Finestructure measurement of vertical mixing in the vicinity of fronts on Georges Bank

D. Ullman, D. Hebert, and J. Barth

The difficulty of measuring cross-frontal fluxes in the vicinity of a moving front is compounded by the fact that the relevant mixing processes may be intermittent in time and patchy in space. A sampling scheme of repeated rapid transects across the front can be used to resolve such processes. During June, 1999 on the southern flank of Georges Bank, we conducted intensive SeaSoar hydrographic surveys in the vicinity of both the tidal mixing front and the shelfbreak front. Two types of surveys, larger scale radiator patterns (~35 km lines traversed in ~3 hours) and smaller scale butterfly patterns (20 km by 10 km completed in ~6 hours), were carried out. A quasi-Cox number computed from conductivity sampled at 24 Hz is a qualitative indicator of vertical mixing. We present the space-time distribution of this parameter relative to the fronts over the tidal cycle in order to identify the important locations and times of small scale mixing.