LIVING PLANKTIC FORAMINIFERA - TRACERS OF CIRCULATION AND PRODUCTIVITY REGIMES IN THE CENTRAL EQUATORIAL PACIFIC

Planktic foraminifera (shelled protozoans from similar to 0.01 to 1 mm in size) respond to equatorial circulation and ecosystem dynamics. In the JGOFS survey I cruise of the equatorial Pacific (9 degrees N-12 d egrees S, 140 degrees W, in February-March 1992), responses to upwelli ng, advection, and biological activity occurred in spite of little upp er-ocean temperature contrast. Rather than being abundant within the e ntire productive equatorial zone, foraminifera concentrated off the eq uator at convergent fronts. For example, non-spinose, mostly herbivoro us species (G. conglomerata. G. tumida. P. obliquiloculata, and N. dut ertrei) dominated near 3 degrees N, in the convergence between the Sou th Equatorial Current and the North Equatorial Countercurrent. Juvenil e forms outnumbered adults within the convergence. indicating that the se foraminifera succeeded and reproduced here (rather than passively a ccumulating by advection) perhaps by maintaining buoyancy to stay with in the convergent, food-rich zone. The South Equatorial Current was fa vored by spinose, endosymbiont-bearing G. aequilateralis and non-spino se, herbivorous G. glutinata, G. menardii, and P. obliquiloculata, per haps an advected assemblage. Species hosting dinoflagellate endosymbio nts (G. sacculifer, G. ruber, and G. conglobatus) prevailed in food-po or oligotrophic regions, perhaps because they obtain nutrition from th eir symbionts. Distributions of living foraminifera suggest that paleo ceanographic transfer functions to estimate primary productivity in th e geological record have merit, but controls of foraminiferal species distributions also include food stocks, light intensity, and advection . Copyright (C) 1996 Elsevier Science Ltd.