Canada has found traces of mass permafrost thaw dating back 400,000 years

Scientists found no evidence that it had any effect on the amount of greenhouse gases in the Earth’s atmosphere

Climatologists have found that about 400 thousand years ago, during the ice age, the area of permafrost in what is now Canada and the northern United States has decreased sharply. An article describing their study was published by the scientific journal Science Advances.

“On the one hand, our observations and similar measurements in Siberia show that the climate of the entire Arctic around 400,000 years ago became more stable. On the other hand, we have not found evidence that in earlier eras due to melting permafrost there were sharp spikes in the concentration of greenhouse gases,” the researchers write.

Scientists suggest that due to the rapid warming of the Arctic as a result of global climate change, the area of permafrost will sharply decrease. According to some estimates, by the end of the XXI century may disappear about a third of the permafrost in southern Siberia and Alaska. As a result, huge amounts of methane and carbon dioxide could enter the atmosphere.

Studying calcite and similar rocks on the walls of several caves in the northern United States and Canada, climate scientists led by Boston College associate professor Jeremy Shakun discovered and studied the effects of such mass permafrost melting. It happened relatively recently by geological standards, about 400,000 years ago.

The stalactites, stalagmites and other calcite deposits in these caves are about 1.5 million years old. Their chemical and isotopic composition can show under what weather conditions and temperature they were formed.

By measuring the proportion of uranium and thorium isotopes in these sediments, climatologists discovered that about 400,000 years ago there was no permafrost in almost all of what is now Canada and Alaska outside the Arctic Circle. A similar warming had occurred earlier.

Around the same time and in a similar way, the climate of Siberia was changing. That is, the permafrost was unstable for most of the Pleistocene. However, its melting, for reasons that are still unclear, had no effect on the Earth’s climate and the concentration of greenhouse gases in its atmosphere.

Scientists believe that a possible reason could be that the periodic disappearance of permafrost has prevented organics from accumulating in large quantities. However, climatologists do not rule out that methane and carbon dioxide, which were formed during the decomposition of plant and animal remains, could have been absorbed by someone or something.

Researchers hope that further study of the climate of the Ice Age will help find an explanation for this anomaly, and to understand why the Arctic climate stabilized sharply 400 thousand years ago. This is critical to accurate estimates of how permafrost melting will affect the planet’s climate in the current century and in subsequent historical periods, the researchers summarized.

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