Air-Sea Gas Exchange

It is important to improve our understanding of air-sea gas exchange processes for various reasons: the ocean can potentially store large amounts of CO2 and therefore plays an important role in the global carbon cycle. An understanding of the processes by which CO2 is exchanged between atmosphere and ocean therefore helps to assess the climatic effects of anthropogenic CO2. Moreover, air-sea exchange plays an important role in the biogeochemical cycling of many gases. This has motivated a number of international and national programs, most notably the SOLAS program: “An improved knowledge of mechanisms underlying air-sea gas exchange is essential for interpreting regional and global scale biogeochemical and physical processes, and hence for the development of models with realistic prognostic capabilities showing the results of changes in forcing” (SOLAS, 2002).

In the coastal environment, where productive but fragile ecosystems are commonly found, oxygen is of major importance. In many heavily populated areas, the subsurface waters of bays and estuaries can reach anoxic – or close to anoxic – conditions. This is caused by the excessive input of nutrients by rivers and surrounding communities. It is therefore desirable to better understand the gas exchange processes typical for the coastal ocean, especially those processes like sill flows and tidal fronts that deliver aerated water to depths below the surface layer (see air-sea gas exchange in tidal fronts).

Dissolved gases can be used to assess the relevant air-sea gas exchange mechanisms by taking advantage of their different physical and chemical properties. For this, especially measurements of dissolved noble gases (He, Ne, Ar, Kr, Xe) present a valuable tool, because of their independence of biogeochemical cycles. Because of the large, approximately order of magnitude range in solubility and molecular diffusivitiy between the noble gases, there is a substantial difference in their response to different air-sea gas exchange mechanisms like bubble injection or diffusion, which allows it to separate the contribution of these exchange mechanisms to the aeration of water.

Research interests: