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- Monitoring estuaries using non-permanent stations: practical aspects and data examplesPublication . Garel, Erwan; Ferreira, ÓscarThis paper deals with the performances of nonpermanent environmental monitoring stations when recording at high-sampling interval (hour) over a long term (months, years) within estuarine waters. Information about data quality and system maintenance requirements are provided based on the experience gained with an autonomous station deployed during 2 years at the Guadiana Estuary (southern Portugal–Spain border). The station includes (1) a multi-parameter probe for water quality (temperature, conductivity, dissolved oxygen, turbidity, chlorophyll and pH) inserted in a tube through a surfacefloating buoy; and, (2) a bottom-mounted current meter. The main issues for the continuous acquisition of valid data were biofouling on the optical (chlorophyll, turbidity, dissolved oxygen), conductivity sensors of the probe and high sediment dynamics at the bed. The definition of a detailed maintenance programme is required for the lengthening of (valid) data time series. The typical variability of the parameters is described at seasonal and tidal time scales and episodic events are identified (coastal upwelling and high freshwater inputs). These examples illustrate how integrated data analysis is fundamental to define and understand the changes induced by specific events on several interrelated parameters, and, more generally, how these systems can contribute to a better understanding of the hydro-ecological processes operating in estuaries.
- Upwelling processes variability and water circulation along the northern margin of the Gulf of CadizPublication . de Oliveira Júnior, Luciano; Relvas, Paulo; Garel, ErwanThe present study investigates the contributions of upwelling mechanisms (coastal upwelling from boundary divergence and Ekman pumping from spatially variable wind) at the northern margin of the Gulf of Cadiz (NMGoC) based on high-resolution wind. The effects of the spatiotemporal upwelling mechanisms variability are then explored using current observations along with sea surface temperature and sea level anomaly. Upwelling favourable conditions occur throughout the year along the NMGoC, with the strongest intensity near Cape Sao ˜ Vicente due to a persistent positive wind stress curl. In winter, the surface water divergence is restricted to the coastal boundary due to strong coastal upwelling events that result in a cross-shore sea-level gradient close to the coast. Towards the summer, the gradient increases and extends further offshore (over the slope) at the western region due to the intensification of the Ekman pumping. Therefore, the seasonal and spatial variability of coastal upwelling and Ekman pumping contributes significantly to the offshore position of the geostrophic Gulf of Cadiz Current over the western shelf slope. Furthermore, a permanent sea level depression corresponds to the location of the strongest Ekman pumping, near Cape Sao ˜ Vicente. The dynamic adjustment of this feature may drive the cyclonic cell and alongshore poleward currents often observed in the area.