With bottom landers, onboard the ship R.V. Pelagia, the researchers explored the Nazaré Canyon off the Portuguese coast. This is one of the largest submarine canyons in the world. The Canyon starts at the beach. At a distance of 150 kilometres from the coast it opens out into a deep-sea area, 5 km deep. Locally the canyon cuts more than one kilometre deep into the continental slope. In the floor of the canyon the researchers measured unusually high biochemical activity. The sediment is enriched in organic material, which can serve as food for the rich floor life in the canyon and the deep-sea area. However, the sediment is possibly mixed with chemical pollutants originating from human activity. In addition to this the water in the canyon was noticeably turbid. This indicates an elevated transport of sediment particles. The sediment accumulates rapidly in the canyon. As a result of this the floor becomes unstable. The researchers demonstrated that the accumulated sediment runs off the slope as submarine mud avalanches into the deep-sea area. This happens at intervals of several decades to several centuries. With the rapid growth of the world population, the use of the continental margin (the transition area between the mainland and the open ocean) is quickly increasing. As a result of this marine ecosystems are being subjected to greater pressure. Ecosystems close to the mainland are comparatively well studied. However, the edges of the continental shelf and the continental slope have for a long time received comparatively little attention.
For further information please contact Dr Eric Epping (Netherlands Institute for Sea Research), tel. +31 (0)222 369444, e-mail epping@nioz.nl or Dr Henko de Stigter, tel. +31 (0)222 369401, e-mail stigter@nioz.nl. De Stigter attended an international congress about canyons held from 7 to 10 April in Spain, where he presented the findings from this study.