Annual biological organic carbon export estimated from the annual carbon budget observed in the surface waters of the western subarctic and subtropical North Pacific Ocean

 The annual flux of biologically produced organic carbon from surface waters is equal to the annual flux of net community production (NCP) at steady state, and is exported as particulate and dissolved organic carbon (POC and DOC) to deep waters. NCP was estimated from the carbon budget of salinity-normalized dissolved inorganic carbon (nDIC) inventories at two time-series stations in the western subarctic (K2) and subtropical (S1) North Pacific Ocean. By using sporadic biogeochemical observations from 2004 to 2013, monthly mean nDIC inventories were integrated from the surface to the annual maximum mixed layer depth and corrected for changes due to net air–sea CO₂ exchange, net CaCO₃ production, vertical diffusion from the upper thermocline, and horizontal advection. The annual organic carbon flux at K2 (1.5 ± 1.6 mol m⁻² yr⁻¹) and S1 (2.8 ± 2.2 mol m⁻² yr⁻¹) were the same, within the range of the error. These fluxes can be classified into three types: POC flux exported vertically (K2, 1.4 mol m^–2 y^–1; S1, 2.5 mol m^–2 y^–1), and vertical diffusive fluxes of DOC (K2, 0.03 mol m^–2 y^–1; S1, 0.25 mol m^–2 y^–1) and suspended POC (K2, 0.03 mol m^–2 y^–1; S1, 0.07 mol m^–2 y^–1). Estimated export fluxes of POC at K2 and S1 were comparable to the sum of the POC fluxes into drifting sediment traps and active carbon export by migrating zooplankton. The export fluxes were twice those reported at other time-series sites in the eastern subarctic and central subtropics.