THE GOAL OF THIS PROJECT IS TO QUANTIFY GLOBAL CARBON CYCLE FLUX RESPONSES TO CLIMATE VARIATION AND TRENDS OVER THE COURSE OF THE OCO-2 MISSION (ALONG WITH THE EARLIER GOSAT RECORD AS APPROPRIATE) AND TO APPLY NEW AND UNIQUE TECHNIQUES TO QUANTIFY THE UNCERTAINTY OF THE CARBON CYCLE RESPONSES TO CLIMATE. OUR PROJECT COMBINES EXPERTISE IN ATMOSPHERIC TERRESTRIAL AND OCEAN SCIENCES TOGETHER WITH DEEP KNOWLEDGE OF ASSIMILATION METHODS TO BRING AN INTEGRATED INTERDISCIPLINARY APPROACH TO THE MISSION. OUR WORK TO DATE HAS SHOWN THAT CLIMATE VARIATION ASSOCIATED WITH THE 2015-2016 EL NINO INCREASED CARBON EMISSIONS IN TROPICAL TERRESTRIAL ECOSYSTEMS BY ~3 PGC/YR WHILE REDUCING ATMOSPHERIC CO2 CONCENTRATIONS OVER THE TROPICAL PACIFIC OCEAN DURING THE ONSET PHASE OF EL NINO. WE DIAGNOSED DRIVERS OF THE CARBON CYCLE ANOMALIES AND SHOWED THAT CO2 ANOMALIES OVER THE TROPICAL PACIFIC RESULTED FROM SURFACE OCEAN PCO2 CHANGES ASSOCIATED WITH THE EL NINO WHILE TERRESTRIAL ECOSYSTEM LOST CARBON TO THE ATMOSPHERE THROUGH WILDFIRE ENHANCED RESPIRATION AND REDUCED PHOTOSYNTHESIS DEPENDING ON THE CONTINENT. FINALLY WE SHOWED THAT THE EXTENSIVE AND INCREASING BODY OF AIRCRAFT VERTICAL PROFILE DATA CAN BE USED TO COMPARE TO POSTERIOR CONCENTRATION FIELDS FROM THE ASSIMILATION MODEL AND USED TO IDENTIFY FLUX ERRORS RESULTING FROM TRANSPORT SYSTEMATIC ERRORS IN THE XCO2 OBSERVATIONS AND OTHER SOURCES. MODELS OF ATMOSPHERIC CO2 CONCENTRATIONS OVER THE NEXT CENTURY DIVERGE WILDLY. OCEAN MODELS DISAGREE ABOUT FUTURE CARBON UPTAKE RATES TERRESTRIAL MODELS DON'T EVEN AGREE ABOUT THE SIGN OF FUTURE CARBON EXCHANGE WITH SOME SHOWING CONTINUED UPTAKE AND OTHERS INDICATING WEAKENING UPTAKE OR EVEN TRANSITIONING TO SOURCES. CURRENT DATA FOR MODEL FALSIFICATION AND IMPROVEMENT ARE INADEQUATE AND CARBON FLUX DATA AT THE SCALE OF CLIMATE ANOMALIES ARE CRITICAL. THE GLOBAL CARBON CYCLE RESPONDS TO GLOBAL CHANGE THROUGH CONCENTRATION AND CLIMATE EFFECTS DESCRIBED BY THE BETA AND GAMMA AND PARAMETERS. IN PROCESS MODELS BETA DESCRIBES THE DIRECT EFFECTS OF CO2 ON CARBON STORAGE THROUGH CHANGES TO AIR-SEA DISEQUILIBRIUM AND LAND PHOTOSYNTHESIS. GAMMA QUANTIFIES THE EFFECTS OF CLIMATE (INCLUDING OCEAN CIRCULATION) ON CARBON STORAGE. THIS PROJECT WILL FOCUS ON INTERANNUAL-TO-DECADAL OBSERVATIONS OF GAMMA BY OBSERVING THE CLIMATE SENSITIVITY OF TROPICAL AND EXTRATROPICAL LAND AND OCEAN FLUXES AND CORRELATING THEM WITH PHYSICAL ENVIRONMENTAL VARIABLES. OUR SPECIFIC OBJECTIVES FOR THIS CONTINUATION INCLUDE: ANALYSIS OF A GLOBAL/REGIONAL REANALYSIS OF CARBON FLUXES USING THE GOSAT AND OCO-2 RECORDS OVER 2010-PRESENT. ATTRIBUTION OF ESTIMATED NET FLUX ANOMALIES TO CHANGES IN GROSS PRIMARY PRODUCTIVITY (USING SIF) FIRE (USING CO) OR RESPIRATION THE RESIDUAL OF THE NET FLUX AND GPP QUANTIFICATION OF EXTRATROPICAL CARBON FLUX ANOMALIES DURING THE OCO-2 OBSERVATION PERIOD AND CONTINUED ANALYSIS OF ONGOING TROPICAL FLUXES. CONTINUED ATTRIBUTIONS OF FLUX ANOMALIES TO CLIMATE AND OCEAN CONDITIONS. EVALUATION OF ESTIMATED SURFACE FLUXES AGAINST INDEPENDENT OBSERVATIONS TO DETECT TRANSPORT MODEL ERROR AND EVALUATE THE OVERALL UNCERTAINTY OF THE FLUXES USING AN INNOVATIVE ADJOINT METHOD. DISTRIBUTION OF LEVEL 4 NET FLUX AND L4B GPP RESPIRATION AND BIOMASS BURNING FLUXES TO THE BROADER COMMUNITY ALONG WITH STANDARD AND ADJOINT-BASED ESTIMATES OF UNCERTAINTY.