DOGEE-SOLAS: The UK SOLAS Deep Ocean Gas Exchange Experiment

The aim of the project is to increase our understanding of air-sea gas transfer including the processes that influence it and how best to accurately parameterize it.

Air-sea gas exchange is important in many global biogeochemical cycles and important issues including anthropogenic CO2 uptake by oceans and the marine source of greenhouse gases such as N2O and CH4 amongst others require the calculation of air-sea gas fluxes. Calculating these fluxes depends on accurately quantifying the gas transfer velocity, kw, a physical transport term that must be derived indirectly from field data such as the measured evasion rates of purposefully released tracer gases.

kw is a function of interfacial turbulence which results from the interactions between several geophysical forcings and accurately quantifying it is not simple. These geophysical forcings include wind speed, sea surface roughness, wave geometry, wave breaking, bubbles and related processes such as whitecapping and surfactants. Earlier studies focused on deriving empirical relationships between kw and wind speed however the relationships identified are highly non-linear and most parameterizations strongly diverge at high wind speeds. It now appears likely that using wind speed alone to predict kw is flawed and more recent efforts have focused on the additional geophysical controls.

The project will involve detailed studies of the aforementioned processes within two dual tracer (SF6 and 3He) release experiments in the North Atlantic designed to measure kw. There will be particular emphasis on the role of surfactants and one of the tracer experiments will involve a deliberately added surfactant. Measurements will also be made of natural surfactants in the field experiments following development of a suitable method (possibly electrochemical). A recent hypothesis that CDOM should be a good predictor of surface active material will also be tested.