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.