A broad swath across the North Pacific basin uptakes a disproportionately large
amount of atmospheric CO2 every year, with the region of most intense uptake located in
the North Pacific transition zone, from ~30°N to 40°N–45°N. Though a net carbon sink
on a mean annual basis, the region varies seasonally between a strong sink in winter and a
neutral to weak source in summer. Herein we use observational carbon data to investigate
processes regulating air-sea CO2 flux in this region on seasonal and annual timescales
by quantifying the impacts of temperature, biology, and physics on seawater pCO2.
Temperature effects dominate the pCO2 signal seasonally, yet support only a portion of the
annual CO2 uptake in the region, via their impact on the solubility of CO2 in seawater.
Instead, processes removing carbon from surface waters dominantly support the region’s
uptake of CO2 on annual timescales: the vertical export of organic carbon to depth, and the
geostrophic advection of dissolved inorganic carbon laterally out of the region. We find
the location of this carbon sink region, traditionally attributed to a combination of
biological and temperature effects, to instead be driven by the steady geostrophic
divergence of DIC at these latitudes.
atmospheric CO2, carbon sink, dissolved inorganic carbon, dynamical control, geostrophic advection, North Pacific, sink-in, time-scales, transition zones