of C. finmarchicus (northern affinities) and Calanus helgolandicus (southern)
followed those changes in the NAO both in the mean, and with striking interannual
detail (Fig. 16.19). So, the plankton respond, partially via advective effects, to the
changes in the global atmospheric circulation. In the 2000s the NAO trend leveled,
and at the time of writing (2011) has plunged to a low negative value. The published
CPR data have not caught up with this change. The dominance of C. helgolandicus in
all of the North Sea persisted through at least 2005 (Fig. 16.20).
Fig. 16.17 Variation of Calanus finmarchicus and Calanus helgolandicus abundance
in the North Sea, Norwegian Bight (west of southern Norway) and Faeroes–Iceland
sector 1958–1996.
(^) (After Planque & Ibanez 1997.)