Impact of Increased Horizontal Resolution of an Ocean Model on Carbon Circulation in the North Pacific Ocean

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 CO2 (Canth) 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 Canth 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 Canth 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 Canth uptake in other parts of the subtropical region. Thus, the improvement of Canth 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.