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Abstract The impact of resolving western boundary currents and mesoscale eddies on a carbon circulation simulation for the North Pacific Ocean is investigated to evaluate the merits of using high‐resolution ocean biogeochemical models for climate projections. Simulations by a 100‐km resolution global ocean biogeochemical model with and without embedding a 10‐km resolution model in the North Pacific Ocean are compared. The major improvement in the high‐resolution simulation is the representation of the Kuroshio, its extension current, and the recirculation gyres formed to its south and north, resulting in a proper representation of the North Pacific subtropical mode water (STMW) and an increase in storage of the anthropogenic CO 2 (C anth ) in STMW by about two‐thirds. The larger storage rate in STMW is caused by supply of a larger amount of warm surface water containing rich C anth to the formation region by the intensified Kuroshio. A huge buoyancy loss from this warm water results in the increased formation of STMW that occupies a vast area in the western subtropical gyre. The surface uptake of C anth in the formation region of STMW is slightly increased but is largely comparable to that of the low‐resolution model. Moreover, there is no structural difference in C anth uptake in other parts of the subtropical region. Thus, the improvement of C anth distribution can be understood as a redistribution of water mass in the subtropical gyre by the improved circulation. The present assessment motivates the use of a high horizontal resolution ocean model in next‐generation projection experiments with carbon cycles.
Tsujino et al. (Mon,) studied this question.