Tomowo WATANABE
Keisuke MIZUNO
Makoto OKAZAKI

National Research Institute of Far Seas Fisheries, Japan

1. Decadal Variation - Interannual and interdecadal variation of the North Pacific subsurface temperature were investigated by using historical temperature/depth profile data set. Strong decadal change occurred in mid-1970s in the mid-latitude region. Cold anomalies appeared in the boundary zone between subtropical and subarctic gyre, and deeper subtropical gyre was formed after mid-1970s. The propagation of temperature anomalies from surface to subsurface and eastward along the subtropical gyre was also found. The pattern of propagating anomalies is similar to the distribution of low salinity water in the eastern North Pacific. Though it is not clear what does the propagation represent, it must play an important role in the progress of the decadal variation of the Pacific Ocean.

2. Subsurface Temperature Monitoring - We are maintaining some subsurface temperature monitoring lines by STD and XBT in the subarctic region of the western north Pacific every summer from 1991 as a part of salmon resource research of our institute. As these lines are located in the area where the strong interannual variability was found, we can monitor the state of interannual variability of the ocean. Year-to-year changes of fronts and characteristics of water mass are already detected from 6 summer meridional sections along 179.5W from 38.5N to 58.5N. Temperature of subsurface temperature minimum layer is colder in 1993-95 than 1991-92 and the subarctic front shifted southward in 1993-95.

3. XCTD - XCTD (eXpendable Conductivity Temperature Depth profiler) is desirable instrument for monitoring the subsurface oceanic structure in the subarctic region of the Pacific. Several field tests of improved XCTD system were carried out. We could get good salinity profiles though it included small but systematic bias . We expect that we can introduce XCTD to subarctic region after resolving the problem and determining precise fall rate of XCTD probe in the near future.

4. Hydrography in the Equatorial Pacific - We made the hydrographic observation along the equator from January to March 1992 on RV Kaiyo-Maru. At the same time, 91/92 El Nino reached its mature stage and many El Nino related structures were found. Thick and warm surface mixed layer in the central region, Kelven wave in the eastern equatorial pacific, etc. In the eastern equatorial pacific, local isopycnal deepening were also found in the intermediate layer. It may suggest that the El Nino's influence reached to the depth.

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