Award: OCE-1634432

This experimental program sought to observe the transfer rates across the air-sea interface of a range of noble gases in varying wind, wave and thermal environments. The purpose being to better understand the gas transfer rates of climatologically relevant gases such as carbon dioxide in variable wind and wave conditions, such that key processes can be quantified. Here we report on the University of Miami component of the study which was primarily concerned with measuring the physical characteristic extant in the laboratory during the gas transfer measurements. Two comprehensive experimental studies were conducted including 14 separate runs in 2017 and 35 runs in 2018. The latter set of experiments included measurements of wave and wind parameters, bubble size distributions and subsurface turbulence all of which are thought to have a strong influence on air-sea gas transfer rates. We observed that the surface wind, wave structure and in particular wave breaking controlled the size and number of entrained bubbles. Increasing the surface winds, wave steepness and the amount of wave breaking resulted in a shift of the bubble sizes toward smaller bubbles in monochromatic waves and toward larger bubbles in short-crested spectral waves. This difference in response based on wave characteristics was attributed to a shift in the amount of wave breaking occurring in each case. We also investigated the effect of bubbles on the spectral distribution of turbulent kinetic energy and on its dissipation rate. Both turbulent kinetic energy and dissipation increased as wave steepness increased, which was associated with an increased number of bubbles with smaller radii. When wave breaking was frequent, the slope of the turbulent kinetic energy spectrum was increased particularly for high wave frequencies. In non-breaking conditions the slope of the turbulent kinetic energy was closer to the predicted theoretical values. Specific outcomes of this work include: 1) Successful completion of 14 experiments in the SUSTAIN facilty in 2017. 2) Successful completion of 35 experiments in the SUSTAIN facilty in 2018. 3) Internal presentation at the University of Miami, Rosentstiel School of Marine and Atmospheric Sciences, COMPASS seminar series. 4) Presentation of results at the 2020 Ocean Sciences meeting 5) Inclusion of the results in the thesis of Andrew W. Smith which is in preparation for completion in the fall of 2020. 6) Anticipated publication of the work in Summer 2020. 7) Archiving of all data on the NSF BCO-DMO project website https://www.bco-dmo.org/project/776111 has been initiated and will be completed shortly. Last Modified: 01/14/2020 Submitted by: Brian Haus