SUBDUCTION PROCESSES IN THE NORTH PACIFIC BASED ON NALYSES OF HIGH-QUALITY DATA

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Origins of waters observed along 137°E were estimated based on the available climatological data, the World Ocean Atlas, to outline waters composing the subtropical permanent pycnocline. The original high-resolution hydrographic climatology was then constructed and analyzed to identify the source regions of Subtropical Mode Water(STMW), Central Mode Water(CMW) and Eastern Subtropical Mode Water and to reveal their formation mechanism. One of noticeable findings is that the low potential vorticity of CMW is caused by small "cross-isopycnal flow" rather than large "lateral induction." It was also revealed that southwestward advection of STMW and CMW contribute to the formation of the subtropical fronts. The similar original climatology also revealed the source region and the advection path way of the dichothermal water in the subarctic pycnocline.Quasi-Lagrangian observations of CMW for the periods over one and half years were successfully done using the profiling floats parking at isopycnal surfaces corresponding to the CMW cores. A one-dimensional mixed layer model of the Lagrangian-type was developed to simulate the subduction processes to be compared with the quasi-Lagrangian data. The effectiveness of the model was confirmed by simulating the formation of the dichothermal water successfully.The intense hydrographic survey in the central North Pacific including the source region of CMW was conducted by R/V Hakuho-Maru to collect multi-variable synoptic data just after the late winter period during which the subduction of the mixed layer water to the permanent pycnocline occurs.All the available Argo float data were analyzed to reveal that the thick mode waters are formed associated with the deep permanent pycnocline associated with anticyclonic eddies and that the barrier layers are formed associated with the subduction of high-salinity water in the southern subtropical gyre.