Study on material circulation in the northwest Pacific Ocean based on sediment trap.

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The oceanic trenches are the last unexplored region of the global environment. We have been continuing a time series of sediment trap experiments in the deepest part of the Japan Trench since August 1986. One trap was set 400 m above the bottom and other was set at the mid-depth of 4-5000 m. Two more traps were added at about 1000 m and 3500 m water depths since 1990. The following main results were obtained.1) Vertical flux of total mass and organic materials in the trench areas were relatively higher than those measured in other oceanic areas.2) A significant temporal variation of total particle flux was observed, but it is not simply related with the surface productivity.3) In general, the deeper trap collected more materilas than the shallow one, indicating transportation of resuspended matter from the trench slope.4) High fluxes of resuspended matter are suggested by the analysis of radio-isotopes, organic material composition, as well as microfossil tests such as coccolith and foraminifera.5) Planktonic tests such as diatom, radiolaria, coccolith, foraminifera, and palynomorph show distinct seasonal variations in their fluxes and species compositions. They are affected by the production rate in the surface layer, dissolution rate of the calcium carbonate, and changes of the water mass above the traps.6) Oxygen and carbon sotopic measurements of individual spciemens of foraminifera indicate that the isotopic compositions of the test are essentially controlled by the temperature and carbon isotope of the sea water in which the specimen grew.