SECONDARY CIRCULATION ASSOCIATED WITH A SHELFBREAK FRONT

Evidence for secondary circulation associated with a shelfbreak front is obtained from a high-resolution, cross-shelf section of hydrographi c, optical and velocity fields. Convergence in the bottom boundary lay er on the inshore side of the front and subsequent upwelling into the interior is evident by a mid-water region of suspended bottom material emanating from the foot of the front and extending to within 35 m of the surface, 80 m above bottom. Downwelling on the offshore side of th e front in the upper water column is inferred from a 20-m downward ben d of the subsurface phytoplankton layer. These observations are in agr eement with recent model predictions for secondary circulation near an idealized shelfbreak front. Convergence in measured cross-shelf veloc ity at the foot of the front is consistent with upwelling of bottom ma terial detected there. An estimate of 9+/-2 m day(-1) of upwelling on the inshore side of the shelfbreak front is obtained, implying a trans it time from the bottom to the surface of 10-16 days.