Sub-Tropical Gyre Study: Anthropogenic Carbon and Biological Degradation in the Twilight Zone (Forschungsantrag M 60/5)

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The proposed multidisciplinary investigation of the water column of the North Atlantic subtropical gyre is oriented along sections last occupied during the US Transient Tracers in the Ocean - North Atlantic Survey (TTO-NAS) of the early 1980's. Together with a sub-polar gyre cruise in 2003 (Prof. M. Rhein), our cruise provides a central contribution to an international (Germany, USA, UK) reoccupation of TTO-NAS stations. A major goal is to use inorganic carbon and chemical tracer data to examine the increase of anthropogenic carbon (Cant) in the North Atlantic over a time interval of 22 years. This is the goal of Teilprojekt A5 of the Kieler Sonderforschungsbereich 460. The data will be assessed using multivariate time-series analysis techniques as well as tracer-Cant correlations in order to quantify the anthropogenic carbon increase. A second goal of the cruise is the examination of remineralization of biogenic materials within the mesopelagic water column, since most constituents are being released from particles in the depth horizon between the base of the euphotic zone and ca. 1.000 m depth. Detailed analysis of the pelagic community in the mesopelagic zone and experiments to asses rates of particle breakdown are planned to examine the remineralization processes. Since nitrogen fixation is assumed to have a substantial influence on nutrient stoichiometric ratios in these waters dephts, studies of nitrogen fixation and biodiversity of diazotrophs are also part of these investigations. Such studies will also allow for examination of the controversial suggestion (Pahlow and Riebesell, 2001) that the nutrient-oxygen stoichiometry of the North Atlantic has been changing.