Award: OCE-1634467

Gases cross between the atmosphere and the ocean in a process called air-sea gas exchange. This exchange is fueled by turbulence at the air-sea boundary and becomes larger as wind speed increases. Scientists have good models and parameterizations for air-sea gas exchange at typical wind speeds (0 to 15 m s-1) which is crucial for predicting how much CO2 there is in the atmosphere and ocean. However, scientists know much less about gas exchange at high wind speeds (especially wind speeds over 25 m s-1). This is because much of gas exchange research is determined on research ships and it is not safe for the ships to operate in very stormy conditions. In order to address this knowledge gap, we performed experiments in a wind-wave tank to investigate gas exchange at high wind speeds (25 to 50 m s-1). The wind wave tank is like a large covered swimming pool that has dozens of wave paddles and an enormous fan that can blow hurricane force winds. Everything is precisely controlled and there are many scientific instruments to monitor how the ocean and air is responding to the huge wind forcing. We set up two mass spectrometers that measured gases (oxygen, argon, neon, krypton and xenon) on the top of the tank. We then performed 34 experiments where we varied the wind speed, the wave type and the water temperature while simultaneously measuring the gases in the air and the water. We also set up an imaging system within the tank to quantify the number and size of bubbles that were produced by the stormy conditions and precisely measured wave characteristics and turbulence. We thus could calculate how the gases changed during the experiment - called the gas flux – and connect the gas flux to the bubble images and to wind, bubble, and wave properties. We found that at very high wind speeds, the gas flux levels off – it does not continue to increase. This had been found previously for momentum but scientists weren’t sure if it would happen for gases too. That conclusion has a big significance for how gases are modeled in high wind conditions – such as hurricanes that are becoming more and more prevalent. We also found the gas fluxes were well connected to the bubble surface area and volume, support for the idea that bubbles are a crucial part of gas exchange for many gases. Bubbles are included in some gas exchange parameterizations but not all and this work shows that they should be and also gives ideas of how to include them. Finally we found the significant wave height predicted the gas values extremely well. The significant wave height is also not included in most parameterizations of gas exchange and this work suggests that if people start including it, they can do a much better job at predicting gas levels in the ocean. Last Modified: 12/23/2020 Submitted by: Rachel Stanley