This complements a recently-funded project to deply biweekly sediment traps for two years on the eastern and western sides of the Gulf of California which will cover work on bulk fluxes, planktonic foraminifera, radiolaria and stable isotopes. This study will concentrate on four preservable groups of phytoplankton microfossils--diatoms, silicoflagellates, dino- flagellates and calcareous nannofossils. Fluxes of each taxon will be determined, and the composition of the trap-based material compared with that of underlying surface sediments recovered by box cores. The study will examine the seasonal succession of phytoplankton, and the internannual and spatial variation thereof, in order to determine the degree to which the original seasonal signal is preserved in the sediments. Changes in phytoplankton will be examined at 1000 year intervals throughout the cored section, on eastern and western sides, to address questions concerning changes in seasonal upwelling and evidence for changed precipitation and river runoff. The study will expand upon a model being developed to describe the transformation of biocoenosis to taphocoenosis for diatoms, and produce a first-range model for calcareous nannofossils and silicoflagellates.