Onset and development of the Iberian poleward flow along the Galician coast

Abstract

Satellite, cruise and mooring observations in October and November 1999 have characterised the onset and development of the poleward flow along the Galician continental shelf and slope. Downwelling favourable winds during the cruise triggered the onset of the poleward flow. An offshore zonal temperature gradient, identifiable near 42 in Sea Surface Temperature imagery, extended shorewards as coastal upwelling was suppressed by downwelling winds. Over the continental slope, the front turned more parallel to shore, as surface warm water was advected northward in the poleward flow. Downwelling winds increased mixing nearshore causing the pycnocline to intersect the upper slope to form a bottom front enhancing poleward geostrophic flow over the shelf. On the slope, a sub-surface salinity maximum was associated with the poleward flow, becoming better defined as the poleward flow persisted. The flow was surface intensified and continuous to 650 m with maximum speeds of 0.2 ms-1. The associated mean poleward transport was estimated at 2 ± 0.5 Sv. Direct transfer of momentum by the wind, elevation of sea level at the coast resulting from onshore Ekman transport, and the JEBAR mechanism all contribute towards the development of the poleward flow over the Galician shelf.