CHALLENGE: THE EXPORT OF ORGANIC CARBON IN THE SOUTHERN OCEAN EXERTS A MAJOR CONTROL OVER THE NUTRIENT SUPPLY TO THE GLOBAL UPPER OCEAN DRIVING UP TO 75 OF THE BIOLOGICAL PRODUCTION NORTH OF 30S. THIS EXPORTED CARBON IS THE RESIDUAL COMPONENT OF ORGANIC MATERIAL PRODUCED VIA PHOTOSYNTHESIS WHICH IS TRANSFERRED AND RESPIRED ACROSS DIFFERENT TROPHIC LEVELS OF THE ECOSYSTEM AND IS DEFINED AS NET COMMUNITY PRODUCTION (NCP). SATELLITES PROVIDE THE MOST SYNOPTIC ESTIMATE OF NCP BY COMBINING OCEAN COLOR DATA OF CHLOROPHYLL AND PRIMARY PRODUCTION WITH ESTIMATES OF THE RATIO OF EXPORT OR NEW PRODUCTION TO PRIMARY PRODUCTION. HOWEVER SATELLITE ESTIMATES SHOW SIGNIFICANT DISCREPANCIES WITH IN SITU CALCULATIONS OF NCP. IN SITU ANNUAL NCP RATES SHOW RELATIVELY LITTLE VARIATION IN THE OCEAN WITH 2-3 MOL C M-2 YR-1 MEASURED IN VARIOUS OCEAN LOCATIONS. IN CONTRAST SATELLITE ESTIMATES OF PRODUCTIVITY AND SUBSEQUENT EXPORT SHOW DIFFERENCES BETWEEN THE SUB-TROPICS AND SUB-POLAR GYRES OF TWO FOLD. THE DISCREPANCY BETWEEN IN SITU AND SATELLITE ESTIMATES IS DUE TO UNCERTAINTY IN THE RETRIEVAL OF BIOLOGICAL QUANTITIES FROM OCEAN COLOR DATA AS WELL AS IMPORTANT GAPS IN OUR UNDERSTANDING OF THE LINK BETWEEN PRIMARY PRODUCTION AND EXPORT. THE EXPORT RATIO AND RESULTING NCP ARE IMPORTANT CONSTRAINTS ON GLOBAL EARTH SYSTEM MODELS AND THEIR ABILITY TO REPRODUCE THE OBSERVED OCEAN NUTRIENT AND CARBON CYCLE IS DIRECTLY RELATED TO THESE PROCESSES. RECONCILING SATELLITE AND IN SITU ESTIMATES OF CARBON EXPORT AND UNDERSTANDING THE ECOLOGICAL PROCESSES THAT DRIVE NCP IN THE SOUTHERN OCEAN WILL ALLOW US TO BETTER CONSTRAIN AND INFORM MODELS THAT AIM TO PROJECT THE FUTURE CARBON CYCLE. OPPORTUNITY: THE SOCCOM PROJECT HAS DEPLOYED MORE THAN 50 FLOATS AS OF JUNE 2016 REPRESENTING THE FIRST LARGE-SCALE ARRAY OF CONTEMPORANEOUS OXYGEN NITRATE PH BACKSCATTER AND FLUORESCENCE MEASUREMENTS WITH THE GOAL OF QUANTIFYING BIOGEOCHEMICAL PROCESSES IN THE SOUTHERN OCEAN THROUGH A MIXTURE OF UNPRECEDENTED YEAR-ROUND MEASUREMENTS DATA-ASSIMILATING AND EARTH SYSTEM MODELS. THESE DATA AND MODEL PRODUCTS COMBINED WITH NOVEL SATELLITE TOOLS AND IMPROVED PROGNOSTIC ECOSYSTEM MODELS PRESENT AN OPPORTUNITY TO ESTIMATE IN SITU NCP AND LINK SATELLITE-DERIVED PRIMARY PRODUCTION TO THE FRACTION OF EXPORTED CARBON BOTH OBSERVATIONALLY AND MECHANISTICALLY THEREBY ADVANCING OUR ABILITY TO UTILIZE SATELLITE DATA TO DETERMINE CARBON EXPORT.GOAL: IN THIS PROPOSAL WE SEEK TO USE FLOAT MEASUREMENTS OF BIOGEOCHEMICAL TRACERS TO PRODUCE MASS-BALANCE ESTIMATES OF NCP PAIRED WITH SATELLITE-DERIVED PRIMARY PRODUCTION TO DETERMINE EXPORT RATIOS FOR THE SOUTHERN OCEAN AND COMPARE THESE AGAINST TRADITIONAL ALGORITHMS. WE WILL THEN USE A REGIONAL BIOGEOCHEMICAL MODEL TO SIMULATE THE OBSERVED IN SITU NCP PATTERNS AND UNDERSTAND THE ECOSYSTEM PROCESSES DRIVING THEM. OUR GOAL IS TO ADDRESS THE FOLLOWING OVERARCHING QUESTION: WHAT ARE THE ECOSYSTEM CONTROLS ON THE RELATIONSHIP BETWEEN PRIMARY PRODUCTION AND EXPORT PRODUCTION IN THE SOUTHERN OCEANRELEVANCE: THE ESSENCE OF THIS PROPOSAL IS TO IMPROVE THE UTILITY OF SATELLITE OBSERVATIONS FOR UNDERSTANDING BIOLOGICAL CARBON EXPORT THROUGH THE SYNTHESIS OF SATELLITE PRODUCTS IN SITU OBSERVATIONAL DATA AND AN ECOSYSTEM MODEL. IN THIS WAY THIS PROPOSAL DIRECTLY RESPONDS TO PROGRAM A.5 CARBON CYCLE SCIENCE 3.6 CROSS-CUTTING RESEARCH TOPICS UNDER BOTH 3.6.3.1 IMPROVED OBSERVATIONS AND 3.6.3.2 MODELING AS WE SEEK TO ADDRESS THE LIMITATIONS ON SCIENTIFIC UNDERSTANDING OF THE CARBON CYCLE DUE TO THE AMOUNT AND QUALITY OF RELEVANT OBSERVATIONS. THROUGH THIS PROPOSAL WE ALSO ADDRESS THEME 1 OF THE A.5 CARBON CYCLE SCIENCE CALL CARBON RESEARCH IN CRITICAL REGIONS DUE TO THE CRITICAL ROLE OF THE SOUTHERN OCEAN IN THE EXCHANGE OF CARBON BETWEEN THE OCEAN AND ATMOSPHERE AND IN ACTING AS THE LARGEST REPOSITORY OF UNUTILIZED SURFACE MACRONUTRIENTS IN THE OCEAN.