Concentrations and Fluxes of Reactive Oxygen Species on the Mauritanian Shelf

We present field work, which studies biogeochemical processes at the Mauritanian shelf edge in the tropical eastern north Atlantic. The importance of photochemically formed reactive oxygen species (ROS) to biogeochemical and biological processes in the ocean is now clear but we still have a poor understanding of the exact mechanisms and critically, the rates and fluxes of these compounds. Previous research has identified that the redox switch of the essential trace metals Copper (Cu), Manganese (Mn) and Iron (Fe) is sensitive to this mostly photochemically produced ROS, like superoxide (O₂^-) and its daughter product, Hydrogen Peroxide (H₂O₂). As O₂^- and H2O2 can act as both an oxidant and a reductant they can exert an important influence in trace metal redox cycling and with this solubility and bioavailability. However, presently we have little information on the formation rates of O₂^- and H₂O₂ from direct photochemical production in the ocean and their relative reactivity with different metal or organic species present in seawater.

In this current field work, we present for the first time data, where we used the superoxide thermal source SOTS-1, an over hours at low levels constantly producing O₂^- source, which we showed earlier, can be used to determine both, concentrations and fluxes of ROS in seawater. The reactivity of O₂^- in the experimental treatments, which included Cu, Mn, Fe but also the reaction with organic matter, was followed by a well-established chemiluminescence technique using the reagent MCLA, a Cypridina luciferin analog, after additions of SOTS-1, but was also compared to data obtained with potassium superoxide (KO₂), another reliable O₂^- the source, as described and used in field work previously. Additionally the experiments with Mn consisted of treatments with the redox state +II and +III, as we aim to examine the current evidence for Mn(III) in the euphotic zone of the open ocean.