Substrate and water masses
The shelf substrate varies greatly across the ecoregion. While sand and muddy-sand areas dominate in the Bay of Biscay, the Cantabrian Sea and Galician shelf are covered by fine sediments with isolated rocky areas in the coastal- and inner-shelf areas, and by sand and mud in the mid- and outer-shelf. The western Iberian Shelf is characterized by sand-sized sediments, with fine sediments forming significant mud bodies on the mid-shelf off the main rivers. In the Gulf of Cadiz, the inner shelf is covered by a sandy sediment belt with local gravels and rocky outcrops, and muddy patches in the proximity of the most important river mouths that also cover most of the mid- to outer shelf. The Gulf of Cadiz continental slope is dominated by muddy and sand sediments, depending on the intensity of the current above the seabed (Figure 8).
The main circulation patterns within the region are characterized by central waters (of 200–700 m depth) and Labrador seawater (approximately 2000 m) flowing from the northwest, while Mediterranean waters spread from their origin at Gibraltar. Deep waters describe slow cyclonic flow. In the Gulf of Cadiz, the water exchange is governed by a two-layered inverse estuarine circulation with Mediterranean water flowing into the Gulf under Atlantic water flowing into the Mediterranean Sea.
Figure 8: Major substrates on the shelf of the Bay of Biscay and the Iberian coast (as compiled by EMODNET seabed habitats; www.emodnet-seabedhabitats.eu).