Influences of two air–sea exchange schemes on the distribution and storage of bomb radiocarbon in the Pacific Ocean

Abstract

A basin-wide ocean general circulation model of the Pacific Ocean is employed to study how the air–sea exchange coefficient affects the distribution and storage of bomb 14C in the ocean. Two numerical experiments are designed, including a constant exchange coefficient (RUN1) and a wind-dependent exchange coefficient (RUN2). RUN1 greatly overestimates the observed surface bomb 14C concentration in 1973, while RUN2 reduces this overestimate due to a decreased flux in the tropical region. The difference of column bomb 14C inventories between the two simulations in the North Pacific in 1973 is mainly controlled by the distribution of bomb 14C in the upper ocean, because the simulated penetration is shallower than the observations. This indicates that the simulated transport of the North Pacific Intermediate water (NPIW) is not strong enough. The surface bomb 14C concentration in 1994 from the two simulations is obviously decreased relative to that in 1973. The inventory distribution characteristic with high-west and low-east in the subtropical Pacific is more distinct in 1994 than in 1973, and the simulated results in 1994 are closer to the observations than those in 1973, especially in RUN2. Regardless of the surface or section distributions of bomb 14C concentrations, the results from RUN2 are closer to the observations than those from RUN1. Therefore, it can be concluded that the wind-dependent exchange scheme provides a more accurate bomb 14C concentration estimate. In addition, a comparison of these two simulations indicates that the simulation of NPIW transport can affect the accurate parameterization comparison used in the simulation of passive tracers in the North Pacific.