Fluctuations of the Gulf Stream on the track

Bremen environmental physicists undertake two-ship expeditions

Planned route with station work of the two Bremen expeditions with MERIAN (MSM09-1) and with THALASSA (Subpolar08). Orange: Ground Echo-Sounder, Black: Location of the Process Study "Mixing in the Deep Western Randstrom" © Institute for Environmental Physics, University of Bremen
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What significance does the North Atlantic have for the European climate? Can the North Atlantic take less and less CO2? Does the sea level rise on the Western European coast? Bremen scientists have been dealing with these questions for ten years now. On July 23, 2008, they will now embark on a new expedition with the research vessel MARIA S. MERIAN to learn more about the climate role of the North Atlantic.

The team headed by Professor Monika Rhein from the Department of Environmental Physics at the University of Bremen wants to explore to what extent the decline in deep water formation - which has been observed for ten years - is linked to a change in Gulf Stream transport. Two months are needed for the examinations. The MERIAN expedition ends on August 18, 2008 in St. John's (Canada). However, a few days later, on 23 August, the researchers in Bremen continue their journey with the French research vessel THALASSA under the direction of the Bremen oceanographer Dagmar Kieke.

Exposing a ground echo sounder © Institute of Environmental Physics, University of Bremen

Ground echo sounder in use

The oceanic circulation brings warm water (Gulf Stream) to the north, where it releases the heat to the atmosphere. The cold water sinks into the depth and flows back to the south. There are three reasons why changes in this circulation are of interest: slowing down would, in addition to slowing down the climate, make it more difficult for the greenhouse gas CO2 to be absorbed into the ocean and, moreover, sea level could rise along the west European coast.

Researchers are using four well-grounded depth sounders along the mid-Atlantic ridge between 46 degrees and 53 degrees north to determine fluctuations in the Gulf Stream. The sensors measure the time it takes for a sound wave to get to the surface and back to the ground.

Researchers calculate transport fluctuations

From the dependence of the speed of sound of temperature and salinity, their distributions can be reconstructed, and from this transport fluctuations can be calculated. The sensors were designed in August 2006 and the data should now be read out. The first attempt in April 2007 failed due to technical problems of MERIAN. display

The production of deep water in the Labrador Sea is investigated by the Bremen researchers with the help of trace material inventories. These trace substances are introduced into the sea surface via contact with the atmosphere and are taken into the depths when the cold water sinks. Changes in these inventories from year to year are the best way to determine the changes in the sunken volume of the deep water. The process is very laborious, because for well-founded statements the distributions in the entire subpolar North Atlantic have to be measured.

Less deep water

From the measurements, the Bremen research group has found out that since 1997, the amount of deep water formed has weakened by 70 percent. Whether this trend will continue, the measurements on the two expeditions will show.

(idw - University of Bremen, 18.07.2008 - DLO)