Abstract. Using measurements of the surface-ocean CO 2 partial pressure (pCO 2 ) and 14 different pCO 2 mapping methods recently collated by the Surface Ocean pCO 2 Mapping intercomparison (SOCOM) initiative, variations in regional and global sea-air CO 2 fluxes are investigated. Though the available mapping methods use widely different approaches, we find relatively consistent estimates of regional pCO 2 seasonality, in line with previous estimates.

International audienceUsing measurements of the surface-ocean CO₂ partial pressure (pCO₂) and 14 different pCO₂ mapping methods recently collated by the Surface Ocean pCO₂ Mapping intercomparison (SOCOM) initiative, variations in regional and global sea–air CO₂ fluxes have been investigated. Though the available mapping methods use widely different approaches, we find relatively consistent estimates of regional pCO₂ seasonality, in line with previous estimates. In terms of interannual variability (IAV), all mapping methods estimate the largest variations to occur in the Eastern equatorial Pacific. Despite considerable spead in the detailed variations, mapping methods with closer match to the data also tend to be more consistent with each other. Encouragingly, this includes mapping methods belonging to complementary types – taking variability either directly from the pCO₂ data or indirectly from driver data via regression. From a weighted ensemble average, we find an IAV amplitude of the global sea–air CO₂ flux of 0.31 PgC yr⁻¹ (standard deviation over 1992–2009), which is larger than simulated by biogeochemical process models. On a decadal perspective, the global CO₂ uptake is estimated to have gradually increased since about 2000, with little decadal change prior to 2000. The weighted mean total ocean CO₂ sink estimated by the SOCOM ensemble is consistent within uncertainties with estimates from ocean-interior carbon data or atmospheric oxygen trends

The interannual variability of net sea–air CO2 flux for the period 1982–2007 is obtained from a diagnostic model using empirical subannual relationships between climatological CO2 partial pressure in surface seawater (pCO2SW) and sea surface temperature (SST), along with interannual changes in SST and wind speed. These optimum subannual relationships show significantly better correlation between pCO2SW and SST than the previous relationships using fixed monthly boundaries. Our diagnostic model yields an interannual variability of ±0.14 PgC yr−1 (1σ) with a 26‐year mean of −1.48 PgC yr−1. The greatest interannual variability is found in the Equatorial Pacific, and significant variability is also found at northern and southern high‐latitudes, depending in part, on which wind product is used. We provide an assessment of our approach by applying it to pCO2SW and SST output from a prognostic global biogeochemical ocean model. Our diagnostic approach applied to this model output shows reasonable agreement with the prognostic model net sea–air CO2 fluxes in terms of magnitude and phase of variability, suggesting that our diagnostic approach can capture much of the observed variability on regional to global scale. A notable exception is that our approach shows significantly less variability than the prognostic model in the Southern Ocean.

[1] This paper reports on a basin-wide inventory of anthropogenic CO 2 in the East (Japan) Sea determined from high-quality alkalinity, chlorofluorocarbon, and nutrient data collected during a summertime survey in 1999 and total dissolved inorganic carbon data calculated from pH and alkalinity measurements. The data set comprises measurements from 203 hydrographic stations and covers most of the East Sea with the exception of the northwestern boundary region. Anthropogenic CO 2 concentrations are estimated by separating this value from total dissolved inorganic carbon using a tracerbased (chlorofluorocarbon) separation technique. Wintertime surface CFC-12 data collected in regions of deep water formation off Vladivostok, Russia, improve the accuracy of estimates of anthropogenic CO 2 concentrations by providing improved airsea CO 2 disequilibrium values for intermediate and deep waters. Our calculation yields a total anthropogenic CO 2 inventory in the East Sea of 0.40 ± 0.06 petagrams of carbon as of 1999. Anthropogenic CO 2 has already reached the bottom of the East Sea, largely owing to the effective transport of anthropogenic CO 2 from the surface to the ocean interior via deep water formation in the waters off Vladivostok. The highest specific column inventory (vertically integrated inventory per square meter) of anthropogenic CO 2 of 80 mol C m À2 is found in the Japan Basin (40°NÀ44°N). Comparison of this inventory with those for other major basins of the same latitude band reveal that the East Sea values are much higher than the inventory for the Pacific Ocean (20À30 mol C m À2 ) and are similar to the inventory for the North Atlantic (66À72 mol C m À2 ). The substantial accumulation of anthropogenic CO 2 in the East Sea during the industrial era has caused the aragonite and calcite saturation horizons to move upward by 80À220 m and 500À700 m, respectively. These upward movements are approximately 5 times greater than those found in the North Pacific. Both the large accumulation of anthropogenic CO 2 and its significant impact on carbonate chemistry in the East Sea suggest that this sea is an important site for monitoring the future impact of the oceanic invasion of anthropogenic CO 2 .