ホクトウブ タイヘイヨウ ニオケル カイヨウガクテキ チョウサ II

Oceanographical observation and biological research in the eastern boundary region of the North Pacific Ocean were carried out on the fisheries training and research ship "Keiten Maru" of Kagoshima University from June to July, 1976. When the present results are compared with those obtained last winter (1975), some differences are found in the oceanic characteristics and the distribution of zooplankton, as summarized follows. 1) In the subsurface water layer, the thermocline can be well observed, and it becomes gradually shallower in an easterly direction. The depth of the thermocline was shallower during this summer than during last winter, though the vertical gradient of the thermocline did not show a remarkable difference. 2) The appearance of a short-time-scale-upwelling around 136°W was suspected during the summer. 3) The remarkable transition zone of salinity was observed around 128°W. 4) Based on a study of each temperature-salinity diagram a discussion of the characteristics of the water masses is given. The temperature-salinity diagrams of this region were divided into five groups this summer, and three groups last winter. 5) The main current axis in the meso-scale eddies of the western waters shifted to the east about 200 miles compared with that of last winter and the maximum-flow-speed was far less in the summer than that observed last winter. The main current axis in the region of the California Current is almost in the same place but the maximum-flow-speed was somewhat slower this summer than that observed last winter. 6) Of the total number of zooplankton in this region Copepoda were in the majority followed by Ceratium. The gross number of occurence of zooplankton, especially Copepoda, was smaller in the summer than in the winter. On the other hand, it is pointed out that Ceratium and Appendicularia were more abundant in the summer than last winter throughout this region