Variability of ΔpCO2 in the subarctic North Pacific. A comparison of results from four expeditions

Time-space variability of surface seawater pCO₂ is examined over the region (150°W^-180°, 46°N^-50°N) of the subarctic North Pacific where large meridional gradients of temperature and nutrient concentrations exist. The data were collected during four trans-Pacific expeditions in three different years (1985–1987), but within the same 30-day period of the year (August — September). Systematic measurement differences between the four data sets are estimated as < 10 μatm. The inter-expedition comparison suggests that surface seawater pCO₂ in the study area is quite variable, with mean differences of up to 25 μatm and local differences up to 60 μatm. Spatial and interannual variability of surface seawater pCO₂ were found to contribute significant uncertainty to estimates of the mean ΔpCO₂ for the study area. Fluxes were calculated using ΔpCO₂ values from the four expeditions combined with gas exchange coefficients calculated from four different wind fields giving a range of - 0.94 to + 4.1 mmol CO₂ m^-2 d^-1. The range of fluxes from the study area is scaled to a larger area of the North Pacific to address how this variability can translate into uncertainties in basin-wide carbon air-sea exchange fluxes.