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Discovered: Cooling system under the sea floor

February 04, 2003

EMBARGO: February 5th, 8 pm

The scientific, technical and logistic support of the geo scientists from Bremen, Prof. V. Spiess, Dr. L. Zühlsdorff and Prof. H. Villinger was instrumental in the discovery of a 50 km long cooling system by US-scientists under the sea floor off the north-west American coast. Its cornerstones are rocky outcrops which reach up to hundreds of meters from the ocean floor. They transfer heat from the earths crust to the waters above. The new studies concerning the heat balance of our planet will be published in the February 6th edition of the scientific journal "Nature".

The international team of scientists studied the eastern flank of the Juan de Fuca Ridge, west of Vancouver Island, Canada. Here, hot magma rises up from the inner earth and builds up new oceanic crust. Heat dissipates easily as long as the sediment layer above the young crust is thin enough. But after about a million years the layer is so thick that heat transport almost ceases.

The marine scientists from Bremen investigated rocky outcrops through their acoustic soundings of the ocean floor. These sea mounts reach up to several hundred meters above the sediment. They are the cornerstones of the formerly unknown cooling system. In the upper layer of the oceanic crust - of which these outcrops are a part - water can circulate freely through many cracks and pores. It was known before that warmer and therefore lighter water exits the crust at such sites. But the now published "Nature" article shows that cold water may enter here as well. It also proves that the water circulates from one sea mount to another and thus effectively cools the sediment covered crust.

Scientists aboard the German research vessel "Sonne" and the American research vessel "Thomas G. Thompson" studied the circulation between two of these bare rocky outcrops. They are located about 450 km off the coast of western Canada and were dubbed "Grizzly Bare" and "Baby Bare". At the larger of the two, "Grizzly Bare", 2°C cold water enters the porous crust and flows slowly to the 52 km distant "Baby Bare". Along the way the water is heated to 65°C and takes up dissolved elements like Magnesia from the surrounding rocks. Through analyzing the exiting waters scientists ascertained how long it takes the water to travel the distance. Roughly 4,300 years for 52 km - not exactly record time.

How the cooling system initially developed is not known at present. But further research in the area is being prepared under the International Ocean Drilling Program (IODP). After all the scientists believe that the sea mounts at the Juan de Fuca Ridge are a good model for understanding this important part of the global heat budget.

Research Center Ocean Margins (University of Bremen)