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.

The role of the Southern Ocean as a source or a sink for CO₂ in the modern ocean is heavily disputed, its interannual variability is unknown, and its control on atmospheric CO₂ during glaciations is suspected but still not understood nor quantified.  We estimate the variability of the air-sea CO₂ fluxes in the Southern Ocean for the 1992-2003 period using the spatio-temporal distribution of atmospheric CO₂ measurements from 12 stations in the Southern Ocean and 43 stations worldwide.  Our results show basin-scale variability of ±0.1 to 0.3 PgC/y that are related to physical variability in the Southern Ocean.

Three years of quasi-continuous atmospheric ¹⁴CO₂ observations in Heidelberg (Germany) have been used together with continuous CO measurements to determine the CO/fossil fuel CO₂ ratio in a regional polluted area. Comparison with bottom-up information on fossil fuel CO₂ and CO emissions for the respective catchment area shows that large discrepancies (up to 60%) between inventory data and observations exist. Therefore both, a lot of care and reliable emissions inventory data are necessary if CO shall be used as a quantitative surrogate for fossil fuel CO₂.

The primary aim of the Centre for Observation of Air-sea Interactions and Fluxes (CASIX) is to estimate accurately the air-sea fluxes of CO₂. Under CASIX, a high resolution ocean general circulation model, coupled to an ocean biogeochemistry model, has been used to provide estimates of surface ocean pCO₂ and air-sea fluxes of CO₂ for the year 2003. An initial global simulation was run at 1 degree horizontal resolution, providing boundary conditions for a limited area North Atlantic model at 1/3 degree resolution. Observed temperature and salinity data were assimilated into the model. Temporal variability in the resulting pCO₂ fields are compared to observations, and the primary production and pCO₂ results of the two different resolution runs are compared.

Intensive atmospheric sampling field programs are envisioned as a key component of integrated research programs such as the North American Carbon Program (NACP) [Sarmiento and Wofsy, 1999; Wofsy and Harriss, 2002].  The intensive sampling provides unique information about the spatial distribution of CO₂ as well as imposes tight constraints on regional budgets that are difficult to obtain from other means. We summarize what we have learned from the numerous COBRA (CO₂ Budget and Rectification Airborne study) experiments [Gerbig et al., 2003a] that have taken place in 2000, 2003, and 2004.  We present the observed spatial variability of CO₂ [Gerbig et al., 2003a; Lin et al., 2004a] and regional budgets derived from regional air parcel-following experiments [Lin et al., 2004b].  These observations are also used as a critical testbed for modeling frameworks [Gerbig et al., 2003b]. We draw conclusions about ways to maximize the value of intensive atmospheric sampling experiments and the role that such experiments should play within programs like the NACP.

The Atlantic's central role in the global thermohaline circulation suggests that this basin should be an important laboratory for understanding the ocean carbon cycle and possible temporal variations in that cycle. Here we present the set up and results from an oceanic box model inversion which focuses on the transport and divergence of total inorganic carbon (TIC) and anthropogenic carbon within the Atlantic.

To understand the difference in CO₂ behavior between planetary boundary layer (PBL) and free troposphere (FT), we conduct CO₂ measurements using a small aircraft and a tower at the forest area in West Siberia. More than 120 vertical CO₂ profiles were observed by newly developed small CO₂ measurement device. Seasonal amplitude in PBL (36.9 ppm) is two times larger than that in FT (15.7 ppm). Diurnal variation in CO₂ profile is affected not only by PBL growth but also by horizontal advection and entrainment flux from FT to PBL.

A new research project has started in 2003 to develop Continuous CO₂ Measurement Equipment (CME) and Automatic Air Sampling Equipment (ASE) for commercial airlines. CMEs are planning to be installed on five aircrafts and fly to South East Asia, East Asia, Europe, North America, Pacific and Australia. Routine air sampling by ASE will be done twice a month between Japan and Australia. After issuing the certification, first observation flight by Boeing 747-400 will be conducted in October, 2005. Preliminary observation by small research aircraft indicates that CME produces reasonable results.

We quantify atmosphere-biosphere carbon exchange at the continental scale across North America during the summers of 2003 and 2004. The 2003 campaign features continental transects across the northern portion of North America with significant influence from biomass burning, while the 2004 study focuses on the greater New England and Quebec region. We use a Lagrangian, adjoint atmospheric model [Gerbig et al. 2003a,b; Lin et al. 2003] coupled to a biosphere model derived from the Vegetation Photosynthesis Model [Xiao et al., 2004]. Our analysis of the 2004 airborne data demonstrates the progression of increasing carbon uptake through the boreal zone during the seasonal transition from early spring to late summer. Data from the coast-to-coast transects of the 2003 campaign allow us to quantify large scale carbon exchange across the continent.

The spatial and temporal variations of atmospheric CO₂ at 8-13 km from April 1993 to March 2005 were observed by measuring CO₂ concentrations in samples collected biweekly from a commercial airliner between Australia and Japan. The 12-year record between 30N and 30S revealed several characteristics for CO₂ interannual variabilities in the upper troposphere. The most significant year-to-year change was found in a large increase in the growth rate during 1997/98 and 2002/03 that were associated with the ENSO events. During these years, changes in north-to-south gradient of latitudinal distribution and seasonal cycle were observed compared to data during the normal years.