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This article presents an Eulerian physical and biogeochemical data set from the Iberian Margin Cape São Vicente Ocean Observatory (IbMa-CSV), a facility of the European Multidisciplinary Seafloor and water column Observatory – European Research Infrastructure Consortium (EMSO-ERIC) located 10 nautical miles south of Cape São Vicente (Portugal), the southwest tip of the Iberian Peninsula and western limit of the northern margin of the Gulf of Cadiz. The observatory was installed on the shelf break, and the data time series spans four months for most of the variables. The upper 150 m were sampled intensively with a wave powered vertical profiler at an average rate of 4.5 profiles per hour recording at 2 Hz when ascending at approximate velocity of 0.2 m/s and 10 Hz when descending at variable velocity. The vertical resolution was always higher than 0.2 m. Measured channels were conductivity, temperature, pressure, chlorophyll a, dissolved O2 concentration, and turbidity. Derived channels are sea pressure, depth, salinity, speed of sound, specific conductivity, dissolved O2 saturation, density anomaly, spiciness and Brunt-Väisälä frequency. The acquired data set includes the flow velocity and direction along the water column, taken from an upward looking 300 kHz Acoustic Doppler Current Profiler (ADCP) recorded every hour for 3 m depth bins extending the same depth range of the vertical profiler. A standard quality control scheme was applied to the data set. The data set is preserved for multiple use and is accessible in the SEANOE repository, under the address: https://www.seanoe.org/data/00836/94769/ (Rautenbach et al., 2022). [ABSTRACT FROM AUTHOR]

Based on acoustic detections from a network of five stations along the south coast of Portugal, 25 transits of tagged meagre were identified between 2019 and 2020, mostly in summer. Comparisons with hourly current measurements from a moored Acoustic Doppler current Profiler and an High Frequency Radar system indicate that meagre move westward with favourable alongshore flows at a confidence level >90% (while eastward transits observations were too few to be significant). Several similar transits of different individuals occurred within two days suggesting a species response to environmental changes. The analysis of surface seawater temperature from ERA5 shows that meagre always swam westward towards colder water, despite their warm water affinities. As such, they reached food-rich upwelling areas when the water temperature was higher than usual (due to the westward advection of warm water), probably optimizing their feeding ability. The demonstrated alongshore meagre movements in response to temperature variations induced by the mesoscale coastal circulation is particularly relevant for the management of this high economic value species in southern Portugal. • The alongshore movements of meagre were identified using acoustic telemetry. • The movement direction was compared with measured coastal currents. • Meagre move westward with favourable alongshore flows. • This behaviour is triggered by temperature variations induced by flow advection. [ABSTRACT FROM AUTHOR]

• The influence of tides on the seafloor morphology of the eastern Gulf of Cádiz. • Water masses close to the near-critical strips would favor the generation of internal waves. • Oceanographic processes interact at different times and spatial scales determining the morphology. • Knowledge of bottom currents and their modulation is needed for understanding sea-floor morphology. Although the effects of tidal dynamics have been studied in shallow marine environments and morphologically restricted straits, the impact of these processes on deep-water marine environments remains to be studied in depth. This study highlights the influence of tides on the seafloor morphology of the eastern Gulf of Cádiz, near the exit of the Strait of Gibraltar. Two moorings, one with an Acoustic Doppler current profiler (ACDP) and another one with a thermistor chain, and local and regional profiles of salinity, temperature, and ADCP reveal the water mass distribution in the study area and associated oceanographic processes. The intermediate water masses flowing along the continental slope are the Eastern North Atlantic Central Water (ENACW) and the Mediterranean Outflow Water (MOW), bound by an interface located regionally at depths greater than 300 m, but identified locally at much shallower depths (up to 150 m) in the studied upper slope. The hydrodynamics of the area are governed by barotropic tidal currents, the MOW upper core, and the internal tides, which act at different time and spatial scales shaping the local terraced sea-floor morphology and determining the dominant sedimentary processes. The obtained results allow a better understanding of how secondary oceanographic processes are modulating the water mass circulation in this particular hot spot and their importance in explaining the formation and evolution of morphological depositional and erosional features. [ABSTRACT FROM AUTHOR]

The present study describes the fluxes and transports of nutrients and chlorophyll a inferred from direct observations carried out off south Portugal, during a research cruise in early October 2006. The covered area corresponds to the western part of the northern margin of the Gulf of Cadiz, from Cape São Vicente (9.0°W) till the Guadiana River mouth (7.4°W). Unlike in the western Iberian margin, the upwelling in this region is rather intermittent during the summer season. It is interleaved by periods when warm waters coming from the eastern part of the Gulf of Cadiz occupy the coastal region. However, our observations were taken during an intense upwelling event that took place at the end of the upwelling season. Ten meridional transects were sampled in a total of 90 CTD casts. Current velocity profiles were acquired along the ship's track with a hull-mounted acoustic Doppler current profiler (ADCP). The analysis of the circulation field and water masses characteristics led to the quantification of the fluxes and transports of chlorophyll a and nutrients in 5 meridional transects along the coast. Results show the prevalence of the alongshore eastward flow over the offshore Ekman transport in the coastal circulation without formation of upwelling filaments. Transport of chlorophyll a showed a near surface maximum (<30dbar), while transport of nutrients were generally higher in the layer below (30–100dbar). The estimates show net eastward alongshore transports of chlorophyll a and nutrients into the Gulf of Cadiz and weak cross-shore exchanges. At the deepest levels, the estimates of the transports by the shallow vein of the Mediterranean Water show an important input of nutrients to the Atlantic. However, waters in the top 100dbar, impoverished in nutrients by biological utilisation due to upwelling, show that nitrate and phosphate transports provided into the Gulf of Cadiz exceed those carried westward by the shallow vein of the Mediterranean Water. [ABSTRACT FROM AUTHOR]

The alongshore subtidal water circulation along the South Portugal inner shelf is characterized by the temporal alternation of equatorward (i.e., broadly eastward) flows related to coastal upwelling processes and poleward (i.e., broadly westward) Coastal Counter Currents (CCCs). The objective of this study is to get insights about the main drivers of CCCs based on kinematic parameters describing the structure of the flow at the moment it changes direction. The parameters are derived from an extensive bottom-mounted ADCP dataset (16 deployments; 34,121 hourly records) collected at a single mooring (23 m water depth). Results show that the so-called incipient flows present contrasted general patterns whether they turn from equatorward to poleward or the opposite. Complementary observations at a nearby station indicate that these characteristics are spatially consistent along the studied area. Although 70% of CCCs are generated under favourable wind conditions (Levanter), these flows generally develop through the bed layer, in particular in summer. Hence, the Levanter wind - expected to promote flow setup through the surface layer - is not the main driver of CCCs in most cases. The general structure of incipient CCCs strongly suggests that the dominant force competing with the wind stress is an alongshore pressure gradient (APG). Furthermore, the maximum equatorward flow magnitude before CCCs setup is significantly correlated with the following (poleward) acceleration of incipient CCCs near the bed. Such relation is consistent with the development of CCCs due to the unbalance of an APG (produced during active upwelling) when wind relaxes. This process is further supported by an analysis of the depth-averaged momentum equation which suggests that the coastal circulation is mainly driven by linear dynamics in the region. • Statistical analysis of the structure of alongshore flows when they reverse. • Poleward (CCCs) and equatorward incipient flows have distinct patterns. • CCCs develop often under favourable wind conditions (Levanter). • CCCs often develop through the bed layer showing the wind is not their main driver. • Data and analytical analyses suggest an alongshore pressure gradient driving force. [ABSTRACT FROM AUTHOR]