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.

Based on simulations with high-resolution transport models we investigate the detectability of surface flux signals in the atmospheric CO₂ concentration and infer some general guidelines for the sampling of the continental troposphere for the purpose of constraining mid-latitude land carbon sinks.

We report the interannual variations of winter CO₂ partial pressure in surface waters (pCO₂^sea) and overlying air (pCO₂^air) and air-sea CO₂ flux in the extensive area (3-34°N) from subtropical to equatorial along 137°E during the period of 1983-2003. The pCO₂^sea varied largely in the equatorial region of 3-6°N, depending on the variations of the oceanographic conditions related to the El Niño-Southern Oscillation (ENSO) events. The pCO₂^sea variations in the subtropical gyre north of 23°N were small due to highly counteracting effects between anti-correlated sea surface temperature (SST) and dissolved inorganic carbon (DIC) anomalies through the entrainment process, irrespective of large variations of SST. By contrast, it was found that there occurred a low negative correlation between SST and DIC in the region restricted around 15-18°N in the North Equatorial Current, which resulted in a large amplitude of variations of pCO₂^sea and hence CO₂ influx. The interannual variations of CO₂ flux depended predominantly on those of the difference between pCO₂^sea and pCO₂^air (ΔpCO₂) south of 18°N but on those of wind speed in the northern region. 

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.

In order to elucidate seasonal and interannual variations of oceanic CO₂ uptake in the Greenland Sea and the Barents Sea, partial pressures of CO₂ in the surface ocean (pCO₂^sea) were measured from 1992 to 2001. The values of pCO₂^sea were lower than the partial CO₂ pressures in the atmosphere (pCO₂^air) throughout the year, and the annual net air-sea CO₂ fluxes in the Greenland Sea and the Barents Sea were evaluated to be 52 ± 31 and 46 ± 27 gC m^-2 yr^-1, respectively, yielding a total oceanic CO₂ uptake of 0.050 ± 0.030 GtC yr^-1. We also found that the annual mean CO₂ uptake was positively correlated with the North Atlantic Oscillation Index (NAOI) via wind strength, but was negatively correlated with DpCO₂ (pCO₂^air-pCO₂^sea) and the sea ice coverage. The results also indicate that the wind speed and sea ice coverage play a major role in determining the interannual variation of CO₂ uptake, with DpCO₂ playing a minor role.

The formation of Antarctic Intermediate Water is investigated in a state of the art numerical model. Results are compared with a previous, lower resolution version of the model, and with data from the World Ocean Circulation Experiment.

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.

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 present a 30+ year record of continuous atmospheric CO₂ concentrations and a 5 year record of continuous O₂ concentrations from Baring Head, New Zealand. When compared to South Pole data, the CO₂ concentrations indicate a persistent, but variable net carbon sink in the Southern Ocean since the late 1970s. The amplitude of the seasonal cycle of O₂ concentrations (expressed as “APO”, Atmospheric Potential Oxygen) shows large inter-annual variability, suggesting high variability in annual air-sea O₂ fluxes, and thus also potentially suggesting high variability in year to year marine productivity in the Southern Ocean.