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Potential for atmospheric acid processing of mineral dusts to supply bioavailable trace metals to the oceans

Anthony Stockdale , Michael Krom

Abstract

Trace metals concentrations in the oceans are influenced by several factors including biogeochemical cycling effects on distributions, concentrations and speciation. The major input of trace metals (and P) to the surface waters of the offshore ocean is mineral dust, predominantly from desert regions. These dusts can be subject to acid processing in the atmosphere due to the presence of anthropogenic acidic gasses (oxides of nitrogen and sulfur), potentially making trace metals more bioavailable when dust is deposited to the oceans. Here we present a study on the release of trace metals from a desert dust when exposed to a series of acid addition treatments. Al, Fe, Co, Cu, Zn, and Pb are preferentially leached from the dust only when the calcite phase has been exhausted and the pH is no longer buffered at circumneutral values. Further acid additions quickly released the majority of leachable trace metals, although lower concentrations of most metals continue to be leached with further acid addition cycles. This contrasts with the behaviour of Ca and P, where in prior work it been shown that dissolution mirrors closely the addition of protons to mineral surfaces. Thus, demonstrating the related but contrasting processes for trace element dissolution.

EN23117  Accepted 17 May 2024

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