Study synthesizes 25 years of technological advances in observing the air–sea exchange of trace gasses

View from bridge of R/V Knorr during a storm in the HiWinGS field program

A study led by the Physical Sciences Laboratory and published in the journal Frontiers in Marine Science synthesizes 25 years of theoretical advances and observing technology development to characterize the air–sea exchange of trace gasses. Air–sea gas transfer parameterizations are critical components of climate models and can be used to compute global carbon amounts and assess the uptake of human production of CO2. Observations from four recent research vessel cruises were analyzed in the context of NOAA's COARE trace gas transfer parameterization: a theory of mixing between the air and ocean. The two gasses used in the analysis allowed researchers to improve understanding of gas solubility effect on the gas exchange.

This study used direct measurements of the air–sea exchange of CO2 and DiMethyl Sulfide (DMS), at wind speeds from 2-25 m/s over the ocean. Gas transfer between the atmosphere and ocean is driven by near-surface processes. For weakly soluble gasses, such as CO2, whitecap processes dominate at high wind speeds (greater than 10 m/s) leading to a strong wind speed dependence. For more soluble gasses, such as DMS, the transfer is nearly linear in wind speed. The COARE parameterization code is described in a supplement, and the codes available at PSL and GitHub.

Air–sea gas transfer parameterizations are critical components of climate models. Such parameterizations applied to marine observations of meteorology and air-sea CO2 concentrations to compute global carbon budgets, assess the uptake of human production of CO2, and project future evolution of atmospheric and oceanic CO2 concentrations. The strong wind speed dependence of CO2 transfer implies an emphasis of high-wind-speed oceanic regions (high latitudes) in the net CO2 budget.

Fairall, C. W. (PSL), M. Yang, S. E. Brumer, B. W. Blomquist (PSL/CIRES), J. B. Edson, S. Pezoa (PSL), E. J. Thompson (PSL), C. J. Zappa, L. Bariteau (PSL/CIRES), T. Bell, E. Saltzmann (2022): Air-sea trace gas fluxes: Direct and indirect measurements. Front. Mar. Sci.,