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Polar oceans play an important role in the global carbon cycle. Measurements of atmospheric and surface sea water PCO2 were conducted during the 1st, 2nd and 3rd Chinese National Arctic Research Expedition cruises in July to September of 1999, 2003 and 2008, respectively. The Arctic carbon sink increases during the past 10 years from 1999 to 2008 accompanying the receding of sea ice cover. Especially, our summer 2008 CO2 data suggest that increased initial ice-melting will enhance air-sea CO2 flux greatly in the western Arctic Ocean. Greater summertime ice melting is projected to occur in the following years with an increasing speed. The increased CO2 uptake by the Arctic Ocean slopes and basins, thus, may provide a negative feedback mechanism to reduce atmospheric CO2 and thus rate of warming. However, such CO2 sink will be weakened gradually as our data also suggest that a complete ice-free condition in the slope and basin areas for a prolong period during the summer may result in an increase in surface pCO2 and reduced CO2 flux (though still higher than today). Furthermore, warming and ice-melt also will promote permafrost thawing in the Arctic continent and thus increases river inputs of dissolved inorganic carbon (DIC) and organic carbon that are expected to be recycled as CO2, thus further reducing the capacity of the Arctic Ocean to absorb the atmospheric CO2