Distribution of Biological Activity in the Lower St Lawrence Estuary as Determined by Multivariate Analysis

Three stations located in the Laurentian Trough were investigated three times during the summer production maximum (in June-July 1990; COUPPB90-1 cruise). A range of multivariate analyses was carried out to extract major physical-biological features in a large data set covering the whole cruise. This study presents the advantages of combining conventional principal component analysis (PCA) with a three-way data analysis. PCA provides the centre of gravity of the different locations for each variable and each sample during the cruise without temporal information. Three-way data analysis produces the trajectory of the different site/time locations for each variable and each sample, and clarifies spatial and temporal relationships between variables. The results reproduce the main patterns of the lower St Lawrence Estuary during the summer plankton bloom and indicate an upstream movement of warm and less saline waters associated with surface production. Apparently these large changes at the surface are not reflected in the deeper layers. Cluster analysis suggests that autotrophic and heterotrophic activities are decoupled when production is low and are correlated only when production increases.