OBJECTIVES IN OUR PROPOSAL WE ADDRESS QUESTION 6 LISTED IN THE NASA TERRESTRIAL ECOLOGY PROGRAM ANNOUNCEMENT HOW ARE THE MAGNITUDES FATES AND LAND-ATMOSPHERE EXCHANGES OF CARBON POOLS RESPONDING TO ENVIRONMENTAL CHANGE AND WHAT ARE THE BIOGEOCHEMICAL MECHANISMS? . WE WILL IMPROVE THE MECHANISTIC REPRESENTATION OF BIOCHEMICAL PROCESSES WITHIN THE COMMUNITY EARTH SYSTEM MODEL (CESM) TO EVALUATE WHETHER WARMING IN THE ARCTIC HAS AND IS LIKELY TO CAUSE AMPLIFYING FEEDBACKS TO CLIMATE. BRIEFLY WE INTEGRATE RESEARCH RESULTS FROM THE ABOVE CAMPAIGN WITH THE COMMUNITY LAND MODEL A MECHANISTIC MODEL OF LAND-ATMOSPHERE EXCHANGE WHICH WE WILL ENSURE IS CONSISTENT WITH WELL TESTED HISTORICAL REMOTE SENSING PRODUCTS (NDVI AND INFERRED LAI). WE HAVE USED DATA ASSIMILATION TO ENSURE THAT THE MODEL AGREES WITH HISTORICAL LAI IN THE REGION AND WILL INCORPORATE COLLECTIONS OF SOLAR INDUCED FLUORESCENCE AND IN THE SECOND PHASE OF THE PROJECT RECENT ABOVE DATA COLLECTIONS. WHERE THE HIGHLY TUNED MODEL DISAGREES WITH APPROPRIATELY SCALED OBSERVATIONS WE WILL INFER A BIOGEOCHEMICAL MECHANISM IS MISSPECIFIED MIS-PARAMETERISED OR MISSING. BY REVISING THE REPRESENTATION OF MECHANISMS IN THE MODEL SUBROUTINES WE CAN TEST A SERIES OF HYPOTHESES TO DEVELOP OUR UNDERSTANDING OF FEEDBACKS BETWEEN GLOBAL SCALE CLIMATE FORCING AND REGIONAL AND LOCAL SCALE IMPACTS. BY PUTTING AN EARTH SYSTEM MODEL AT THE CENTER OF OUR APPROACH WE HAVE THE OPPORTUNITY TO INFER BOTH IMPACTS OF FORCING ON ECOSYSTEM SERVICES AND LIKELY FEEDBACKS OF THESE CHANGES ON FUTURE GLOBAL CLIMATE. METHODS; OUR DATA ASSIMILATION SYSTEM BRINGS TOGETHER CESML ONE OF THE MOST HIGHLY DEVELOPED AND EXTENSIVELY USED ESMS WITH A LEADING-EDGE COMMUNITY ENSEMBLE DATA ASSIMILATION TOOL THE DATA ASSIMILATION RESEARCH TESTBED (DART). TOGETHER THEY REPRESENTS ONE OF THE MOST ADVANCED DA SYSTEMS YET DEVELOPED FOR SUCH A COMPLETE COUPLED ESM. WE PROPOSE TO USE THE BIOPHYSICAL AND ECOLOGICAL RELATIONSHIPS IN THE COMMUNITY LAND MODEL (CLM) TO TRANSLATE THE WEALTH OF ABOVEGROUND OBSERVATIONS OF BIOLOGICAL AND BIOPHYSICAL CONTROLS INTO ESTIMATES OF BELOWGROUND CARBON WATER AND ENERGY EXCHANGE. WE WILL USE AN ENSEMBLE KALMAN FILTER WITHIN THE DATA ASSIMILATION RESEARCH TESTBED TO MINIMIZE MODEL ERROR IN ESTIMATES OF MODEL STATES AND PROCESSES THAT ARE OBSERVABLE FROM SATELLITE REMOTE SENSING. THIS ITSELF IMPROVES ESTIMATES OF BELOWGROUND PROCESSES WHICH CAN BE VERIFIED AGAINST EXTENSIVE BUT SMALL SCALE IN-SITU ESTIMATES FROM NASA DOE NEON LTER AND PI-LED OBSERVATIONS WHERE AVAILABLE. IT ALSO ALLOWS US TO INVESTIGATE AND TEST ALTERNATIVE MODEL APPROACHES WITH FEWER CONFOUNDING PROCESSES. OUR DATA CONSTRAINED MODEL ESTIMATES OF CARBON DYNAMICS THEN ENABLE US TO PREDICT CARBON DIOXIDE AND METHANE FLUXES OVER ARCTIC AND BOREAL REGIONS WITH QUANTIFIED UNCERTAINTIES. SIGNIFICANCE AND RELEVANCE TO NASA THIS PROPOSAL IS DIRECTLY RESPONSIVE TO THE ABOVE PHASE 2 SOLICITED RESEARCH IN (4) INTEGRATING RESEARCH RESULTS FROM ABOVE INTO A COHERENT MODELING FRAMEWORK TO DIAGNOSE AND PREDICT ECOSYSTEM DYNAMICS AND THE CONSEQUENT SOCIETAL IMPACTS OF CHANGES TO THE ECOSYSTEM. IT WILL IMPROVE THE UNDERSTANDING AND REPRESENTATION OF TERRESTRIAL ECOSYSTEMS IN EARTH SYSTEM MODELS BY PROVIDING ADVANCED DATA ASSIMILATION CAPABILITIES TO CONSTRAIN CLM WITH OBSERVATIONS IMPROVE FORECASTING ABILITY AND IDENTIFY AREAS FOR MODEL DEVELOPMENT. IT WILL COMBINE MEASUREMENTS AND MODELS LEVERAGING INVESTMENTS FROM MULTIPLE AGENCIES AND WILL IMPROVE QUANTITATIVE AND PREDICTIVE UNDERSTANDING OF ABOVE- AND BELOWGROUND PROCESSES AND TRAITS IN TERRESTRIAL ECOSYSTEMS ACROSS ARCTIC AND BOREAL REGIONS. THIS APPROACH FORMALLY CHARACTERIZES UNCERTAINTIES THROUGHOUT CLM AND HAS BEEN EXPLICITLY DEVELOPED FOR IMPROVING THE PREDICTABILITY OF EARTH SYSTEM MODELS. AS COMMUNITY TOOLS ANY CODE DEVELOPMENTS FOR DART AND CLM WILL BE AVAILABLE TO ALL THROUGH WELL DOCUMENTED REPOSITORIES.