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

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

Simposio; Blowing South: Southern Hemisphere Dust Symposium; 2021

IFAECI, Núcleo Mileno Paleoclima, AACS, CR2, UNLPam, INCITAP, CICTERRA, CESIMAR, GEOTRACES, ipam

In regions where atmospheric processing is weak due to low anthropogenic emissions, fertilization of iron-limited oceans by mineral dust aerosols strongly depends on iron solubility at the sources. Southern SouthAmerica (SSA) is one of the most pristine environments, and the main contributor of dust to the southernoceans, in turn the most sensitive ocean basin to iron fertilization. Thus, the present-day lack of fertilizationof the southern oceans by SSA dust is hypothesized to reflect low iron bioavailability inherited from thesources. However, a dearth of geochemical studies of active dust sources in SSA prevents testing thishypothesis. To remedy this, we conducted the first systematic sampling of active dust sources in SSA, whichwe combined with previous sampling of wind-borne dust close to the sources. Iron leaching experimentsshowed that the fertilization potential of SSA dust is low compared to dust from other regions. Based oncharacterizations of grain size, size-resolved mineralogy, elemental chemistry and iron speciation, we foundthat variability in labile iron of present-day dust-emitting surface sediments and close-to-source dust isdictated by multiple factors, being enhanced by high clay contents, small grain size and higher proportionsof paramagnetic versus magnetic iron, irrespective of iron oxidation state. The independence of the mostlabile, water-soluble iron on grain size may imply that we currently underestimate the role of coarseglaciogenic 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.