We apply to Classical Labrador Sea Water (CLSW) the “transit-time distribution” (TTD) method to estimate the inventory and uptake anthropogenic carbon (∆C). A parametric model of TTDs representing bulk-advective and mixing processes is constrained with WOCE CFC data. The constrained TTDs are then used to propagate ∆C into the interior of the CLSW. Compared to many past studies the key advantage of this methodology is that mixing is not assumed to be a negligible component of transport.

We have conducted long-term regular monitoring of vertical profiles of ¹³C/¹²C ratio of atmospheric CO₂ over three sites in Siberia and a site in Japan. Time-series and seasonality of the ¹³C/¹²C ratio at each altitude levels at the four site were examined. Apparent isotopic signature was calculated from the relationship between CO₂ mixing ratio and the ¹³C/¹²C ratio in individual vertical profiles.

The effect of rainfall on mass transfer across the air-water interface was investigated through the CO₂ absorption experiments in a turbulent open-channel flow with the free surface. The results show that the rainfall enhances both the turbulent mixing near the free surface on the liquid side and the CO₂ transfer across the interface. The mass transfer coefficient on the liquid side is well correlated by both the mean vertical momentum flux of rainfall, M, and the mean kinetic energy of rain droplets impinging on the unit area of the air-water interface, KEF. However, it was not concluded which of M and KEF is a better parameter for expressing the rainfall effects on the mass transfer. The comparison between the mass transfer coefficient obtained in this study and that obtained in wind-driven turbulence suggests that it is of great importance to consider the rainfall effect on the CO₂ exchange rate between the atmosphere and ocean in precisely estimating the global carbon cycle in a climate model.

We evaluate the impact on modeled atmospheric CO₂ concentrations of explicitly representing the tropospheric CO₂ source from reduced carbon oxidation. We also calculate the bias in inverse flux estimates that results from omitting this influence.

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.

Tropical drought can significantly impact inter-annual variations in the terrestrial CO₂ fluxes. Concentrations and carbon isotope ratios of atmospheric CO₂ can help to quantify this impact, however, their use requires a model estimation of the terrestrial isotope disequilibirum, i.e. the difference between the isotopic signature of photosynthesis and respiration, which can only be achieved by accurately accounting for changes in relative contributions of C3 and C4 plants (C4 fraction) and physiological effects of root-zone water stress.

Systematic measurements of the CO₂ concentration and its carbon isotopic ratio (d¹³C) have been carried out at 7 locations in China since March or July 2003. Seasonal cycles of the CO₂ concentration and d¹³C were clearly observable, especially at Longfengshan, Shangdianzi and Fukang. The d¹³C value of source producing the seasonal CO₂ cycle at each site, d_S, was estimated from the observed CO₂ and d¹³C seasonal cycles.  The average value of d_S derived for the 6 sites was calculated to be -25.6 (±1.8) ‰, which is larger than those observed at mid-latitudes in the western Pacific region, probably due to smaller discrimination of ¹³C by C₄ plants in the continent of China. 

We present a statistical analysis of aircraft and surface measurements of the CO₂ mixing ratio over the US Rocky Mountains during 1993 – 2002 at latitudes close to that of the Issyk-Kul station in Kyrgyzstan. Average characteristics of the CO₂ mixing ratio and its annual variations show only small height variability in the troposphere over well mixed mountain regions. Comparison of Issyk-Kul optical data with US aircraft and surface measurements shows satisfactory agreement. Also some differences at low altitudes were obtained owing to possible regional differences between mountain regions of Central Asia and USA.