The Influence of Natural, Anthropogenic, and Wildfire Sources on Iron and Zinc Aerosols Delivered to the North Pacific Ocean
Zachary B. Bunnell, Matthias Sieber, Douglas S. Hamilton, Chris M. Marsay, Clifton S. Buck, William M. Landing, Seth G. John, Tim M. Conway
Abstract
Abstract Atmospheric deposition is an important source of iron (Fe) and perhaps zinc (Zn) to the oceans. We present total and water‐soluble aerosol Fe and Zn isotopic compositions, size‐fractionated aerosol Fe isotopic compositions, and aerosol enrichment factors from the North Pacific GEOTRACES GP15 section (Alaska‐Tahiti) during the low dust season. We found distinct bulk aerosol provinces along this latitudinal transect: Asian aerosols (especially crustal dust) dominate at higher latitudes (52–32°N) while North American heavier‐than‐crustal wildfire aerosols dominate in Equatorial Pacific deployments (20°N to 20°S). Soluble aerosol Fe was isotopically lighter‐than‐crustal along the full transect, strongly indicative of a pervasive anthropogenic Fe contribution to the Pacific. Comparison to a global aerosol deposition model corroborates that an isotopically heavy endmember is required for wildfire Fe, attributed to pyroconvective entrainment of soil particles. For Zn, the entire GP15 section is dominated by non‐crustal anthropogenic sources, reflected by light isotopic compositions (bulk: −0.12 ± 0.08‰ and soluble: −0.17 ± 0.14‰).