Seasonal and interannual dynamics of Calanus finmarchicus in the Gulf of Maine (Northeastern US shelf) with reference to the North Atlantic Oscillation

The Continuous Plankton Recorder and the Comprehensive Ocean-Atmosphere Dat a Set were used to study the temporal dynamics over 30 years of the Calanus finmarchicus surveys in the Gulf of Maine. Changes in Calanus abundance we re compared to those in the sea-surface temperature in the Gulf of Maine an d in the North Atlantic Oscillation index. Three major components of tempor al dynamics were analyzed: seasonal cycle, interannual, and interdecadal va riability. Seasonal cycles of C. finmarchicus abundance were different in h igh versus low NAO years, with higher overall abundance and a more pronounc ed annual signal during high NAO years. Interannual fluctuations of C,f. ab undance and NAO index were also positively correlated, with abundance "resp onding" to the NAO index with a lag of 4 years. The NAO index was also posi tively correlated to the winter SST, leading it by 2 years. SST, on the oth er hand, was positively correlated with Calanus finmarchicus (leading it by 2 years). Over the past three decades, C. finmarchicus abundance in the Gu lf of Maine showed an increasing trend, a phenomenon seen also in the sea s urface temperature of the Gulf of Maine and ill the NAO index. These observ ations are consistent with the hypothesis that in the Gulf of Maine changes in the water column (as indicated by SST) are related to changes in the at mospheric system (as indicated by the NAO index) so that positive anomalies in the index favor changes in the water column (still to be investigated), which correspond to conditions favorable to increases in abundance of Cala nus finmarchicus. (C) 2000 Elsevier Science Ltd. All rights reserved.