Articles | Volume 17, issue 14
Research article
27 Jul 2017
Research article |  | 27 Jul 2017

Estimation of bubble-mediated air–sea gas exchange from concurrent DMS and CO2 transfer velocities at intermediate–high wind speeds

Thomas G. Bell, Sebastian Landwehr, Scott D. Miller, Warren J. de Bruyn, Adrian H. Callaghan, Brian Scanlon, Brian Ward, Mingxi Yang, and Eric S. Saltzman

Abstract. Simultaneous air–sea fluxes and concentration differences of dimethylsulfide (DMS) and carbon dioxide (CO2) were measured during a summertime North Atlantic cruise in 2011. This data set reveals significant differences between the gas transfer velocities of these two gases (Δkw) over a range of wind speeds up to 21 m s−1. These differences occur at and above the approximate wind speed threshold when waves begin breaking. Whitecap fraction (a proxy for bubbles) was also measured and has a positive relationship with Δkw, consistent with enhanced bubble-mediated transfer of the less soluble CO2 relative to that of the more soluble DMS. However, the correlation of Δkw with whitecap fraction is no stronger than with wind speed. Models used to estimate bubble-mediated transfer from in situ whitecap fraction underpredict the observations, particularly at intermediate wind speeds. Examining the differences between gas transfer velocities of gases with different solubilities is a useful way to detect the impact of bubble-mediated exchange. More simultaneous gas transfer measurements of different solubility gases across a wide range of oceanic conditions are needed to understand the factors controlling the magnitude and scaling of bubble-mediated gas exchange.

Short summary
The mechanisms that determine the air–sea exchange of gases such as carbon dioxide are not well understood. During a research cruise in the North Atlantic, we simultaneously measured the air–sea transfer of two gases with contrasting solubility over a range in wind and wave conditions. We compare the transfer of these gases to improve understanding of how bubbles from breaking waves may mediate air–sea gas fluxes.
Final-revised paper