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Palaeomagnetic, astrochronological, and environmental magnetic perspective on Oligocene-Miocene climate, using drift sediments from the northwest Atlantic Ocean

Palaeomagnetic, astrochronological, and environmental magnetic perspective on Oligocene-Miocene climate, using drift sediments from the northwest Atlantic Ocean
Palaeomagnetic, astrochronological, and environmental magnetic perspective on Oligocene-Miocene climate, using drift sediments from the northwest Atlantic Ocean
The Antarctic ice sheet oscillated between nearly deglaciated and near-­‐modern proportions, sometimes within ~110 kyr, during transient glacial phases of the Oligocene-­‐Miocene icehouse world (5.33-­‐33.9 Ma). Ice sheet hysteresis is closely coupled with carbon-­‐cycle feedback mechanisms that are strongly affected by ocean circulation. However, the absence of high-­‐resolution records representing the North Atlantic end member, a key region driving modern climate variability and ocean circulation, hamper full understanding of Oligocene-­‐Miocene ocean circulation and climate. In this thesis, I integrate palaeomagnetic, X-­‐ray fluorescence (XRF), and environmental magnetic records to date and reconstruct current variability from contourite drift sediments, recovered at Integrated Ocean Drilling Program (IODP) Site U1406 (northwest Atlantic). The revised splice ensures stratigraphic continuity for the studied section. The presented novel palaeomagnetic data processing protocol, which is applicable to all weakly magnetised sediments, ensures the use of only high quality directional data for the construction of a reliable magnetostratigraphy between Chrons C6Ar – C9n (21-­‐27 Ma). Astronomical tuning using XRF-­‐based ln(Ca/K), a proxy for CaCO3 content, provides independent dates for the identified geomagnetic reversals. I determine the best age estimates of reversals using a set of criteria to reconcile the Oligocene-­‐Miocene geomagnetic polarity time scale. Congruent obliquity-­‐paced CaCO3 cycles at Ocean Drilling Program Site 926 (equatorial Atlantic) and IODP Site U1406 suggest that one corrosive bottom water mass influences the CaCO3 content of the boreal Atlantic. The location and occurrence of contourite drift sediments at IODP Site U1406 advocates that the Deep Western Boundary Current (DWBC) is the candidate for such corrosive bottom waters. DWBC variability around the Oligocene-­‐Miocene Transition (~23 Ma) is traced using the detrital magnetic fraction, containing titanohaematite, recognised through detailed rock and environmental magnetic measurements. During the last ca. 1 Myr of the Oligocene, the decrease in CaCO3-­‐corrected concentration and coercivity of titanohaematite indicates an invigorated DWBC. If these characteristics of the DWBC are substantiated, this will have major implications for CO2 reconstructions on orbital time scales and Oligocene-­‐Miocene climate models.
Universty of Southampton
Van Peer, Tim
da231293-36c0-4d9f-b86c-8b1f059b5134
Van Peer, Tim
da231293-36c0-4d9f-b86c-8b1f059b5134
Xuan, Chuang
3f3cad12-b17b-46ae-957a-b362def5b837

Van Peer, Tim (2017) Palaeomagnetic, astrochronological, and environmental magnetic perspective on Oligocene-Miocene climate, using drift sediments from the northwest Atlantic Ocean. University of Southampton, Doctoral Thesis, 217pp.

Record type: Thesis (Doctoral)

Abstract

The Antarctic ice sheet oscillated between nearly deglaciated and near-­‐modern proportions, sometimes within ~110 kyr, during transient glacial phases of the Oligocene-­‐Miocene icehouse world (5.33-­‐33.9 Ma). Ice sheet hysteresis is closely coupled with carbon-­‐cycle feedback mechanisms that are strongly affected by ocean circulation. However, the absence of high-­‐resolution records representing the North Atlantic end member, a key region driving modern climate variability and ocean circulation, hamper full understanding of Oligocene-­‐Miocene ocean circulation and climate. In this thesis, I integrate palaeomagnetic, X-­‐ray fluorescence (XRF), and environmental magnetic records to date and reconstruct current variability from contourite drift sediments, recovered at Integrated Ocean Drilling Program (IODP) Site U1406 (northwest Atlantic). The revised splice ensures stratigraphic continuity for the studied section. The presented novel palaeomagnetic data processing protocol, which is applicable to all weakly magnetised sediments, ensures the use of only high quality directional data for the construction of a reliable magnetostratigraphy between Chrons C6Ar – C9n (21-­‐27 Ma). Astronomical tuning using XRF-­‐based ln(Ca/K), a proxy for CaCO3 content, provides independent dates for the identified geomagnetic reversals. I determine the best age estimates of reversals using a set of criteria to reconcile the Oligocene-­‐Miocene geomagnetic polarity time scale. Congruent obliquity-­‐paced CaCO3 cycles at Ocean Drilling Program Site 926 (equatorial Atlantic) and IODP Site U1406 suggest that one corrosive bottom water mass influences the CaCO3 content of the boreal Atlantic. The location and occurrence of contourite drift sediments at IODP Site U1406 advocates that the Deep Western Boundary Current (DWBC) is the candidate for such corrosive bottom waters. DWBC variability around the Oligocene-­‐Miocene Transition (~23 Ma) is traced using the detrital magnetic fraction, containing titanohaematite, recognised through detailed rock and environmental magnetic measurements. During the last ca. 1 Myr of the Oligocene, the decrease in CaCO3-­‐corrected concentration and coercivity of titanohaematite indicates an invigorated DWBC. If these characteristics of the DWBC are substantiated, this will have major implications for CO2 reconstructions on orbital time scales and Oligocene-­‐Miocene climate models.

Text
Van Peer, Tim_PhD_Thesis_Nov_17_ - Author's Original
Restricted to Repository staff only until 20 November 2020.
Available under License University of Southampton Thesis Licence.

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Published date: 20 November 2017

Identifiers

Local EPrints ID: 416832
URI: http://eprints.soton.ac.uk/id/eprint/416832
PURE UUID: 181d16b9-929b-4867-99d5-91e76c3dc96b
ORCID for Tim Van Peer: ORCID iD orcid.org/0000-0003-3516-4198
ORCID for Chuang Xuan: ORCID iD orcid.org/0000-0003-4043-3073

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Date deposited: 11 Jan 2018 17:30
Last modified: 14 Mar 2019 01:34

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Contributors

Author: Tim Van Peer ORCID iD
Thesis advisor: Chuang Xuan ORCID iD

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