The role of frontal processes in air-sea gas exchange

Burkard Baschek and David Farmer

Institute of Ocean Sciences, Sidney, Canada

5th International Symposium on Stratified Flows, proceedings, ed. G.A. Lawrence, R.Pieters, and Y. Yonemitsu, pp. 617-621, 2000.

The role of strong vertical motions associated with plunging jets overa sill on the air-sea gas exchange was studied in the estuarine regimeof Haro Strait, B.C., in October 1999. Measurements were carried outwith an acoustic resonator for measuring bubble size distributions atdifferent depths, towed CTD, vessel-mounted ADCP, and Echo Sounder. In addition, air photos were taken in order to map the extent of the tidalfronts in the region.

In these fronts, small breaking waves generate gas bubbles at the seasurface which are then trapped by highly energetic eddies and are drawndown to depths of up to 120m. The vertical current speed in thesedownwelling regions sometimes exceeded 0.5 m/s. Together with the measuredbubble size distributions it was used in a model to calculate the bubblecloud behaviour including gas dissolution effects as a function of depthproviding estimates of the gas flux into the ocean. These violent processesmay play an important role in the aeration of the water masses exchangedbetween semi-enclosed basins and the open ocean.