PHYTOPLANKTON ARE CHARACTERIZED BY TREMENDOUS DIVERSITY THAT CRITICALLY AFFECTS OCEAN ECOSYSTEM FUNCTIONING. THE EXPORTS PHYTOPLANKTON BES PROGRAM ELEMENT SEEKS TO ADDRESS THE ROLE THAT PHYTOPLANKTON DIVERSITY PLAYS IN DETERMINING (1) NET PRIMARY PRODUCTION (NPP) (2) STANDING STOCK OF PHYTOPLANKTON CARBON IN THE EUPHOTIC ZONE (3) EXPORT EFFICIENCY OF PHYTOPLANKTON CARBON OUT OF THE EUPHOTIC ZONE AND (4) FLUX TRANSMISSION OF THIS MATERIAL BELOW THE EUPHOTIC ZONE INTO THE TWILIGHT ZONE. THE EXPORTS OPTICS PROGRAM ELEMENT SEEKS TO QUANTIFY THE OPTICAL MEASUREMENTS THAT LINK ECOSYSTEM FUNCTION TO REMOTELY SENSED PRODUCTS VIA CARBON-BASED OPTICAL PROXIES. IN THIS PROPOSAL WE CONTRIBUTE TO THESE PROGRAM ELEMENTS BY FOCUSING ON PHYTOPLANKTON DIVERSITY AND OPTICAL PROPERTIES/PROXIES OF KEY PHYTOPLANKTON COMMUNITY STRUCTURE ELEMENTS (I.E. CONCENTRATION COMPOSITION AND SIZE) AND HOW THOSE FACTORS INFLUENCE EXPORT FROM AND TRANSFORMATION BELOW THE EUPHOTIC ZONE. THE ABILITY TO DIFFERENTIATE PHYTOPLANKTON BASED UPON THEIR FUNCTIONAL DIFFERENCES IS CRUCIAL TO QUANTIFY HOW DIFFERENT GROUPS IMPACT CARBON STOCKS AND FLUXES. WE INTEND TO MEASURE PHYTOPLANKTON DIVERSITY AND OPTICAL PROPERTIES BY CONSTRUCTING A CONTINUOUS UNDERWAY FLOW-THROUGH SYSTEM FOR THE SURVEY SHIP DESCRIBED IN THE EXPORTS SCIENCE PLAN. OUR SYSTEM WILL CONSIST OF IMAGING-IN-FLOW CYTOMETRY HYPERSPECTRAL ABSORPTION AND ATTENUATION (SCATTERING BY DIFFERENCE) MULTISPECTRAL BACKSCATTERING AND MULTI-EXCITATION CHLOROPHYLL FLUORESCENCE. WATER SAMPLES FROM CTD CASTS TO TWILIGHT DEPTHS WILL ALSO BE MEASURED IN DISCRETE MODE TO QUANTIFY THE TRANSFORMATION AND CHANGE IN DIVERSITY OF ALGAL CELLS (AND THEIR ASSOCIATED OPTICAL PROPERTIES) AS THEY SINK THROUGH THE WATER COLUMN.