Can Biomass Burning Explain Isotopically Light Fe in Marine Aerosols?

Alyssa M Sherry1, Ariel D Anbar1,2, Pierre Herckes1 and Stephen J Romaniello2, (1)Arizona State University, School of Molecular Sciences, Tempe, AZ, United States, (2)Arizona State University, School of Earth and Space Exploration, Tempe, AZ, United States
Abstract:
Iron (Fe) is an important micronutrient that limits primary productivity in large parts of the ocean. In these regions, atmospheric aerosol deposition is an important source of Fe to the surface ocean and thus has a critical impact on ocean biogeochemistry. Fe-bearing aerosols originate from many sources with potentially distinct Fe isotopic compositions. Consequently, Fe isotopes may provide a new tool to trace the sources of aerosol Fe to the oceans.

Mead et al. (2013) first discovered that Fe in the fine fraction of Bermuda aerosols is often isotopically lighter than Fe from known anthropogenic and crustal sources.­1 These authors suggested that this light isotopic signature was likely the result of biomass burning, since Fe in plants is the only known source of isotopically light Fe. More recently, Conway et al. found that Fe in the soluble fraction of aerosols collected during 2010-2011 North Atlantic GEOTRACES cruises also showed light isotope values, which they likewise attributed to biomass burning.2 These studies are further supported by new modeling work which suggests that biomass burning aerosols should contribute significant amounts of soluble Fe to tropical and southern oceans.3

To test if biomass burning releases aerosols with a light Fe isotope composition, we are conducting lab-scale biomass burning experiments using natural samples of vegetation and leaf litter. Burn aerosols were collected on cellulose filters, then digested and analyzed for trace metal concentrations using inductively-coupled mass spectrometry (ICP-MS). Fe isotopes were determined by using multiple collector ICP-MS following separation and purification of Fe using anion exchange chromatography. We will discuss metal concentration and isotope data from these experiments with implications for the interpretation of Fe isotope signals in aerosol samples.

1Mead, C et al. GRL, 2013, 40, 5722–5727. ­2­Conway, T et al. Goldschmidt Abs 2015 593. 3Ito, A. ES&T Lett, 2015, 2, 70-75.

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