Physical and biogeochemical fluxes in shelf waters of the NW Iberian upwelling system. Hydrography and dynamics
TL;DR: In this paper, the differences between two oceanographic patterns observed in the Galician shelf/slope are described and analyzed using wind, CTD and current meter data obtained during two cruises INCOCEANO-I and INCOCEA-II, conducted in April-May 1997 and September 1998, respectively.
About: This article is published in Journal of Marine Systems.The article was published on 2005-02-01. It has received 5 citations till now. The article focuses on the topics: Current meter & Upwelling.
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TL;DR: In this article, the authors investigated the relation between river drainage, NAO index and the North-South wind component intensity over the three months prior to the end of the estuarine colonization and the densities of S. solea and S. senegalensis in the nursery grounds.
Abstract: Spawning grounds of the soles, Solea solea and Solea senegalensis, are distant from the estuarine nurseries where juveniles concentrate. Recruitment of these species is highly dependent on the success of the larval migration towards the inshore nursery grounds. Unfavourable climate and hydrodynamic circulation may lead to high mortality rates at this stage. The relation between river drainage, NAO index and the North-South wind component intensity over the three months prior to the end of the estuarine colonization and the densities of S. solea and S. senegalensis in the nursery grounds were investigated for both species based on a discontinuous historical dataset (from 1988 to 2006) for the Tagus estuary. Multiple linear regression models were developed for sole density and environmental data (separately for each species). Results showed that river drainage is positively correlated with juveniles’ densities of both species, possibly due to the existence of chemical cues used by larvae for movement orientation. NAO index and the North-South wind component intensity relations with soles densities were non-significant. It was concluded that the high complexity of the Portuguese upwelling system makes it hard to detect causal relations of the environmental variables tested. The importance of river flow for coastal ecosystems was stressed. Since climate change scenarios predict a strong decrease in rain fall over the Portuguese river basins, as well as a concentrated period of heavy rain in winter, it was hypothesised that future river drainage decrease over much of the year may lead to lower recruitment success for soles, especially for S. senegalensis.
51 citations
TL;DR: Spatio‐temporal trends in upwelling patterns were studied along the Canary Upwelling System for the period 1967–2006 because this index is less sensitive to external factors compared to UISST.
Abstract: Spatio-temporal trends in upwelling patterns were studied along the Canary Upwelling System for the period 1967-2006. The northwestern coast of African from lat 20 degrees N to 32 degrees N is observed to be under a permanent upwelling regime characterized by coastal sea surface temperatures (SST) colder than the oceanic ones at the same latitude. The temperature difference is termed the temperature upwelling index (UI(SST)). This regime is consistent with the wind-derived Ekman transport (UI(W)), which is observed near the coast and is directed offshore. This index shows the existence of upwelling-favorable conditions all year but has an annual cycle characterized by more upwelling-favorable conditions from April to September, with a maximum in July, and less upwelling-favorable conditions from October to March, with a minimum in December to January. Although both indices can be used to characterize the phenomenon, only UI(W) values were used to quantify upwelling change during the four decades under review because this index is less sensitive to external factors compared to UI(SST). A strong decrease in upwelling intensity has been observed in all seasons. In particular, the summer (winter) decrease is on the order of 45% (20%) of the mean amplitude of the upwelling cycle.
49 citations
01 Jan 2005
TL;DR: An overview of the main oceanographic features of the eastern North Atlantic boundary, with emphasis toward the upper layers, is presented in this article, where the principal features discussed are: water mass boundaries; forcing by wind, density and tides; topographic features and effects; fronts; upwelling and downwelling; poleward flows; coastal currents; eddies.
Abstract: An overview of the main oceanographic features of the eastern North Atlantic boundary, with emphasis toward the upper layers, is presented. The principal features discussed are: water mass boundaries; forcing by wind, density and tides; topographic features and effects; fronts; upwelling and downwelling; poleward flows; coastal currents; eddies. The occurrence and spatial and seasonal
variability of these features is described in five regional sections: Celtic Sea and western English Channel; Bay of Biscay; western Iberia; Gulf of Cadiz; northwest Africa. This paper is intended to provide a base of physical oceanographic knowledge in support of research in fisheries, biological and chemical oceanography, and marine biology.
48 citations
TL;DR: The continental shelf of NW Iberia is of particular interest due to the complex North Atlantic rifting tectonics and modern oceanographic processes that led to its current geomorphological configuration and sediment dynamics as mentioned in this paper.
Abstract: The continental shelf of NW Iberia is of particular interest due to the complex North Atlantic rifting tectonics and modern oceanographic processes that led to its current geomorphological configuration and sediment dynamics. The shelf forms a narrow slow-dipping north-bearing geomorphological structure with a well-defined shelf break located at water depths of 160–180 m. It is a continental margin with sedimentation rates of about 1.5±2.0 mm a −1 (the highest values in recent bottom sediments of the ria) subjected to a highly energetic seasonal regime of waves and tides, seasonal upwelling and coast-parallel currents, significantly modulated by the North Atlantic Oscillation. Sediment provenance is dominated by inputs of continental sediments via runoff and riverine discharges and, to a lesser extent, by an upwelling-enhanced bioclastic input. Present-day sedimentation in the area occurs closely associated with two geomorphologically distinct sedimentary environments: the rias inner shelf sedimentary systems and the open continental shelf, and their subsequent evolution since the last glacial.
12 citations
Dissertation•
01 Jan 2007
TL;DR: Tese de doutoramento em Biologia (Biologia Marinha), apresentada a Universidade de Lisboa atraves da Faculdade de Ciencias, 2007.
Abstract: Tese de doutoramento em Biologia (Biologia Marinha), apresentada a Universidade de Lisboa atraves da Faculdade de Ciencias, 2007
7 citations
References
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TL;DR: In this article, the authors presented evidence of a warm, salty surface current flowing poleward along the Iberian Peninsula using a sequence of satellite infrared images and concomitant in situ hydrographic data obtained during the winter of 1983-1984.
Abstract: Evidence of a warm, salty surface current flowing poleward along the Iberian Peninsula is presented using a sequence of satellite infrared images and concomitant in situ hydrographic data obtained during the winter of 1983–1984. The current, which flows over 1500 km along the upper continental slope-shelf break zone off western Portugal, northwest and northern Spain, and southwest France, is 25–40 km wide, about 200 m deep, and characterized by velocities of 0.2–0.3 m s−1. According to the hydrographic data acquired during late November and early December 1983, the current's salinity signal off Portugal is about 0.2 practical salinity units, and its waters are ∼0.5°C warmer than the surrounding ones. The satellite observations, however, which span a longer time period and cover a much larger area, indicate that the current's typical thermal signature is 1°–1.5°C. The current's associated geostrophic volume transports show an increase from about 300×103 m3 s−1 near 38°3′N to 500–700×103 m3 s−1 at 41°–42°N. The origin of this poleward flow and the causes for its increasing transport off western Iberia are investigated. Onshore Ekman convergence induced by southerly winds along the Portuguese west coast provides about one fifth of the computed transports in the correct direction. A mechanism giving better quantitative agreement with the observations is the geostrophic adjustment of the eastward oceanic flow driven by the large-scale meridional baroclinic pressure gradient in the eastern North Atlantic as the flow reaches the continental slope of the western Iberian Peninsula. Topographic trapping by the bathymetric step existing along the shelf break explains both the width and the path of the observed current. The role of “dam break” type mechanisms is discarded owing to strong discrepancies between the available models and the present observations. Since satellite images reveal that similar situations occurred during many winters, the flow identified here appears as a characteristic feature of the winter circulation off southwest Europe. Furthermore, the occurrence of analogous poleward flows in eastern boundary layers of the subtropical and mid-latitude oceans suggests that these currents are typical features of those regions' winter circulation.
381 citations
TL;DR: The results of a fine resolution hydrology survey conducted off the northern Portuguese coast at the end of the upwelling season are presented in this paper, where the most striking features were the up-welling front and the associated southward jet.
214 citations
01 Jul 1998
TL;DR: In this paper, the distribution of the water masses and their circulation in the eastern North Atlantic region off the northern half of the west coast of the Iberian Peninsula are analyzed based on CTD measurements made in May 1993 during the MORENA 1 cruise.
Abstract: The distribution of the water masses and their circulation in the eastern North Atlantic region off the northern half of the west coast of the Iberian Peninsula are analysed here based on CTD measurements made in May 1993 during the “MORENA 1” cruise. The upper layers of the ocean, down to about 100 m, showed a typical spring, non-upwelling situation with a very shallow seasonal thermocline overlying thicker remnants of the mixed layer from the previous winter. Below, Central Water extended between a subsurface salinity maximum near depths of 100–140 m and a salinity minimum at about 500 m. Using quantitative water mass analysis and geostrophic calculations, a poleward surface current reaching down to depths of 250 m and transporting relatively warm and saline Eastern North Atlantic Central Water (ENACW) of subtropical origin was characterised, centred at a few tens of km offshore the shelf break, therefore indicating that the northward current identified previously in this region during winter (the Portugal Coastal Countercurrent) continues to be present through the spring season. A large-scale transition zone, the Galicia Front, was found in the northwest area of the study region, reaching from the surface layers down to the depths of the Mediterranean Water. To the north of this front, relatively fresh Central Water of Western Atlantic origin replaced the subtropical branch of ENACW. At the deeper Central Water levels, ENACW from subpolar North Atlantic origin was present through the whole study region. The influence of the upper and lower cores of Mediterranean Water was present, centred at levels of 800 and 1100 m, as indicated by their characteristic thermohaline maxima. The deduced flow of Mediterranean Water was towards the north in the whole study region, in clear relation with the Portugal Slope Undercurrent, and showed some tendency to branch towards the west through the gap between the Vigo Seamount and the Galicia Bank. The Mediterranean upper core occupied a relatively thin layer, O (100 m), and underwent a strong dilution of about 45% from the south to the north of the study region; the lower core spread over a larger depth range, of about 400–500 m, and decayed only by about 20% through the region. Below the Mediterranean Water, the influence of North Atlantic Deep Water spread through the study region, and an intermediate layer of Labrador Sea Water was also present, particularly offshore in the northwest zone.
195 citations
TL;DR: In this paper, it was shown that steric height near the coast varies seasonally in phase with the measurements at the tide gages and that the high elevations in winter are a consequence of the circulation of the subarctic cyclonic gyre of the North Pacific Ocean.
Abstract: Coastal sea elevations measured at tide gages in the northern North Pacific when adjusted for the atmospheric pressure show a seasonal high in winter (November–February). This high is well out of phase with the midocean response of geopotential anomaly (steric height) to the heating and cooling cycle, which produces highest steric elevations in July–October. We attempt to show that steric height near the coast varies seasonally in phase with the measurements at the tide gages and that the high elevations in winter are a consequence of the circulation of the subarctic cyclonic gyre of the North Pacific Ocean. The flow of the coastal limb of this gyre (along the eastern, northern, and western boundary of the ocean) is intensified in winter, and in geostrophic balance the sea surface slopes upward toward the coast, accounting for the winter rise. Sea elevation along the eastern boundary as determined from steric height does not slope uniformly downward from the equator toward higher latitudes but has several maxima and minima. These appear to be the consequence of the sea surface slopes associated with the quasi-geostrophically balanced system of cyclonic and anticyclonic gyres in middle and high latitudes and zonal flows near the equator.
178 citations