Pelagic processes and nitrogen cycle in coastal waters off southern central Vietnam: mesocosm experiments, field work and modelling

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Pelagic system dynamics will be studied off southern central Vietnam in the South China Sea with a focus on the nitrogen cycle and vertical fluxes along hydrographical and biogeochemical gradients from coastal to oceanic conditions. Pelagic system responses on different new nutrient sources for primary production (upwelling, river discharge, atmospheric input by N-fixation) will be assessed during the monsoon and intermonsoon seasons. Stable N-isotope analyses will be performed on water column inventories (nutrients, suspended particles, mesozooplankton), particle fluxes and surface sediments in relation to N-fixation, new production and denitrification. Field work comprises samplings on grid stations and short time-series process studies including vertical flux measurements with shallow moored and/or drifting traps. The project contributes to biogeochemical province descriptions, and links the coastal realm with the shelf/ocean margin pelagical and oceanic conditions over the adjacent deep sea basin. This is done jointly with German partners regarding hydrography, exports from estuaries, sediment geochemistry and annual deep particle fluxes. Collaboration with Vietnamese institutes on plankton variability, nutrient availability and production patterns, and on satellite remote sensing also aims at capacity building in biological oceanography.