Improving Constraints on Carbon Fluxes using Measurements of Atmospheric CO2 and Ocean pCO2
Abstract:Spatial and temporal variations in the large-scale distribution of tropospheric CO2 provide valuable constraints on regional to hemispheric-scale carbon exchange between the atmosphere and land and ocean reservoirs. These constraints have been widely exploited in top-down inverse analyses that combine atmospheric measurements of CO2, prior information on component CO2 fluxes, and representations of atmospheric transport. The inversion procedure typically estimates surface carbon fluxes by minimizing the differences between measured and modeled atmospheric CO2 concentrations.
Here we report on regional to hemispheric-scale inter-annual CO2 flux estimates for the period 1990-2012, derived from a hierarchy of top-down methods, ranging in complexity from a simple two-box hemispheric analysis, with mixing rates constrained by SF6 data, to Bayesian synthesis inversions developed using the GEOS-Chem atmospheric transport model. A primary aim of this inter-comparison is to investigate the impact on CO2 flux estimates, of recently derived prior ocean fluxes developed using pCO2 measurements from the SOCAT database (http://www.socat.info/). Sensitivity of flux estimates to assumptions on atmospheric transport, and in particular, inter-hemispheric mixing, will also be discussed.