Analysis and modeling of physical processes in Coastal Margins of the Strait of Gibraltar

El presente trabajo de investigación aborda el estudio de los procesos submesoescalares en los bordes costeros del Estrecho de Gibraltar, focalizando sobre tres aspectos principales; Se han analizado los procesos submesoescalares de transporte en el Estrecho de Gibraltar, resaltando la zona del Umbral de Camarinal, y prestando especial atención a los procesos de transporte transversal, las convergencias y divergencias que tienen lugar en la zona central del estrecho, y los patrones de circulación a pequeña escala a lo largo de la costa norte. Este análisis se realizó basándose en imágenes de temperatura superficial de alta resolución (7m) adquiridas mediante un sensor hiperespectral aerotransportado, complementadas con un experimento de suelta de trazador (rodamina), medidas continuas de termosalinógrafo, perfiles de corriente ADCP/VMADCP, y simulaciones con modelos numéricos. Las dinámicas de periodos mareales y de corto periodo en la Bahía de Algeciras han sido analizadas basándonos en datos de perfiles CTD y de corriente VMADCP registrados durante una campaña oceanográfica realizada en la Bahía de Algeciras en dos fases; la primera coincide con condiciones de mareas muertas y la segunda en condiciones de maras vivas. Las estructuras “en escalera” presentes en los perfiles de densidad indicaban una notable actividad de mezcla en la vertical. Finalmente, se estudiaron los procesos de intercambio de masas de agua entre la Bahía de Algeciras y el Estrecho de Gibraltar a escala subinercial. Durante la campaña oceanográfica se observó que las propiedades físicas de la capa superficial dentro de la bahía sufrían un cambio drástico en aproximadamente dos semanas. Se ha estudiado el mecanismo responsable de activar los procesos de intercambio de masas de agua entre los dos dominios con la ayuda de los datos de corriente superficial adquiridas recientemente a partir del sistema de radares costeros de alta frecuencia desplegados en el lado oriental del estrecho, complementados con imágenes de temperatura superficial y clorofila adquiridas por el sensor MODIS. XX    El análisis indica que el acoplamiento entre los procesos de afloramiento inducidos por la marea interna y la generación de ondas internas de gran amplitud, y los vórtices ciclónicos formados en el margen costero, podría ser el mecanismo que explique los frecuentes máximos de clorofila observados en el margen costero de la zona de estudio. Además, como consecuencia de los patrones de circulación a pequeña escala inducidos por las ondas internas, el material en suspensión es desplazado desde el margen costero hacia la zona central del estrecho, para luego ser transportado hacia el Mar de Alborán, contribuyendo parcialmente al aumento de su productividad primaria. Estas ondas internas generadas en la zona del Umbral de Camarinal tienen un efecto remoto sobre los procesos de mezcla en la vertical dentro de la Bahía de Algeciras debido a su interacción con la dinámica de la marea interna local. La presencia de ambos procesos es necesaria para producir una mezcla vertical efectiva en la zona de la picnoclina. Con respecto a las dinámicas de intercambio entre la Bahía de Algeciras y el Estrecho de Gibraltar a escala subinercial, la aplicación de una descomposición en FEO al campo de corriente superficial en la zona de contacto indica que el modo más importante está relacionado con las fluctuaciones del Chorro Atlántico en la zona central del estrecho, principalmente debido a las fluctuaciones de la presión atmosférica en el Mediterráneo Occidental. Los otros dos modos más relevantes están relacionados con las corrientes costeras inducidas por el forzamiento del viento zonal en la zona noroccidental del estrecho y del Mar de Alborán, y con el transporte de masas de agua provocado por los vientos que soplan dentro de la bahía con una significativa componente norte

Directory of Atmospheric, Hydrographic and Biological datasets for the Canary Current Large Marine Ecosystem

Environmental and biological data-sets were recovered from oceanographic surveys and other observation sources (e.g. tide gauges) since the 40s. This rescue and mining exercise was carried out in cooperation with the countries bordering the CCLME and other nations undertaking research in the region (i.e. Morocco, Mauritania, Senegal, Gambia, Guinea, Guinea Bissau, Cape Verde, Spain, Norway, Germany and France). A total of 425 data-sets, 27 databases and 21 time-series sites have been identified in the area. A substantial part of them were rescued from archives supported in paper copy. Finally, a directory of meta-data referring 99 data-sets and data-bases has been published. This catalogue and the recovered data offer an exceptional opportunity for the researchers in the CCLME to study the dynamics and trends of a multiplicity of variables, and will enable them to create their own time-series, baselines and climatologies under a spatial and temporal perspective. It will produce new and valuable information on changes produced during the last 35 years in this region, going from climatic changes to shifts in species diversity and populations due to natural and human induced factors. This directory is the first result of the project “Enhancing oceanography capacities on Western Africa Countries” funded by the Spanish Agency for International Development Cooperation (AECID) and coordinated by the IOC-UNESCO and the IEO. The project aims to reinforce transboundary cooperation in the CCLME and to facilitate access and data flow to existing scientific information and its utilization by the scientists, politicians, industry and civil society.http://unesdoc.unesco.org/images/0023/002314/231430E.pd

Baroclinic M2 circulation in Algeciras Bay and its implications for the water exchange with the Strait of Gibraltar: Observational and 3-D model results

The M2 tidal circulation in Algeciras Bay (Strait of Gibraltar) is analyzed using a 3-D, nonlinear, baroclinic, hydrodynamic model, in conjunction with observed data series. Results show the influence of the density stratification on the vertical structure of the M2 currents in Algeciras Bay, although its tidal dynamics shows major differences with respect to the Strait of Gibraltar. Whereas the M2 currents in the Strait present mainly barotropic behavior, the baroclinic effects prevail in Algeciras Bay. A notable finding is the presence of a tidal M2 counter-current system between the upper Atlantic and the lower Mediterranean water layers within the Bay, with amplitudes of up to 25 cm s−1. The interface between the two layers oscillates in antiphase relation with respect to the free-surface elevation, with amplitudes of almost 20 m. The presence of the submarine Algeciras Canyon was found to be determinant in the three-dimensional structure of tidal currents within the Bay, strengthening the baroclinic tidal regime of currents. This situation has quantitative consequences for the flow-exchange processes between Algeciras Bay and the outer Strait, with rates 20 times higher than those obtained when considering only the barotropic behavior, as well as inflow/outflow lateral recirculation volumes during half a tidal cycle that account for more than 20% of the net accumulated volume. This flow-exchange system was found to be affected by the nonlinear interaction processes between the first baroclinic period of resonance of Algeciras Bay and the M2 tide

The importance of sub-mesoscale processes for the exchange of properties through the Strait of Gibraltar

This article presents a detailed analysis of the sub-mesoscale transport processes in the Strait of Gibraltar. The interest is focussed on the Camarinal Sill region, and special attention is paid to the across-strait transport processes, the divergences and convergences in the central zone, and the small-scale circulation patterns along the northern coastal margin. The analysis is based on high-resolution (7 m) SST images acquired by an air-borne hyper-spectral scanner, and has been complemented with a rhodamine-release experiment, continuous thermo-salinograph records, acoustic Doppler current (ADCP) profiles from both moorings and vessel-mounted experiments, and numerical modelling. It is deduced from the analysis that the coupling between the upwelling processes, induced by the internal tide and the generation of large-amplitude internal waves, and the cyclonic eddies formed on the coastal margin, seems to be the mechanism that explains the chlorophyll maxima frequently found on the coastal margin of the studied area. Further, as a consequence of the small-scale patterns of circulation induced by the internal waves, the suspended substances are displaced from the coastal margins toward the central zones and later are carried by the westward current toward the convergence zones created by the internal waves, where they may be retained and accumulate. Then, in the eastward phase of the tidal current over the Camarinal Sill, these nuclei of concentrated substances (nutrients, chlorophyll, and plankton) are transported toward the Alboran Sea, where they must contribute, in part, to the primary productivity there

Internal waves in the Strait of Gibraltar and their role in the vertical mixing processes within the Bay of Algeciras

This article presents some of the results of an oceanographic survey carried out in the Bay of Algeciras (Strait of Gibraltar) as part of a research project intended to assess the environmental quality of the Bay. One of the most interesting findings was the step-like patterns presented by density profiles within the Bay, which were indicative of notable vertical mixing activity there. The analysis of the observations indicates that those mixing processes may be explained by the interaction between the local internal tide dynamics and the large amplitude internal waves entering the Bay, which seem to originate from the Camarinal Sill region