Seasonal and Inter-Annual Variations in pCO2sea and Air-Sea CO2 Fluxes in Mid-Latitudes of the Western and Eastern North Pacific during 1999-2006: Recent Results Utilizing Voluntary Observation Ships

We have investigated the seasonal and inter-annual variations of the difference in partial pressure of CO2 between surface seawater (pCO(2)(sea)) and overlying air (pCO(2)(air)) and the air-sea CO2 flux in the mid-latitudes of the western North Pacific (WNP; 25-40 degrees N, 140-170 degrees E) and eastern North Pacific (ENP; 25-40 degrees N, 120-150 degrees W) from 1999 to 2006 using the latest voluntary observation ship data. In the WNP and ENP, the area-averaged Delta pCO(2) (pCO(2)(air) - pCO(2)(sea)) was at its minimum in late summer (-4.6 to 6.7 mu atm in the WNP and -32.5 to -20.5 mu atm in the ENP) and at its maximum in late winter (51.0 to 59.8 mu atm in the WNP and 35.1 to 46.2 mu atm in the ENP). The WNP acts as a moderate sink for atmospheric CO2 (4.1 to 5.5 mmol m(-2) d(-1)), while the ENP acts as a weak sink (1.1 to 1.9 mmol m-2 d(-1)). Because Delta pCO(2) is mainly controlled by pCO(2)(sea), we have evaluated the effect of the factors controlling pCO(2)(sea): sea surface temperature (SST), salinity (SSS), dissolved inorganic carbon (TCO2), and total alkalinity (AT). In the WNP, not only SST but also TCO2 plays an important role in the seasonal pCO(2)(sea) variation, while the SST could only explain most of the pCO(2)(sea) variation in the ENP. From 1999 to 2006, pCO(2)(sea) increased at a significantly lower rate (0.53 +/- 0.11 mu atm yr(-1)) than pCO(2)(air) (1.81 +/- 0.01 mu atm yr(-1)) in the WNP, and at a slightly lower rate in the ENP (1.32 +/- 0.16 mu atm yr(-1)). The air-sea CO2 flux increased at a rate of 0.19 +/- 0.05 mmol m(-2) d(-1) yr(-1) in the WNP and 0.09 +/- 0.03 mmol m(-2) d(-1) yr(-1) in the ENP, suggesting that the WNP is a stronger sink for atmospheric CO2.