Fischer, G. University of Bremen, g05f@zfn.uni-bremen.de
Wefer, G. University of Bremen, gwefer@allgeo.uni-bremen.de

 
SEASONAL CHANGES IN CARBON ISOTOPE COMPOSITION OF SINKING MATTER IN THE ATLANTIC AND SOUTHERN OCEAN: RELATIONSHIPS TO ORGANIC CARBON FLUXES ABD TO ENVIRONMENTAL AND BIOLOGICAL FACTORS
 
Natural variations in the carbon isotopic composition and the isotopic fractionation of surface ocean plankton have been attributed primarily to the concentration of ambient CO2 (aq), growth rate, phytoplankton species changes and cell geometry. Only few studies investigate the seasonal carbon isotope variation under these aspects. We computed the seasonal isotope fractionation of sinking matter sampled in various warm and cold water environments of the Atlantic Ocean using measured SSTs. We compared them to surface water CO2 (aq) variations computed in equilibrium with the atmosphere, to the organic carbon fluxes and to species changes. At neither site, we obtained a relationship between CO2 (aq) and the fractionation. In the tropical-subtropical Atlantic, where carbonate-secreting primary producers dominate, increasing carbon fluxes are mostly associated with decreasing fractionation, the latter yielding a fairly low seasonality (1-2 per mil). In contrast, in the Southern Ocean where diatoms dominate sedimentation, the seasonality of the isotope fractionation may be as high as 7.4 per mil; high fractionation values correspond to enhanced carbon fluxes associated with abrupt changes in the diatom composition. Species-specific growth rate and/or changes in diatom cell-volume-to-surface-ratio are discussed to account for such large variations in fractionation. BIOGEOCHMISTRY OF LAKES AND OCEANPHYTOPLANKTON AND MICROBIAL BIOGEOCHMISTRY AND DIVERSITYECOLOGY OF AQUATIC ORGANISMS POSTER
 
Day: Thursday, Feb. 4
Time: Poster
Location: Sweeney Center
 
Code: CS55TH0113S