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UP: Umweltphysik

UP 1: SOLAS

UP 1.2: Hauptvortrag

Montag, 22. März 2004, 11:40–12:20, HS 118

Methods for in situ Measurement of Air-Sea Gas Exchange Rates — •Peter S. Liss — School of Environmental Science, University of East Anglia

The flux of gases between the atmosphere and the oceans can be calculated from the product of the concentration difference across the sea surface and a kinetic term, often called a transfer velocity. In this talk I will concentrate on the latter term, and in particular ways by which it can be determined from measurements at sea.

The transfer velocity is frequently parameterised in terms of wind speed, although the actual exchange process is also affected by factors including wave height and slope, wind fetch, sea state, bubble field and degree of white capping, all of which directly or indirectly affect the amount of mixing in the surface water. Because these factors are largely wind driven they are often amalgamated together in terms of wind speed, and the data displayed as transfer velocity versus wind speed plots.

Other properties which may be important for air-sea gas transfer rates include surfactants and the chemical reactivity of the gas in seawater. The importance of these latter two factors is less well established, with considerable controversy over the role of surfactants, and with chemical reactivity only likely to be important for gases with very rapid aqueous phase chemistry.

There is currently significant uncertainty in in situ values for the transfer velocity, with the degree of uncertainty greatest at high wind speed, where few field data points exist. Over the last decade several novel approaches have been applied to the task of measuring air-sea gas exchange rates at sea or remotely. In this talk I will review the more promising of these approaches and point the ahead for future field studies. Finally, a brief description will be given of the SOLAS (Surface Ocean - Lower Atmosphere Study) international research project, a significant part of which is devoted to better understanding and improved field measurements of the kinetics of air-sea exchanges.