Pulses in the eastern margin current and warmer water off the north west European shelf linked to North Sea ecosystem changes

Abstract

The North Sea ecosystem has recently under- gone dramatic changes, observed as altered biomass of indi- vidual species spanning a range of life forms from algae to birds, with evidence for an approximate doubling in the abun- dance of both phytoplankton and benthos as part of a regime shift after 1987. Remarkably, these changes, in part recorded in the Phytoplankton Colour Index of the Continuous Plankton Recorder (CPR) survey, are notable as episodic shifts occurring in 1988/89 and 1998 imposed on a gradual decadal trend. These biological events are shown to be a response to coin- cident changes in oceanic input and water temperature. Geo- strophic transports have been calculated from a hydrographic section across the Rockall Trough, and a time series of sea- surface temperature derived from satellite observations. The 2 pulses of oceanic incursion into the North Sea in circa 1988 and 1998 coincided with strong northward advection of anom- alously warm water at the edge of the continental shelf.