Das Projekt "Biogeochemische Stoffflüsse in vietnamesischen Gewässern: Reaktion auf ENSO-Ereignisse und holozäne Erwärmung" wird vom Umweltbundesamt gefördert und von Universität Hamburg, Zentrum für Meeres- und Klimaforschung, Fachbereich Geowissenschaften, Institut für Biogeochemie und Meereschemie durchgeführt. Monsoon-driven upwelling along the southeastern coast of Vietnam in summer and along the northern edge of the Sunda Shelf in winter generates the biologically most productive off-shelf regions in SE-Asian waters. Runoff from nearby rivers such as the Mekong has been assumed to contribute to the fertility of these regions. The upwelling is significantly suppressed or fails during El Nino events which are predicted to increase in both frequency and amplitude on top of a global warming trend. The extent to which these events (and their cold counterparts) affect the ecological and biogeochemical conditions in this area, however, is not known and future perturbations of the upwelling System are difficult to describe.Sediment traps deployed in the upwelling centers have shown that in contrast to what has been assumed earlier, only small proportions of the annual fluxes are produced during the upwelling seasons and there is little indication of riverine suspended solids directly reaching the trap sites. During both El Nino and ENSO-neutral conditions, the major part of the fluxes is related to the passage of cold-core eddies, affecting the water column down to depth of greater than 500 m. These eddies enhance productivity by upward nutrient pumping, but synchronously resuspend large amounts of solids from the shelf and slope and advect the plumes to the trap sites. This influx appears to carry a mixed Signal of northern, central and southern Vietnam rivers including the Mekong, indicating strong resuspension and resedimentation processes along the coast. The advected material masks primary production Signals in the upwelling areas and produces large discrepancies between proxy and actual data. This proposal aims (1) to determine the pathways and extent of advective transport from the Mekong and southern-central Vietnam rivers across the shelf to the upwelling area; (2) to record particle fluxes in the upwelling zones, quantify the role of primary productivity versus lateral advection events, and assess their forcings; (3) to describe the link between the coupled monsoon intensity, eddy formation, river runoff, ecosystem structure and biogeochemical fluxes, and to calculate ENSO-induced biogeochemical anomalies; (4) to regionally test and improve proxies for these key processes for subsequent use in and refining of paleooceanographic studies.