Micro-phytoplankton of the equatorial Pacific: 140°W meridianal transect during the 1992 El Niٌo

1992 El Niño micro-phytoplankton (>15 μm) were investigated in 40 samples collected throughout the upper 200 m of the water column at five stations during the U.S. JGOFS Survey I cruise TT007. Stations were located along the 140°W meridian at latitudes 9°N, 5°N, 2°N, 0°, and 5°S. Two hundred and twenty-four species of dinoflagellates, diatoms, coccolithophorids, silicoflagellates and one prasinophycean encountered are also known from other regions of the Pacific and/or other warm water oceans. Total cell concentrations and concentrations of cells of representatives of the three major groups of phytoplankton observed in this study are lower than reported for La Niña phytoplankton. El Niño cell concentrations of micro-phytoplankton found in other studies vary and may be more or less than that of La Niña micro-phytoplankton cell concentrations. Distribution patterns of dinoflagellates, diatoms and coccolithophorids show a specific signature. Dinoflagellates are most common in near-surface waters of all stations, coccolithophorids are most common in the near surface of the extreme stations, and diatoms most common in the southern station. Relative abundances of diatoms and coccolithophorids increase with depth. Consequently, each of the stations differ in its biogeochemical characteristics and their potentials for export of particular biogenic remains. Total cell concentrations do not correlate well to chlorophyll a or to auxiliary pigments, supporting the conclusion that the biomass of phytoplankton in El Niño equatorial Pacific is dominated by cells smaller than investigated in this report.