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Geochemical evidence of Milankovitch cycles in Atlantic Ocean ferromanganese crusts

Geochemical evidence of Milankovitch cycles in Atlantic Ocean ferromanganese crusts
Geochemical evidence of Milankovitch cycles in Atlantic Ocean ferromanganese crusts

Hydrogenetic ferromanganese crusts are considered a faithful record of the isotopic composition of seawater influenced by weathering processes of continental masses. Given their ubiquitous presence in all oceans of the planet at depths of 400–7000 meters, they form one of the most well-distributed and accessible records of water-mass mixing and climate. However, their slow accumulation rate and poor age constraints have to date limited their use to explore 100 ka paleoclimatic phenomena. Here it is shown how the Pb isotope signature and major element content of a Fe-Mn crust from the north-east Atlantic responded to changes in the intensity and geographic extent of monsoonal rainfall over West Africa, as controlled by climatic precession during the Paleocene. The studied high-spatial resolution (4 μm) laser-ablation multi-collector inductively coupled plasma mass spectrometer (LA-MC-ICP-MS) Pb isotope data is a nearly 2 order of magnitude improvement in spatial and temporal resolution compared to micro-drill subsamples. The record demonstrates cyclicity of the 206Pb/204Pb and 208, 207Pb/206Pb ratios at the scale of single Fe-Mn oxide laminae, in conjunction with variations in the Fe/Mn ratio, Al, Si and Ti content. Time-frequency analysis and astronomical tuning of the Pb isotope data demonstrates the imprint of climatic precession (∼20 ka) modulated by eccentricity (∼100 and 405 ka), yielding growth rates of 1.5–3.5 mm/Ma consistent with previous chemostratigraphic age models. In this context, boreal summer at the perihelion causes stronger insolation over West Africa, resulting in more intense and geographically extended monsoonal rainfalls compared to aphelion boreal summer conditions. This, in turn, influences the balance between the weathering endmembers feeding the north-east Atlantic basin. These results provide a new approach for calibrating Fe-Mn crust records to astronomical solutions, and allow their isotopic and chemical archive to be exploited with an improved temporal resolution of 1000–5000 years.

astronomical parameters, astronomical tuning, Fe-Mn crust, ITCZ, Pb isotopes, West African Craton
0012-821X
Josso, Pierre
7da4acf5-b481-49df-931e-160d4ed199e5
van Peer, Tim
da231293-36c0-4d9f-b86c-8b1f059b5134
Horstwood, Matthew S.A.
ea822a1f-2895-4dca-994d-c566e81800a3
Lusty, Paul
1ef4795f-3882-4b26-900d-c30afc681408
Murton, Bramley
9076d07f-a3c1-4f90-a5d5-99b27fe2cb12
Josso, Pierre
7da4acf5-b481-49df-931e-160d4ed199e5
van Peer, Tim
da231293-36c0-4d9f-b86c-8b1f059b5134
Horstwood, Matthew S.A.
ea822a1f-2895-4dca-994d-c566e81800a3
Lusty, Paul
1ef4795f-3882-4b26-900d-c30afc681408
Murton, Bramley
9076d07f-a3c1-4f90-a5d5-99b27fe2cb12

Josso, Pierre, van Peer, Tim, Horstwood, Matthew S.A., Lusty, Paul and Murton, Bramley (2021) Geochemical evidence of Milankovitch cycles in Atlantic Ocean ferromanganese crusts. Earth and Planetary Science Letters, 553, [116651]. (doi:10.1016/j.epsl.2020.116651).

Record type: Article

Abstract

Hydrogenetic ferromanganese crusts are considered a faithful record of the isotopic composition of seawater influenced by weathering processes of continental masses. Given their ubiquitous presence in all oceans of the planet at depths of 400–7000 meters, they form one of the most well-distributed and accessible records of water-mass mixing and climate. However, their slow accumulation rate and poor age constraints have to date limited their use to explore 100 ka paleoclimatic phenomena. Here it is shown how the Pb isotope signature and major element content of a Fe-Mn crust from the north-east Atlantic responded to changes in the intensity and geographic extent of monsoonal rainfall over West Africa, as controlled by climatic precession during the Paleocene. The studied high-spatial resolution (4 μm) laser-ablation multi-collector inductively coupled plasma mass spectrometer (LA-MC-ICP-MS) Pb isotope data is a nearly 2 order of magnitude improvement in spatial and temporal resolution compared to micro-drill subsamples. The record demonstrates cyclicity of the 206Pb/204Pb and 208, 207Pb/206Pb ratios at the scale of single Fe-Mn oxide laminae, in conjunction with variations in the Fe/Mn ratio, Al, Si and Ti content. Time-frequency analysis and astronomical tuning of the Pb isotope data demonstrates the imprint of climatic precession (∼20 ka) modulated by eccentricity (∼100 and 405 ka), yielding growth rates of 1.5–3.5 mm/Ma consistent with previous chemostratigraphic age models. In this context, boreal summer at the perihelion causes stronger insolation over West Africa, resulting in more intense and geographically extended monsoonal rainfalls compared to aphelion boreal summer conditions. This, in turn, influences the balance between the weathering endmembers feeding the north-east Atlantic basin. These results provide a new approach for calibrating Fe-Mn crust records to astronomical solutions, and allow their isotopic and chemical archive to be exploited with an improved temporal resolution of 1000–5000 years.

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More information

Published date: 1 January 2021
Additional Information: Funding Information: PJ, MH and PL publish with the permission of the Executive Director, British Geological Survey (UKRI). This research was supported by Natural Environmental Research Council ( NERC ) grants NE/M011186/1 (awarded to B. Murton) and NE/M011151/1 (awarded to P. Lusty), which fund the MarineE-Tech project. The authors gratefully thank the reviewers for their comments and suggestions that greatly improved the impact of the manuscript and the team involved in the RRS James Cook JC142 expedition to Tropic Seamount in 2016. All relevant data to this publication can be access through the British Geological Survey National Geoscience Data Centre (NGDC): DOI https://doi.org/10.5285/7a9eb43f-a5c4-450c-9fe1-c60f2703a1d1 . Funding Information: PJ, MH and PL publish with the permission of the Executive Director, British Geological Survey (UKRI). This research was supported by Natural Environmental Research Council (NERC) grants NE/M011186/1 (awarded to B. Murton) and NE/M011151/1 (awarded to P. Lusty), which fund the MarineE-Tech project. The authors gratefully thank the reviewers for their comments and suggestions that greatly improved the impact of the manuscript and the team involved in the RRS James Cook JC142 expedition to Tropic Seamount in 2016. All relevant data to this publication can be access through the British Geological Survey National Geoscience Data Centre (NGDC): DOI https://doi.org/10.5285/7a9eb43f-a5c4-450c-9fe1-c60f2703a1d1. Publisher Copyright: © 2020 Copyright British Geological Survey (c) UKRI 2020 Copyright: Copyright 2020 Elsevier B.V., All rights reserved.
Keywords: astronomical parameters, astronomical tuning, Fe-Mn crust, ITCZ, Pb isotopes, West African Craton

Identifiers

Local EPrints ID: 449607
URI: http://eprints.soton.ac.uk/id/eprint/449607
ISSN: 0012-821X
PURE UUID: e484b4ef-9fd2-42f6-b225-8e289ea23c99
ORCID for Tim van Peer: ORCID iD orcid.org/0000-0003-3516-4198

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Date deposited: 09 Jun 2021 16:30
Last modified: 22 Jun 2022 02:04

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Contributors

Author: Pierre Josso
Author: Tim van Peer ORCID iD
Author: Matthew S.A. Horstwood
Author: Paul Lusty
Author: Bramley Murton

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