Evidence for effects on the North Sea ecosystem due to varying oceanic inflow over the last 100 years

Oceanic inflow is estimated to contribute more than 90% of the nutrient input into the North Sea (NSTF, 1993). Variability in the volume, chemical properties, biological content and source of the inflowing water is thus likely to have a considerable effect on North Sea ecosystems. Changes seen in the plankton over the last 40 years, measured by the Continuous Plankton Recorder (CPR) survey, allow clear periods to be identified that appear to be associated with variability in inflow. Monthly estimates of inflow, outflow and netflow across a section between Orkney and Utsira in Norway, have been derived from runs of the NORWECOM model for two depth intervals: surface to 150m and >150m. A comparison is made between these modelled physical measurements and plankton results for the period 1958 to 1999. Distinguished plankton periods that appear to reflect changing inflow events are discussed in relation to hydrometeorological and fisheries variability and earlier plankton studies over approximately the last 100 years.