Research papersRecent benthic foraminifers of the Basque continental shelf (Bay of Biscay, northern Spain): Oceanographic implications

- The distribution of benthic foraminifers of the Basque shelf has been studied.
- The distribution of benthic foraminifers is mainly related to the type of sediment.
- The distribution is also controlled by environmental factors related with depth.
- Surface currents transport estuarine and deep water species eastward.
- The presence of hypoxia resistant species suggests upwelling currents on the shelf.

We describe the spatial distribution of recent benthic foraminifer assemblages from the western area of the Basque shelf in relation with some environmental parameters. A total of 138 species have been identified, being the most abundant Cassidulina laevigata, Gaudryina rudis, Lobatula lobatula, Rosalina globularis and Textularia sagittula. Multivariate analyses (cluster Q-type and Detrended and Canonical Correspondence Analysis) performed with the benthic foraminifers of these samples show the separation of two main groups of species related with the sediment grain size: (1) coarse to very coarse sand and (2) medium sand and sandy silt. Seven clusters are characterised by their typical foraminifer assemblage and average values of particular parameters: clay-silt content of the sediment, depth, and percentage of foraminifer species indicative of hypoxia. The main features of marine currents of the area are reflected by these foraminifer assemblages. Thus, the occurrence of specimens typical of the estuaries as Ammonia tepida, Criboelphidium williamsoni and Haynesina germanica in this shelf, points to an eastward lateral transport forced by the littoral current below 60 m. The occurrence of small individuals of littoral (Asterigerina mamilla) and deep water (Globocassidulina subglobosa) species in the middle-outer shelf is indicative of wind, water density and tide forced N-S surface currents. In the outer shelf species characteristic of deep and cold waters appear (Fontbotia wuellestorfi, Hoeglundina elegans), together with abundant individuals of species resistant to hypoxia (Bulimina marginata, Hyalinea balthica, Melonis barleeanum, C. laevigata and Uvigerina peregrina) that suggest upwelling currents through the canyons located in this area. These species are then transported eastward following the Normal Circulation current between 100-200 m depth.