Satellite-derived sea surface temperature, mesoscale variability, and foraminiferal production in the North Atlantic

Abstract

Planktonic foraminiferal flux was collected at four sediment trap locations spanning a 34° latitude range in the North Atlantic during 1988-1990. Satellite-derived sea surface temperature (SST) and CTD data were integrated with time-corrected flux data to determine the effects of seasonal hydrographic changes on foraminiferal production and species succession in surface waters. The thermal structure of the upper water column controls foraminiferal production by regulating levels of phytoplankton production and by directly influencing the preferred temperature habitats of individual species in the community. Sediment traps deployed at the two southern sites (34°N and 48°N) were part of the U.S. Joint Global Ocean Flux Study (JGOFS) and were located in regions influenced by upwelling events induced by mesoscale eddy activity. The timing of maximum foraminiferal production at each trap location coincides with the northward progression of the spring bloom in the North Atlantic. The magnitude of total flux during bloom periods varies considerably with location and is positively correlated with the amount of primary productivity in surface waters. Foraminiferal production is highest at JGOFS 48 and probably results from the greater influence of mesoscale variability in this region on local hydrographic conditions. The upwelling associated with cyclonic cold-core eddies appears to be an effective mechanism for increasing local foraminiferal production in the North Atlantic by enhancing food availability. The preferred production of individual species during upwelling periods may depend on the vertical distribution of chlorophyll in the water column. Seasonal variation in SST is also an important factor controlling the relative abundance of species with preferred thermal habitats. A distinct seasonal species succession occurs at both JGOFS sites but is absent at higher latitudes due to decreases in both faunal diversity and seasonal temperature variations with increasing latitude in the North Atlantic. Foraminiferal :flux data, expressed in terms of relative abundance, is the best direct method of comparing species distributions of living populations with fossil assemblages in the sedimentary record. Preferred temperature ranges for G. ruber, G. bulloides, and N. pachyderma are estimated in this study. The tolerance limits for these species and other ecological inferences derived from these flux data may prove useful for paleoceanographic reconstruction in deep-sea cores. Future studies will be necessary, however, to establish the consistency of these results among different ocean basins.