Variations and trends of CO2 in the surface seawater in the Southern Ocean south of Australia between 1969 and 2002
Measurements of the partial pressure of CO2 in surface seawater (pCO2sw) were 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 of pCO2sw for the four...
| Published in: | Tellus B |
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| Main Authors: | , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Blackwell
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| Subjects: | |
| Online Access: | http://hdl.handle.net/2115/862 https://doi.org/10.1111/j.1600-0889.2005.00130.x |
| Summary: | Measurements of the partial pressure of CO2 in surface seawater (pCO2sw) were 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 of pCO2sw for the four cruises showed the same pattern north of the Subantarctic Front (SAF), while year-to-year changes were noted south of the SAF. We evaluated the long-term trend of the pCO2sw representative of the zone between oceanographic fronts by taking into account changes in the seasonal variation in pCO2sw and the long-term increase of the sea surface temperature (SST) of the Southern Hemisphere. The observed growth rate of pCO2sw was 0.7±0.1µatm/yr at its minimum, which was observed at the SST of 15°C north of the Subtropical Front (STF), 1.0±0.5µatm/yr in the Subantarctic Zone (SAZ) between STF and SAF, 1.5±0.4µatm/yr in the Polar Frontal Zone (PFZ) between SAF and the Polar Front (PF), and 1.8±0.2µatm/yr 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 of pCO2sw due to the remarkable CO2 drawdown by the biological activity in January 2002. The relatively low growth rates of pCO2sw close to the STF and in the SAZ are probably associated with the formation of Subtropical Mode Water and Subantarctic Mode Water in their respective zones. Between the north of the STF and PZ, the growth rate of total dissolved inorganic carbon (DIC) was calculated to be about 0.5-0.8µmol/kg/yr via the buffer factor. |
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