Short‐timescale thermohaline variability and residual circulation in the central segment of the coastal upwelling system of the Ría de Vigo (northwest Spain) during four contrasting periods

Abstract

Sixteen hydrographic surveys were carried out in the middle segment of the Ría de Vigo (northwest Spain) at 3‐ to 4‐day intervals during February, April, July, and September 2002 (four surveys per period). Simultaneously, an acoustic Doppler current profiler (ADCP) mooring recorded the velocity profile. Combination of direct current measurements with the output of an inverse model based on the time course of the distributions of salinity and temperature allowed an objective analysis of the effect of the meteorological forces on the hydrodynamics of the Ría. Remote shelf winds explained more than 65% of the variability of the subtidal circulation, which responded immediately to this forcing (lag time, <2 days). Shelf winds created a simple two‐layered circulation pattern, with a surface outgoing current under northerly winds and a surface ingoing current under southerly winds. A three‐layered circulation developed during the transitions from northerly to southerly winds and vice versa. At the same time, an empirical orthogonal function (EOF) analysis demonstrated the lack of contribution of local winds to the subtidal dynamics of the ría. Continental runoff and heat exchange with the atmosphere explained less than 5% and 25% of the variability observed in the subtidal circulation of the Ría de Vigo.