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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‰).
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Bulk Aerosol Trace Element Concentrations and Deposition Fluxes During the U.S. GEOTRACES GP15 Pacific Meridional Transect
Abstract Atmospheric deposition of aerosols transported from the continents is an important source of nutrient and pollutant trace elements (TEs) to the surface ocean. During the U.S. GEOTRACES GP15 Pacific Meridional Transect between Alaska and Tahiti (September–November 2018), aerosol samples were collected over the North Pacific and equatorial Pacific and analyzed for a suite of TEs, including Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Pb. Sampling coincided with the annual minimum in dust transport from Asia, providing an opportunity to quantify aerosol TE concentrations and deposition during the low dust season. Nevertheless, peak concentrations of “crustal” TEs measured at ∼40–50°N (∼145 pmol/m3Fe) were associated with transport from northern Asia, with lower concentrations (36 ± 14 pmol/m3Fe) over the equatorial Pacific. Relative to crustal abundances, equatorial Pacific aerosols typically had higher TE enrichment factors than North Pacific aerosols. In contrast, aerosol V was more enriched over the North Pacific, presumably due to greater supply to this region from oil combustion products. Bulk deposition velocity (Vbulk) was calculated along the transect using the surface ocean decay inventory of the naturally occurring radionuclide,7Be, and aerosol7Be activity. Deposition velocities were significantly higher (4,570 ± 1,146 m/d) within the Intertropical Convergence Zone than elsewhere (1,764 ± 261 m/d) due to aerosol scavenging by intense rainfall. Daily deposition fluxes to the central Pacific during the low dust season were calculated using Vbulkand aerosol TE concentration data, with Fe fluxes ranging from 19 to 258 nmol/m2/d.
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- PAR ID:
- 10363778
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Global Biogeochemical Cycles
- Volume:
- 36
- Issue:
- 2
- ISSN:
- 0886-6236
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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