전구순환모형에서 모사한 북태평양 CFC의 분포

Abstract

Chlorofluorocarbons (CFCs) are useful tracers to assess ocean general circulation models (OGCM) on decadal timescales. It is because they are chemically and biologically inert in the ocean and have well known histories of the atmospheric concentrations and solubility properties in seawater, and thus CFCs can be readily incorporated into OGCMs. In this study, we investigate the uptake and distributions of two CFCs (CFC11 and CFC12) in the North Pacific Ocean in a global OGCM. We employ MOM3 for an OGCM and Ocean Carbon Model Intercomparison Project (OCMIP) II protocols for CFCs simulation. The simulated CFCs distribution is compared with observations and three model simulations from OCMIP II. The model reproduces the representative feature of the observed CFC distributions over the North Pacific Ocean: high concentration in the northern and western areas. Surface CFCs concentrations is closely related to the sea surface temperature in most areas; higher in northern areas (especially high in the Okhotsk sea) and lower in southern areas. CFCs inventories, which are vertically-integrated CFC concentrations, indicate that CFCs absorbed in the west-northern area of the North Pacific are transported westward around 40 °N and southward south of 40 °N. Mean penetration depth of CFCs, defined by the water column inventory divided by the maximum CFCs concentration, reaches up to 700 m in the subtropical gyre, in accordance with the observations. However, in most areas, the mean penetration depth is shallower than observations. This may result from restoring surface boundary conditions used in this study, which has been known to weaken convective overturning. This result suggests that in this model the penetration depth of CO2 is likely to be underestimated.