Breaking land bridge made the Antarctic icy

Researchers identify the cause and onset of Antarctic Vegletscherung

Sea currents before the break of the land bridge (circle) and afterwards. After opening the connection, the circumpolar current was formed. © Bijl et al. / PNAS
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Once, Antarctica was a life-friendly, meager continent. However, when the great ice age began around the South Pole, was only partially clarified. Now an international research team has found that the great cooling began about 49 million years ago: at that time, the land bridge broke between the Antarctic and Australia and the cold, the Antarctic isolating circumpolar current formed, as the researchers in the journal "Proceedings of the National Academy of Sciences "report.

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About 50 million years ago, Australia and the Antarctic were connected by a narrow land bridge - similar to today's North and South America. The centerpiece of this connection was today's Tasmania. In addition to this was a greenhouse climate, it was mild even on today's South Pole, the Antarctic had a rich vegetation. But then the southern continents drifted apart and the Tasmanian land bridge broke. With far-reaching consequences: Until then, the exchange of water masses between the southwestern Pacific and the Indian Ocean was prevented. Now, at least in the upper ocean floor, the ocean currents had a clear path. The Antarctic circumpolar current was born, which still today encloses the sixth continent in a broad, cold flow band.

"Although it was known that Australia and the Antarctic since about 80 million years ago today slowly but inexorably drift apart, " says Peter Bijl, paleoclimate researcher at the University of Utrecht and first author of the study. "So far, we did not know exactly when and how the movements of the earth's plates influenced ocean currents in this region."

Searching for traces along the former land bridge

Indications for the tectonically induced upheavals were fossil remains of unicellular algae. The research team spotted them on both sides of the former land bridge in early 2010 during an expedition of the IOPP Integrated Ocean Drilling Program. The species composition of the algae offered a much different picture before the opening of the Tasmanian land bridge than afterwards. "From 49 million years ago today, the species composition in the samples on both sides of the Tasmanian land bridge is similar, " says co-author Ursula Röhl of MARUM. "We see in it an indication that the ocean currents were not stopped." Display

When the Antarctic circumpolar current arose, it isolated Antarctica from the warmer regions further north. The result: the sixth continent began to cool down. The scientists were able to prove this with the aid of molecular analyzes of microorganisms and pollen from the drilled sample material. These studies show that from 49 million years ago, both the surface temperatures of the Sdipolar Army and the air temperatures over the Antarctic cooled. The end of the former greenhouse climate was initiated. A few million years later, the first Antarctic glaciers formed, which then grew together to form the continental wide inland ice. (Proceedings of the National Academy of Sciences, 2013; doi: 10.1073 / pnas.1220872110)

(MARUM - Center for Marine Environmental Sciences at the University of Bremen, 28.05.2013 - NPO)