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Atmospheric Dust Inputs, Iron Cycling, and Biogeochemical Connections in the South Pacific Ocean from Thorium Isotopes

Pavia, Frank J. and Anderson, Robert F. and Winckler, Gisela and Fleisher, Martin Q. (2020) Atmospheric Dust Inputs, Iron Cycling, and Biogeochemical Connections in the South Pacific Ocean from Thorium Isotopes. Global Biogeochemical Cycles, 34 (9). Art. No. e2020GB006562. ISSN 0886-6236. doi:10.1029/2020gb006562.

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One of the primary sources of micronutrients to the sea surface in remote ocean regions is the deposition of atmospheric dust. Geographic patterns in biogeochemical processes such as primary production and nitrogen fixation that require micronutrients like iron (Fe) are modulated in part by the spatial distribution of dust supply. Global models of dust deposition rates are poorly calibrated in the open ocean, owing to the difficulty of determining dust fluxes in sparsely sampled regions. We present new estimates of dust and Fe input rates from measurements of dissolved and particulate thorium isotopes ²³⁰Th and ²³²Th on the FS Sonne SO245 section (GEOTRACES process study GPpr09) in the South Pacific. We first discuss high‐resolution upper water column profiles of Th isotopes and the implications for the systematics of dust flux reconstructions from seawater Th measurements. We find dust fluxes in the center of the highly oligotrophic South Pacific Gyre that are the lowest of any mean annual dust input rates measured in the global oceans, but that are 1–2 orders of magnitude higher than those estimated by global dust models. We also determine dust‐borne Fe fluxes and reassess the importance of individual Fe sources to the surface South Pacific Gyre, finding that dust dissolution, not vertical or lateral diffusion, is the primary Fe source. Finally, we combine our estimates of Fe flux in dust with previously published cellular and enzymatic quotas to determine theoretical upper limits on annual average nitrogen fixation rates for a given Fe deposition rate.

Item Type:Article
Related URLs:
URLURL TypeDescription ItemData
Pavia, Frank J.0000-0003-3627-0179
Anderson, Robert F.0000-0002-8472-2494
Winckler, Gisela0000-0001-8718-2684
Fleisher, Martin Q.0000-0002-1141-8723
Additional Information:© 2020 American Geophysical Union. Issue Online: 10 September 2020; Version of Record online: 10 September 2020; Accepted manuscript online: 06 August 2020; Manuscript accepted: 03 August 2020; Manuscript revised: 05 July 2020; Manuscript received: 24 January 2020. This work was supported by U.S. National Science Foundation Grant OCE‐1555726 to LDEO and an NSF Graduate Research Fellowship to F.J.P. (DGE‐1644869). The UltraPac Expedition (SO245) was funded by the Federal Ministry of Education and Research of Germany (Grant 03G0245A). We thank the captain and crew of the FS Sonne, as well as SO245 Chief Scientist Tim Ferdelman for ensuring safe and successful sampling. We are grateful to Bernhard Fuchs, Claudia Ehlert, and Sebastian Vivancos for assistance with water sampling, pump deployment, and recovery on SO245. Comments from two anonymous reviewers and the associate editor greatly improved the paper. Data Availability Statement: Dissolved and particulate ²³⁰Th and ²³²Th data from this study are archived at the Biological and Chemical Oceanography Data Management Office ( and on Pangaea (dissolved:, particulate:
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-1644869
Bundesministerium für Bildung und Forschung (BMBF)03G0245A
Subject Keywords:Thorium, GEOTRACES, Iron, Dust, Nitrogen Fixation, South Pacific
Issue or Number:9
Record Number:CaltechAUTHORS:20200818-100915778
Persistent URL:
Official Citation:Pavia, F. J., Anderson, R. F., Winckler, G., & Fleisher, M. Q. (2020). Atmospheric dust inputs, iron cycling, and biogeochemical connections in the South Pacific Ocean from thorium isotopes. Global Biogeochemical Cycles, 34, e2020GB006562.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:104993
Deposited By: Tony Diaz
Deposited On:18 Aug 2020 18:18
Last Modified:28 Feb 2023 17:31

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