Nutrient distributions across the Porcupine Bank

Spring-summer hydrographic transects across the Porcupine Bank, west of Ireland, were made to characterize the nutrient distributions across this shelf edge region. An April transect indicated some surface depletion of nutrients in the region over the Porcupine Bank and across the Irish Shelf front with slightly increased surface values over deeper waters. Above the Porcupine Bank, within a dense dome of cold, relatively less-saline water, higher nutrient values relative to water at the same depth on either side were measured. By May, surface nitrogen was exhausted whilst a small [O(0.1 mu M)] amount of phosphate remained indicating a nitrogen-limiting nutrient supply for phytoplankton production. The nitrogen to phosphate ratio was 15. The dome structure over the Porcupine Bank persisted until at least July when the last transect was made and retained relatively high nutrient values. The dome may be a result of a Taylor Column formation with an associated partly-closed circulation pattern around the bank. This suggests a region where reduced shelf-ocean exchange is occurring. (C) 1998 international Council For the Exploration of the Sea.