We analysed the temporal variations of the CO₂ system in the Southern Ocean south of Tasmania and compared the seasonality of the carbon dioxide fugacity (fCO₂) and the air-sea CO₂ flux during spring and summer for two different years: 1996/97 and 2002/03. In summer, the CO₂ flux presents large and contrasting interannual changes in the Permanent Open Ocean Zone (POOZ, 53-61°S): the oceanic CO₂ sink varies from about –0.3 mmol.m^-2.d^-1 in 1997 to –20.6 mmol.m^-2.d^-1 in 2003. This strong sink in February 2003 was related to an increased phytoplankton biomass in this high-nutrient, low-chlorophyll (HNLC) region.

An accurate knowledge of the thermodynamics of the carbonic acid system in seawater is crucial to our understanding of the behavior of carbon dioxide in seawater. In particular, this knowledge is needed whenever a particular property needs to be calculated from measurements of other related properties; e.g., the estimation of the partial pressure of CO2 in air that is in equilibrium with a sample of sea water, p(CO2), from measurements of the total dissolved inorganic carbon, CT, and of the total alkalinity, AT, of a water sample. This calculation is particularly important for ocean models, which transport CT and AT, but which need to calculate p(CO2) at the sea surface so as to represent air-sea exchange processes. Numerous determinations of dissociation constants for carbon dioxide in seawater media have been published over the years. In each case the authors have recommended “best” values for the dissociation constants, and often the constants are represented in these papers by interpolating equations or tables. Furthermore, a number of investigators have attempted to assess the thermodynamic consistency of the various published values for these dissociation constants with analytical measurements made on natural seawater. Despite all this work, the results of these efforts are, as yet, not conclusive. I shall present a review of the situation and will try to provide a clear description of the magnitude of the problems, their possible sources, and their importance to understanding the behavior of CO2 in seawater.

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.

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. 

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.

Since 1993, regular seasonal water sampling has been conducted along a ship-track between Island and Newfoundland in the open ocean of the North Atlantic subpolar gyre in the frame of the long-term SURATLANT program. In this study, we analyse the interannual variation of the carbon dioxide system, including seawater fugacity (fCO₂) and air-sea CO₂ fluxes for the period 1993-2004. During 1993-1997, the data present a clear seasonality in this region marked by a strong CO₂ sink in summer and near-equilibrium in winter. For recent years, 2001-2004, we observed a dramatic change of the source/sink seasonality. An extreme case was observed in 2003 when oceanic fCO₂ was above equilibrium during all seasons. This strong anomaly was driven by ocean warming.

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.

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.