The cerium anomaly and manganese cycling processes in oxygen deficient zones

A major challenge in understanding trace elemental cycling in oxygen deficient zones (ODZs) comes from understanding continental input processes. Trace elements can be supplied to ODZs through direct inputs of rivers, but many elements are substantially modified as a result of reductive processes on continental shelves. The cerium anomaly proxy is particularly relevant for studying ODZs, since the redox potential of cerium reactions is very similar to that of manganese. Manganese chemistry appears to vary significantly between the three modern ODZs, with subsurface manganese maxima observed in the Arabian Sea and Mexican ODZs, but not in the Peru ODZ. Since the cerium anomaly can be used to identify water masses, which are directly influenced by the bottom waters of the continental shelf, it is possible to use that parameter in order to differentiate direct inputs of manganese and other trace elements by riverine inputs from continental shelf driven redox cycling. We have collected cerium anomaly data from the Mexican and Arabian Sea ODZs, helping to identify the sources of subsurface manganese plumes in those regions.