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Surface waters of the NW Iberian margin: Upwelling on the shelf versus outwelling of upwelled waters from the Rías Baixas

AuthorsÁlvarez-Salgado, Xosé Antón ; Gago, Jesús ; Martín Míguez, Belén ; Gilcoto, Miguel ; Pérez, Fiz F.
Box model
Spanish rias
Issue Date2000
CitationEstuarine, Coastal and Shelf Science 51(6): 821-837 (2000)
AbstractA set of hydrographic surveys were carried out in the Ría of Vigo (NW Spain) at 2–4 d intervals during four 2–3 week periods in 1997, covering contrasting seasons. Residual exchange fluxes with the adjacent shelf were estimated with a 2-D, non-steady-state, salinity–temperature weighted box model. Exchange fluxes consist of a steady-state term (dependent on the variability of continental runoff) and a non-steady-state term (dependent on the time changes of density gradients in the embayment). More than 95% of the short-time-scale variability of the exchange fluxes in the middle and outer rı´a can be explained by the non-steady-state term that, in turns, is correlated (R2>75%) with the offshore Ekman transport. Conversely, 96% of the variability of exchange fluxes in the inner rı´a rely on the steady-state term. The outer and middle rı´a are under the direct influence of coastal upwelling, which enhances the positive residual circulation pattern by an order of magnitude: from 102 to 103 m3 s 1. On the contrary, downwelling provokes a reversal of the circulation in the outer rı´a. The position of the downwelling front along the embayment depends on the relative importance of Ekman transport (Qx, m3 s 1 km 1) and continental runoff (R, m3 s 1). When Qx/R>7 2 the reversal of the circulation affects the middle rı´a. Our results are representative for the ‘Rı´as Baixas’, four large coastal indentations in NW Spain. During the upwelling season (spring and summer), 60% of shelf surface waters off the ‘Rı´as Baixas’ consist of fresh Eastern North Atlantic Central Water (ENACW) upwelled in situ. The remaining 40% consists of upwelled ENACW that previously enters the rı´as and it is subsequently outwelled after thermohaline modification. During the downwelling season (autumn and winter), 40% of the warm and salty oceanic subtropic surface water, which piled on the shelf by the predominant southerly winds, enters the rías.
Description17 páginas, 1 apéndice, 7 figuras, 3 tablas
Publisher version (URL)http://dx.doi.org/10.1006/ecss.2000.0714
Appears in Collections:(IIM) Artículos
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