Der Transport von Wärme, Wasser und Salz in den Arktischen Ozean (The transport of heat, mass and salt into the Arctic Ocean)


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bcisewski [ at ] awi-bremerhaven.de

Abstract

Most of the exchange of water, salt and heat between the Arctic Mediterranean and the worlds oceans occurs through the Framstrait and the Greenland Sea. Our present knowledge on the respective northward and southward water mass transports is essentially based on current meter moorings, geostrophic calculations from hydrographic measurements and a variety of drifters. In order to explore the spatial velocity structure - horizontally on scales of eddies larger than 10 to 20 km and vertically in the order of 10 m - we have used a ship-mounted ADCP on several expeditions of RV Polarstern since 1990 to investigate the velocity field within the uppermost 400 m. These measurements provide snap-shots of the velocity field on scales not resolved by moorings, and they also serve as reference for the conversion of geostrophic into absolute velocities. Furthermore, in combination with water mass analyses it was possible to calculate the individual transports of the characteristic water masses for the whole water column in addition to the total transport in the area. The combination of high resolution hydrographic and velocity measurements at identical grid points allows to avoid the interpolation problems involved in the evaluation of mooring measurements.The mean circulation of the Greenland Sea is dominated by a large cyclonic and predominantly barotropic gyre. The calculated absolute velocities across the 75°N standard section question the existence of Koltermanns (1991) postulated deep anticyclonic gyre. At 75°N the East Greenland Current (EGC) is identified over a distance of 140 km as a narrow jet which carries ice and polar water to the South. The total volume transport calculated for the region of the EGC is comparable with results of moored current meters and ranges between 12 and 29 Sv (Fahrbach et al., 1995 and Woodgate et al., 1999).In contrast to the EGC the Westspitsbergen Current (WSC) carries Atlantic Water (AW) to the North and exhibits a much larger mesoscale variability. The velocity field in the WSC is characterized by variable meanders and mesoscale eddies with typical horizontal dimensions of 50 km, whereas jet-like structures dominate in the EGC. Since the AW provides the major contributions to the meridional heat transport five realizations of the 75°N standard section were used to investigate its interannual variability. During the summers 1990 - 1998 the AW transports ranged between 2 and 7 Sv. The total heat transport across 75°N is estimated as 52 TW in September 1997 and 42 TW in September 1998. The total salt transport ranges between 5.2 and 5.6 × 106 kg s-1. Finally, based upon five hydrographic sections taken between 70°N - 82°N and 25°W - 25°E during August/September 1997 a circulation and transport scheme for the principle water masses is constructed and compared to the results of Mauritzens inverse box model (Mauritzen, 1994). Both transport schemes are in good agreement. Between 75°N and 79°40N the mean temperature of the AW decreases by 0.8°C while its density increases. The observed AW cooling is caused by a strong heat loss to the atmosphere of about 130 W m-2.



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Eprint ID
4377
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Cisewski, B. (2001): Der Transport von Wärme, Wasser und Salz in den Arktischen Ozean (The transport of heat, mass and salt into the Arctic Ocean) , Reports on Polar and Marine Research, 378, 184, Dissertation .


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