Low source-inherited iron solubility limits fertilization potential of South American dust

SIMONELLA L.; COSENTINO, N.J.; MONTES, L. ; CROOT, P.L.; PALOMEQUE M.; GAIERO, D.M.

GEOCHIMICA ET COSMOCHIMICA ACTA

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2022

0016-7037

In regions where atmospheric processing is weak due to low anthropogenic emissions, fertilization of iron-limited oceans by non-volcanic mineral dust aerosols strongly depends on iron solubility at the sources. Southern South America (SSA) is one of the most pristine environments, and the main contributor of dust to the southern oceans, which in turn are the most sensitive oceans to iron fertilization. Thus, the present-day lack of fertilization of the southern oceans by SSA dust is hypothesized to reflect low iron bioavailability inherited from the sources. However, a dearth of geochemical studies of active dust sources in SSA prevents testing this hypothesis. To remedy this, we conducted the first systematic sampling of active dust sources in SSA, which we combined with previous sampling of wind-borne dust close to the sources. Iron leaching experiments showed that the mass-normalized fertilization potential of SSA dust is low compared to dust from other regions. Based on characterizations of grain size, size-resolved mineralogy, elemental chemistry and iron speciation, we found that variability in labile iron of present-day dust-emitting surface sediments and close-to-source dust is dictated by multiple factors; being enhanced by high clay contents, small grain size and higher proportions of paramagnetic versus non-paramagnetic iron, irrespective of iron oxidation state. The independence of the most labile, water-soluble iron on grain size may imply that we currently underestimate the role of coarse glaciogenic dust as a supplier of bioavailable iron during ice ages, during which enhanced supply of dust-borne bioavailable iron to the southern oceans is observed.