A regeneration model to estimate addition fluxes and removal constants of trace metals in seawater

Abstract

A model is presented for flux evaluation of trace metals in situ. For the practically feasible simplified model, mere estimation of metals in various dissolved states (e.g. Cr(III) and Cr(VI)) and in particulate phase, in a single vertical profile at least, together with temperature, salinity, O₂, titration alkalinity (TA), Ca²⁺, NO₃^-, HPO₄^2- and H₄SiO₄ parameters enable evaluation of the amount of metal removed in situ, to a first approximation. From the evaluated net metal removed (M_R), estimation could be made for removal constants, i.e. removal times (t), residence times (τ) and removal rate constants (ψ), not only for the average ocean but also for the oxygen-minimum zone. Besides, M_R can be used to calculate t, τ and ψ of various species of the metal concerned, that are not yet available. The present model evaluates t, τ and ψ for total chromium from a single station, which are consistent with the reported values, and shows that chromium is removed with fast-settling particulate matter. This study also reveals that t, τ and ψ values of 0.001 years 7 years and 0.150 y^-1, respectively, for Cr(III) in the oxygen-minimum zone and 0.006 y, 211y and 0.005 y^-1 in the marine environment, respectively.