Abstract:
Planktonic Foraminifera collected from the vicinity of the North Atlantic Current and the Gulf Stream during late winter-early spring and fall of 1964 are described and their distributions are recorded. Variations in faunal composition seem to be related largely to water regime dynamics and seasonal cycle. Among the fall collections, three distinctive assemblages can be recognized: a western group in the vicinity of the Gulf Stream, containing predominantly Sargasso Sea-Gulf Stream species dominated by Globigerinoides ruber; a northern group, dominated by Globigerina quinqueloba egelida, new subspecies, reflecting the influence of cold, northern waters adjacent to the North Atlantic Current; and an eastern group, dominated by Globigerina incompta, apparently developed within the limits of the North Atlantic Current. The last group seemingly represents an anomaly, as North Atlantic Current surface temperatures were relatively high at the time of collection, and dominance of a warm-water form, such as Globigerinoides ruber, might have been expected. The anomaly suggests that the North Atlantic Current is a partially closed gyre, fed by both slope waters and Gulf Stream. Temperatures are considered to be close to threshold for both cold and warm-water species.
Distributional patterns displayed by the late winter-early spring collections are compatible with the proposed model. Also, these collections, taken over a period of almost three months, reflect marked seasonal changes in faunal composition, particularly in Sargasso Sea-Gulf Stream elements.
Twenty-five species and subspecies are described. One species, Globigerina atlantisae, and one subspecies, Globigerina quinqueloba egelida, are new.
