Influence of biological carbon export on ocean carbon uptake over the annual cycle across the North Pacific Ocean

We evaluate the influences of biological carbon export, physical circulation, and temperature-driven solubility changes on air-sea CO2 flux across the North Pacific basin (35 degrees N-50 degrees N, 142 degrees E-125 degrees W) throughout the full annual cycle by constructing mixed layer budgets for dissolved inorganic carbon (DIC) and pCO(2), determined on 15 container ship transects between Hong Kong and Long Beach, CA, from 2008 to 2012. Annual air-sea CO2 flux is greatest in the western North Pacific and decreases eastward across the basin (2.70.9molCm(-2)yr(-1) west of 170 degrees E, as compared to 2.10.3molCm(-2)yr(-1) east of 160 degrees W). East of 160 degrees W, DIC removal by annual net community production (NCP) more than fully offsets the DIC increase due to air-sea CO2 flux. However, in the region west of 170 degrees E influenced by deep winter mixing, annual NCP only offsets similar to 20% of the DIC increase due to air-sea CO2 flux, requiring significant DIC removal by geostrophic advection. Temperature-driven solubility changes have no net influence on pCO(2) and account for <25% of annual CO2 uptake. The seasonal timing of NCP strongly affects its influence on air-sea CO2 flux. Biological carbon export from the mixed layer has a stronger influence on pCO(2) in summer when mixed layers are shallow, but changes in pCO(2) have a stronger influence on air-sea CO2 flux in winter when high wind speeds drive more vigorous gas exchange. Thus, it is necessary to determine the seasonal timing as well as the annual magnitude of NCP to determine its influence on ocean carbon uptake.