Northward Intrusion of Antarctic Intermediate Water in the Western Pacific

Abstract

The northward intrusion of Antarctic Intermediate Water (AAIW) is examined using historical data combined with synoptic observations from a repeated hydrographic section in the western Pacific Ocean. The results of this analysis suggest that AAIW is traced as a salinity minimum to only about 15°N via the New Guinea Coastal Undercurrent and the Mindanao Undercurrent. There is no northward extension of AAIW farther to the north along the western boundary. Although relatively high oxygen water does exist in the Okinawa Trough, it is connected with high-oxygen water in the South China Sea (SCS) through the Luzon Strait but not from the south as an extension of AAIW. Local circulation seems to play an essential role in localizing the oxygen maximum in the SCS. Evidence exists to suggest that high-oxygen water enters the SCS as part of the Pacific deep water around the still depth (?2000 m) of the Luzon Strait; from there, part of it upwells and is entrained into shallower isopycnal surfaces by vertical mixing and eventually flows back to the Pacific through the Luzon Strait at depths of AAIW.