A combined study of micrometeorological flux measurement of carbon dioxide (CO₂) and methane (CH₄) and measurement of their stable carbon isotopes at a paddy field indicated that CH₄ production can affect not only greenhouse gas budget of wetland ecosystem but also isotopic signature of respired CO₂.

We investigated the interannual variability of the partial pressure of carbon dioxide (pCO₂) in the surface waters of the western subarctic gyre (155°E to 165°E, 48°N to 53°N) and the Alaska Gyre (AG, 195°E to 210°E, 45°N to 52°N) for a period of 9 years. We used automated measurements of pCO₂ in the surface water (pCO_2sw) and the air (pCO_2air) as well as sea surface temperature (SST) and salinity (S) obtained from the Japanese-Canadian joint Volunteer Observing Ship (VOS) program. We observed annual trends in the pCO_2sw and based on simple least square fit to observed data, the surface waters in the WSG showed a gradual pCO_2sw increase of 0.4 ppm yr^-1 which was three times larger than in the AG (1.8 ppm yr^-1) for the 9-year period. In the WSG, this was about half of the estimated atmospheric pCO₂ increase for the whole period (10 ppm or 1.2 ppm yr^-1), whereas gas exchange explained much of the increase in the AG (pCO_2air increased 1.6 ppm yr^-1). Interestingly, the two gyres showed opposite annual trends in the SST and salinity and in the WSG we observed a salinity and SST increase of 0.018 yr^-1 and 0.07°C yr^-1 (0.56°C for the whole study period), respectively, whereas we observed a small freshening of 0.015 yr^-1 and a cooling trend of about 0.11°C yr^-1 in the AG. We examine the possible mechanisms to explain the annual trends in pCO₂, based on the observed changes in SST and salinity as well as observations made by other investigators.

Mode Waters provides a privileged pathway for the transport of heat, salt and anthropogenic CO₂ into the ocean interior. The carbon cycle decadal variability in response to environmental changes is investigated using historical and recent data collected during the INDIGO (1985-1987) and OISO (1998-2003) oceanographic campaigns conducted in the South West Indian Ocean, an important zone for Mode Waters formation. The observed change in dissolved inorganic carbon over the 15-year period was 8 µmol/kg in Subantarctic Mode Water (500-800m), which is less than the anthropogenic carbon increase alone (13 µmol/kg). This difference may be explained by natural or climate-induced changes in ocean processes. Predictions from a global ocean-carbon model (OPA-PISCES) are used as a means to help interpret changes in the controlling processes: ocean dynamics, biological activity and air-sea interactions.

Begur-Pals site (41,58ºN, 3,14ºE, Catalonia, Spain) is weekly sampled for CO₂ and other GHG (CH₄, CO, N₂O, SF₆) since January 2000. This CO₂ serial data shows at the middle of each summer a sudden increase and decrease of the CO₂ peak. It is a process that can be either attributed to a highest transpiration rate than ecosystem production due to the lack of summer precipitation, to biomass burning from Mediterranean forest fires, to tourist activities in the coast, or to CO₂ pumping from waters in the Western Mediterranean sea (according to wind backtrajectories). A sampling strategy using sites with high towers with continuous measurements has been developed. Sites are placed at the vortexes of a rhombus: two extremes are continental sites in the center of the Ebro’s watershed and a marine site is located in the Menorca Island. The other two are high towers in the Catalonian coast.

Systematic observations of the atmospheric CO₂ concentration, and carbon and oxygen isotope ratios of CO₂ (d¹³C and d¹⁸O) have been maintained at Japanese Arctic Observatory in Ny Ålesund (79°N, 12°E) and Antarctic station, Syowa (69°S, 40°E). The interannual variations of the CO₂ concentration and d¹³C in association with the occurrence of ENSO event were clearly observed at the both sites. The d¹⁸O values observed at Syowa Station showed significant increasing trend after 1999.

The coupled feedback processes of energy and carbon cycles are an essential mechanism for understanding global environmental change. We developed a simplified one-dimensional carbon and energy cycle coupled model to quantify the feedback processes between energy and carbon cycles. The model was calibrated to reproduce the historical variations in temperature and atmospheric CO₂ concentration. The model results of vertical ocean temperature profiles, and latitudinal NPP and NEP distributions were in good agreement with the observation data and terrestrial biosphere model results. The regional difference of terrestrial ecosystem response by climate feedback appeared in the middle and high latitudes. The north-south distribution is important to investigate the terrestrial ecosystem because the opposite response appeared in the middle and high latitude. The future change of carbon cycle and climate was also simulated up to the year 2100 based on the IPCC scenario. The atmospheric CO₂ concentration reaches 735 ppmv in 2100 and global average temperature increases 1.9 K for 2000-2100.

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).

We used recent ocean bomb radiocarbon inventory estimates for the time of GEOSECS (mid-1970s) and WOCE (mid-1990s) from Peacock [2004] and Key et al. [2004], corrected for missing ocean areas [Naegler 2005], to develop a new parameterisation of the piston velocity – wind speed relationship of CO₂ air-sea gas exchange. For monthly mean climatological winds on a 1°x1° grid, this results in a gas exchange parameter a_q,660 of 0.32±0.04 (in cm hr^-1 m^-2 s²) and a net oceanic CO₂ uptake of 1.53±0.18 PgC/yr for the mid-1990s, when using the Takahashi et al. [2002] pCO₂ data.