Gas Exchange (GasEx) Process Studies

Currently, large uncertainties in the air-sea flux of CO₂ prevent verification of the partitioning of fossil fuel CO₂ between the ocean and the terrestrial biosphere. These uncertainties limit the ability of models to realistically predict future atmospheric CO₂ levels. Techniques are now in hand to improve estimates of air-sea fluxes. The first gas exchange experiment, GasEx-98, occurred in the CO₂ sink region of an anticyclonic warm core ring in the eastern North Atlantic during May and June of 1998.Air-sea gas exchange was studied using a variety of direct and indirect approaches. For more information please visit the GasEx-98 web site.

The second study, GasEx-2001, took place in the upwelling region of the eastern Equatorial Pacific in February and March, 2001. The low annual mean wind speeds in the Equatorial Pacific and high ΔpCO₂ values, offered a unique opportunity to directly determine the fluxes in a low wind stress environment and to elucidate the factors controlling the flux. Most of the GasEx-2001 experiments involved measurements taken by and around a drifting array of near-surface instruments. For more information please visit the GasEx-2001 web site.

The latest GasEx study was conducted in the Atlantic sector of the Southern Ocean (SO-GasEx) between 29 February and 12 April, 2008. The scientific work concentrated on quantifying gas transfer velocities using deliberately injected tracers, measuring CO₂ and DMS fluxes directly in the marine air boundary layer, and elucidating the physical, chemical, and biological processes controlling air-sea fluxes with measurements in the upper-ocean and marine air. The oceanic studies used a Lagrangian approach to study the evolution of chemical and biological properties over the course of the experiment using shipboard and autonomous drifting instruments. The SO-GasEx) experiment was designed to address the following questions:

• What are the gas transfer velocities at high winds?
• What is the effect of fetch on the gas transfer?
• How do other non-direct wind effects influence gas transfer?
• How do changing pCO₂ and DMS levels affect the air-sea CO₂ and DMS flux, respectively in the same locale?
• Are there better predictors of gas exchange in the Southern Ocean other than wind?
• What is the near surface horizontal and vertical variability in turbulence, pCO₂, and other relevant biochemical and physical parameters?
• How do biological processes influence pCO₂ and gas exchange?
• Do the different disparate estimates of fluxes agree, and if not why?
• With the results from Southern Ocean GasEx, can we reconcile the current discrepancy between model based CO₂ flux estimates and observation based estimates?
 

For more information please visit the SO-GasEx web site.