We carried out airborne campaigns over Europe in order to analyze atmospheric CO₂ variability at the regional scale. Data reveal a higher standard variation in the planetary boundary layer (PBL) against a lower one in the free troposphere (FT), where the air is more well mixed. Ground data generally agree well with airborne measurements when done in the FT, but not in the PBL where they are exposed to local disturbances. Ground stations located in the FT are shown to be representative of a regional scale while PBL observatories provide only locally representative measurements.

The results of atmospheric CO₂, CH₄ and CO measurements are presented. The measurements were made in air samples collected at heights of 4, 25, 100, 200 and 300 m above ground, and in the atmospheric column in Obninsk, Russia (55.11 N, 36.57  E, 183 m asl).

Four CARIOCA Lagrangian buoys drifted in the North-East Atlantic Ocean between 38° and 45°N between February and August 2001. Daily cycles of pCO₂, SST and DIC are observed even in winter. Biological rates of carbon consumption, gross and net primary production,are determined in situ from the amplitude of the diel cycles and the time evolution of surface dissolved inorganic carbon. Over the 6 months period, February-August, the ocean in the studied area is a sink for atmospheric CO_2.The mean absorbed flux is equal to 3.8 mmoles/ m²/ day.

We estimated the production of bomb radiocarbon using available information on atmospheric nuclear bomb tests, the simple (radio-)carbon cycle model GRACE (Global RadioCarbon Exploration Model) and atmospheric observations as constraints. Subsequent forward simulations of the bomb radiocarbon inventory in the different carbon reservoirs turned out to be in very good agreement with recent observation-based estimates, therewith for the very first time allowing to close the global bomb radiocarbon budget. Besides confirming original stratospheric bomb ¹⁴C data published in the reports of the Health and Safety Laboratories [Telegadas, 1971, and references therein], our results confirm recent observation-based ocean bomb radiocarbon inventory estimates for the time of GEOSECS (1970s) and WOCE (1990s) from Peacock [2004] and Key et al. [2004], but refute the GEOSECS ocean inventory estimates from Broecker et al. [1985, 1995].

In order to further our understanding of the biophysical and biogeochemical mechanisms that control the fate of fossil fuel carbon emissions, we are simulating an hourly global atmospheric carbon dioxide concentration field ([CO₂]) for the year 2000 with realistic diurnal, synoptic and seasonal variability, including quantified errors.  In addition, we are simulating carbonyl sulfide (COS) for a continental mixed temperate forest to test a hypothesis that errors in seasonal simulations of CO₂ result from incorrect specification of springtime onset of photosynthesis rather than incorrect timing of ecosystem respiration.

This presentation describes in-situ atmospheric CO₂ measurements at Waliguan Observatory (WLG, 36°17'N, 100°54'E, 3816m asl) since 1994, together with 5-day isobaric back trajectory analysis.  We also use the Hybrid Single-Particle Lagrangian Integrated Trajectory (Hysplit-4) transport/diffusion model to simulate the CO₂ variation at WLG in January 1999 and compared with observations. A case study for polluted air mass transport event with a short-term elevated CO₂ has been conducted to further investigate the impact of source, sink and long-range transport of atmospheric CO₂.

We estimate the natural and anthropogenic components of the air-sea flux of CO₂ in the Indian Ocean. The increase in atmospheric CO₂ driven by human activity has caused the air-sea CO₂ flux, to increase significantly over the industrial era. We estimate the flux in the year 1780 to be approximately 0.2Gt/yr, increasing by 0.26Gt/yr to 0.5Gt/yr in 2000. The estimate of the natural (preindustrial) flux is highly sensitive to uncertainties in modern-day CO₂ disequilibrium measurements. By contrast, the estimate of the anthropogenic flux is only weakly sensitive to these measurements. Our anthropogenic estimate is smaller than other studies due to the removal in our methodology of the widely made weak-mixing and constant-disequilibrium assumptions, both of which cause positive bias.

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.