Dissolved reactive manganese at pelagic redoxclines (part I): A method for determination based on field experiments

► A method for determination of a dissolved reactive manganese fraction (dMnreact) is presented. ► dMnreact is easily oxidised under atmospheric oxygen within less than 48 h. ► dMnreact is assumed to consist mainly of Mn (III) thus forming a semi-quantitative measure. ► dMnreact detects a chemical species as well as a unique chemical environment.