Ancient sea ice core sheds light on modern climate change

Date:
September 9, 2021
Source:
University of Birmingham
Summary:
A 170 m record of marine sediment cores extracted from Ade'lie
Land in Antarctica is yielding new insights into the complicated
relationship between sea ice and climate change.



FULL STORY ==========================================================================
A 170 m record of marine sediment cores extracted from Ade'lie Land in Antarctica by the Integrated Ocean Drilling Programme is yielding new
insights into the complicated relationship between sea ice and climate
change.


==========================================================================
In a new study published in Nature Geoscience,researchers at the
University of Birmingham, have collaborated in an international project
to identify how fluctuations in sea ice levels have interconnected with
both algae blooms and weather events linked to El Nino over the past
12,000 years.

They found that Antarctic winds strongly affect the break-out and
melting of sea ice, which in turn affects the levels of algae which
can grow rapidly in surface waters when sea ice is reduced. Changes in
the levels of algae growth in the waters surrounding the Antarctic are important enough to affect the global carbon cycle.

The researchers used techniques such as CT scan (computed tomography)
imaging and analysis of microfossils and organic biomarkers, to examine
the relationship between sea ice and large algae growth "bloom" events at annual timescales. The findings, produced in partnership with research institutes in New Zealand, Japan, France, Spain and the USA, span the
entire Holocene period and have yielded a highly detailed picture of
these relationships that can help predict future sea ice, climate and biological interactions.

The researchers found that algal bloom events occurred nearly every year
before 4,500 years ago. However, a baseline shift to less frequent algal
blooms and the type of algal production after 4.5 thousand years ago,
saw bloom events responding to the El Nino Southern Oscillation (ENSO)
and other climate cycles as sea-ice levels rapidly increased. Recent
work by many of the same team links the expansion of sea ice at this
time to glacial retreat and the development of the Ross Ice Shelf,
which acts to cool Antarctic surface waters to create a "sea-ice factory".

Dr James Bendle, of the University of Birmingham's School of Geography,
Earth and Environmental Science, is a co-author on the paper. He said:
"While there's a clear relationship between temperatures rising in the
Arctic over recent decades and sea ice melting, the picture is more
complex in the Antarctic.

That's because some areas of the Antarctic are warming, but in some areas
sea ice has been increasing. Since sea ice reflects incoming sunlight,
not only is the warming effect slowed down, but algae are unable to photosynthesize as easily. Climate models currently struggle to predict observed changes in sea ice for the Antarctic, and our findings will help climate researchers build more robust and detailed models." He added:
"The relationship we have observed with these changing conditions
and the ENSO wind fields is particularly significant. We know that El
Nino amplifies the effects of climate change in some regions, so any
insights linking this with Antarctic sea ice is fascinating and has implications for how future long-term loss of sea ice may affect food
webs in Antarctic waters, as well as carbon cycling processes within
this globally important region." Dr Katelyn Johnson, of GNS Science,
in New Zealand, is the lead author on the paper. She said: "While sea
ice that persists from year to year can prevent these large algal blooms
from occurring, sea ice that breaks out and melts creates a favourable environment for these algae to grow. These large algae `bloom events'
occur around the continent, form the base of the food webs and act as
a carbon sink".

"Unlike the Arctic where rising temperatures have led to reduced sea ice,
the relationship in the Antarctic is less clear, as is the subsequent
impact on primary productivity. Our new record provides a longer-term view
of how sea ice and climate modes like ENSO impact the frequency of these
bloom events, allowing climate modellers to build more robust models." ========================================================================== Story Source: Materials provided by University_of_Birmingham. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Katelyn M. Johnson, Robert M. McKay, Johan Etourneau, Francisco J.

Jime'nez-Espejo, Anya Albot, Christina R. Riesselman, Nancy A. N.

Bertler, Huw J. Horgan, Xavier Crosta, James Bendle, Kate
E. Ashley, Masako Yamane, Yusuke Yokoyama, Stephen F. Pekar,
Carlota Escutia, Robert B. Dunbar. Sensitivity of Holocene East
Antarctic productivity to subdecadal variability set by sea
ice. Nature Geoscience, 2021; DOI: 10.1038/s41561-021-00816-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210909124226.htm

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