Is there a connection between high transport of water through the Rockall Trough and ecological changes in the North Sea?

Changes in the ecosystem of the North Sea may occur as pronounced inter-ann ual and step-wise shifts as well as gradual trends. Marked inter-annual shi fts have occurred at least twice in the last two decades. the late 1980s an d the late 1990s. that appear to reflect an increased inflow of oceanic wat er and species. Numerical modelling has demonstrated a link between altered rates of inflow of oceanic water into the northern North Sea and a regime shift after 1988. In 1989 and 1997 oceanic species not normally found in th e North Sea were observed there, suggesting pulses of oceanic water had ent ered the basin and triggered the subsequent ecosystem change. The oceanic w ater has origins mainly west of Britain in the Rockall Trough, where the lo ng-term mean volume transport is around 3.7 Sv northwards (1 Sv=10(6) m(3) s(-1)), but in early 1989 and early 1998 was observed to be more than twice the mean value. reaching over 7 Sv. These periods of high transport coinci ding with the inferred pulses of oceanic water into the North Sea suggest a connection through the continental shelf edge current. (C) 2001 Internatio nal Council for the Exploration of the Sea.