Selenium Speciation in the Eastern Tropical and Subtropical South Pacific Ocean

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Three selenium species, selenite, selenate, and organic selenide, were determined simultaneously in the eastern tropical, and subtropical South Pacific Ocean. Selenite shows a typical nutrient-like profile. Selenate also shows a nutrient-type profile. The highest correlation between selenite and silicate (r＝0.98～1.00, p＜0.00001) indicates that selenite is supplied from decomposition of selenite-silicate compounds in the hard tissue of phytoplankton. On the other hand, the correlation coefficient between selenite and nitrite＋nitrate (phosphate) is higher than that between selenite and silicate in the subtropical South Pacific Ocean. These results indicate that selenite is supplied from the decomposition of not only the hard tissue of plankton body but also the soft tissue. The organic selenide was detected in deep waters. This might be due to the presence of refractory selenium compounds such as selenium-humic acid complex. The selenite/selenate ratio in deep water is not necessarily decreased with increasing total selenium concentrations. This might be due to the irregular addition of selenium to deep waters via sinking particulate matter.
近畿大学理工学総合研究所の論文