New Release of NOAA COARE Air-Sea Gas Transfer Parameterization

January 9, 2006

Christopher Fairall and Jeffrey Hare of the NOAA Earth System Research Laboratory (ESRL), and Tim Bates of NOAA Pacific Marine Environmental Laboratory (PMEL) are collaborating with scientists from the University of Hawaii Department of Oceanography (UH) to extend and verify the NOAA COARE flux parameterization to characterize the flux of dimethyl sulfide (DMS) from the ocean to the atmosphere. Their recent findings will be submitted this week for publication in the American Geophysical Union's "Geophysical Research Letters."

Background: DMS, which is the principal oceanic biological component of the global sulfur cycle, is released into the ocean by phytoplankton and subsequently invades the atmospheric boundary layer as a trace gas via sea-air turbulent transfer. Once in the atmosphere, DMS is transformed to aerosols and is believed to be the principal contributor to cloud condensation nuclei (CCN) over most of the open ocean. Greater concentrations of CCN tend to lead to higher cloud albedo. This provides a strong link between oceanic biology and the surface energy budget of the ocean (i.e., ocean thermodynamics) that has been suggested to be a fast biological climate feedback mechanism.

The NOAA COARE flux parameterization was originally developed for traditional meteorological air sea fluxes of momentum, heat and moisture. The algorithm was extended to account for CO2 in 2000 and ozone in 2004. A breakthrough in observational technology allowed the NOAA-UH team to perform the first ever direct eddy correlation (EC) measurements of DMS flux from a ship (the NOAA Ship Ronald H. Brown). This breakthrough was made possible by recent advances in various aspects of EC measurement methods: realtime motion corrections of sonic anemometer signals (ESRL), a new technology in fast DMS measurements (UH), and accurate measurements of seawater DMS concentrations (PMEL). These initial experimental results were verified by a subsequent cruise in the Atlantic. Previously, the transfer rate of DMS from water to air could only be estimated by assuming DMS transfer physics were the same as CO2. The new measurements demonstrate this analogy is acceptable for low to moderate wind speeds, but in stronger winds DMS is not released from the ocean as quickly as CO2. This difference was predicted by the NOAA COARE parameterization because the much lower solubility of CO2 leads to a greater transfer enhancement by ocean bubbles. This research supports NOAA's mission goal of understanding climate variability and change to enhance society's ability to plan and respond.

Contact: Christopher Fairall