Hydrographic structure and transport of the Oyashio south of Hokkaido and the formation of North Pacific Intermediate Water

Citation
I. Yasuda et al., Hydrographic structure and transport of the Oyashio south of Hokkaido and the formation of North Pacific Intermediate Water, J GEO RES-O, 106(C4), 2001, pp. 6931-6942
Citations number
29
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Earth Sciences
Journal title
JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS
ISSN journal
2169-9275 → ACNP
Volume
106
Issue
C4
Year of publication
2001
Pages
6931 - 6942
Database
ISI
SICI code
0148-0227(20010415)106:C4<6931:HSATOT>2.0.ZU;2-Q
Abstract
Hydrographic structure and transport of the Oyashio south of Hokkaido were described with conductivity-temperature-depth and lowered acoustic Doppler current profiler (LADCP) survey performed in June 1998. The southwestward O yashio transport just off the Hokkaido coast was 10.1 Sv in the density of 26.6-27.5 sigma (theta), in which 2.5 Sv was from the Okhotsk Sea and 7.6 S v was from the Western Subarctic Gyre (WSAG). The Oyashio northeastward cou ntercurrent was 4.9 Sv, The cross-gyre Oyashio transport in the area from t he east coast of Hokkaido to the Subarctic Front was estimated to be 5.2 Sv ; 2.4 Sv in 26.6-27.0 sigma (theta) was mainly composed of low potential vo rticity Okhotsk Sea water and 2.8 Sv in 27.0-27.5 sigma (theta) mostly from WSAG, suggesting that the Okhotsk Sea water (WSAG water) would contribute to the formation of the upper (lower) part of the North Pacific Intermediat e Water (NPIW). The Oyashio water was lower in oxygen than in the subtropic al areas south of the Subarctic Front in the density of 26.9-27.6 sigma (th eta), possibly because of the absence of the Antarctic Intermediate Water ( AAIW) influence with the relatively high oxygen water that might be transpo rted along the western boundary of the North Pacific Ocean and along the Ku roshio Extension, increasing the oxygen in the areas south of the Subarctic Front. Just south of the Subarctic Front, a cold- and fresh-core anticyclo nic eddy was observed with a salinity minimum in the core, suggesting one p ossible formation process of NPIW. The density of the potential vorticity m inimum in the southwestward Oyashio near Hokkaido was at around 26.65 sigma (theta), which was lower than 26.8-26.9 sigma (theta) observed in the earl y 1990s. This is possibly because the potential vorticity vertical profiles in the Okhotsk Sea and WSAG significantly changed corresponding to the wat er mass regime shift occurred in the Subarctic Pacific in the mid-1990s [Ka wasaki, 1999].