12 October 1995

     Below is a description of the analysis (modified from DuRand, M.D.
and R.J. Olson, in press, Contributions of phytoplankton light
scattering and cell concentration changes to diel variations in beam
attenuation in the equatorial Pacific from flow cytometric measurements
of pico-, ultra-, and nanoplankton, Deep-Sea Research):

     Niskin bottles from the CTD rosette were sampled during three diel
time series on the equator at 140 degrees W (TT008 #1, TT012 #1,
and TT012 #2) and were analyzed on a flow cytometer to obtain
phytoplankton concentration for cells < 20 um diameter.  The eukaryotic
phytoplankton were analyzed immediately on board the ship using an
EPICS V flow cytometer modified to analyze 50 ml seawater samples at
5-10 ml min-1 (Olson et al., 1991, 1993).  Samples were kept at room
temperature in the dark until analysis; the surface samples were
analyzed first (the upper 45 m samples were analyzed within an hour)
and all depths were completed within two hours of collection.  During
each cruise the phytoplankton groups were sorted on the flow cytometer
and examined microscopically.  Typically, the most abundant population
of eukaryotic phytoplankton consisted of 1-2 um-diameter coccoid cells
(referred to here as the ultraphytoplankton).  The population referred
to here as the nanophytoplankton primarily consisted of 2-3 um diameter
coccoid cells, but also included cells as large as 20 um.

     The picoplankton Synechococcus and Prochlorococcus were analyzed
on shore from samples preserved with 0.125% glutaraldehyde and
stored in liquid nitrogen (Vaulot et al., 1989, Olson et al., 1993),
using a high sensitivity configuration of an EPICS 753 flow cytometer
(Olson et al., 1993).  Synechococcus were distinguished by their high
phycoerythrin fluorescence and Prochlorococcus by their low forward
light scatter and chlorophyll fluorescence.

Olson, R.J., E.R. Zettler, S.W. Chisholm and J.A. Dusenberry.  (1991)  Advances
     in oceanography through flow cytometry, pp. 351-399 in S. Demers (ed.),  
     Particle Analysis in Oceanography, NATO ASI Series G 27, Springer-Verlag,
Olson, R.J., E.R. Zettler and M.D. DuRand.  (1993)  Phytoplankton analysis 
     using flow cytometry, pp. 175-186 in P.F. Kemp, B.F. Sherr, E.B. Sherr 
     and J.J. Cole (eds.),  Handbook of Methods in Aquatic Microbial Ecology, 
     Lewis Publishers, Boca Raton.
Vaulot, D., C. Courties and F. Partensky.  (1989)  A simple method to preserve
     oceanic phytoplankton for flow cytometric analyses.  Cytometry, 10,