Using high-quality data for the CO₂-system and related properties obtained 10-year apart, we estimated decadal increases of anthropogenic CO₂ along the A10 section of the World Ocean Circulation Experiment (WOCE) Hydrographic Program (WHP). Increases of anthropogenic CO₂ were found down to an isopycnal surface of 27.3σ_θ (approx. 1000 dbar). In the sub-Antarctic Mode Water (SAMW), the increase was 6.9 ± 2.0 μmol kg^-1 on average, while in the Antarctic Intermediate Water (AAIW), it was 4.2 ± 1.9 μmol kg^-1. The increase in SAMW was larger in the west than that in the east of the section. No significant increases were detected in North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW).

There is growing evidence that the rate of anthropogenic CO₂ uptake in the ocean is changing over time. Several programs are poised to assess current and future ocean CO₂ uptake rates, but there are issues with how to extrapolate these measurements to decadal-scale changes over entire ocean basins. One possibility is to exploit the growing network of ARGO floats that are collecting profiles throughout the global oceans. We explore the viability of this approach and make recommendations for how the ARGO network might be made more useful for biogeochemical applications.

Changes in dissolved inorganic carbon (DIC) and apparent oxygen utilization (AOU) in the water column are quantified for meridional hydrographic sections through the Atlantic from 63 ˚N to 60 ˚S between 1988/1993 and 2003/2005.  Changes are most pronounced in the upper 1000 m water column.  DIC changes range from -5 to 40 µmol/kg and AOU changes by a similar amount.  The remainder is caused by changes in positions of fronts, gyres, remineralization and ventilation as manifested by changes in watermass properties.  In particular AOU increases of similar magnitude as increases in DIC point towards a significant contribution of oxidation of organic matter to the DIC increase.  The large changes in biogeochemical properties of the upper water column of the Atlantic have been one of the big surprises in the decadal reoccupation of the transects.

We present a synthesis Bayesian inverse method to optimize one year of daily fluxes at model resolution (50x50 km over Europe) by inversion of continuous CO₂ measurements, daily averaged over Europe (10 sites). Based on a synthetic data analysis, we studied the impact of three different spatial and temporal correlations on flux errors. We found that the present network is too sparse to efficiently constrain European fluxes at model resolution even with the assumption of perfect transport. However, the agreement between the optimized fluxes and the true fluxes is improved when aggregated in space and time, mainly for 8-10 days fluxes over Western Europe. This region is indeed surrounded by our network. The spatial correlation scheme used was found to have a negligible impact on this agreement. Adding a white noise on pseudo-data to simulate transport model errors largely degrades the agreement. Using real data, European flux variations becomes unreasonably large due to the inability of our transport model to properly represent the CO₂ concentrations at continental sites.

The CROZEX cruises (November 2004 to January 2005) had the objective to test whether natural iron fertilisation from the Crozet plateau promotes algal blooms. Results from the cruises show that algal blooms created an oceanic CO₂ sink downstream of the Crozet plateau. Vertical advection of water into the mixed layer occurred close to two islands on the plateau. Data from 18 cruises between 1991 and 2002 are used to quantify the seasonal variability of surface pCO₂ and CO₂ air-sea exchange in the region.

Results of airborne CO₂ and CO observations from the NSF/NCAR C-130 platform during the Gulf of Tehuantepec Experiment (GOTEX 2004) and the Airborne component of the Carbon in the Mountains Experiment (ACME 2004) will be presented. A modified commercial vacuum ultraviolet fluorescence instrument monitored CO mixing ratios. CO measurements were used to help identify air masses recently influenced by combustion emissions. CO₂ mixing ratios were measured using a pressure- and temperature-controlled LI-COR 6252 analyzer.  Control of time response allowed operation of the CO₂ instrument in two modes for application to either low altitude eddy covariance or higher altitude mixing ratio measurements. Performance will be assessed, including accuracy estimates derived from intercomparison activities.

This presentation will interpret results from the TransCom 3 interannual time dependent inversion. First, the long-term mean carbon exchange will be compared across the three different TransCom 3 inversion levels: the annual mean, seasonal, and interannual control experiments. We will highlight the agreement among these experiments in spite of the differing degrees of freedom, and the differing CO₂ observing networks employed. Comparison will be made to independent decadal estimates of land and ocean carbon uptake and will include the sensitivity to different CO₂ networks. We will also interpret the model mean interannual carbon fluxes as they relate to key indices of climate variability. In particular, correlation to the El Niño/Southern Oscillation index will be made suggesting a propagation carbon flux anomalies from the tropics to the extra tropics following the peak of the ENSO warm phase in the tropical Pacific ocean. These correlations will be explained via anomalies in temperature and precipitation from NCEP reanalysis.

The carbon dioxide transport at the Niwot Ridge AmeriFlux site was investigated in both gravity and streamline coordinates. For this forested site with a 6% slope, both nighttime drainage flow and daytime upslope flow played important roles in the CO₂ budget. Both the CO₂ respiration at night and the CO₂ uptake during the day are underestimated if the horizontal transport of CO₂ is not monitored; and the two components may not cancel out.

In the present study atmospheric CO₂ retrievals based on Aqua satellite AIRS (Atmospheric Infrared Sounder) instrument observations are compared with forward model predictions. There is quite good agreement in seasonal cycles as well as North-South gradients when averaged over large scales. At smaller scales there are contrasts between upper troposphere CO₂ above continents versus oceans in the retrievals and there are signatures off Africa which seem likely artifacts caused by aerosols. As a consequence retrievals cannot be used at this stage to constrain surface sources and sinks without causing large biases. Interestingly there is good agreement in the shape of the N-S gradient at low-to-mid latitudes in the Northern hemisphere between simulations based on one transport model (LMDZ) and retrievals, but disagreement when comparing with simulations based on a second transport model (TM3). This raises questions about lower to upper troposphere transport and their representation in these models.

We have employed a Multi-parameter Linear Regression (MLR) analysis procedure to determine the uptake of anthropogenic CO₂ between two east-west hydrographic surveys of the North Pacific that occurred in 1994 and 2004. The results revealed water column integrated uptake rates of anthropogenic CO₂ that ranged from 1.1 to 1.3 mol m^-2 yr^-1 depending on location. The combined effect of the tilted density surfaces and the younger waters with higher anthropogenic CO₂ concentrations leads to higher total column inventories in the western North Pacific.