The geochemical behavior of molybdenum in the modern Yangtze Estuary and East China Sea shelf

Abstract Rivers are the main source of molybdenum (Mo) to the oceans, and estuaries represent an important interface between rivers and oceans within which Mo can be sequestered or isotopically fractionated. Determining the behavior of Mo in estuaries is thus essential for a full understanding of the global Mo cycle. Here, we present a case study of the modern Yangtze Estuary and adjacent East China Sea shelf, generating Mo concentration and isotopic data for both aqueous and solid phases (i.e., suspended particulate matter, or SPM, primarily consisting of clay minerals and Al-Fe-Mn-oxides). Aqueous Mo concentrations increase rapidly from ~13.9 nM (river water) to ~115 nM (seawater) through the mixing zone of the innermost continental shelf. Minor deviations from a salinity-based mixing relationship (positive at