Monitorización de las propiedades termohalinas del flujo de agua Mediterránea a través de Gibraltar en los últimos 13 años

Un fondeo profundo desplegado por primera vez en Septiembre de 2004 y que ha sido mantenido regularmente hasta el día de hoy en el umbral de Espartel (Estrecho de Gibraltar, EdG) nos ha permitido analizar la variabilidad de la temperatura y la salinidad del agua Mediterránea a su paso por el EdG, antes de incorporarse a la circulación Atlántica. Ésta serie temporal sigue a día de hoy fondeada en el mismo punto, alcanzando una longitud de 13 años. A pesar de numerosos accidentes, la serie de Temperatura y Salinidad son lo suficientemente largas para realizar estimaciones sobre tendencias en la última década. La línea de fondeo tiene unos 20 metros de longitud y de despliega en el umbral de Espartel (360m), se compone de distintos instrumentos, entro otros un sensor de Conductividad-Temperatura (CT, Seabird SBE37-SMP) situado a unos 14 metros del fondo y que por lo tanto registra las propiedades termohalinas del agua Mediterránea, cuyos datos son los usados en ésta comunicación. La serie de temperatura muestra repetidos mínimos entre el final del invierno y principios de primavera, éstos mínimos de temperatura potencial son la respuesta a la formación de WMDW (Western Mediterranean Deep Water) que se forma por convección profunda en el Golfo de León levantando la interfase del WMDW más antigua y por lo tanto haciendo más fácil su ventilación a través del EdG. Por otro lado la serie muestra tendencias positivas de 6.89 ± 3.24 10-3°Cyr-1, en acuerdo con trabajos anteriores, que además parecen incrementarse a partir del año 2013. Este aumento de salinidad podría ser interpretado como una señal de la WMT (Western Mediterranean Transition) iniciada en los inviernos de 2005, 2006 y que se caracteriza por un máximo de salinidad y densidad. Al ser más densa la WMT quedó situada en las capas más profundas y sólo tras un nuevo evento de formación intenso como fue el de 2012-2013 podría la WMT incorporarse al flujo de salida en el estrecho.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Drainage of deep Mediterranean Water, its transition through the Strait of Gibraltar: spatial and temporal variability

La presente tesis está organizada en cuatro capítulos en los que se estudia el flujo de agua saliente del Mar Mediterráneo a través del Estrecho de Gibraltar, para ello se han abordado varios procesos relacionados con el intercambio de aguas Atlánticas y Mediterráneas a través del Estrecho. El primer objetivo es identificar los mecanismos que influyen en la ventilación de las aguas profundas Mediterráneas residentes en el Mar de Alborán. Para ello en primer lugar se investiga el papel que juegan las estructuras de escala regional en la ventilación de aguas profundas mediante datos medidos in-situ, datos de satélite y simulaciones numéricas realizadas a tal fin. De éste estudio se deduce que la dinámica del Estrecho de Gibraltar es fundamental en la ventilación de las aguas profundas del Mar de Alborán, la cual a su vez es facilitada por la presencia casi permanente del giro anticiclónico del Mar de Alborán Occidental. Seguidamente, mediante modelos numéricos regionales y a nivel de cuenca se estudia el modo en que el forzamiento mareal interfiere no solo en la circulación en el propio Estrecho sino también en la ventilación de aguas profundas desde el mar de Alborán o en los procesos de formación de estas mismas aguas. Se concluye que la dinámica mareal debe ser resulta en los modelos a escala regional y de cuenca que pretenden reproducir algunas características relevantes del intercambio a largo término y, muy probablemente, otros importantes procesos que tienen lugar más allá del Estrecho, como la formación de agua profunda en el Golfo de León. A lo largo del tercer capítulo se ha estudiado en qué medida la marea en el Estrecho de Gibraltar afecta a los procesos biogeoquímicos de la vecina cuenca del Mar de Alborán, inusualmente productiva en comparación con el resto del Mar Mediterráneo. El resultado es una productividad primaria en el Mar de Alborán que se reproduce satisfactoriamente cuando el forzamiento mareal se incluye en un modelo regional físico‐ecológico. Más específicamente se encuentra que la diferencia entre tener o no en cuenta las mareas puede suponer hasta un 60% más de producción primaria en la cuenca Oeste de Alborán. Finalmente se realiza un intensivo análisis de datos de temperatura potencial y salinidad medidos en transeptos meridionales a lo largo del Estrecho. De éste modo aplicando un análisis de clusters se determinar cuál es el patrón espacio-temporal de los hasta seis tipos de agua que intervienen en el intercambio de flujos en el Estrecho. En particular se han detectado cuatro masas de agua Mediterráneas en el flujo saliente en la sección del contorno Este del Estrecho, a pesar de que una de ellas, puede no estar presente en determinados años. La señal de estas aguas se suaviza lentamente a medida que fluyen hacia el Oeste, y lo hacen abruptamente una vez sobrepasan el umbral de Camarinal. Según lo anterior, al Oeste del umbral sería más apropiado hablar de una única agua Mediterránea. Con respecto a la variabilidad temporal se observa que las señales estacionales son más evidentes en las aguas Atlánticas, mientras que la variabilidad interanual es más notable en las aguas Mediterráneas. Estas cuestiones ofrecen una nueva visión sobre la dinámica y las propiedades del flujo Mediterráneo de agua que abandona éste mar fluyendo a través del Estrecho

Lagrangian particle tracking for the assessment of the flushing efficiency of harbor structures: the case of the Port of the Bay of Algeciras, Strait of Gibraltar

The Bay of Algeciras, an inlet of about 9 x 11 km located at the eastern margin of the Strait of Gibraltar, opens to the south, where the Atlantic jet leaves the Strait and starts spreading into the Alboran Sea. In its western side, the Bay hosts one of the main ports in Europe, neuralgic base of the major traffic load from Europe to Africa and from Europa to the rest of the oversea countries. The massive transport of liquid and solid bulk or bunkering activity, daily carried out in the Bay, combined with the harsh weather conditions that often lash the zone, give the ideal scenario for an incipient ecological disaster. This high environmental risk motivates the interest for a deeper understanding of the small scale dynamics of the Bay and the role played by the port structures in case of oil spill or other surface contaminations. A series of Lagrangian particles tracking (LPT) experiments were carried out to investigate the flushing patterns of the Bay and 8 different docks inside the local port, under a representative variety of external conditions, such as tide phase and strength, and winds. A 2D LPT algorithm has been adapted to fully exploit the outputs of a very high resolution (∼30m) three-domain-nested hydrodynamic model, with the aim of resolving the complex circulation within the structures of the harbor. Winds are a clearly dominant factor, with westerlies featuring e-folding times one order of magnitude lower than easterlies. Fortnightly tidal modulation presents a counter-intuitive effect, with spring tides that, despite promoting higher ventilation in a first instance, end up providing higher accumulation of particles inside the docks and higher e-folding times than neap tides. Tide phase affects the current direction at the entrance of the docks during the first few hours of simulation and its effect is progressively masked throughout the experiment. In the 45% of the experiments, a significant quantity of particles flow out to the Alboran Sea (55% in the whole Bay experiment), confirming the importance of the Bay on the exportation of pollutant/properties to the nearby basin.Universidad de Málaga. Campus de Excelencia Internacional del Mar, CEIMAR. Campus de Excelencia Internacional Andalucía Tec

Mediterranean outflow and its link with upstream conditions in Alboran Sea

The Western Alboran Gyre (WAG) at the eastern entrance of the Strait of Gibraltar can influence the Mediterranean outflow (MOW) by favoring or hampering the flow of Levantine and Western Mediterranean (LIW and WMDW) waters, the main constituents of the MOW. Observations collected at Camarinal sill in the Strait and AVISO data are used to investigate this issue.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

The influence of tides on the exchange through the Strait of Gibraltar and on properties of the Mediterranean Sea

A. Ishlinsky Institute for Problems in Mechanics, Rusi

Interaction flow bathymetry at tidal scale in the main sill of the Strait of Gibraltar

Data collected in the north and south channels of the main sill of the Strait of Gibraltar (Camarinal sill) are used to investigate processes connected to the internal hydraulics of the exchange through the Strait at tidal frequencies. Observations strongly suggest the setting up of hydraulic jumps at both the western and eastern flank of the sill, the latter associated with the reversal of the Mediterranean undercurrent during spring tides. The northern site is more sensitive to processes triggered by the formation and release of the jump formed east of the sill during intense enough ebb tide cycles, which is thus better traced at this location; the southern site detects more neatly the fluctuations and footprints associated with the hydraulic jump regularly formed to the west of the sill during flood tides. A detailed inspection of the high resolution bathymetry of the area reveals the existence of two enclosed depressions at either side of the sill, almost certainly carved by the bottom flow over the millennia, whose shape and morphology are suggestive of this spatial differentiation.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Blackspot seabream early life stages dispersal by hydrodynamic modelling (Strait of Gibraltar - Alboran Sea)

The Blackspot seabream (Pagellus bogaraveo) is a commercially appreciated demersal fish, widespread in the north-eastern Atlantic and middle-western Mediterranean. The Strait of Gibraltar (SoG) is an important fishing area where artisanal fleets from Spain and Morocco target this species using special longline gears known as “voracera”. Different studies on the health status of this species claim an overexploitation of the resource without any kind of objective management measures implemented yet by the associated countries. Improving the knowledge of the population dynamics, and particularly during the spawning window, is crucial for a better management of the fishing effort for this species. There is an agreement in literature in considering the SoG as an especially energetic and dispersive spawning zone for this species. Once spawned, eggs and larvae (ELS) are assumed to be scattered by the currents towards both sides of the SoG, mostly to the eastwards Alboran basin, where high concentrations of juveniles occur. A high resolution hydrodynamic model coupled to a Lagrangian particle tracking system is employed to assess the potential dispersal pathways of blackspot seabream ELS spawned in the SoG. Recursive releases of passive tracers in different virtual spawning spots and depths within the SoG region are tracked under different tidal conditions in order to obtain an overall characterization of the spatial dispersion patterns of the studied species. Semidiurnal tidal currents emerge as the primary factor in determining the horizontal dispersion and pathway of the spawning products, although the spring-neap tidal cycle and the spawning depth can be also important variables depending on the region considered as well as the arrival zone for the ELS dispersal paths over the Alboran SeaUniversidad de Málaga. Campus de Excelencia Internacional CEIMA

Hydrochanges Gibraltar Campaign - characterization of Mediterranean Outflow through the Strait of Gibraltar

The precise characterization of the Mediterranean outflow through the Strait of Gibraltar is a very well know issue although a question rather far to be resolved completely. Many scientific efforts have been invested to try to define the exact composition and evolution of the Mediterranean waters (MWs) raising at the entrance of the strait and crossing one of the most dynamically active site of the worldwide oceans. In the framework of the Hydrochanges European programme, the “Gibraltar International Campaign” was carried out onboard the R/V Tethys II by the French Mediterranean Institute of Oceanography (MIO) in June 2012, with the chance to perform a series of highresolution CTD meridional transects. The instrument used is a Moving Vessel Profiler (MVP), a towed free-falling CTD, which enables a very high spatial resolution semi-autonomous monitoring of the column water. This work presents the hydrological data set retrieved in the campaign and proposes their usage as tool for the characterization of the composition and the evolution of the Mediterranean outflow along the strait. Two main assumptions are discussed: the generally accepted hypothesis of only two main Mediterranean waters crossing the strait, the Levantine IntermediateWater (LIW) and theWestern Mediterranean DeepWater (WMDW), and the novel theory, principally supported by the MIO group since last years, of the presence of up to four Mediterranean waters raising at the strait entrance: two intermediate waters, the LIW and the Winter Intermediate Water (WIW) and a further dense water, the Tyrrhenian Deep Water (TDW) flanking the WMDW. In both cases the mixing within these MWs and between them and the Atlantic inflowing waters, namely the Surface Atlantic Water (SAW) and the North Atlantic Central Water (NACW), are analyzed and discussed. A classical mixing triangle approach is proposed for the first assumption, with the definition of a third vertex as a general Atlantic water, and a novel approach based on a simplified cluster analysis of the Temperature/Salinity/Density diagrams of the transects, is applied to the six water masses considered in the second assumption. The latter is also applied to the GIBEX2 (Gibraltar Experiment) dataset in order to confirm, by a completely subjective approach, the rather arbitrary definition of the MWs accepted so far. A clear differentiation of the MWs along the cross-strait direction is observed, with intermediate waters laying on the northern Spanish slope and the denser ones flowing along the southern slope. However, this structure is deeply modified by the very strong mixing occurring in the strait and it ends to nearly disappear at west of the Camarinal Sill. The temporal variability, strictly related to the tidal dynamics, is very high, inducing strong changes in this structure throughout the strait, up to substantially modify it. In order to investigate this temporal variability, the recent series of current and thermohaline characteristics of the MWs, sampled simultaneously at Espartel and in two (north and south) extremes of the Camarinal Sill by the Physical Oceanography Group of the University of Málaga, have also been examined with interesting results on the characterization of the outflow evolution along the strait.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Water renewal mechanisms of the Bay of Algeciras in the Strait of Gibraltar

The Bay of Algeciras (BA) is a marine environment subject to high levels of anthropogenic pressure. Here we analyze observations collected at the Bay and the results of an ocean circulation model to investigate its circulation and variability. Special attention is paid to the identification of the mechanisms enhancing the exchange of water with the adjacent Strait of Gibraltar and therefore contributing to maintain satisfactory levels of water quality.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech