Monthly time series of atmospheric carbon dioxide (CO₂), the relative amount of carbon-13 in CO₂ (¹³C), hydrogen (H₂) carbon monoxide (CO), and methane (CH₄) are examined and related to each other and to an index of the status of ENSO. Making use of simple 12-month running mean and difference filters isolates the year-to-year variability in the concentrations and apparent sources of these constituents.

Increasing ocean stratification associated with global warming has been posited to serve as a positive feedback on global warming, reducing the oceanic uptake of anthropogenic carbon dioxide. We suggest that a poleward shift of westerly winds combined with future increases in atmospheric carbon dioxide may drive an increase in the CO₂ uptake in the Southern Ocean, representing a negative feedback on atmospheric anthropogenic CO₂.

Temporal and spatial distributions of the δ¹⁸O value of atmospheric CO₂ (dC_a) can be used to constrain regional ecosystem carbon exchanges and linkages between carbon and water cycling. However, our understanding of the substantial observed temporal and spatial variability in dC_a is limited. Among many contributing factors, seasonal and inter-annual variations in climate are likely to be important. In this study we investigate the impact of dry climatic conditions on the ecosystem-atmosphere C¹⁸OO isoflux.

We conducted this study in the U.S. Southern Great Plains using five-year monthly-averaged precipitation δ¹⁸O values (δ_p) from the National Atmospheric Deposition Program (NADP) network, Mesonet meteorological forcing, and MODIS-derived NDVI and land-cover characterization. These data are used to force the isotope ecosystem model ISOLSM [Riley et al., 2002; Riley et al., 2003] at 10 km resolution across the region for relatively drier (2003) and wetter (2004) years. The model has been calibrated and tested in the dominant herbaceous vegetation types in the region [Biraud et al., this issue].

In a Carbon Cycle Data Assimilation System (CCDAS) one infers the values of the parameters controlling the function of a process model using various observations. One can then calculate quantities of interest from the optimized parameters and the model. One can also calculate the uncertainties on the parameters and propagate these to uncertainties of the calculated quantities. In Rayner et al. [2005] we assimilated atmospheric observations over two decades, into a terrestrial model and calculated fluxes over this period. Here we extend this work by calculating the response of the calibrated terrestrial biosphere to a GCM simulation of future climate. Using this combination we are able to comment on the fate of terrestrial carbon pools and fluxes under climate change, calculate the uncertainties of the response, and determine which parameters in the model are responsible for this uncertainty. We include an extra parameter that scales the climate change signal from the GCM projection. We thus extend the sensitivity and uncertainty analysis to include the climate sensitivity.

The Amazon region of South America plays a significant role in global cycles of water, energy and carbon, yet it is also one of the most challenging biogeographical areas of the world to model correctly. Numerous global climate models have problems with anomalous die-back of the Amazon rain forest variously attributed to inadequate representation of rainfall, faulty soil moisture dynamics or an inability to correctly simulate the drought tolerance of the vegetation. Such misrepresentation of the Amazon in global climate models can cause larger than observed excursions of the global carbon cycle. This poster explores soil moisture and drought stress for Amazonia with the Simple Biosphere Model (SiB3) and possible reasons and solutions to the rain-forest die back problem, which should lead to more reasonable estimates of carbon fluxes at the ecosystem scale.

We present a comprehensive analysis of the recent inter-annual variation of the atmospheric CO₂ growth rate, with a special focus on the 2002-2003 period, using a state of the art atmospheric inversion, process driven model simulations (land and ocean), and recent biomass burning estimates. The inverse estimates compare favourably well with the model simulations over North Asia and indicate a large contribution of the fire anomaly to the total anomaly, for that region in 2003. Over Europe, the spatial distribution of the inverse and bottom-up flux anomalies for 2003 have similarities but the time evolution of the total fluxes still need to be reconciled.

This research investigates how land use in the shortgrass steppe of eastern Colorado impacts short and long-term water, carbon and energy dynamics.  A large and homogeneous area of Conservation Reserve Program (CRP) grassland near Briggsdale, Colorado, was selected for this experiment and divided into three 40 hectare plots. An open-path eddy flux system was established in each plot and measurements made during a baseline comparison prior to land use transformation.  The three treatments include an un-grazed grassland (control), a moderate intensity grazing treatment, and a dry-land agricultural rotation (winter wheat-hay millet; considered optimal for this low rainfall area of Colorado).  We report on the trajectories of carbon, water and energy fluxes in theses three land use systems and analyze how altered carbon storage and water use efficiency may impact short-term land surface-atmosphere interactions, as well as long-term source-sink relationships, water conservation, productivity and sustainability.

A Time Dependent Inverse (TDI) model is used to estimate CO₂ fluxes for 64 regions of the globe from atmospheric data in the period January 1988–December 2001. These estimated are then used for understanding interannual variability in fluxes and simulating the CO₂ concentrations at various sites. The NIES/FRCGC transport model driven by interannually varying meteorology is used in both part of the analysis. Estimated atmospheric CO₂ concentrations agree closely with those observed at various sites globally.

Using a coupled 3D hydrodynamic-biogeochemical model system for the Northwest-European shelf we simulated the years 1993-96, which exhibit an extremely strong transition from a NAOI-high to a NAOI-low regime. The induced temperature-shift had two consequences for the carbon budget of the North Sea: Firstly it increased the CO₂ solubility and secondly it destabilized the water column in spring 1996. The latter effect was the precondition for mixing events which brought new nitrogen for primary production into the upper layer. Consequently the air-sea flux was 540 Gmol C a^-1 in 1996, the NAOI-low year, and it was 203 Gmol C a^-1 in 1995, the year with the highest NAOI.

Is the massive Amazon forest a CO₂ sink, a source or is it in equilibrium?  

There is a large uncertainty in carbon fluxes estimates for the tropics as a whole and in particular for the Amazon region in South America, bringing the attention to the lack of information to call the region a carbon source or sink. The production of scientific consistent and long term data series for the region is a process that has to advance step by step.