Collaborative Research: Autonomous eddy covariance air-sea CO2 flux system for moored buoys

Accurate prediction of carbon dioxide exchange between the atmosphere and oceans is an important earth system model requirement, but the exchange estimates in state-of-the-art climate models remain uncertain. One model factor that requires improvement is the rate of gas transfer across the air-sea interface, and the micrometeorological eddy covariance (EC) flux technique can provide field measurements needed to improve and validate transfer rate models across a broad range of wind and wave conditions. While the EC technique is widely employed on land, several technical hurdles have hindered wider adoption of this approach for CO2 flux data collection at sea, particularly on unattended floating platforms. Recent work by this team has demonstrated that fast-response closed-path CO2 sensors, central to the EC technique, can be modified to substantially reduce CO2 error due to ship and buoy motion effects. Under this new program, the team will further improve these sensors and also adapt approaches used for larger shipboard CO2 flux systems to develop a small, robust, accurate, and low power system suitable for use on a growing number of autonomous ocean observing platforms. The goals of this project are to 1) design, build and field-demonstrate a next generation infrared gas analyzer engineered to effectively remove motion interference that has plagued previous air-sea gas exchange field experiments, and 2) build and deploy a compact end-to-end eddy covariance CO2 flux system suitable for autonomous measurements through all weather conditions and on small ocean observing platforms where power demands must be minimized. Offshore buoy field demonstrations will be conducted near a long-term CO2 measurement site in the Gulf of Maine where supporting ocean and meteorological observations will provide data needed for sensor and system assessment and validation. The work will be performed using a team approach that formally partners industry, academia, and ocean observing system engineers. The project's final buoy-based flux measurement system will be designed in collaboration with NSF OOI to facilitate integration onto existing and future ocean observing platforms, paving a way for expanded at-sea direct covariance CO2 flux measurements to support a broad range of carbon cycle and air-sea interaction studies and applications. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.