Gas supersaturation in the surface ocean: The roles of heat flux, gas exchange, and bubbles

In this paper, a one-dimensional model of mixed layer dynamics is used to examine the roles of heat flux, gas exchange, and bubble processes in producing nitrogen and argon gas supersaturation in the surface subtropical Pacific ocean at U.S. JGOFS Station ALOHA during 1989–1990. The N2/Ar ratio is measured within a high degree of accuracy by mass spectrometry, and the ratio is sensitive to the mode of bubble gas transfer. Our results demonstrate that bubble processes are essential to produce observed supersaturation levels. N2/Ar ratios at Station ALOHA indicate that air injection of small (totally-dissolving) bubbles is the dominant process during the summer, but during the fall and winter, larger (partially-dissolving) bubbles become more important. Given current measurement techniques, it is possible to distinguish between small and large bubbles when inert gas supersaturations are high ( > 2%) and when the dynamic range in predicted inert gas ratios is largest (late fall). Existing models that parameterize bubble dynamics as a function of wind speed do not reproduce the high observed supersaturations that this study indicates are influenced by large bubble processes.