Siberian winters have been warmer for millennia

Climate information from permafrost fundamentals close significant data gaps

Eroded cliff of the Russian island of Muostakh, east of the port city of Tikisi. The picture gives an idea of ​​why in the early days of permafrost research it was suspected that there were no ice wedges but entire glaciers in the ground. © Thomas Opel, Alfred Wegener Institute
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Information from the bottom: For the first time, scientists have decoded climate data from millennia-old permafrost ice wedges in Siberia. Their conclusion: The winters have been getting warmer there for 7, 000 years. The course of the warming points to the reasons: Until industrialization, there are variations in solar radiation, but then the influence of humans is clearly visible, as the researchers report in the journal "Nature Geoscience".

Glaciers are sought in vain in the Russian Lena Delta: In the Siberian tundra, the ice does not form above ground on mountain slopes or on high plateaus, such as in Antarctica or Greenland. Instead, it arises in the underground: If the permanently frozen ground contracts in the great winter cold, cracks develop. Melting water flows from the surface into these cracks in spring - but the ground is still around minus ten degrees cold, and the water freezes again. "If this process then repeats in the following winters, over the decades and centuries, an ice body is created, which reminds of a huge wedge, " explains Hanno Meyer from the Alfred Wegener Institute (AWI) in Potsdam. "Ice wedges are a typical feature of the permafrost regions."

Ice wedges provide winter dates

Just as in the Antarctic glaciers, the ice wedges, which are up to 40 meters deep and six meters wide, contain information about the climate, some of which go back as far as 100, 000 years. "The meltwater comes from the snow of a winter, " explains climate researcher Thomas Opel from the AWI. "If it freezes in the frost column, information about the winter temperature in that year is included."

Scientists are taking ice samples on an ice wedge exposed to wind and sea on the eroding cliffs of the Russian permafrost island of Muostakh. Volkmar Kochan / rbb

An analysis of the different oxygen isotopes from a total of 42 ice samples from the Lena Delta gave the researchers an insight into how the climate in winter has developed over the past 7, 000 years in the Siberian permafrost regions. In the process, the ice wedges close a significant gap in the data: So far, fossil pollen, diatoms or tree rings from the Arctic have served as the basis for such climate constructions but above all they provide information about the summer. not the winter.

Warming in winter, cooling in summer

The new data are therefore the first clearly dated winter temperature data from the Siberian permafrost region - and they show a clear trend: "In the last 7, 000 years, winters in the Lena Delta have steadily worsened, " says first author Meyer. "A development that we know so far from hardly any other Arctic climate archive." In absolute terms, the scientists can not express the increase in temperature. An increasing ratio of oxygen isotopes alone indicates a relative warming. display

This temperature increase in winter confirms existing climate models, but so far has not been proven: "Most climate models show a long-term cooling in the summer and a long-term cooling in the Arctic for the past 7, 000 years Warming up in winter, "says co-author Thomas Laepple of the AWI. "For the latter, however, there were no temperature data, just because most climate archives mainly summer information store." The ice wedges contain the information that was missing in the climate models so far.

Causes: solar radiation and industrialization

The scientists found clear indications of the causes of the warming, because the created climate curve can be clearly divided into two sections: "Until the beginning of industrialization around the year 1850, we can shift the development towards a Changing Earth's position to the sun, "says Meyer. The duration and intensity of solar radiation have thus increased from winter to winter and warmer winters.

A 35-meter high wall of ice and frozen sediments on the island of Sobo Sise in the Lena Delta, Siberia. Thomas Opel, Alfred Wegener Institute

"However, with the onset of industrialization and increasing emissions of greenhouse gases like carbon dioxide, the greenhouse effect caused by mankind was added, " the climatologist continues. "Our data curve shows a significant increase from this point, which differs significantly from the previous long-term warming."

In a next step, the researchers now want to check whether the same signs of long-term winter warming of the Arctic can be found in other permafrost regions of the world. "We have data from an area 500 kilometers east of the Lena Delta that supports our findings, " said Opel. "We do not know what the Canadian Arctic looks like, for example. We suspect that the development is similar there, but we can not prove this assumption yet. "(Nature Geoscience, 2015; doi: 10.1038 / ngeo2349)

(Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research, 27.01.2015 - AKR)