ADCP-Referenced Kuroshio and Oyashio Water Transports for North Pacific Intermediate Water Formation*

Abstract

The ADCP-referenced geostrophic circulation of the Oyashio and Kuroshio waters in the density range 26.6?27.2 σ? in the Kuroshio?Oyashio interfrontal zone is examined by synoptic observations with a CTD and shipboard ADCP in May 1992 and May 1994 in order to investigate the absolute transports of the source waters for North Pacific Intermediate Water (NPIW) formation. The Kuroshio and Oyashio components are calculated by the ADCP-referenced transport combined with the mixing ratio assuming isopycnal mixing between pure Kuroshio and Oyashio waters. As a result, the Kuroshio transport involved in the NPIW formation is estimated to be 7?8 Sv (Sv ≡ 106 m3 s?1), which is the net component along the Kuroshio Extension (KE) from the separation point near the Cape Nojima to the east side of the first crest of the KE. The Oyashio transport is estimated to be 5?6 Sv, which consists of coastal 1?2 Sv and offshore 3?4 Sv separated by warm core rings, and which subsequently merges with the KE at the east side of the first crest, forming new NPIW.