Marc A. García

Seasonal changes of water mass structure and shelf slope exchanges at the Ebro Shelf (NW Mediterranean)

Among several field efforts undertaken in the framework of the EU MAST-III FANS project, three oceanographic cruises covering the Ebro shelf and slope regions (NW Mediterranean) were carried out on board R/V Garcia del Cid between November 1996 and July 1997. A major aim of these three cruises was to provide insight into the seasonal variability of the distribution of physico-chemical oceanographic parameters and the shelf/slope circulation. In this paper we discuss the observed changes in the hydrographic structure, the spatial distribution of nutrients, chlorophyll and suspended particulate matter and the local circulation in relationship to the seasonal variability of the Ebro river discharge rates and the water column stratification. The added effects of mesoscale circulation structures and of the exchanges across the shelf edge are also addressed.

Water masses and distribution of physico-chemical properties in the Western Bransfield Strait and Gerlache Strait during Austral summer 1995/96

In the framework of the FRUELA project, two oceanographic surveys were conducted by R/V Hesperides in the eastern Bellingshausen Sea, western basin of the Bransfield Strait and Gerlache Strait area during December 1995 and January 1996. The main hydrographic structures of the study domain were the Southern Boundary of the ACC and the Bransfield Front. The characteristics and zonation of local water masses are discussed in terms of temperature, salinity, dissolved oxygen, nutrient and inorganic carbon concentrations. Concentration intervals for water mass labelling, on the basis of chemical parameters in addition to the common θ/S-based classification, are defined. Silicate seems to be a very good discriminator for local water masses.

Flow variability at the tip of the Antarctic Peninsula

Recently ventilated water leaves the landlocked northwestern Weddell Sea near the Antarctic Peninsula and possibly spreads out into the basins of the world oceans at shallow to intermediate depths. To determine the pathways of the water through the complex topography and the flow variability, water-mass circulation and properties are described in the northwestern Weddell Sea and along the boundary of the Powell Basin by means of data from current-meter moorings and hydrographic sections. The mean flow is strongly controlled by the topography. Meso-scale, seasonal and interannual fluctuations are superimposed. The mean northward volume transport of shelf water, which represents the potential source water for intermediate layer ventilation, is estimated for the time interval between May 1996 and March 1998 to be 2.4±1.0 Sv. Water-mass properties suggest that much of this water leaves the Weddell Sea to Bransfield Strait and therefore does not reach the Weddell Scotia Confluence. The water masses are able to serve as the only source of Bransfield Strait deep water since the shelf water properties in the northwestern Weddell Sea vary over time within a range that corresponds to the required source waters. The Scotia Sea is supplied by water from the Powell Basin, which has varied significantly over the past two decades.

Transitory hydrographic structures and distribution of fish larvae and neustonic crustaceans in the north-western Mediterranean

Abstract A hydrographic and zooplankton survey (neuston and water column) was performed over the Blanes submarine canyon (western Mediterranean) in June 1993. Abundance of fish and crab larvae was very low when compared with previous studies conducted in the same area. The horizontal distribution of fish and crab larvae whose adults inhabit the continental shelf was restricted to the coast. The offshore occurrence of low-salinity waters of continental origin, together with the absence of a component perpendicular to the coast in the system of currents observed throughout the study area, support the observed pattern of distribution. The occurrence of mesopelagic fish larvae and of the oceanic neustonic isopod Idotea metallica in some coastal stations may be associated with episodic inshore-offshore exchanges of water masses identified by drifting buoy trajectories.

Wind waves off the Ebro Delta, NW Mediterranean

Abstract A descriptive investigation on the wind wave climate off the Ebro delta has been conducted on the basis of time series of data collected after 1978. Sea states have been classified into phenomenological cathegories according to available directional data. For selected records, illustrating the different wave conditions, statistical and spectral analyses have been performed so as to assess the short-term characteristics of the wave climate. Regarding the longer-term evolution, correlations among the main wave parameters have been established. Theoretical probability distributions have been fitted to the observed frequency histograms in order to complete the description of the average wave climate. Furthermore, some statistics of extreme wave heights have also been considered.

Feasibility and usefulness of steady-state calculations of the mean circulation in the vicinity of the Ebro mouth. Model tests against field data

Abstract A steady-state quasi-3D finite element model is forced with in situ measured wind conditions in order to obtain an estimate of the mean circulation off the Ebro delta and to assess its consequences upon water fluxes. The model is spectral in the vertical direction and is run with a reduced number of vertical degrees of freedom (modes). The boundary conditions prescribed on the ocean contours account for the existence of a slope jet. The hypothesis is that the direct wind forcing on the upper layer and the shelf mesoscale circulation are the main mechanisms driving the flow in the area and that it should be possible to reproduce the main current features even in the vicinity of the Ebro river mouth with this relatively simple model setup, as the usual river freshwater discharge rates are rather low. This is clearly different from the case of other region of freshwater influence systems, in which the river plume dynamics and the related density currents play relevant roles. The model results are compared with surface drifter trajectories obtained during field campaigns.

A note on FANS conclusions: From research analyses to management implications

Abstract This short paper deals with the “practical” application of some of the results obtained during the research project FANS. More specifically, the paper reviews the main features of the field site where the FANS project took place (viz. the Ebro delta in the Spanish Mediterranean coast) and how to use the obtained knowledge on water/sediment/nutrient fluxes in the area for problem-solving analyses. These analyses cover erosion/flooding risk studies, ecosystem status studies and “functionality” studies. The paper finally considers the practical benefits of putting together the obtained knowledge about water/sediment/nutrient fluxes for solving problems in a more integrated manner.