https://scitechdaily.com/discovery-regarding-arctic-sea-ice-and-permafrost-has-significant-implications-for-the-future/
Discovery Regarding Arctic Sea Ice and Permafrost Has Significant
Implications for the Future
By University of Oxford January 19, 2020
Sea-Ice-Free Arctic Makes Permafrost Vulnerable to Thawing
Permafrost is ground that remains frozen throughout the year; it covers
nearly a quarter of Northern Hemisphere land. The frozen state of
permafrost enables it to store large amounts of carbon; about twice as
much as in the atmosphere. The rate and extent of future thawing of
permafrost, and consequent release of its carbon, is hard to predict
from modern observations alone.
However, a crucial past relationship between summer sea ice in the
Arctic and permafrost, discovered in this study, is now understood, with
significant implications for the future.
Professor Gideon Henderson, an author of the study based at the
Department of Earth Sciences, University of Oxford, said: ‘We were
surprised to find that times when permafrost melted in the past did not
simply match up with times when the Earth was at its warmest, but were
much more likely when the Arctic was free of ice in the summer. This
discovery about the past behavior of permafrost suggests that the
expected loss of Arctic sea ice in the future will accelerate melting of
the permafrost presently found across much of Siberia.’
Significant decreases of Arctic sea ice have been observed in recent
years, and the Arctic is expected to be free of summer sea ice in the
coming decades. Such loss of sea ice is likely to lead to an
acceleration of thawing of permafrost in Siberia and to the consequent
release of carbon.
The new research relies on challenging field work to discover and
explore Siberian caves. Caves are powerful recorders of periods when
permafrost was absent in the past. Stalagmites, stalactites and
flowstones can only form when there is liquid water, and therefore not
when overlying land is permanently frozen. The presence of stalagmites
in caves under present permafrost thus demonstrate periods when
permafrost was absent in the past.
Development of new approaches to date stalagmites using measurements of
natural uranium and lead, allow dating of the recovered stalagmites —
and therefore of periods of permafrost absence — for the last one and a
half million years. Stalagmites grew intermittently from 1,500,000 to
400,000 years ago, and have not grown for the last 400,000 years. The
timing of stalagmite formation, and therefore absence of permafrost, do
not relate simply to global temperatures in the past but are notably
more common when the Arctic Ocean was free of summer sea-ice.
This study shows that several processes may lead to the relationship
between Arctic sea-ice and permafrost. The absence of sea ice leads to
an increase in heat and moisture transfer from ocean to atmosphere and
therefore to warmer air transported far overland into Siberia. Moisture
transport also increases snow fall over Siberia during the autumn
months. This blanket of snow insulates the ground from the extreme cold
of winters leading to an increase in average annual ground temperatures,
destabilizing the permafrost. Consequently, in regions with increased
snow cover and insulation, permafrost will start to thaw, releasing
carbon dioxide that was trapped for millennia.
Reference: “Palaeoclimate evidence of vulnerable permafrost during times
of low sea ice” by A. Vaks, A. J. Mason, S. F. M. Breitenbach, A. M.
Kononov, A. V. Osinzev, M. Rosensaft, A. Borshevsky, O. S. Gutareva and
G. M. Henderson, 8 January 2020, Nature.
DOI: 10.1038/s41586-019-1880-1
The international team involved in the study consists of scientists from
the Geological Survey of Israel, The University of Oxford, UK,
Northumbria University, UK, The Institute of Earth’s Crust of the
Russian Academy of Sciences (Irkutsk, Russia), and the Speleoclub
Arabica (Irkutsk, Russia).
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