Collaborative Research: A new system for air-sea CO2 flux measurements from moored and unmanned surface platforms

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The oceans play a key role in the global carbon budget, currently absorbing roughly one quarter of anthropogenic CO2 emissions. The flux of CO2 across the air-sea interface is represented in models using an exchange coefficient or "transfer velocity" that is highly uncertain both in magnitude and spatial distribution, leading to uncertainty in current and future carbon budgets. The ability to measure air-sea CO2 exchange on short time scales over a broad range of ocean and atmospheric conditions is necessary to develop more accurate parameterizations of gas exchange with more realistic representation of physical processes affecting turbulence at the air-sea interface. This research aims to develop the capability to directly measure air-sea CO2 fluxes from buoys, with the potential to dramatically expand the database of direct flux measurements. If successful, this project will provide new capabilities for ocean time-series observations and the potential for incorporation into existing and future buoy-based ocean observing systems. These capabilities can adapt to other low-power, mobile platforms (spar buoys, catamarans, gliders) that will enable new observational approaches and insights into processes at a range of spatial and temporal scales. Future measurements enabled by this project also have the potential to impact broader policy by providing more accurate information for agencies and policy makers on how and where oceans take up and release carbon.This project will build and test the first CO2 flux measurement system that can be deployed on a buoy platform. The measurement approach utilizes the eddy covariance technique, which provides a direct flux measurement with high spatial (1-10 km2) and temporal (10-60 min) resolution. Previously, eddy covariance air-sea CO2 flux measurements have been restricted to research vessels, resulting in spatial and temporal limits on the collection of data that can be used to improve understanding of air-sea gas exchange. This research aims to develop the capability for robust, high-resolution, low-power, buoy-based CO2 flux measurements by directly addressing the primary technological obstacles to development of buoy-based eddy covariance CO2 flux systems: the small magnitude of the flux (poor signal-to-noise ratio), sensor performance limitations, low power availability, and harsh sampling conditions. Improvements to the sensor CO2 performance in collaboration with an instrument manufacturer will provide a clear pathway to commercialization and use by the broader oceanographic research community. The survivability and power-optimization challenges will be addressed by adapting the principle investigator?s experiences with both shipboard and buoy-based systems. The project will leverage ready access to extensive lab and field facilities that include ships, buoys, an indoor deep dive tank, and access to the Gulf of Maine for field work.