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Marine sediments contain a missing chemical link in global ocean processes

Scientists have discovered that a particular form of soluble manganese (Mn) found in marine sediments is significantly more abundant than previously thought. This research, carried out by researchers at the University of Delaware, the Oregon Health and Science University and McGill University in Canada, transforms our understanding of the role of Mn in ocean biogeochemistry.

An essential element for life, Mn plays a critical role in photosynthesis and the biogeochemical cycles of nutrients such as carbon, nitrogen and iron. Improved understanding of soluble Mn could shed light on the complex connections between biology, geology and chemistry in ocean environments. It may also advance our understanding of deep-sea Mn nodule formation and organic matter bacterial decomposition in the ocean's low oxygen environments.

Like other trace metals, Mn exists in multiple oxidation states: Mn(II), Mn(III) and Mn(IV). However, manganese was thought to exist primarily in two forms in marine waters and sediments. Previous analytical methods did not discriminate other soluble forms, especially Mn(III). With improved techniques, scientists showed that soluble Mn(III) accounts for up to 90 percent of the Mn found in marine sediments.

Soluble Mn(III) is important because it can oxidize other reduced chemicals by accepting an electron becoming Mn(II), or reduce other oxidized chemicals by donating an electron and becoming manganese dioxide. As a result, the newly discovered abundance of soluble Mn(III) in the marine environment will have important implications for electron-transfer reactions in ocean biogeochemistry.

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  • scientists use box cores to collect sediment in the saint lawrence estuary
Scientists use box cores to collect sediment in the St. Lawrence Estuary.
George Luther, University of Delaware

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