past climate change, and could provide a
critical resource for developing future climate change models.



FULL STORY ==========================================================================
A new study has highlighted the crucial role that sea ice across the
Southern Ocean played in controlling atmospheric carbon dioxide levels
during times of past climate change, and could provide a critical resource
for developing future climate change models.


==========================================================================
For the study an international team of researchers, led by Keele
University and including experts from the University of Exeter,
demonstrated that seasonal growth and destruction of sea ice in a warming
world enhances the amount of marine life present in the sea around
Antarctica, which draws down carbon from the atmosphere and stores it
in the deep ocean.

Having captured half of all human-related carbon that has entered
the ocean to date, the Southern Ocean around Antarctica is crucial
for regulating carbon dioxide levels resulting from human activity,
so understanding the processes that determine its effectiveness as a
carbon sink through time are crucial to reducing uncertainty in future
climate change models.

To understand this process further, the researchers studied data relating
to one period where atmospheric CO2 levels changed rapidly.

This occurred after the Last Ice Age, around 18,000 years ago, when the
world transitioned naturally into the warm interglacial world we live
in today.

During this period, CO2 rose rapidly from around 190 parts per million
(ppm) to 280 ppm over around 7,000 years, but one period in particular
stands out; a 1,900 year period where CO2 levels plateaued at a nearly
constant level of 240 ppm.



==========================================================================
The cause of this plateau, which occurred around 14,600 years ago, is
unknown, but understanding what happened during this period could be
crucial for improving climate change projections.

Professor John Love, from Exeter's Biosciences department and co-author
of the study said: "My research group and I are very excited about being
part of this important investigation. We developed new techniques in cell biology to find, collect and analyse the rare and very tiny particles
and cells that had been frozen in the ice for millennia.

"Like flies in amber, these minute fragments give us a unique window into
past events, enabling our colleagues in the Earth, Atmosphere and Ocean sciences to develop a better understanding of climate change then, and
now." Lead author Professor Chris Fogwill, Director of Keele University's Institute for Sustainable Futures said: "The cause of this long plateau
in global atmospheric CO2 levels may be fundamental to understanding the potential of the Southern Ocean to moderate atmospheric CO2." To resolve
this question, researchers travelled to the Patriot Hills Blue Ice Area
of Antarctica to develop new records of evidence of marine life that
are captured in ice cores, with support from Antarctic Logistics and Expeditions (ALE).



==========================================================================
Blue ice areas are the perfect laboratory for Antarctic scientists due
to their unique topography. Created by fierce, high-density katabatic
winds, the top layer of snow is effectively eroded, exposing the ice
below. As a result, ice flows up to the surface, providing access to
ancient ice below.

Professor Chris Turney, a visiting Fellow at Keele's Institute for
Liberal Arts and Sciences from UNSW Sydney said: "Instead of drilling kilometres into the ice, we can simply walk across a blue ice area and
travel back through time.

"This provides the opportunity to sample large amounts of ice for
studying past environmental changes in detail. Organic biomarkers and
DNA from the Southern Ocean are blown onto Antarctica and preserved
in the ice, providing a unique record in a region where we have few
scientific observations." Using this approach the team discovered
that there was a marked increase in the number and diversity of marine organisms present across the 1,900 year period when the CO2 plateaued,
an observation which had never been recorded before.

This provides the first recorded evidence of increased biological
productivity and suggests that processes in the high latitude Southern
Ocean may have caused the CO2 plateau. However, the driver of this marked change remained unknown, and the researchers used climate modelling to
better understand the changes in the Southern Ocean to understand the
potential cause.

This modelling revealed that the plateau period coincided with the
greatest seasonal changes in sea ice during a pronounced cold phase
across the Southern Ocean known as the Antarctic Cold Reversal. During
this period, sea ice grew extensively across the Southern Ocean, but as
the world was warming rapidly, each year the sea ice would be rapidly
destroyed during the summer.

The researchers will now use these findings to underpin the development
of future climate change models. The inclusion of sea ice processes that control climate-carbon feedbacks in a new generation of models will be
crucial for reducing uncertainties surrounding climate projections and
will help society adapt to future warming.


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


========================================================================== Journal Reference:
1. C. J. Fogwill, C. S. M. Turney, L. Menviel, A. Baker, M. E. Weber,
B.

Ellis, Z. A. Thomas, N. R. Golledge, D. Etheridge, M. Rubino, D. P.

Thornton, T. D. van Ommen, A. D. Moy, M. A. J. Curran, S. Davies,
M. I.

Bird, N. C. Munksgaard, C. M. Rootes, H. Millman, J. Vohra,
A. Rivera, A.

Mackintosh, J. Pike, I. R. Hall, E. A. Bagshaw, E. Rainsley,
C. Bronk- Ramsey, M. Montenari, A. G. Cage, M. R. P. Harris,
R. Jones, A. Power, J.

Love, J. Young, L. S. Weyrich, A. Cooper. Southern Ocean carbon sink
enhanced by sea-ice feedbacks at the Antarctic Cold Reversal. Nature
Geoscience, 2020; DOI: 10.1038/s41561-020-0587-0 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200622133008.htm

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