Research of marine geochemical cycles of novel trace metals.

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In order to understand the biogeochemical cycles in the ocean, we investigated the distributions and behaviors of the novel trace metals in the ocean.Firstly, the global distribution of silver, one of the novel trace metals, was studied from the Bering Sea to the Southern Ocean. The distribution was analyzed with a "pipe model" to reveal the biogeochemical process of silver in the ocean. Judging from the elevated silver concentrations in high-latitude regions, silver in the surface water is mainly supplied via vertical mixing from mid-water.Secondly, a determination method of platinum in natural waters was established by combining anion-exchange resin concentration method and isotope-dilution inductively coupled plasma mass spectrometry (ID-ICPMS). By determining platinum in the estuary of Tokyo Bay with this ID-ICPMS method, it is shown that platinum is scavenged at the estuary region vigorously. The results were also compared with those by cathodic stripping voltammetry(CSV). The lower platinum concentrations with CSV method imply that platinum is complexed strongly with organic compounds in the urban rivers. To estimate the sources of platinum into Tokyo Bay, the rain water and rural river water were analyzed with the ID-ICPMS method. The platinum concentrations in both waters were so low that both waters cannot be the main source for Tokyo Bay. Anthropogenic input from urban areas and (or) dissolution of particulate matter in the estuary are thought to elevate the platinum concentrations in Tokyo Bay.In the open ocean, the seawater samples collected around the Japan Trench areas were analyzed with this ID-ICPMS method. The vertical profile of platinum shows a quasi-nutrient type, ranged from 0.3 to 1 pM, in this station. Lateral transport of lithogenic materials, indicated from previous sediment trap experiments, may affect the elevated platinum concentrations in deep waters.