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In order to clarify the CO2 exchange between the seawater and the overlying air during the sea-ice formation, we have carried out tank experiments in a low-temperature room. CO2 concentration above the sea-ice began to increase since the beginning of the sea-ice formation, and increased at larger rates with time and the decrease in air temperature. This increase of CO2 concentration in air was mainly caused by the increase in dissolved inorganic carbon concentration in the brine of the upper part of sea-ice, changes in CO2 solubility and dissociation constants of carbonic acid. The CO2 flux increased logarithmically with time, and reached a level of 2 × 10−4 to 5 × 10−4 g-C m−2 hr−1 at 50 mm ice thickness. We found that the CO2 flux was correlated well with the salinity and negatively with the volume of the brine in the upper part of the sea-ice. These suggested the larger role of the difference in partial pressure of CO2 between brine and air as compared to that of competitive change in the brine volume. Present results suggest the necessity to examine the CO2 exchange between the seawater and air in seasonal sea-ice areas. [ABSTRACT FROM AUTHOR]

In order to elucidate the seasonal and interannual variations of oceanic CO2 uptake in the Greenland Sea and the Barents Sea, the partial pressure of CO2 in the surface ocean ( pCO2sea) was measured in all seasons between 1992 and 2001. We derived monthly varying relationships between pCO2sea and sea surface temperature (SST) and combined them with the SST data from the NCEP/NCAR reanalysis to determine pCO2sea and air–sea CO2 flux in these seas. The pCO2sea values were normalized to the year 1995 by assuming that pCO2sea increased at the same growth rate (1.5 μatm yr−1) of the pCO2 in the air ( pCO2air) between 1992 and 2001. In 1995, the annual net air–sea CO2 fluxes were evaluated to be 52 ± 20 gC m−2 yr−1 in the Greenland Sea and 46 ± 18 gC m−2 yr−1 in the Barents Sea. The CO2 flux into the ocean reached its maximum in winter and minimum in summer. The wind speed and Δ pCO2 (= pCO2air– pCO2sea) exerted a greater influence on the seasonal variation than the sea ice coverage. The annual CO2 uptake examined in this study (70°–80°N, 20°W–40°E) was estimated to be 0.050 ± 0.020 GtCyr−1 in 1995. The interannual variation in the annual CO2 uptake was found to be positively correlated with the North Atlantic Oscillation Index (NAOI) via wind strength but negatively correlated with Δ pCO2 and the sea ice coverage. The present results indicate that the variability in wind speed and sea ice coverage play a major role, while that in Δ pCO2 plays a minor role, in determining the interannual variation of CO2 uptake in this area. [ABSTRACT FROM AUTHOR]

Measurements of the partial pressure of CO2 in surface seawaterwere made in the Southern Ocean south of Australia during four cruises in January to February 1969, December 1983 to January 1984, December 1994 to January 1995 and January 2002. The spatial distribution offor the four cruises showed the same pattern north of the Sub-Antarctic Front (SAF), while year-to-year changes were noted south of the SAF. We evaluated the long-term trend of therepresentative of the zone between oceanographic fronts by taking into account changes in the seasonal variation inand the long-term increase of the sea-surface temperature (SST) of the Southern Hemisphere. The observed growth rate ofwas 0.7± 0.1μatm yr−1 at its minimum, which was observed at the SST of 15°C north of the Subtropical Front (STF), 1.0± 0.5μatm yr−1 in the Sub-Antarctic Zone (SAZ) between STF and SAF, 1.5± 0.4μatm yr−1 in the Polar Frontal Zone (PFZ) between SAF and the Polar Front (PF) and 1.8± 0.2μatm yr−1 in the Polar Zone (PZ) between PF and 62°S, determined as the northern edge of the Seasonal Sea Ice Zone (SSIZ) on the basis of surface salinity and satellite images. These increases were caused by the uptake of anthropogenic CO2 as well as variations in the thermodynamic temperature effect, ocean transport and biological activity. In the SSIZ between 62 and 66.5°S, we could not clearly evaluate the long-term trend ofdue to the remarkable CO2 drawdown due to biological activity in January 2002. The relatively low growth rates ofclose to the STF and in the SAZ are probably associated with the formation of Subtropical Mode Water and Sub-Antarctic Mode Water in their respective zones. Between the north of the STF and the PZ, the growth rate of total dissolved inorganic carbon was calculated to be about 0.5–0.8μmol kg−1 yr−1 via the buffer factor. [ABSTRACT FROM AUTHOR]

abstract On the basis of measurements of the partial pressure of carbon dioxide in surface seawater (p CO2 w ) between Japan and the Hawaiian Islands in winter and summer, we examined the relationship between p CO2 w and the sea surface temperature (SST) in the North Pacific Subtropical Gyre (NPSG). In winter, p CO2 w correlated well with the SST (0.14–0.24% °C-1 ), suggesting a monotonous change in the carbonate system. However, in summer, five different p CO2 w –SST relationships were found in the NPSG (including the Kuroshio Extension) due to changes in the relative contribution of ocean dynamics (upwelling, vertical mixing and advection), biological activity in the absence (very low level) of macro-nutrients and thermodynamics. The increase in p CO2 w corresponding to a unit increase in the SST from January to July was low (<2.5% °C-1 ) west (leeward side) of the Hawaiian Islands (19–22°N, 158–168°W) and in the Kuroshio Extension (33–35°N, 140–165°E), and high (∼3% °C-1 ) south of the Kuroshio Extension (25–30°N, 180–165°W) and the Hawaiian Islands (15–19°N, 157–162°W). This suggested that the drawdown of dissolved inorganic carbon was affected by the enhanced biological activity due to upwelling events associated with eddies and/or the transport of dissolved nutrients from gyre edges to the interior. [ABSTRACT FROM AUTHOR]