The >20 um size fraction of marine phytoplankton sinks faster than smaller components and is an important size fraction to consider in global flux out of the euphotic zone through the oceanic water column to the sediments. In order to understand the abundance and biomass of the >20 um phytoplankton in the equatorial Pacific, multiple opening and closing net collections as well as water bottle samples will be studied through this program from the seasonal JGOFS EQPAC cruises. The priority will be to 2 seasonal time-series cruises within 20 north and south of the equator in the area known to have the greatest flux of material to the sediments. The netplankton will be concentrated from different strata by a multiple opening and closing new system deployed at depths chosen to complement a similar zooplankton sampling scheme as well as to concentrate phytoplankton from the upper surface layers and just below the euphotic zone in a depth region identified as very active biogeochemically. The seasonal survey cruises will allow meridional interpretations of the larger phytoplankton from water bottle samples and vertical net hauls. The larger diatoms and dinoflagellates are excellent indicators of the different water masses encountered, and the life histories and vertical zonation of the more heavily silicified diatom species found in equatorial water will be used to test a possible relationship between degree of silicification and growth-limiting conditions seen in higher latitude waters.
