Dilution of North Pacific Intermediate Water studied with chlorofluorocarbons

Abstract

Assessment was made of residual ratio of North Pacific Intermediate Water (NPIW) produced in subpolar region of the North Pacific using chlorofluorocarbons, CFC-11 and CFC-12 (CCl₃F and CCl₂F₂), along 175°E. NPIW on density horizons less than 26.80σ_θ remained more than 80% north of 30°N. It was suggested that new NPIW laterally spreads over the northern North Pacific without hardly being diluted by the surroundings. For density horizons greater than 26.80σ_θ north of 30°N, NPIW remained less than 60%. The difference in the residual ratio between <26.80σ_θ and >26.80σ_θ north of 30°N suggests that NPIW is produced on density horizons less than 26.80σ_θ, which contacts the atmosphere in the subpolar region, and that NPIW is diluted by upwelling deep water on density horizons greater than 26.80σ_θ in high latitude of the North Pacific. NPIW on a density horizon of 26.80σ_θ remained about 50% south of 30°N. The decrease in the horizontal distribution of the residual ratio of NPIW suggests that half the new NPIW produced in the subpolar region is laterally spread over the North Pacific with the southward movement of NPIW.