May 22, 2022

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Evidence that an ice-free Arctic Ocean allowed old CO2 and methane emissions

Speleothems like these form more rapidly when the permafrost has thawed. Image: by James St John, via Wikimedia Commons

As the world warms, more greenhouse gases will enter the atmosphere. Now researchers think an ice-free Arctic Ocean explains how and why.

by Tim Radford, Climate news network, January 10, 2020

LONDON – At the bottom of a Siberian cave, Israeli, Russian and British scientists have identified evidence of periodic carbon losses by permafrost. And the unexpected link is not just with peak periods of global warming past, but with an ice-free Arctic Ocean.
The escape into the atmosphere of prodigious volumes of methane and carbon dioxide from thawing soils is not achieved with the average increase in planetary temperature, but with long periods in which the Arctic Ocean is free of ice every summer.

First fact: about a quarter of the land in the northern hemisphere is now, and has been for much of the last half a million years, permanently frozen and with it twice as much atmospheric carbon (in the form of peat and conserved vegetation) that exists freely in the planetary atmosphere.

Fact two: In recent decades, sea ice has shrunk and shrunk rapidly, and the polar ocean, by 2050, could be almost completely ice-free during the summer months.
“This finding about permafrost behavior suggests that the expected loss of Arctic sea ice will accelerate the melting of permafrost that is currently found in much of Siberia.”

And this turn in the history of a rapidly warming Arctic is preserved in stalagmite formations in a cave on the edge of the Siberian Arctic Circle.

The chronology of the development of stalagmites and stalactites can be established precisely by the pattern of uranium and lead isotope deposits in formations, accumulated imperceptibly by the constant dripping of water from lands very high above.
That is, speleothems, a general word of the geologist, for both stalactite and stalagmite, form more rapidly when the permafrost has thawed. And unexpectedly, thawing periods did not coincide with the peaks of interglacial warming over the past 1.35 million years. However, they coincided with periods when the Arctic was ice-free in the summer.

“This finding about the behavior of permafrost suggests that the expected loss of Arctic sea ice in the future will accelerate the melting of permafrost that is currently found in much of Siberia,” said Gideon Henderson of Oxford University, and a of the authors of a new study in the journal Nature.

The argument is this: if there is no sea ice, more heat and moisture is transmitted from the ocean to the atmosphere, with warmer air flowing over Siberia and therefore more autumn snowfall. A blanket of snow insulates the soil under the extreme cold of winter, so that soil temperatures rise, to disturb the permafrost and initiate a thaw that leads to accelerated decay of plants and increasing escape. of carbon dioxide and methane that would otherwise have been frozen. to permafrost.
Therefore, stalagmites survive as proof of these warmer soils and survive as a direct link with periods of ice-free ocean.

“If these processes continue during modern climate change, the future loss of Arctic sea ice in the summer will accelerate the thawing of Siberian permafrost,” the scientists say.

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