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The Southern Ocean is an important sink of atmospheric carbon dioxide(CO2).However,the magnitude of the CO2 sink is uncertain because of the scarcity of in-situ observations due to its remote and rough waters.Empirical relationships were deduced based on the in-situ partial pressure of carbon dioxide(pCO2)in surface seawater and its main controls including Chlorophyll a(Chl-a)and Sea Surface Temperature(SST)obtained during the 26th CHINARE cruise in late spring(November)and early summer(December)2009.An extrapolation method based on multiple linear regressions was set up for combining the empirical relationship with satellite data to compute the sea-air carbon fluxes and carbon uptake in the Southern Ocean(south of 50°S).The empirical relationships are validated with independent measurements from the Lamont-Doherty Earth Observatory(LDEO)database.The mean standard deviation differences(Std)between extrapolated and measured pCO2 from Global Surface pCO2(LDEO)database(7.69 to 26.16 μatm)is consistent with the precision of our regressions(13.6 to 21.3 μatm).Including the effects of sea ice,we estimate a Southern Ocean CO2 source to the atmosphere in November 2009 of 1.65 Tg C with an uncertainty of ±0.73 Tg C by uncertainty propagation formula.While in December 2009,we estimated a CO2 sink of-2.34 Tg C with an uncertainty of ±1.03 Tg C.The carbon source and sink of the South Atlantic Ocean,the South Indian Ocean and the South Pacific Ocean were estimated.For the austral summer,the South Atlantic Ocean remained a strong carbon sink while the South Indian Ocean declined sharply from a CO2 sink of-0.78 Tg C in December 1999 to-0.043 Tg C in December 2009.Our results imply that from the annual declining trend,the Indian Ocean would be a carbon source in summer.