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Evaluation of geomagnetic relative palaeointensity as a chronostratigraphic tool in the Southern Ocean: refined Plio-/Pleistocene chronology of IODP Site U1533 (Amundsen Sea, West Antarctica)

Evaluation of geomagnetic relative palaeointensity as a chronostratigraphic tool in the Southern Ocean: refined Plio-/Pleistocene chronology of IODP Site U1533 (Amundsen Sea, West Antarctica)
Evaluation of geomagnetic relative palaeointensity as a chronostratigraphic tool in the Southern Ocean: refined Plio-/Pleistocene chronology of IODP Site U1533 (Amundsen Sea, West Antarctica)

International Ocean Discovery Program (IODP) Expedition 379 to the Amundsen Sea margin of West Antarctica recovered drill cores at two sites spanning the Latest Miocene–Holocene interval with the aim of reconstructing past West Antarctic Ice Sheet dynamics. The recovered Plio-/Pleistocene sediment sequences offer an opportunity to apply and test different dating approaches in an Antarctic deep-sea drift setting, where the records are nearly continuous and unaffected by scouring of icebergs or grounded ice. Here, through palaeomagnetic analysis of continuous u-channel samples and application of X-ray fluorescence (XRF) scanning, we revise the IODP Exp. 379 Site U1533 age model for the uppermost Pliocene and Pleistocene composite interval (0.0–2.9 Ma). We first refine the magnetostratigraphic age model with high-resolution u-channel analysis and interpreted directional data. Consistent with shipboard results, all major geomagnetic polarity chrons and subchrons are identified in the Pleistocene section. The new high-resolution u-channel dataset also allows us to identify a geomagnetic polarity excursion at ∼884 ka (interpreted as the Kamikatsura excursion) and another excursion at ∼2734 ka with confidence (potentially the Porcupine excursion). Based on the improved polarity stratigraphy, we then develop two new highly resolved age models for Site U1533 using: (i) barium enrichment cycles identified in XRF scanning data, and (ii) geomagnetic relative palaeointensity (RPI). In our first age model, we correlate cyclic variations in sedimentary barium enrichment, inferred to represent changes in export productivity, to glacial‒interglacial cycles of the Lisiecki and Raymo (2005) benthic foraminiferal oxygen isotope (δ 18O) stack (LR04). Nearly all Pleistocene Marine Isotope Stages (MIS) are interpreted to be present in the barium enrichment record of Site U1533, assuming simultaneous changes in Antarctic sea-ice extent/local export productivity and global oxygen isotope stratigraphy. We then construct the second, independent age model using the Plio-/Pleistocene RPI record developed for Site U1533, which represents the longest (nearly) continuous RPI record currently available for the Antarctic margin. Comparison of the two, independently derived age models shows a variable offset, on average ± 12 kyr, with the RPI-based ages consistently older than the barium-based ages in the interval from 1.9 to 2.9 Ma and then consistently younger from 0.0 to 1.9 Ma. We interpret these offsets to result from a combination of lock-in depth effects in the younger interval (due to the relatively low sedimentation rates at this site, ∼2 cm/kyr), temporal offsets between global δ 18O changes in the deep ocean and productivity response on the Antarctic margin, and/or systematic miscorrelation in the construction of the two age models. Finally, we construct a hybrid age model for the Pleistocene section of Site U1533 by combining a mixture of RPI- and barium-based age tie points that are deemed to be robust. The Site U1533 RPI record is then used, together with other Southern Ocean RPI records, to construct an Antarctic RPI stack (designated as ‘ANT-1600’) for the interval 0.0–1.6 Ma. Although sedimentation rates at two-thirds of the sites selected for the stack are lower than 10 cm/kyr, the new ANT-1600 stack is strongly coherent with the SINT-2000 RPI stack (Valet et al., 2005) on time scales of ∼20–200 kyr, allowing for its use as a regional RPI reference curve in future studies. Overall, we demonstrate that RPI at Antarctic margin/Southern Ocean sites provides a viable and valuable independent dating method for application to Plio-/Pleistocene Antarctic sediments.

Antarctica, Barium enrichment, Palaeomagnetism, Pleistocene, Productivity, Relative palaeointensity
0277-3791
Hopkins, Becky
63b18654-d29f-4bfa-a054-8f1b2a82ecbf
Xuan, Chuang
3f3cad12-b17b-46ae-957a-b362def5b837
Hillenbrand, Claus-Dieter
8dc0c76e-e79b-4c8f-90ed-07035aabab98
van Peer, Tim E.
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Jin, Yuxi
a7d27955-300a-491d-85ab-32e3363ba59e
Frederichs, Thomas
88bad96b-061e-4eae-aae8-0be4ff358b74
Gao, Liang
41ed71f1-5c4b-4467-b28d-2b667e427a8c
Bohaty, Steve M.
4427b09f-d8b7-4bb9-a437-c52744fc4961
Hopkins, Becky
63b18654-d29f-4bfa-a054-8f1b2a82ecbf
Xuan, Chuang
3f3cad12-b17b-46ae-957a-b362def5b837
Hillenbrand, Claus-Dieter
8dc0c76e-e79b-4c8f-90ed-07035aabab98
van Peer, Tim E.
a0cd6c0c-54ff-4712-b861-76c90df08b66
Jin, Yuxi
a7d27955-300a-491d-85ab-32e3363ba59e
Frederichs, Thomas
88bad96b-061e-4eae-aae8-0be4ff358b74
Gao, Liang
41ed71f1-5c4b-4467-b28d-2b667e427a8c
Bohaty, Steve M.
4427b09f-d8b7-4bb9-a437-c52744fc4961

Hopkins, Becky, Xuan, Chuang, Hillenbrand, Claus-Dieter, van Peer, Tim E., Jin, Yuxi, Frederichs, Thomas, Gao, Liang and Bohaty, Steve M. (2024) Evaluation of geomagnetic relative palaeointensity as a chronostratigraphic tool in the Southern Ocean: refined Plio-/Pleistocene chronology of IODP Site U1533 (Amundsen Sea, West Antarctica). Quaternary Science Reviews, 325, [108460]. (doi:10.1016/j.quascirev.2023.108460).

Record type: Article

Abstract

International Ocean Discovery Program (IODP) Expedition 379 to the Amundsen Sea margin of West Antarctica recovered drill cores at two sites spanning the Latest Miocene–Holocene interval with the aim of reconstructing past West Antarctic Ice Sheet dynamics. The recovered Plio-/Pleistocene sediment sequences offer an opportunity to apply and test different dating approaches in an Antarctic deep-sea drift setting, where the records are nearly continuous and unaffected by scouring of icebergs or grounded ice. Here, through palaeomagnetic analysis of continuous u-channel samples and application of X-ray fluorescence (XRF) scanning, we revise the IODP Exp. 379 Site U1533 age model for the uppermost Pliocene and Pleistocene composite interval (0.0–2.9 Ma). We first refine the magnetostratigraphic age model with high-resolution u-channel analysis and interpreted directional data. Consistent with shipboard results, all major geomagnetic polarity chrons and subchrons are identified in the Pleistocene section. The new high-resolution u-channel dataset also allows us to identify a geomagnetic polarity excursion at ∼884 ka (interpreted as the Kamikatsura excursion) and another excursion at ∼2734 ka with confidence (potentially the Porcupine excursion). Based on the improved polarity stratigraphy, we then develop two new highly resolved age models for Site U1533 using: (i) barium enrichment cycles identified in XRF scanning data, and (ii) geomagnetic relative palaeointensity (RPI). In our first age model, we correlate cyclic variations in sedimentary barium enrichment, inferred to represent changes in export productivity, to glacial‒interglacial cycles of the Lisiecki and Raymo (2005) benthic foraminiferal oxygen isotope (δ 18O) stack (LR04). Nearly all Pleistocene Marine Isotope Stages (MIS) are interpreted to be present in the barium enrichment record of Site U1533, assuming simultaneous changes in Antarctic sea-ice extent/local export productivity and global oxygen isotope stratigraphy. We then construct the second, independent age model using the Plio-/Pleistocene RPI record developed for Site U1533, which represents the longest (nearly) continuous RPI record currently available for the Antarctic margin. Comparison of the two, independently derived age models shows a variable offset, on average ± 12 kyr, with the RPI-based ages consistently older than the barium-based ages in the interval from 1.9 to 2.9 Ma and then consistently younger from 0.0 to 1.9 Ma. We interpret these offsets to result from a combination of lock-in depth effects in the younger interval (due to the relatively low sedimentation rates at this site, ∼2 cm/kyr), temporal offsets between global δ 18O changes in the deep ocean and productivity response on the Antarctic margin, and/or systematic miscorrelation in the construction of the two age models. Finally, we construct a hybrid age model for the Pleistocene section of Site U1533 by combining a mixture of RPI- and barium-based age tie points that are deemed to be robust. The Site U1533 RPI record is then used, together with other Southern Ocean RPI records, to construct an Antarctic RPI stack (designated as ‘ANT-1600’) for the interval 0.0–1.6 Ma. Although sedimentation rates at two-thirds of the sites selected for the stack are lower than 10 cm/kyr, the new ANT-1600 stack is strongly coherent with the SINT-2000 RPI stack (Valet et al., 2005) on time scales of ∼20–200 kyr, allowing for its use as a regional RPI reference curve in future studies. Overall, we demonstrate that RPI at Antarctic margin/Southern Ocean sites provides a viable and valuable independent dating method for application to Plio-/Pleistocene Antarctic sediments.

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Accepted/In Press date: 1 December 2023
e-pub ahead of print date: 1 January 2024
Published date: 1 January 2024
Additional Information: Funding Information: We thank the officers, crew, shipboard and shore-based scientists from IODP Expedition 379 for their work in gathering the material used in this study. We thank the IODP Gulf Coast Repository (College Station, Texas) staff for the collection and preparation of u-channel samples. We thank the Exp. 379 chief scientists Julia Wellner and Karsten Gohl for commenting on the manuscript prior to submission. We also thank the International Association of Sedimentologists (IAS) for their funding, and the British Ocean Sediment Core Research Facility (BOSCORF) for supporting the generation of the X-radiography data used in this study. Additional funding comes from the National Environmental Research Council INSPIRE Doctoral Training Partnership (NE/S007210/1). C.-D.H. acknowledges funding by NERC UK-IODP grant NE/T010975/1. T.E.v.P. was supported by NERC Grant NE/M021254/1 and supported as a Research Fellow by the University of Leicester. The authors are grateful for constructive suggestions provided by Stefanie Brachfeld and another anonymous reviewer, which have significantly improved the manuscript.
Keywords: Antarctica, Barium enrichment, Palaeomagnetism, Pleistocene, Productivity, Relative palaeointensity

Identifiers

Local EPrints ID: 486707
URI: http://eprints.soton.ac.uk/id/eprint/486707
ISSN: 0277-3791
PURE UUID: a1203bf3-4369-41b6-b09e-f92b333af582
ORCID for Chuang Xuan: ORCID iD orcid.org/0000-0003-4043-3073
ORCID for Tim E. van Peer: ORCID iD orcid.org/0000-0003-3516-4198

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Date deposited: 02 Feb 2024 17:32
Last modified: 18 Mar 2024 03:26

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Contributors

Author: Becky Hopkins
Author: Chuang Xuan ORCID iD
Author: Claus-Dieter Hillenbrand
Author: Tim E. van Peer ORCID iD
Author: Yuxi Jin
Author: Thomas Frederichs
Author: Liang Gao
Author: Steve M. Bohaty

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