Schematic Map of the Arctic and North Atlantic Oceans, important currents (blue for surface, black for deep) and the distribution of the ice sheets of the last glacial. The location of the investigated sediments is given by the star. Source: IFM-GEOMAR.
	Drilling platform "Vidar Viking" in the foreground. Swedish icebreaker Oden Eisbrecher "Oden" and Russian icebreaker "Sovetskiy Soyuz" in the background smashed the drifting sea ice in order to keep the position of the drilling platform stable. Source: IODP
	Sea ice with a snow-covered pressure ridge in the Arctic Ocean (Source: Swedish Polar Research Secretariat).

Arctic Ocean circulation as we know it today is an exceptional situation compared with the geological past. This was shown by researchers of the Leibniz Institute of Marine Sciences (IFM-GEOMAR) in Kiel from geochemical analyses of central Arctic marine sediments. Their results suggest that Arctic deep circulation was strongly influenced by sea ice formation during most of the past 15 million years and was not predominantly controlled by inflowing Atlantic waters, as is the case today. This also implies that the formation sites of North Atlantic Deep Water, which has been a very important component of global ocean circulation and of heat transfer between low and high latitudes, were most of the time located further south, similar to glacial periods. The study will be published online in the new journal „Nature Geoscience“ on December 2nd.

The Arctic Ocean only has a limited exchange with the global ocean, whereby the Fram Strait between Greenland and Svalbard is the only deep water connection to the Atlantic Ocean. It is this connection that supplies oxygen to the deep Arctic Ocean. Today a pronounced and stable freshwater layer at the surface originating from inputs of the large Russian rivers almost completely prevents any significant deep water formation in the Arctic Ocean itself. The results of Brian Haley and colleagues from the IFM-GEOMAR now show that this was an exception rather than the rule for most of the past 15 million years.

The Kiel team made their discovery when they carried out geochemical analyses on sediments of the Arctic Coring Expedition (ACEX, Leg 302 of the Integrated Ocean Drilling Program (IODP)) and of a RV Polarstern expedition, which had been recovered near the North Pole on the Lomonosov Ridge between 1.000 und 1.200 m water depth. They reconstructed the seawater isotope ratio of the element neodymium (143Nd/144Nd) from the sediments. The Nd, which has characteristic isotope ratios in rocks as a function of their type and age, is transported to the ocean through weathering, where it provides information on the sources of water masses. To their surprise, the geochemists found that the isotope signature of the seawater was strongly different from the present day values, with the exception of the warm periods of the past 400.000 years. “It is even more surprising that this isotope signature indicated a pronounced influence of the weathering of basaltic rocks”, says Brian Haley. On the Circum-arctic landmasses such rocks, however, only exist in the form of the Siberian “Putorana flood basalts”.

From this geologically unique setting and taking into account the evolution of the continental ice sheets of the past 140.000 years, it was then possible to reconstruct the circulation history of the deep Arctic Ocean. The signature of the basalts can only have arrived at 1.000 m water depth in the central Arctic Ocean if vast amounts of new sea ice formed near the basalt areas in the Kara Sea area. How did the signature arrive at the seafloor? “During sea ice formation the salt of the sea water freezes out and is rejected, thereby forming highly saline brines, which were denser than the surrounding sea water. These brines sank and transported the dissolved Nd isotope signature of the basalts to the sea floor where the sediment cores were recovered”, explains Martin Frank, co-author of the study. Further, the obtained Nd isotope variations imply that the inflow of Atlantic waters was significantly reduced during most of the past 15 million years and during the glacial periods of the past 400.000 years. This also suggests that during these periods of time the main area of Atlantic deep water formation was not located in the Norwegian-Greenland Sea, similar to today, but further south.

The arctic IODP ACEX drilling project was coordinated by the European consortium ECORD (European Consortium for Ocean Research Drilling). This organization consists of partners from 17 European nations participating in the „International Ocean Drilling Programme“. ECORD is also responsible for the planning and coordination of special operations, for which normal drilling vessels cannot be used, as was the case for the ACEX project. For such purposes special platforms are used to achieve the scientific goals.

Contact:

Dr. Brian Haley, Phone: +49 431 – 600 2252, bhaley@ifm-geomar.de

Prof. Martin Frank, Phone: +49 431 – 600 2218, mfrank@ifm-geomar.de

Dr. Andreas Villwock (public relations), Phone: +49 431 – 600 2802, avillwock@ifm-geomar.de

Further Information:

The publication in “Nature Geoscience” of 2.12.2007 (the printed article will only appear in January 2008) is entitled:

„Influence of brine formation on Arctic Ocean circulation over the past 15 million years”

Brian A. Haley¹, Martin Frank¹, Robert F. Spielhagen^{1, 2}, Anton Eisenhauer¹

¹Leibniz Institute of Marine Sciences at the University of Kiel (IFM-GEOMAR), Kiel, Germany.

²Academy of Sciences, Humanities and Literature, Mainz, Germany

www.nature.com/ngeo (Nature Geosciences)

www.ifm-geomar.de/index.php?id=995 (Paleo-oceanographic research at IFM-GEOMAR)

Last Update this page: 02.12.2007.