A study on evaluation of redox condition of Tokyo Bay using chemical states of sedimentary iron as an indicator by means of Mössbauer spectroscopy
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We applied 57Fe Mössbauer spectroscopy to sediment cores and tried to build method of estimating historical redox condition of Tokyo Bay in Japan, by using chemical state of iron as an index. As a result of measurement, there are more iron (hydr) oxide and less pyrite in sediment core sampled at Yokohama (near center of Tokyo Bay) than sediment cores sampled at inner part of the bay. This is in good agreement with water quality data and indicates that the amount of dissolved oxygen at different points can be compared by the amount of iron (hydr)oxide or pyrite. We also observed pyrite in most samples and revealed that anoxic condition had widely occurred in Tokyo Bay. In addition, a good negative correlation was found between the pyrite abundance ratio in the sediment and dissolved oxygen in seawater in summer. It was suggested that the abundance ratio of pyrite can be a quantitative indicator for the occurrence of anoxic water masses.
Keywords57Fe Mössbauer spectroscopy Hypoxia Tokyo Bay Sediment core Pyrite
This work was supported by Grant-in-Aid for Scientific Research (C) JP15K00515 and JP18K11613. Water quality data for Honmoku monitoring spot was provided by Yokohama Environmental Monitoring Center. Water quality data for Tokyo light beacon and Chiba light beacon was provided by Japan Oceanographic Data Center. Water quality data for Chiba wave observation towers was provided by Tokyo Bay Environmental Information Center.
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