Ocean circulation and bioproductivity in the Weddell Gyre: geochemical findings

Ocean circulation and bioproductivity in the Weddell Gyre: geochemical findingsW. GEIBERT1, C. HANFLAND1, J.SCHWARZ1, R.USBECK1,2, A.WEBB3, AND I.ANSORGE31Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany; wgeibert@awi-bremerhaven.de2FIELAX, Company for Scientific Data Management, Bremerhaven, Germany3University of Cape Town, Dept. of Oceanography, Cape Town, South AfricaAtypical distribution of tracersThe Weddell Gyre is one of the key areas for ocean circulation, and consequently for global climate. Here, deep waters reach the surface, and new production of bottom water brings surface signals at depth. This unusual situation is mirrored in the distribution of naturally occuring radionuclides like Radium isotopes or 227Ac in the water column. Not only tracers for ocean circulation show anomalies here. Tracers of particle flux also indicate atypical processes, reaching from the sea surface to the sediment.Atypical productivityResults of an expedition to the Eastern Weddell Gyre (Polarstern Expedition ANT XX/2) now have given a more comprehensive view of the whole Weddell Gyre. Together with measurements of nutrient distribution and other parameters, they reveal that the Weddell Gyre may not only be important in terms of ocean circulation, but it may also represent a site of suprisingly high bioproductivity. Pronounced differences between the Western part of the Gyre and its Eastern part were observed.Here, we present a comprehensive set of radiotracer data from the Weddell Gyre, together with oxygen and nutrient distribution data. Additionally, data of chlorophyll-a illustrate the vertical distribution of phytoplankton, explaining why satellite measurements lead to an underestimation of productivity in the Weddell Gyre. First results for sediment accumulation rates in the Eastern Weddell Gyre will also be presented.