Shipboard measurements of atmospheric and surface seawater pCO sub(2) in the North Pacific carried out from January 1999 to October 2000 on the voluntary observation ship MS Alligator Liberty

Partial pressures of CO sub(2) in surface seawater (pCO sub(2) super(sea)) and the overlying air (pCO sub(2) super(air)) were measured in the North Pacific (mainly 30-40 degree N) from January 1999 to October 2000 (9 cruises) onboard the voluntary observation ship MS Alligator Liberty. Distributions of pCO sub(2) super(air) and pCO sub(2) super(sea) showed that the western North Pacific (west of 180 degree ) acted as a sink for atmospheric CO sub(2) throughout the year except for August, whereas the eastern North Pacific (east of 160 degree W) acted as a sink for only half the year (November to May). Total dissolved inorganic carbon (TCO sub(2)) estimated from pCO sub(2) super(sea) and total alkalinity showed a larger seasonal decrease (April to June) in the western North Pacific than in the eastern North Pacific, in accordance with the seasonal decrease in nitrate + nitrite (NO sub(x) = NO sub(3) super(-) + NO sub(2) super(-)). The 9.5 C/N ratio calculated from the relationship between decreased TCO sub(2) and [NO sub(x)] implied a larger influence of biological activity in the western North Pacific. Using pCO sub(2) super(sea) estimated from the relationship between pCO sub(2) super(sea) and sea surface temperature, we assessed the monthly CO sub(2) fluxes in the western North Pacific for the year 2000. The fluxes ranged from ca. 0 Gt-C yr super(-1) in the summer to ca. -0.4 Gt-C yr super(-1) in the winter, with an annual average of -0.2 Gt-C yr super(-1), which corresponds to about 10% of the annual oceanic CO sub(2) uptake over the 1990s.