Underwater air-sea eddy covariance

We present a new approach to quantifying air-sea flux and gas transfer velocity (K600) from underwater eddy covariance (EC) of dissolved oxygen. EC flux was measured 35 cm below the air-water interface using an acoustic dopplerDoppler velocimeter (ADV) coupled with a fast-responding dissolved oxygen optode probe, integrated on a floating platform. A micro-electro-mechanical systems-based inertial motion unit integrated with the ADV enabled compensation of measured velocities for platform motion and changing sensor orientation. Deployments of 16 and 30 hours were conducted under low to moderate wind conditions in Sage lLot Pond, a small estuarine embayment. We compared wind-speed based parameterizations to EC-determinations of ed flux and K600 and identified significant shortcomings of wind-speed based relationships due to directional differences in fetch. Root mean squared wave velocity was consistently and linearly correlated with EC-determined K600 across both deployments and was indicative of a more direct relationship to near surface turbulence compared to wind velocity. The performance, applicability, and comparison to traditional wind-based parameterizations suggest that this new aquatic EC technique is highly advantageous for the determination of air-sea exchange, especially in dynamic near-shore systems. Finally, this new system has the potential for other applications, such as scaling to open-ocean air-sea exchange and adaptation other solutes, and represents a significant advancement for the aquatic eddy covariance technique that has previously been primarily applied to exchange across the sediment-water interface.