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The spatial footprint of hydrothermal scavenging on ²³⁰Th_(XS)-derived mass accumulation rates

Middleton, Jennifer L. and Mukhopadhyay, Sujoy and Costa, Kassandra M. and Pavia, Frank J. and Winckler, Gisela and McManus, Jerry F. and D'Almeida, Marcelle and Langmuir, Charles H. and Huybers, Peter J. (2020) The spatial footprint of hydrothermal scavenging on ²³⁰Th_(XS)-derived mass accumulation rates. Geochimica et Cosmochimica Acta, 272 . pp. 218-234. ISSN 0016-7037. https://resolver.caltech.edu/CaltechAUTHORS:20200116-100625090

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Abstract

Mid-ocean ridges are valuable archives of sedimentary flux records used to investigate atmospheric, oceanographic, and solid Earth responses to climate variability. Constant flux proxies, such as extraterrestrial helium-3 (³He_(ET)) and excess thorium-230 (²³⁰Th_(XS)), constrain vertical mass accumulation rates independent of the biases associated with lateral sediment transport and age model resolution. However, thorium scavenging by hydrothermal particles can perturb local ²³⁰Th_(XS) deposition and complicate its application as a constant flux proxy in near-ridge environments. We characterize the footprint of hydrothermal scavenging on sedimentary ²³⁰Th_(XS) using coupled ³He_(ET)-²³⁰Th_(XS) analyses in cores from the Mid-Atlantic Ridge and the Juan de Fuca Ridge. Samples deposited >10 km from the Juan de Fuca Ridge indicate reliable off-axis behavior of both constant flux proxies. In contrast, samples deposited <10 km from the Juan de Fuca Ridge axis and within the axial valley of the Mid-Atlantic ridge suggest 50-80% deficits in sedimentary ²³⁰Th_(XS) relative to its production rate. These deficits contrast with sedimentary ²³⁰Th_(XS) surpluses recently observed on the East Pacific Rise. The spatial footprint of hydrothermal scavenging varies globally and temporally, likely as a function of the intensity of local hydrothermal activity. The combined ridge data suggest that near-vent sediments (within ∼5 km, but variable by ridge) receive relatively high ²³⁰Th_(XS) deposition rates as a direct result of hydrothermal particle scavenging, while more distal sediments receive relatively low ²³⁰Th_(XS) deposition rates due to diffusive loss of overlying seawater ²³⁰Th_(XS) towards the vent. Aside from the East Pacific Rise, far-field sediments are likely to exhibit typical ²³⁰Th_(XS) deposition rates at distances greater than ∼10 km of the ridge axis. However, ²³⁰Th_(XS) systematics within the axial valleys of slow-spreading ridges may be complicated by other factors. Combined ³HeET-²³⁰Th_(XS) studies at multiple ridges are needed to further characterize the nature of hydrothermal scavenging and to evaluate the potential of sedimentary ²³⁰Th_(XS) anomalies to record large-scale variability in past hydrothermal activity.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.gca.2020.01.007DOIArticle
ORCID:
AuthorORCID
Middleton, Jennifer L.0000-0001-7147-2388
Costa, Kassandra M.0000-0001-8715-638X
Pavia, Frank J.0000-0003-3627-0179
Winckler, Gisela0000-0001-8718-2684
McManus, Jerry F.0000-0002-7365-1600
Huybers, Peter J.0000-0002-3734-8145
Additional Information:© 2020 Elsevier Ltd. Received 15 October 2019, Accepted 7 January 2020, Available online 16 January 2020. All the data in this paper are available in the references and supplementary tables. We thank F. Apen and Z. Chen for technical assistance with helium isotope and ICP-MS analyses and S. Jones and B. Boulahanis for valuable discussion. We additionally thank D. Lund and D. McGee for their valuable and thoughtful reviews. We acknowledge financial support from the National Science Foundation grant AGS-1338832. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Funders:
Funding AgencyGrant Number
NSFAGS-1338832
Record Number:CaltechAUTHORS:20200116-100625090
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200116-100625090
Official Citation:Jennifer L. Middleton, Sujoy Mukhopadhyay, Kassandra M. Costa, Frank J. Pavia, Gisela Winckler, Jerry F. McManus, Marcelle D'Almeida, Charles H. Langmuir, Peter J. Huybers, The spatial footprint of hydrothermal scavenging on 230ThXS-derived mass accumulation rates, Geochimica et Cosmochimica Acta, Volume 272, 2020, Pages 218-234, ISSN 0016-7037, https://doi.org/10.1016/j.gca.2020.01.007. (http://www.sciencedirect.com/science/article/pii/S0016703720300193)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:100759
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:16 Jan 2020 18:14
Last Modified:06 Feb 2020 17:50

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