Abstract
Along one transect in the eastern equatorial Pacific Ocean the micro-phytoplankton (>15 gm in one dimension) biomass in the upper 200 in was examined. The samples were taken during the most recent El Nifio event and examined in the light microscope. In this size fraction, dinoflagellates were the highest contributors to both the cell numbers and the biomass, while coccolithophorids had similar importance to diatoms. At each station 81-137 species were found, but 2- 7 species made up 50% of the cell abundance. Margalef's diversity index peaked deeper than the microphytoplankton biomass maximum in most of the stations. Both the mean cell size and biomass per cell increased with depth, although biomass per volume (pg C @M-3) decreased with depth because of the species composition and the different ratios of Volume: Carbon in major taxonomic groups. Biomass profiles were not clearly related to water density ((Tt) or main nutrient (NO3-) profiles except at the highest latitudes (12'N, 9'N and 12'S) stations. Nor were surface nitrate concentrations well correlated with micro-phytoplankton biomass integrated to 200 in. Vertically the higher micro numbers and biomass were trends near the surface followed by decreases with depth throughout the transect. The integrated diatom biomass in the upper 200 m of this transect did not directly reflect the biogenic silica zone on the underlying ocean'floor, and we attribute this discrepancy to the periodic El Nifio conditions.
Liu, Duan (1995). Micro-phytoplankton biomass of the equatorial Pacific in spring 1992. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1995 -THESIS -L5713.