Journal of Oceanography, Vol. 57 (No. 1), pp. 79-91, 2001
Graduate School of Fisheries Science, Hokkaido University, Minato-cho 3-1-1, Hakodate, Hokkaido 041-8611, Japan
(Received 25 August 1999; in revised form 23 September 2000; accepted 26 September 2000)
Abstract: In the central North Pacific Subarctic Gyre, CTD hydrographic measurements were carried out yearly in late June from 1990 to 1998 at 9 stations along 180° meridian from 48°N to 51.2°N. Vertical sections of 9-year means, anomalies for each year and others of potential temperature, salinity, potential density and geostrophic velocity (referred to 3000 m) were calculated based on this data set. Empirical Orthogonal Function (EOF) analysis was adopted in the investigation of spatial characteristics and its temporal variation in vertical sections. The spatial distribution of the 1st mode EOF of velocity shows the westward Alaskan Stream and the eastward Subarctic Current. This mode explains 37.6% of the total variance. Two positive maxims appear in its amplitude in 1991 and 1997, which is similar to the variation in volume transport of the eastward Subarctic Current. These variations are closely related to the vertical movement of Ridge Domain deep water.