Northeast Atlantic surface water masses and corresponding frontal zones were alike in April and August, although April frontal zones were enlarged compared to August. The observed water masses and fronts are the Subpolar Water (SW), the Subpolar Front (SF), the North Atlantic Current (NAC), North Atlantic Transitional Water (NATW), the Azores Frontal Zone (AFZ) and the Azores Current (AC). During August, clusters of relative and absolute frequencies of planktic Foraminifera corresponded with water masses as conventionally distinguished on oceanic conditions. However, the distinct faunal assemblages deviated from the observed oceanic regime in April, when the transition between the immutable winter and the highly variable spring periods resulted in broad frontal zones. Under those conditions absolute frequencies and information indices prove to be better suited to characterize oceanic conditions than assemblage composition. The highly mixed and migrating fronts strongly influenced the planktic community and affected the horizontal as well as vertical species distribution. |
