Abstract
During 2000 and 2001 and at the beginning of 2002, current meters were deployed at 25, 50 and 110 m water depths along two transects: one offshore of San Sebastian and the other offshore of Hondarribia. At the same time, hydrographical cruises and the collection of sediment samples were undertaken over the coastal section. The aim of the study was to improve the knowledge of seasonal changes in the coastal water circulation. The main results obtained are three-dimensional measurements of water flow, a description of the seabed sedimentology between 50 and 90 m depth, and an improved description of the effect of the circulation patterns on the dispersion of pollutants. Two different patterns of surface water circulation were identified, related to oceanographic and meteorological conditions in autumn-winter and spring-summer. Analyses undertaken on three-dimensional current meter data also improved the understanding of seasonal variations in marine currents. All the field data were incorporated into a numerical model for the simulation of currents. This numerical model contributed, together with the field measurements, to the improvement of the description of general seasonal variability patterns in the currents. The effect of this circulation on the dispersion of pollutants was also analysed.
Highlights
The offshore currents are related to superimposition between the prevailing oceanic current, tidal currents, wind-induced currents and, inside the surf zone, currents generated by waves breaking
Wind-induced currents become more important in the open sea, within the upper layers of the water column
At stations offshore of San Sebastián, the predicted maximum surface tidal speed is around 30 cm s-1, which is considerably lower than the overall maximum measured speed of around 1.3 m s-1 (SS50) (Fig. 4)
Summary
The offshore currents are related to superimposition between the prevailing oceanic current (at a large spatial and time scale), tidal currents, wind-induced currents and, inside the surf zone, currents generated by waves breaking. Water movement in the Cantabrian Sea, southern. 1. – The location of the study area and the coastal section, between San Sebastian and Hondarribia (indicated with a rectangle). Bay of Biscay, is not well understood. The general description of marine currents in the Basque region is almost exclusively confined to those in the surface waters (Ibáñez, 1979). A brief description of the present knowledge on major hydroclimatic agents in the Basque region—mainly wind forcing and hydrodynamics—is provided below
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