Evaluation of the net CO2 uptake in the Canada Basin in the summer of 2008

The third Chinese National Arctic Research Expedition (CHINARE) was conducted in the summer of 2008. During the survey, the surface seawater partial pressure of CO2 (ρCO2) was measured, and sea water samples were collected for CO2 measurement in the Canada Basin. The distribution of ρCO2 in the Canada Basin was determined, the influencing factors were addressed, and the air-sea CO2 flux in the Canada Basin was evaluated. The Canada Basin was divided into three regions: the ice-free zone (south of 77°N), the partially ice-covered zone (77°–80°N), and the heavily ice-covered zone (north of 80°N). In the ice-free zone, ρCO2 was high (320 to 368 μatm, 1 μatm=0.101 325 Pa), primarily due to rapid equilibration with atmospheric CO2 over a short time. In the partially ice-covered zone, the surface ρCO2 was relatively low (250 to 270 μatm) due to ice-edge blooms and icemelt water dilution. In the heavily ice-covered zone, the seawater ρCO2 varied between 270 and 300 μatm due to biological CO2 removal, the transportation of low ρCO2 water northward, and heavy ice cover. The surface seawater ρCO2 during the survey was undersaturated with respect to the atmosphere in the Canada Basin, and it was a net sink for atmospheric CO2. The summertime net CO2 uptake of the ice-free zone, the partially ice-covered zone and the heavily ice-covered zone was (4.14±1.08), (1.79±0.19), and (0.57±0.03) Tg/a (calculated by carbon, 1 Tg=1012 g), respectively. Overall, the net CO2 sink of the Canada Basin in the summer of 2008 was (6.5±1.3) Tg/a, which accounted for 4%–10% of the Arctic Ocean CO2 sink.