Arctic and Atlantic: exchange for 17.5 million years

Connection already exists much longer than expected

Location of the drillship on the Lomonosov Ridge near the North Pole. © IODP
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So far, scientists believed that there was only about ten million years ago a connection between the Arctic and the Atlantic. Now researchers have found in a new study that the Fram Strait between Greenland and Svalbard already opened 17.5 million years ago. The results are based on new data from deep well cores as well as oceanographic and geophysical models.

This process is of great importance not only for the development of the Arctic Ocean, but also for the establishment of the great ocean currents in the Atlantic, including the deep water that supplies the Atlantic Ocean with oxygen. The international team of scientists with the participation of the Leibniz Institute for Marine Sciences (IFM-GEOMAR) in Kiel and the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven reports on its findings in the current issue of the scientific journal Nature.

"Through this corridor, oxygen-rich water was able to flow into the formerly decoupled Arctic basin for the first time, " says Professor Martin Frank, Paleo-Oceanographer at the Leibniz Institute for Marine Sciences and co-author of the study, "in other words - the deep Arctic began to breathe",

Lomonosov back pierced

Knowledge of the oceanographic development of the Arctic Ocean has until recently been limited to one million years before today. Further information was not available to the researchers because it was not possible to drill in an ice-covered ocean of several 100 -meter-long sediment cores. In the summer of 2004, as part of an ambitious expedition - the Integrated Ocean Drilling Program (IODP) Leg 302, ACEX - the entire 428-meter sediment cover of the Lomonosov Ridge near the North Pole was drilled using a drilling platform and two icebreakers to extract sediment cores.

The focus of the researchers was very fast on a striking transition in the sediments in about 200 m depth. There, black-gray deposits with a high content of organic carbon suddenly gave way to dark brown sediment layers with a low organic carbon content. Additional data suggested that the deeper, darker layers were deposited in an oxygen-free basin similar to today's Black Sea. But how old are these sediments and when did this striking transition take place? display

Supply of oxygen-rich water for 17.5 million years

The dating of Arctic sediments is not easy, as only very few fossils are preserved in the oxygen-rich layers of the top 200 meters. Here special isotope measurements by Professor Martin Frank were able to close the data gap over age. With the help of an isotope of the element beryllium, the 10Be, the Pal o-Oceanographer in Kiel has developed a reliable dating of the last twelve million years. Together with other data, the scientists were able to determine the beginning of the supply of oxygen-rich water to the Arctic 17.5 million years ago today.

This point coincides with a new plate tectonic reconstruction of the opening of the Fram Stra e. The geophysical and oceanographic calculations provide a sufficient depth of water between the Arctic and Atlantic at this early stage to ensure an efficient exchange with the North Atlantic. Frank also sees this development as important for the global climate: "The early coupling between the Atlantic and the Arctic led to a change in the deepwater circulation in the Atlantic Ocean, which in turn was due to the climate change in the North Atlantic Space impacted. "

(idw - Leibniz Institute of Marine Sciences, 21.06.2007 - DLO)