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One of the largest and most persistent features in the Alboran Sea is the Western Alboran Gyre (WAG), an anticyclonic recirculation bounded by the Atlantic Jet (AJ) to the north and the Moroccan coast to the south. Eulerian budgets from several months of a high-resolution model run are used to examine the exchange of water across the Eulerian WAG’s boundary and the processes affecting the salinity, temperature, and vorticity of the WAG. The volume transport across the sides of the WAG is found to be related to vertical isopycnal movement at the base of the gyre. Advection is found to drive a decay in the salinity minimum and anticyclonic vorticity of the Eulerian WAG. Given the large contributions of advection, a Lagrangian analysis is performed, revealing geometric aspects of the exchange that are hidden in an Eulerian view. In particular, stable and unstable manifolds identify a stirring region around the outer reaches of the gyre where water is exchanged with the WAG on a time scale of weeks. Its complement is an inner core that expands with depth and exchanges water with its surroundings on much longer time scales. The 3D evolution of one parcel, or lobe, of water as it enters the WAG is also described, identifying a general Lagrangian subduction pathway.

Small pelagic fish species, such as sardine and anchovy, can exhibit dramatic decadal-scale shifts in abundance in response to climate variability. Understanding the mechanisms and the relationships among the different components of the food web through which environmental forcing can drive the observed fish variability remains a challenging problem. The modelling study described herein, focusing on the Canary Current System, implements and builds on earlier modelling efforts by Rose et al. (2015) and Fiechter et al. (2015) in the California Current System. This new application of the modelling framework to the Canary Current system provides an approach that bridges a comprehensive database with end-to-end (climate-to-fish) modelling, thereby enabling the investigation of the sources of variability of sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus). The aim of the modelling effort is to gain insights into the underlying mechanisms that drive the observed biological variability. Particular attention is given to the absence of regime shifts between sardine and anchovy in the Canary Current, which is a distinctive feature among the four major eastern boundary upwelling ecosystems. A model simulation for 1958–2007 was performed and analysed. The biological traits and behaviours prescribed for sardine and anchovy for the Canary Current give rise to different spatial distribution of their populations, and in contrast with other eastern boundary upwelling ecosystems, to synchronous (rather than asynchronous) variability of their abundance and biomass. Analyses of years with anomalously high increases and declines of the adult populations implicate food availability (instead of temperature or other environmental drivers) as the main factor determining recruitment for both sardine (via spawning and survival of feeding age-0 individuals) and anchovy (via survival of feeding age-0 individuals). The common dependence of sardine and anchovy on food, together with the domain-wide response of zooplankton to climate forcing generated in the model, provides a plausible explanation for the synchronization of the two populations. Our results also point at differences between sardine and anchovy; while the two species thrive under enhanced upwelling-favourable winds, anchovy larvae become particularly vulnerable to drift mortality, and thus do better than sardine under more moderate upwelling conditions.

This chapter revises biogeophysical issues of connectivity processes for fish populations in the Alboran Sea—Strait of Gibraltar—Gulf of Cadiz area. Connectivity of early life history stages between distant spawning grounds is crucial to incorporate vital developmental rates that condition survival probabilities at critical ontogenic stages. Hydrodynamics is pivotal to the process and most particular for pelagic species originating from adult fish adapted to recurrent patterns. Therefore, special focus has been placed on the hydrodynamics of the region, particularly on the Alboran Sea where the swift and energetic eastward-flowing Atlantic Jet entering the basin from the Strait of Gibraltar determines the surface circulation patterns. The Jet establishes an obvious zonal west-to-east connectivity, prevents the one in the opposite east-to-west direction and works as a hydrodynamic barrier that hampers the north-to-south connectivity. The chapter addresses these processes, discusses possible mechanisms to achieve connectivity between north and south shores, which have to overcome the hydrodynamic barrier, and assesses the feasibility of east-to-west connectivity by means of intermediate-depth currents. Implications on the populations and ecosystems of the Alboran Sea and on the three main harvested species potentially affected by hydrodynamic connectivity in the basin (European hake, the sardine, and the blackspot seabream) are also commented. Preprint

The Red Sea, home to the second-longest coral reef system in the world, is a vital resource for the Kingdom of Saudi Arabia. The Red Sea provides 90% of the Kingdom’s potable water by desalinization, supporting tourism, shipping, aquaculture, and fishing industries, which together contribute about 10%–20% of the country’s GDP. All these activities, and those elsewhere in the Red Sea region, critically depend on oceanic and atmospheric conditions. At a time of mega-development projects along the Red Sea coast, and global warming, authorities are working on optimizing the harnessing of environmental resources, including renewable energy and rainwater harvesting. All these require high-resolution weather and climate information. Toward this end, we have undertaken a multipronged research and development activity in which we are developing an integrated data-driven regional coupled modeling system. The telescopically nested components include 5-km- to 600-m-resolution atmospheric models to address weather and climate challenges, 4-km- to 50-m-resolution ocean models with regional and coastal configurations to simulate and predict the general and mesoscale circulation, 4-km- to 100-m-resolution ecosystem models to simulate the biogeochemistry, and 1-km- to 50-m-resolution wave models. In addition, a complementary probabilistic transport modeling system predicts dispersion of contaminant plumes, oil spill, and marine ecosystem connectivity. Advanced ensemble data assimilation capabilities have also been implemented for accurate forecasting. Resulting achievements include significant advancement in our understanding of the regional circulation and its connection to the global climate, development, and validation of long-term Red Sea regional atmospheric–oceanic–wave reanalyses and forecasting capacities. These products are being extensively used by academia, government, and industry in various weather and marine studies and operations, environmental policies, renewable energy applications, impact assessment, flood forecasting, and more.

Temperature and salinity series near the seafloor at Espartel sill (Strait of Gibraltar) have been used to analyze the thermohaline variability of the Mediterranean outflow. The series shows temperature drops by the end of most winters/early-springs, which are the remote response to Western Mediterranean Deep Water (WMDW) formation events in the Gulf of Lion that uplift old WMDW nearby the Strait. This process distorts the seasonal cycle of colder/warmer water flowing out in summer/winter likely linked to the seasonality of the Western Alboran Gyre. The series show positive trends in agreement with previous values, which are largely increased after 2013. It is tentatively interpreted as the Western Mediterranean Transition (WMT) signature that started with the very cold winters of 2005 and 2006. It was only after the large new WMDW production of 2012 and 2013 harsh winters that WMT waters were made available to flow out of the Mediterranean Sea.

The present study addresses the hypothesis that the Western Alborán Gyre in the Alborán Sea (the westernmost Mediterranean basin adjacent to the Strait of Gibraltar) influences the composition of the outflow through the Strait of Gibraltar. The process invoked is that strong and well-developed gyres help to evacuate the Western Mediterranean Deep Water from the Alborán basin, thus increasing its presence in the outflow, whereas weak gyres facilitate the outflow of Levantine and other intermediate waters. To this aim, in situ observations collected at the Camarinal (the main) and Espartel (the westernmost) sills of the strait have been analysed along with altimetry data, which were employed to obtain a proxy of the strength of the gyre. An encouraging correlation of the expected sign was observed between the time series of potential temperature at the Espartel Sill, which is shown to keep information on the outflow composition, and the proxy of the Western Alborán Gyre, suggesting the correctness of the hypothesis, although the weakness of the involved signals does not allow for drawing definitive conclusions.

Se trata de un resumen (Abstract) de la contribución. El acuerdo de transferencia de copyright del trabajo completo es incompatible con el depósito del mismo en RIUMA. Se describe la implementación inicial de un método simplificado de grabación en directo de sesiones de clase en asignaturas de las Escuelas de Ingeniería de la Universidad de Málaga. La simplificación se logra al incorporar en la actividad diaria del aula ciertas características típicas de la grabación en diferido de mini videos docentes. En una configuración mínima se graba únicamente el audio y el video en pantalla de la clase, evitando los desafíos técnicos y las dificultades que implica la grabación de otros elementos como la pizarra. Esto implica el uso de anotaciones en pantalla en tiempo real para reemplazar completamente las anotaciones en la pizarra. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. I Plan Propio Integral de Docencia. Universidad de Málaga. Universidad de Málaga. Vicerectorado de Personal Docente e Investigador, Proyectos de Innovación Educativa (PIE 17-018)

In this work, a multi-parameter inter-comparison of diverse ocean forecast models was conducted at the sea surface, ranging from global to local scales in a two-phase strategy. Firstly, a comparison of CMEMS-GLOBAL and the nested CMEMS-IBI regional system was performed against satellite-derived and in situ observations. Results highlighted the overall benefits of both the GLOBAL data assimilation in open-waters and the increased horizontal resolution of IBI in coastal areas, respectively. Besides, IBI proved to capture shelf dynamics by better representing the horizontal extent and strength of a river freshwater plume, according to the results derived from the validation against in situ observations from a buoy moored in NW Spain. Secondly, a multi-model inter-comparison exercise for 2017 was performed in the Strait of Gibraltar among GLOBAL, IBI and the nested SAMPA high-resolution coastal forecast system in order to elucidate the accuracy of each system to characterize the Atlantic Jet (AJ) inflow dynamic. A quantitative validation against High Frequency radar (HFR) hourly currents highlighted both the steady improvement in AJ representation in terms of speed and direction when zooming from global to coastal scales though a multi-nesting model approach and also the relevance of a variety of factors at local scale such as a refined horizontal resolution, a tailored bathymetry and a higher spatio-temporal resolution of the atmospheric forcing. The ability of each model to reproduce a 2-day quasi-permanent full reversal of the AJ surface inflow was examined in terms of wind-induced circulation patterns. SAMPA appeared to better reproduce the reversal events detected with HFR estimations, demonstrating the potential added value of coastal models with respect to coarser parent regional systems. Finally, SAMPA coastal model outputs were also qualitatively analysed in the Western Alboran Sea to put in a broader perspective the context of the onset, development and end of such flow reversal episodes.

Observations from a high frequency radar system and outputs from a high resolution operational ocean model working at the Strait of Gibraltar have been analyzed and compared during the period February 2013 to September 2014 in order to evaluate their capability to resolve the surface circulation of the region. The description of the mean circulation patterns has been statistically assessed, showing good agreement, particularly in the central region of the strait corresponding with the Atlantic Jet (AJ) stream, although some short scale features are not reproduced by the model. In the frequency domain very high concordance is observed. Tidal maps of diurnal and semidiurnal constituents are in good agreement with previous observations. The analysis of the model and radar response to the wind forcing reveals that the low resolution of the model wind-forcing field and its deeper superficial level smoothes the wind effect on the simulated currents. The first three EOF modes account for the 86% of model and radar variances. The coincidence between the observed and simulated patterns is very significant for the first two modes, which account for the mean velocity field and the latitudinal shifting of the AJ consequence of the flow-topography interaction. The third mode captures the wind-induced circulation, and greater discrepancies are found in this case. Results underline the complementary character of both systems: radar observations improve the model description, resolving short scale processes, while the model completes the radar information when the time or spatial coverage is poorer.

Data collected in the north and south channels of the main sill of the Strait of Gibraltar (Camarinal sill) have been used to investigate processes connected to the internal hydraulics of the exchange through the Strait at tidal frequencies. They 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, whereas the southern site detects the fluctuations and footprints associated with the hydraulic jump regularly formed to the west of the sill during flood tides more neatly. A detailed inspection of the high resolution bathymetry of the area reveals the existence of two enclosed depressions at either side of Camarinal sill, almost certainly carved by the bottom flow over the millennia, whose shape and morphology are suggestive of this spatial differentiation. In addition to the expected fortnightly periodicity of the spring-neap tidal cycle, the observed hydrodynamic features show a pronounced diurnal inequality caused by the tidal currents of the diurnal constituents.

Sánchez Leal, Ricardo ... et al.-- 11 pages, 5 figures, supplementary material http://advances.sciencemag.org/cgi/content/full/3/11/eaao0609/DC1, The pathways and transformations of dense water overflows, which depend on small-scale interactions between flow dynamics and erosional-depositional processes, are a central piece in the ocean’s large-scale circulation. A novel, high-resolution current and hydrographic data set highlights the intricate pathway travelled by the saline Mediterranean Overflow as it enters the Atlantic. Interaction with the topography constraints its spreading. Over the initial 200 km west of the Gibraltar gateway, distinct channels separate the initial gravity current into several plunging branches depth-sorted by density. Shallow branches follow the upper slope and eventually detach as buoyant plumes. Deeper branches occupy mid slope channels and coalesce upon reaching a diapiric ridge. A still deeper branch, guided by a lower channel wall marked by transverse furrows, experiences small-scale overflows which travel downslope to settle at mid-depths. The Mediterranean salt flux into the Atlantic has implications for the buoyancy balance in the North Atlantic. Observations on how this flux enters at different depth levels are key to accurately measuring and understanding the role of Mediterranean Outflow in future climate scenarios, We also acknowledge funding and data provided by projects INGRES3 (CTM2010-21229), STOCA (IEO 2009), PESCADIZ (IEO), INDEMARES (LIFE07 NAT/E/000732+), MOC2 (CTM2008-06438-C02-01), MED-OUTFLOW (CTM2008-03422-E/MAR and CTM2010-11488-E), PELCOSAT (IEO), SEMANE (X. Carton), DILEMA (CTM2014-59244-C3-2-R), and INPULSE (CTM2016-75129-C3-1-R) as well as SISMER, PANGEA, IEO, ICES, BODC, and NOAA data centers. Additional funding was provided by the CONTOURIBER (CTM2008-06399-C04-01/MAR) project. Part of the research was conducted in the framework of the “Drifters” Research Group of the Royal Holloway, University of London, UK

The effects of tidal forcing on the exchange flow through the Strait of Gibraltar and the circulation in the near-field region are revisited with a regional numerical model. Also a basin-scale model run is conducted in a first attempt to assess the impact of these local processes on the Western Mediterranean thermohaline circulation. In the Strait of Gibraltar, tides are found to (1) increase the exchange flow volume transport, (2) modify the hydrological properties of Atlantic inflowing waters through the enhancement of mixing, and (3) facilitate the drainage of Mediterranean deep water. In the far-field, the model reveals that these local processes can favor deep convection in the Gulf of Lion. Some thoughts are provided offering possible explanations.

A primitive-equation model has been used to investigate the meteorologically-driven circulation of the Bay of Algeciras. It is shown that the mean circulation of Atlantic Water (AW) is characterized by an anticyclonic cell, while Mediterranean Water (MW) follows a preferred cyclonic pathway. Meteorological forcing distorts substantially the AW mean circulation pattern, and only modulates that of the MW. Winds drive a vertical circulation cell in the Atlantic layer consistent with Ekman dynamics, whereas the horizontal circulation pattern is markedly dependent on the swift Atlantic jet entering the Mediterranean and changes from clearly anticyclonic to cyclonic as the jet separates or approaches the strait’s northern shoreline. This occurs through atmospheric pressure-driven acceleration/deceleration of the jet, in agreement with internal hydraulics theory predictions. It is also found that the renewal of AW is largely modulated by tides, with meteorological forcing playing a secondary role. The opposite applies to the renewal of MW.

The stability of the mean state of the surface circulation of the Western Alboran Sea, characterized by a jet of Atlantic water (AJ) surrounding the Western Alboran Gyre (WAG), is investigated with a submesoscale-resolving operational ocean model. It is shown that this circulation state collapses through the interaction between the AJ-WAG system and a growing cyclonic eddy that arises close to the Spanish coast. This eddy develops as the WAG partially blocks the positive potential vorticity (PV) flux coming from the Strait of Gibraltar. It is found that tides increase the positive PV flux with respect to a non-tidal simulation, thus making the destabilization of the mean circulation state more likely. Atmospheric pressure driven flows are also shown to have the potential to destabilize the circulation by rising dramatically the PV flux within a time scale of some days. This provides an explanation as to why the circulation of the Western Alboran Sea exhibits more variability toward winter time, when meteorological fluctuations are enhanced.

An 18-month time series of temperature collected in the vicinity of the Guadalquivir estuary mouth has been analyzed to investigate tidal signals in the temperature records. Two sources of similar importance are acting jointly to produce these signals, the gravitational tide generating potential that acts through the tidal currents induced by the vertical tide at the estuary's mouth and the radiational potential whose origin is the sun's radiation. The most important signal is the radiational diurnal S1, which exhibits a seasonal modulation. The next one in importance is M2, introduced via the advective term, which shows semiannual modulation due to the change of sign of the horizontal temperature gradient. The S2 constituent is a mixture of radiational (via the first harmonic of S1) and gravitational contributions, the former being about twice the latter. The harmonic constants of all these constituents are time-dependent so that caution is needed to interpret results deduced from time series of few months., Partial financial funding from the Spanish Ministry of Science and Innovation through CTM2010-21229-C02-01, CTM2008-04150/E projects and also from Regional Andalucía Government P08-RNM-03738 project are acknowledged.

Recent observations collected at different places in the Strait of Gibraltar are used to investigate the temporal and spatial variability of tidal currents in this region. The analysis of a five-year long time series of velocity observations at the Espartel sill (western end of the strait) shows that harmonic constants fluctuate seasonally exhibiting smaller amplitude in winter. This fact, along with an increased subinertial flow during the winter induces a marked decrease in the relative importance of the tide to the total flow compared to the summer. New computations of tidal transport at the key sections of Espartel and Camarinal, together with historical information reported for the Eastern Exit of the strait, have been analyzed jointly to highlight the internal along-strait divergence of the tidal transport in each layer and the transfer of the tidal signal from one layer to the other. This study covers the whole length of the strait, thus extending previous results reported for the central-eastern strait. Most of the topographically forced divergence is accounted for by large vertical displacements of the interface, although velocity observations collected on the continental shelf of the northern strait suggest that coastal recirculation plays some role in the volume conservation at tidal frequencies.

Different datasets have been analyzed to identify the origin of the temperature and salinity seasonal and interannual fluctuations in the surface layer of the eastern North Atlantic Ocean, close to the Gulf of Cadiz. The analysis was motivated by the surprising short-term salinity trend recorded by a monitoring station deployed in the Atlantic layer of the Strait of Gibraltar between years 2003 and 2007, which has been described and investigated by Millot (2007. Geophys. Res. Lett. 34, L21609. doi:10.1029/2007GL031179.). Temperature and salinity display similar annual cycles whose maxima occur by the end of the year, the former leading the latter by one month approximately. Despite their similarities, their origin is not the same. More than 80% of the variability of the temperature seasonal cycle is accounted for by the annual cycle of surface heat flux, while advective fluxes are secondary. This is not true for salinity, which both seasonal and interannual fluctuations are shaped by the advection and the evaporative annual cycle jointly. For the advection contribution, the identified external agent is the wind stress that drives the upwelling season in the eastern mid-latitude boundary of the North Atlantic. Vertical advection of salinity associated with the Ekman pumping and horizontal advection caused by the upwelling jet and the fluctuations of the North Atlantic Subtropical Gyre are behind the local advective changes. The strengthening (weakening) of the seasonal upwelling in summer (winter) decreased (increased) the local salinity in the Gulf of Cadiz, giving rise to the observed cycle in the data recorded at Gibraltar. Short term trends in the wind-inducing upwelling off the Iberian Peninsula during the above mentioned period triggered concomitant changes of the salinity in the waters that fed the inflow and produced the short–term trend observed in the Strait of Gibraltar.

[1] A total of 5077 Argo float profiles in the period 01/2002-05/2010 have been used to analyze salinity and temperature trends in the Atlantic waters adjacent to the Strait of Gibraltar in order to identify the source of recent changes observed in the inflow to the Mediterranean Sea. Positive salinity trends of 0.038 ± 0.009 year−1 and 0.013 ± 0.003 year−1 have been found for the Surface Atlantic Water and the Eastern North Atlantic Central Water, respectively. For temperature, no significant trend is observed in the surface layer while positive trend of 0.05 ± 0.02 °C/year is obtained for the thermocline waters. The Mediterranean Water layer does not show any significant trend for the entire period, but a switch from positive to negative trends is observed in year 2006. In contrast to previous findings, these thermohaline variations are driven by intrinsic water masses changes, instead of isopycnal vertical displacements, probably related to an enhancement of the net freshwater losses in the area.

[1] The baroclinic response to barotropic tidal forcing in the Camarinal Sill area, within the Strait of Gibraltar, is investigated with a three-dimensional, fully nonlinear, nonhydrostatic numerical model. The aim of numerical efforts was the assessment of three-dimensional effects, which are potentially significant in the area because of rather irregular bottom topography, variable background stratification, and complex structure of barotropic tides. Model results reveal a complex baroclinic response under relatively moderate flood tidal currents, which includes the formation of internal hydraulic jumps upstream of the sill, internal cross waves close to the channel walls, and a plunging pycnocline at the lee side of the sill crest. These structures exhibit significant cross-channel spatial dependence and may appear to be aligned together across the channel. This fact makes their identification difficult from the surface pattern captured by remote sensing images. Under strong barotropic forcing (spring tides) the upstream hydraulic jumps are shifted to the lee side of Camarinal Sill, where a single internal hydraulic jump is formed. Significant first- and second-mode hydraulic jumps are also generated near smaller secondary sills in Tangier basin, thus extending the occurrence of intense water mixing and energy dissipation to other zones of the strait.