The effect of bubble‐mediated gas transfer on purposeful dual‐gaseous tracer experiments

For air‐water gas exchange across unbroken surfaces, the only gas‐dependent parameter affecting the transfer velocity is the molecular diffusivity of the transferring species. In contrast, bubble‐mediated transfer processes can cause the transfer velocity to depend on both molecular diffusivity and aqueous‐phase solubility. This can complicate the analysis of data from dual‐gaseous tracer gas transfer experiments. Bubble effects also complicate the estimation of transfer velocities for other gases from the transfer velocity calculated using the dual‐tracer data. Herein a method for incorporating the effects of bubble‐mediated gas transfer processes on the transfer velocity is presented. This new procedure is used to analyze the data from two recent dual‐tracer gas transfer experiments. Transfer velocities that include the effect of bubbles are calculated using the data from two previous oceanic dual‐gaseous tracer experiments. Comparing these transfer velocities with transfer velocities calculated by neglecting the effect of bubbles shows that bubble‐mediated transfer increased the transfer velocity of helium 3 by 5% at a wind speed of 10.6 m s−1. However, when using the transfer velocities for helium 3 to calculate transfer velocities for carbon dioxide under the same conditions, including the effect of bubbles decreases the transfer velocity of carbon dioxide by 18%. This shows that bubble‐mediated transfer does not have a large effect on the analysis of dual‐tracer data, but it is important in relating transfer velocities determined using helium 3 and sulfur hexafluoride to transfer velocities of more soluble gases at wind speeds above 10 m s−1.