Satellite‐derived phytoplankton pigment structures in the Portuguese upwelling area

Abstract

A series of 25 Nimbus 7 coastal zone color scanner images obtained from July 1981 to September 1983 in Portuguese coastal waters was analyzed in order to study the space‐time distribution of phytoplankton pigment. In the images from winter and spring, the phytoplankton distributions showed no significant spatial patterns. During the upwelling season, from late June to October, several recurrent patterns were observed. Filaments of high pigment concentration extended zonally 200 km off the west coast of Portugal, north of Lisbon. Pigment‐rich plumes were observed south of capes along the west coast, south of Lisbon, and parallel to the south coast of Portugal. The location of the filaments and plumes coincided with topographic features such as submarine ridges. South of Lisbon the location of plumes was also related to coastal morphology. The temporal variability of the pigment patterns was compared with the wind‐induced offshore Ekman transport calculated from measurements made at two meteorological stations, located at Lisbon and Faro, on the south coast. A significant relationship was found: well‐developed phytoplankton structures were generally related to moderate or intense offshore transport, whereas the absence of plumes corresponded to either weak offshore transport or coastal convergence. For each of the three coastal areas in this study, scatter plots showed linear relationships between digital counts of phytoplankton concentration and sea surface temperature. The spatial variation of the temperature range decreased in time after the onset of an upwelling event. One cause of this variation could be the north‐south change in temperature of the upwelled Eastern North Atlantic Central Water along the Portuguese coast.

Microplankton composition, production and upwelling dynamics in Sagres (SW Portugal) during summer of 2001

“…Upwelled water masses have characteristics of the ENACW subtropical branch (temperature > 13°C, σ t < 27.1 kg m -3 ). These findings are consistent with the patterns already described for the Algarve coast (Fiúza, 1983(Fiúza, , 1984Sousa and Bricaud, 1992). Winds are mostly moderate (6-8 m s -1 ), and relatively intense velocities (8-10 m s -1 ) are only registered in July (P2), revealing a decrease in wind stress conditions in comparison with previous years (Relvas and Barton, 2002).…”

“…Wooster et al, 1976;Fiúza et al, 1982), whilst occasional upwelling occurs along the southern coast of Portugal (Algarve) with favourable westerly winds. After a prolonged period of northerly winds, fertile water can circulate around the Cabo S. Vincente, the southwestern tip of the peninsula, and flow eastwards along the southern coastal shelf (Fiúza, 1983;Sousa and Bricaud, 1992;Relvas and Barton, 2002). In contrast, a warm counter current, originating in the Gulf of Cadiz ( Fig.…”

Surface expression of Mediterranean Water dipoles and their contribution to the shelf/slope – open ocean exchange

“…A portion of the water transported offshore from the shelf re-circulates back on time scales of about 1 month (Barton et al, 2001). Filaments off Iberia are recurrently located in several fixed points (around 41 • N, 40 • N, 38.5 • N, 38 • N and 37 • N), which seem to be systematically associated with irregularities of the bathymetry or of the coastline (Fiúza, 1982;Sousa and Bricaud, 1992;Haynes et al, 1993). This systematic association led Røed and Shi (1999) to investigate the effect of irregularities in the bathymetry and coastline geometry on the formation, evolution and persistence of cool filaments and other mesoscale structures in the coastal upwelling regions.…”

Seasonal cycle of plankton production in the Iberian margin based on a high resolution ocean model

“…Bode et al, 1996;Casas et al, 1997;Castro et al, 2006;Moita, 2001;Silva et al, 2009); satellite ocean color images (Álvarez et al, 2012a;Oliveira et al, 1994;Peliz and Fiuza, 1999;Sousa and Bricaud, 1992) or frequently a combination of both (e.g. Álvarez-Salgado et al, 2002Álvarez-Salgado et al, , 2003Joint et al, 2002;Ribeiro et al, 2005).…”