NOAA ACE (Niall)
NOAA 2005 – 2007
Much uncertainty remains in our understanding of the ways in which atmospheric, terrestrial and oceanic carbon reservoirs interact, and the controls, magnitude and location of fluxes that determine atmospheric CO2 mixing ratio and terrestrial and oceanic sequestration. Analysis of the rate of increase of atmospheric [CO2] suggests that carbon uptake by terrestrial ecosystems offsets fossil fuel emissions by 1.5-2.0 Gt per year. Several studies suggest that a significant proportion of that sink lies in northern deciduous and boreal ecosystems, but the range of estimates by different techniques is large and research also indicates a strong tropical sink. Furthermore, inverse estimates of the role of tropical regions in global carbon exchange may be underestimated because of the paucity of real data and because deep convection in the tropics may mask the tropical signal in the existing network of [CO2] measurements. With expanded research in neo-tropical regions during the last few years, the weakest link in our current understanding of the global carbon cycle, and concomitant potential for greatest return on research effort, is in the old- world tropics, particularly in Africa. With joint funding from the US National Oceanic and Atmospheric Administration (NOAA) and the National Aeronautics and Space Administration (NASA) this project is addressing some of these shortcomings in our understanding of the temporal and spatial dynamics of carbon exchange in Africa. The project includes both biogeochemical forward modeling, using remote sensing data and land surface models, and atmospheric inverse modeling of carbon dynamics across the African continent. Field measurements in support of the modeling activities are being carried out in Southern Africa (Kruger National Park, South Africa) and West Africa (the Gourma region of northern Mali). The field component is a directed effort to obtain vital new data and process understanding to constrain and parameterize models for regional and continental carbon cycle assessments. We are planning an additional field site in under-represented Central Africa for the coming year, with possible site locations in Zambia or Congo- Brazzaville.
The project will provide more tightly constrained estimates of the spatial and temporal variation in carbon uptake and release from Africa. Satellite data from the AVHRR series and from MODIS and other Terra satellite instruments, and assimilated climate data, are being used to parameterize a land surface model (SiB3) to estimate the historical and contemporary variation in vegetation activity across the continent and predict spatially and temporally continuous fields of net carbon, water and stable isotope exchange. In parallel with this “forward modeling” of African carbon dynamics, we are preparing both regional and global inverse analyses of atmospheric [CO2] and stable isotope concentrations. These analyses will use the existing flask measurement network augmented by new high precision [CO2] measurements in Africa. We expect that the novel combination of forward and inverse estimates of African carbon exchange will lead to model enhancements and reductions in uncertainty, lead to improved estimates of the spatial and temporal dynamics of carbon and water exchange in Africa, and lead to an improved understanding of the impacts of climate, climate variability and land use in regional carbon dynamics and the contributions of Africa to the global carbon cycle.