Antarctic: solved puzzles about "hole in the ice"

Researchers explain the phenomenon of Weddell Polynya in 1974

The Great Weddell Polynya in the years 1974 to 1976. © Gordon and Comiso / Lamont-Doherty Earth Observatory
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Antarctic satellite data showed an enigmatic, massive hole in the winter ice of the Weddell Sea in 1974. But why it had come to this so-called Weddell Polynya, remained unclear for a long time. Before an expedition could set off to make direct measurements on site, the ice closed again. Now scientists have finally found an explanation for the phenomenon.

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Polynya is a Russian word that roughly means "hole in the ice". For the scientists, the discovery of the Weddell Polynya in 1974 was a sensation, because the open space stretched over 250, 000 square kilometers, roughly the area of ​​all western federal states together. But what made the hole? What conditions favored his continued existence until 1976? This was a mystery for thirty-three years. A German-American research team, including an oceanographer from the Leibniz Institute for Marine Sciences (IFM-GEOMAR) in Kiel, has published new findings on the causes of Weddell Polynya in the current issue of the journal Journal of Climate.

The study shows for the first time a correlation between decadal climatic fluctuations in the southern hemisphere and the occurrence of the Great Weddell Polynya. "The data has shown us an interesting and unusual development in the regional climate events shortly before the formation of Polynya, " says Martin Visbeck, Professor of Physical Oceanography at IFM-GEOMAR and co-author of the study.

Antarctic chain fraction

The research team noted in the data a link between the Polynya and the weakening of the winds in the area of ​​the circumpolar current and the Antarctic continent. The Circumpolar Current is like a mighty waterway that orbits the continent and plays a major role in Antarctic climatic events. display

The weakening of the wind triggered a kind of chain reaction in the interaction between atmosphere, ocean and ice formation, the researchers said. The decrease of the winds led to less precipitation and favored a stronger mixing of the water column in the Weddell Sea. This in turn allowed for a rise of warmer deep water to the surface. "This warmer water melted the ice of the Weddell Sea and brought us the great Polynya", explains the oceanographer Visbeck the complex events.

Unique event

Back in the mid-1970s, even mainframes could not evaluate the huge amount of data that satellites transmitted from space to Earth in real time. When, after a time delay, the big hole in the ice opened up in front of the scientists in the data, the phenomenon had already disappeared again. The reversed chain reaction, triggered by an increase in winds over the last 20 years, had begun, according to the scientists Visbeck, Arnold Gordon and Josefino Comiso.

"Unfortunately, there was no way for us at that time to examine this imposing hole in the ice by means of ship observations and on-site measurements, " says Visbeck somewhat mournfully. Since then, scientists have been spellbound year after year looking at the sea ice data from the Antarctic. The Weddell Polynya showed since 1976 but never again. It remains an extraordinary phenomenon.

(idw - Leibniz Institute for Marine Sciences, 24.07.2007 - DLO)