Carbon microcycle: CO2 gradients in the ocean surface (CµC)

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The carbonate system has a pivotal role in marine biogeochemical cycles. It is central to the exchange of CO2 between the ocean and atmosphere, and, therefore, determines the atmospheric burden with greenhouse gases and the extent of ocean acidification. However, research of the carbonate system has ignored the upper 5 m of the ocean’s water column, including its uppermost top, the sea-surface microlayer. This is because interferences from research vessels and rosette samplers do not allow sampling of this zone without disturbing its integrity.I propose to investigate the carbonate system and pCO2 gradients in the surface ocean (upper 5 meters), potentially driven by biological and physical processes. The microlayer is in direct contact with the atmosphere, and I hypothesize that partial pressures of CO2 in the microlayer determine “real” air-sea fluxes, i.e. compared to fluxes based on data from 5 meter. I will adapt a state-of the-art research catamaran to measure parameters of the carbonate system in situ in the surface ocean and in the microlayer at high resolution. In controlled tank experiments, I will assess uncertainties of established sampling techniques for measurements of gases in the microlayer and adjacent underlying thin layers, in order to modify the sampling strategy accordingly. With the modified catamaran and an autonomous floating chamber measuring in situ CO2 fluxes, I will participate in an expedition to the south Pacific to collect field data and to investigate the formation of near-surface pCO2 gradients. With data at high resolutions, I will be able to provide a mechanistic understanding on the formation of surface gradients and determine the main underlying environmental forces. Results will provide air-sea CO2 fluxes based on near-surface and microlayer aqueous pCO2 values, and biases by computing fluxes from underlying water masses. Overall, this project will support future assessment of global air-sea fluxes of climate-relevant gases. In addition, I will provide a first data base with sufficient resolution to the European Space Agency to investigate if the carbonate system can be monitored on a global scale from satellite missions.