Gas Fluxes and Steady State Saturation Anomalies at Very High Wind Speeds

Gas exchange at high wind speeds is not well understood-few studies have been conducted at wind speeds above 20 ms(-1) and significant disagreement exists between gas exchange models at high wind speeds. In this study, noble gases (He, Ne, Ar, Kr, and Xe) were measured in 35 experiments in the SUSTAIN wind-wave tank where the wind speeds ranged from 20 to 50 m s(-1) and mechanical waves were generated as monochromatic or with a short-crested JONSWAP frequency spectrum. Bubble size spectra were determined using shadowgraph imagery and wave statistics were measured using a wave wire array. The steady state saturation anomalies and gas fluxes initially increased as wind speeds increased but then leveled off, similar to prior studies of heat and momentum flux coefficients. Noble gas fluxes and steady state saturation anomalies are correlated most strongly with bubble volumes for the less soluble noble gases and with wind speed and wave Reynolds number for the more soluble noble gases. In the JONSWAP experiments, significant wave height was the most important predictor for gas steady state saturation anomalies with correlation coefficients of greater than 0.92 for He, Ne, and Ar (P < 0.05). Furthermore, invasion fluxes were larger than evasion fluxes when other conditions were similar. Taken together, these lab-based experiments suggest more attention should be paid to parameterizations based on wave characteristics and bubbles and that current wind-speed based gas exchange parameterizations should not be applied to conditions with very high wind speeds.

Automated summary

Gas exchange at high wind speeds is not well understood, and there is disagreement between gas exchange models. This study measured noble gases in experiments with wind speeds ranging from 20 to 50 m/s. The results showed that gas fluxes and steady state saturation anomalies increased with wind speeds, but then leveled off. Bubble volumes were strongly correlated with less soluble noble gases, while wind speed and wave Reynolds number were correlated with more soluble noble gases. Significant wave height was identified as the most important predictor for gas saturation anomalies in the JONSWAP experiments.