The findings by the Leibniz Institute of Marine Sciences (IFM- GEOMAR) in Kiel, Germany, have dire implications for climate change in the Northern Hemisphere.
Hitherto, the circulation of the Arctic Ocean was driven by the formation of sea ice rather than the inflow of North Atlantic deep water.
Recently, however, the shrinkage of sea ice due to global warming has resulted in the startling reversal, according to the study by the German scientists, which is published in the new journal Nature Geoscience.
The latest findings are based on geo-chemical analyses of sediment cores taken from the depths of the Arctic Ocean as part of the EU- funded ECORD (European Consortium for Ocean Research Drilling) project.
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.
But the findings by 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 geo- chemical analyses on sediments of the Arctic Coring Expedition and of an expedition by the German seagoing research vessel, the Polarstern. The sediment cores had been taken from the seabed near the North Pole on the Lomonosov Ridge between 1,000 und 1,200 metres water depth.
The scientists were particularly interested in changes in the isotope ratio of the element neodymium. Neodymium has different isotope ratios depending on the age and type of rock.
When rocks are weathered, the element is washed into the sea, where it provides information on the sources of the water in the ocean. The cores enabled the researchers to study changes in the sources of water in the Arctic Ocean going back 15 million years.
The scientists were surprised to find that the isotope signature for much of the history of the ocean is very different from the signature found today.
The isotope ratios in much of the core correspond to basalt rocks such as those found in the Kara Sea area. This suggests that for most of the last 15 million years, the seawater above the sediments came from within the Arctic Ocean itself.
In contrast, today much of the deep water in the Arctic Ocean flows in through the Fram Strait from the Atlantic.
Güncelleme Tarihi: 18 Şubat 2008, 13:50