Determining Air-Sea Exchange from the Sea-Side: A New Floating Aquatic Eddy Covariance Platform

The air-sea exchange of biogeochemically relevant gases is fundamental to our understanding of marine primary production and its effect on the climate. Oxygen is a commonly used tracer of primary productivity in marine environments, but gas exchange across the air-sea interface has presented significant challenges to standard aquatic methods, such as Lagrangian and Eulerian techniques, that rely on wind-derived assumptions about this air-sea exchange. To better constrain this air-sea exchange and evaluate marine primary production we developed a new aquatic eddy covariance system located on a floating platform where the sensing elements are located just below the sea surface. The system employs an acoustic Doppler velocimeter for measuring turbulent transport and a fast-response oxygen sensor to determine oxygen exchange from high-frequency, direct-covariance measurements. The newly developed, moored platform includes high-frequency measurements of the float movement to correct for accelerations due to surface waves and currents that are vital for making accurate turbulence measurements. The system has the advantages of sampling under natural in-situ conditions and integrating primary production throughout the water column and, in shallow ecosystems, the benthic surface. It is expected that this new system will have a variety of applications for both coastal and pelagic ecosystems and will provide a new tool for the analysis of biogeochemical cycling and atmosphere-sea exchange.