Biogeochemistry of organic matter in the ocean.

Source and fate of organic matter once entered to the surface water of the ocean are briefly reviewed. Phytoplankton photosynthesis and terrestrial input through the airborne and waterborne processes give rise to change the concentration of organic matter in the euphotic layer. Regional and seasonal variabilities of the concentration of the organic matter gives much influence on the downward flux of organic matter at the bottom of the euphotic layer, which is the most important factor to govern the regeneration rate of the nutrients in the aphotic layer through the decomposition of organic matter. Fate of the organic matter of the sinking particles transferred to the deep water are discussed on the basis of the vertical flux data of organic matter measured by sediment trap experiment conducted in the North Pacific.