Measurements of concurrent changes in both the atmospheric O₂ and CO₂ mixing ratios have been proven to be useful independent information for the partitioning of anthropogenic CO₂ into its different sinks [e.g. Keeling et al., 1996]. This information is used along with the “classical” partitioning models that make use of CO₂ concentration and (radioactive as well as stable) isotopic composition information [e.g. Keeling et al., 1995]. Global carbon budget reconstruction needs long time series observations of global means. Downscaling to a more regional assessment introduces a closer relation to possible annual and regional variations in prescribed oxidative ratios of biospheric and combustion processes. With the goal of improving the knowledge on the temporal and local variability of the O₂/ CO₂ signal, we present the results of the analysis on an extended data set from the remote station of Lutjewad (The Netherlands) and compare them with the findings of different other sampling stations in Europe, starting from 2001 till present.

First atmospheric δO₂/N₂, CO₂ and δ¹³C flask measurements from vertical aircraft sampling in the lower troposphere above Griffin Forest (GRI), Perthshire, UK, (56°37’N, 3°47’W) and from ground based flask sampling at the high altitude site Jungfraujoch (JFJ), Switzerland (3580m above sea level (a.s.l.), 46°33’N, 7°59’E), and the mountain site Puy de Dôme (PUY), France (1480m a.s.l., 45°46’N, 2°58’E) are presented.

We use the theoretically ideal tracer ¹⁴CO₂ to estimate the fossil fuel CO₂ enhancement in boundary layer air at two sites in New England and Colorado. Improved D¹⁴C measurement precision of 1.6-2.6‰ provides fossil fuel CO₂detection capability of 0.8-1.5 ppm. Using the tracers CO and SF₆, we obtain two additional independent estimates of the fossil fuel CO₂ component, and we assess the biases in these methods by comparison with the ¹⁴CO₂-based estimates. Large differences are observed between the SF₆-based estimates and those from the ¹⁴CO₂ and CO methods. The CO-based estimates show seasonally coherent biases, underestimating fossil fuel CO₂ in winter and overestimating in summer.

We present here a test of convection uncertainty within a single model framework driven by the same meteorological fields. Our primary goal is to explore to what extent do convection schemes impact atmospheric CO₂ distribution, by testing three referred cloud convection schemes ranging from a very simple to a relatively complex form [Table 1]. Our second goal is to examine the sensitivity of atmospheric CO₂ to its regional emission/sink uncertainty [Fig. 1] constrained by IPCC 2001 at a “fixed” convection scheme to clarify the pros and cons of the convection schemes.

An inverse modeling system has been developed based on the Bayesian principle for estimating the carbon fluxes of the 48 regions globally and 28 regions over North America in monthly steps for 2003 using CO₂ concentration measurements at 95 atmospheric baseline stations and with regularization using remote sensing-based surface flux field. Preliminary inversion results of global carbon flux and a carbon flux field over North America have been obtained.

Measurements of the radiocarbon content of atmospheric carbon dioxide are a potentially powerful, yet relatively unexplored method of improving the understanding of natural carbon dynamics and verifying fossil fuel emissions. Development of ¹⁴CO₂ as a tracer has been limited by measurement capabilities given that seasonal and spatial variation in D¹⁴C is currently of the same order as traditional instrument precision: 3-5 per mil. We have demonstrated 1-2 per mil reproducible measurement precision at the Center for Accelerator Mass Spectrometry of Lawrence Livermore National Laboratory. Here we present preliminary measurements of the natural variability of ¹⁴CO₂ from the SIO network of background air sampling stations.

We examine the growth-rate of atmospheric CO₂ in 2002 and 2003. Observations show consecutive increases of greater than 2 ppmv per year for the first time on the Mauna Loa record. We use a statistical regression to show that increasing anthropogenic emissions and ENSO activity are unable to account for the CO₂ growth-rates of 1992 and 1993 following the Pinatubo volcanic eruption, or the anomalously high growth-rate of 2003. Increased forest fires in the northern hemisphere, consistent with remote-sensing and carbon monoxide measurements, seem likely to have contributed significantly to the 2003 anomaly. We hypothesise that the hot and dry Eurasian summer of 2003 led to an increase in forest fire emissions from Siberia, and may also have directly suppressed land-carbon uptake. Model results lead us to expect a steady increase in airborne fraction as climate change weakens the natural carbon sink and accelerates CO₂ rise.

The ocean margins form the transition zone between terrestrial and open ocean areas and represent up to 30% of total ocean productivity, yet their role in the global carbon cycle is ill quantified. In order to address this issue, a bi-weekly time-series program was established in Santa Monica Bay in January 2003 to measure the seasonal evolution of the upper ocean carbon cycle at this coastal site. Our measurements reveal a strong seasonal cycle with an amplitude in salinity normalized dissolved inorganic carbon (DIC) reaching nearly 200 µmol/kg and pCO₂ changes of more than 200 µatm. The seasonal cycle of DIC is characterized by a maximum in late winter/early spring, which is caused by upwelling bringing high DIC concentrations from the upper thermocline during this time of the year. The concomitant supply of high levels of nutrients fuels an intense bloom, whose strength varies from year to year in response to large interannual variations in upwelling. In 2003 and 2004, substantial surface DIC decreases were observed under nitrate depleted conditions i) right after the occurrence of upwelling, and i) about three months after upwelling. This implies that during these times, either organic matter production occurred with a very high stoichiometric C:N ratio and/or an additional source of new nitrogen existed that supplied nitrogen without supplying DIC. The seasonal cycle of pCO₂ follows that of DIC with a late winter/early spring maximum, whose levels far exceed that of the atmosphere, and a summer-time minimum with undersaturated pCO₂ values. Annually, Santa Monica Bay acts as a weak to moderate sink for atmospheric CO₂. We suggest that this is mainly due to biological production and in part driven by the uptake of anthropogenic CO₂.

Inverse modeling methods are now commonly used for estimating surface fluxes of carbon dioxide, using atmospheric mass fraction measurements combined with a numerical atmospheric transport model. Michalak et al. [2004] recently developed a geostatistical approach to flux estimation that takes advantage of the spatial and/or temporal correlation in fluxes and does not require prior flux estimates. In this work, a geostatistical implementation of a fixed-lag Kalman smoother is developed and applied to the recovery of gridscale carbon dioxide fluxes for 1997 – 2001 using data from the NOAA-CMDL Cooperative Air Sampling Network.

To examine concentration variations of atmospheric CO₂ in the sub-tropical region of East Asia, systematic air sampling with subsequent laboratory analysis has been made in the southernmost part of Japan since June 1993. A time series of measured CO₂ concentrations was analyzed for long-term trend, seasonal cycle and interannual variability, and the temporal CO₂ variations deduced were interpreted in terms of atmospheric transport and CO₂ flux regions.