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 Data 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 were compared to those in the sea-surface temperature in the Gulf of Maine and in the North Atlantic Oscillation index. Three major components of temporal dynamics were analyzed: seasonal cycle, interannual, and interdecadal variability. Seasonal cycles of C. finmarchicus abundance were different in high versus low NAO years, with higher overall abundance and a more pronounced annual signal during high NAO years. Interannual fluctuations of C.f. abundance and NAO index were also positively correlated, with abundance "responding" to the NAO index with a lag of 4 years. The NAO index was also positively correlated to the winter SST, leading it by 2 years. SST, on the other hand, was positively correlated with Calanus finmarchicus (leading it by 2 years). Over the past three decades, C. finmarchicus abundance in the Gulf of Maine showed an increasing trend, a phenomenon seen also in the sea surface temperature of the Gulf of Maine and in the NAO index. These observations 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 atmospheric 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 Calanus finmarchicus.