Abstract. Simultaneous air-sea fluxes and concentration differences of dimethylsulfide (DMS) and carbon dioxide (CO 2 ) 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 ( k w ) 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 k w , consistent with enhanced bubble-mediated transfer of the less soluble CO 2 relative to that of the more soluble DMS. However, the correlation of k w 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.

High‐resolution images of the ocean surface are examined using digital processing, achieving quantifications of actively breaking (WA), maturing (WB), and total (WT = WA + WB) whitecaps. The images are selected from two data sets of the North Atlantic and Southern Ocean to sample a maximal range of environmental conditions. A total of 125,860 images were processed and averaged to establish 622 10 min periods. Parameterizing WA, WB, and WT with wind speed achieved modest correlations while also displaying large variabilities. Parameterizing WT with wind speed and specific Reynolds numbers achieved correlation coefficients ranging from 0.76 to 0.79. The filtering of WT into its active stage of evolution WA and subsequent fittings with wind speed and specific Reynolds numbers achieved reduced correlation coefficients ranging from 0.62 to 0.66. We suggest that the contribution of WB serves to conceal and thus underestimate the variability of actively breaking waves.

<p><strong>Abstract.</strong> Simultaneous air/sea fluxes and concentration differences of dimethylsulfide (DMS) and carbon dioxide (CO<sub>2</sub>) were measured during a summertime North Atlantic cruise in 2011. This dataset reveals significant differences between the gas transfer velocities of these two gases (Δ<i>k<sub>w</sub></i>) over a range of wind speeds up to 21 m  s<sup>−1</sup>. 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 Δ<i>k<sub>w</sub></i>, consistent with enhanced bubble-mediated transfer of the less soluble CO<sub>2</sub> relative to that of the more soluble DMS. However, the correlation of Δ<i>k<sub>w</sub></i> with whitecap fraction is no stronger than with wind speed. Models used to estimate bubble-mediated transfer from in situ whitecap fraction under-predict 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.</p>

No abstract

High-resolution measurements of actively breaking whitecap fraction (WFA) and total whitecap fraction (WFT) from the Knorr11 field experiment in the Atlantic Ocean are compared with estimates of whitecap fraction modeled from the dissipation source term of the ECMWF wave model. The results reveal a strong linear relationship between model results and observed measurements. This indicates that the wave model dissipation is an accurate estimate of total whitecap fraction. The study also reveals that the dissipation source term is more closely related to WFA than WFT, which includes the additional contribution from maturing (stage B) whitecaps.