Date

2018

Department or Program

Chemistry

Primary Wellesley Thesis Advisor

Rachel H.R. Stanley

Additional Advisor(s)

Christopher R. Arumainayagam

Additional Advisor

Mala L. Radhakrishnan

Abstract

Gas flux at high wind speeds is not fully understood, and bubbles are rarely accounted for in models of air-sea gas exchange. Observing noble gas fluxes under bubble-rich and high wind conditions provides needed insight into fundamental gas exchange laws. The noble gases are ideal tracers for measuring gas exchange because they are inert and only respond to physical forcing; their range of physical properties results in unique responses to environmental changes for each gas. To quantify the effect of physical processes on gas fluxes, we took discrete and continuous measurements of noble gas ratios at the University of Miami Rosenstiel School of Marine and Atmospheric Science’s SUrge STructure Atmospheric InteractioN (SUSTAIN) wind-wave tank.

Over five days of experiments, we implemented 10-meter (U10) equivalent wind speeds ranging from 10-36 m s-1, water temperatures ranging from 18 to 27.5 degrees Celsius, and wave conditions including regularly breaking waves, irregularly breaking waves, and waves targeted to break at our sampling location. We used a Gas Equilibration Mass Spectrometer (GEMS) system to continuously measure noble gas ratios (with Ne, Ar, Kr and Xe), with a temporal resolution of ~15 minutes, during the experiments. The GEMS was calibrated using cold-welded copper tube discrete samples, which also yield concentrations of the noble gases, including helium. Bubbles were imaged during the experiments with a submerged shadowgraph, and physical parameters such as short-scale surface roughness, wave amplitude and water velocity were continuously monitored.

Although the SUSTAIN tank cannot truly replicate oceanic processes, we can use the data to make direct links between physical conditions and gas fluxes. These links should prove useful to increasing our mechanistic understanding of air-sea gas exchange and improving gas transfer parameterizations, especially for bubble-rich and high wind conditions.

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