Climate history in the ice

Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research

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Researchers from 14 institutions in ten European countries searched the Antarctic ice for three years for a place to study the climate history of the last 1.5 million years. The consortium Beyond EPICA Oldest Ice (BE-OI) under the leadership of Olaf Eisen from the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI) in Bremerhaven recently reported the results presented at a conference of the "European Geosciences Union" in Vienna.

The researchers selected one of the coldest, driest and lifeless places on Earth: "Little Dome C" is located three hours of snowmobile ride (30 kilometers) from the Antarctic station Dome Concordia, which operates France and Italy on the ice of Wilkes-Land at an altitude of 3233 meters above sea level. The researchers hardly ever observe precipitation there, and the average annual temperature is minus 54.5 degrees Celsius. Higher than minus 25 degrees it is very rare there and in winter the temperatures sometimes fall below minus 80 degrees.

900, 000 year old ice cream

Where the Concordia Station stands today, researchers drilled 3270 meters into the Antarctic ice between 1996 and December 2004 as part of the European EPICA (European Project for Ice Coring in Antarctica) project. With precise analyzes of the cores obtained in this way, researchers were able to reliably reconstruct the climate history of the past 800, 000 years. "During this time, long periods of cold alternated with shorter warm periods at a rate of about a hundred thousand years, " explains AWI researcher and BE-OI project coordinator Olaf Eisen.

As this ice also contains tiny bubbles that still contain air from the time the ice formed, the climate researchers can measure the content of the important greenhouse gases carbon dioxide and methane. And they find clear connections: If the climate on Earth was cold, there was much less carbon dioxide and less methane in the air than in warmer epochs.

From the centuries before that time, however, the researchers have so far no ice cores in whose air bubbles they could measure the then content of greenhouse gases. Especially in this epoch, however, the rhythm has changed dramatically, alternating between cold periods and warmer periods: "More than 1.2 million years ago, such a cycle lasted only about 40, 000 years, triggered by regular changes in the inclination of the Earth's axis. This was followed by a 300, 000-year transitional period, before the hundred-thousand-year rhythm began around 900, 000 years ago, "explains Olaf Eisen. display

Time window into the climate history

Climate researchers know this development from investigations of the sediments that have accumulated on the ocean floor during these times. Such analyzes provide clues to the temperatures of the time and to the masses of ice sheets that were lying over Antarctica, Greenland and, at times, North America and northern Europe. Data on the greenhouse gases Carbon dioxide and methane and their correlations with the development of the climate, the researchers, however, receive only from the air bubbles that were trapped in the ice during this time.

"There are therefore very good reasons to drill after the 800, 000-year-old EPICA samples into ice at least 1.5 million years old, " explains Olaf Eisen. This would enable the researchers not only to study the climatic context of the "mid-Pleistocene transitional period" but also the 40, 000-year rhythm before it. As the molecules contained in the ice diffuse a little over millennia, smearing the analyzes, the researchers are looking for ice with a higher resolution, in which ten thousand years of climate history are embedded in a drill core at least one meter long Role play.

Search for the oldest ice cream on earth

In the past three years researchers from ten European countries, supported by colleagues from the US, Australia, Japan and Russia, in the Antarctic in the BE-OI project, therefore, were searching for ice that meets these criteria. On flights across the Antarctic, they used radar beams to analyze the subsurface layers of ice, which they also examined directly with up to 400-meter-deep test wells. From these results, the researchers concluded on the conditions in deeper and thus older layers.

Here, the "Little Dome C" emerged as the best candidate for at least 1.5 million years old ice out, which still has a good resolution in its oldest areas and that under the huge pressure of the overlying masses also does not melt at its base. If the European Union gives the green light for the second phase of BE-OI, as hoped, the researchers will be coordinated by Carlo Barbante of the University of Venice on the "Little Dome C" build a field camp in which containers will live in fairly simple conditions during drilling.

Bore from 2021

Probably in mid-November 2021 can then start a hole, are obtained with the ten-centimeter thick ice cores. In three Antarctic summer, this hole will then be continued from mid-November to early February, reaching a depth of 2730 meters by 2024, when the ice should be at least 1.5 million years old. By 2025, the first data from the drill core analyzes should be available, from which the international research team will then determine the relationships between greenhouse gases and the climate in the mid-Pleistocene transitional period and the previous ones want to examine the past epochs.

BE-OI is the European contribution to the worldwide search for the right place for an ice drilling. The consortium will undertake the preliminary studies for the site selection around Dome C and Dome Fuji, both potentially suitable regions in the eastern Antarctic. Other science consortia are exploring other locations within IPICS (International Partnerships in Ice Core Sciences). This project is funded by the European Union in the Horizon 2020 Research and Innovation Program under the number 730258.

Source: Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research

- Nadja Podbregar