Spring–summer climatological circulation in the upper layer in the region of Cape St. Vincent, Southwest Portugal

Abstract

Geostrophic transport and hydrographic measurements derived from a historical database (1900–1998) were used to study the spring–summer mean circulation in the upper layer south and west of Cape St. Vincent, Southwest (SW) Portugal. The larger-scale circulation scheme is forced by equatorward winds from May to September, when the Iberian coastal transition zone (CTZ) is dominated by a generalized upwelling of cold, low-salinity water. A partially separated surface jet intensified at the shelf break conveys ∼1 Sv of upwelled water equatorward parallel to the bathymetry, while offshore a poleward flow transports ∼0.4–0.6 Sv of upwelled water. Although alongshore transports dominate the circulation pattern of the upper layers, cross-shore transports are significant at the climatological scale. Anticyclonic circulation with an exchange of ∼0.5 Sv from the equatorward jet to the offshore poleward flow and the partial re-circulation further north, back into the equatorward flow are discussed. A coherent, cyclonic re-circulation pattern inshore of the upwelling jet is also speculated. From these results the shelf break is considered a climatological border at both sides of which two major re-circulation cells occur. The climatological equatorward flow has offshore protrusions, interpreted as recurrent episodes of major contortions of the upwelling flow. These features bring about considerable “cross-shelf flow” re-circulation reaching up to 50% of the main flow. The most significant exchanges are found to be associated with major changes of orientation of the coastline. Off Cape St. Vincent the upwelling front stretches to both west and south and contributes to the cross-shelf re-circulations. Additionally, convergence of the upwelling flow and a branch of the Azores current, with associated re-circulation is found diagonally from the cape. On the southern coast the upwelling jet is seen to meander offshore in the vicinity of Cape St. Maria. Individual synoptic cruise data showed agreement with the climatological circulation features. We conclude that these oceanographic features leave an imprint on the climatic circulation in spite of the “smoothing out” of recurrent events over the spring–summer period of the years of 1900–1998.

Population genetics of Zostera noltii along the west Iberian coast: consequences of small population size, habitat discontinuity and near-shore currents

“…A coastal warm water counter-current runs south to north from the Gulf of Cadiz along the southern Portuguese coast (Relvas & Barton 2002), sometimes as far as the Rio Sado, creating an obstacle to dispersal between northern and southern populations. Additionally, the equatorward current of cold water becomes separated from the coast around the latitudes of the Tagus River (Sanchez & Relvas 2003). There are 2 other features that can function as geographical barriers and may increase the effect of coastal currents on dispersal and gene flow.…”

Coccolithophore variability from the Shackleton Site (IODP Site U1385) through MIS 16-10

“…The high seasonally-controlled temperature variability and zonal gradients are the main features of surface waters at the location of Site U1385 (Peliz et al, 2005;Eynaud et al, 2009). The northward displacement and strengthening of the Azores highpressure cell causes upwelling-favorable northerly winds between April and October (Fiúza et al, 1982;Fiúza, 1984;Sousa and Bricaud, 1992;Sánchez and Relvas, 2003). The PC develops at this time and transports recently upwelled, cold and nutrient-rich waters along the Iberian margin (Wooster et al, 1976), stimulating the primary productivity.…”

Seasonal trends of the reproductive cycle of Octopus vulgaris in two environmentally distinct coastal areas

“…The factors that trigger the onset of the reproduction seem to be related with the seasonal occurrence of favorable oceanographic conditions, such as higher temperatures and salinities, favored by the easterly winds which are common during summer in the coastal areas close to Cape St a Maria (Sánchez and Relvas, 2003;García-Lafuente et al, 2006). Ecologically, the GCS is a less dynamic and oligotrophic system, in which species tend to direct all of their energy onto a single spawning peak, such as in the case of the sardine Sardina pilchardus, the anchovy Engraulis encrasicolus and the wedge sole Dicologlossa cuneata (Baldó et al, 2006).…”