Planktonic foraminiferal fluxes in the Santa Barbara Basin: response to seasonal and interannual hydrographic changes

Results of a three-year time-series sediment trap experiment in the Santa B arbara Basin indicate linkages between water-column dynamics and variations in plankton fluxes on both seasonal and interannual time scales. The two-w eek collection interval utilized for this study allows evaluation of high-f requency changes in the production and flux of planktonic foraminifera, whi ch are compared to those of siliceous microorganisms (diatoms, radiolaria a nd silicoflagellates). Annual hydrographic conditions in Santa Barbara Basi n are influenced by seasonal changes in insolation, the wind field and sour ce waters. This study includes periods of weak to moderate El Nino conditio ns followed by a transitional period to a non-El Nino state. Planktonic for aminiferal fluxes and species turnover are related to seasonal and interann ual changes in source waters and water column conditions. Globigerina bullo ides, G. quinqueloba and Neogloboquadrina pachyderma (dextral) dominate the planktonic foraminiferal population in this location and are present throu ghout the year. Globigerina bulloides and G. quinqueloba have similar flux patterns, and highest Auras occur in association with diatom blooms. The fl ux patterns of G. bulloides and G. quinqueloba in general are inversely rel ated to that of N. pachyderma (dextral). Globigerina quinqueloba seems to r espond earlier to the onset of upwelling than G. bulloides. Three temperatu re-limited species, Neogloboquadrina dutertrei, Orbulina universa and Globi gerinoides ruber, are present in lower numbers and show more restricted sea sonal ranges. In the thermal regime of the Santa Barbara Basin, N. dutertre i, like O. universa, disappears during upwelling, Neogloboquadrina dutertre i occurs in highest abundance when the water column is thermally stratified and there is a well developed deep chlorophyll maximum. Increased fluxes o f Globigerinoi ruber the most thermally restricted of the dominant species in the basin, are associated with the presence of warm oceanic diatoms and warm-water radiolarians. Total planktonic foraminiferal fluxes were lower i n 1995 than during the previous two years, which were characterized by El N ino conditions. (C) 2000 Elsevier Science Ltd. All rights reserved.