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An investigation into Hf and Fe isotopes in ferromanganese deposits and their applications to paleoceanography

An investigation into Hf and Fe isotopes in ferromanganese deposits and their applications to paleoceanography
An investigation into Hf and Fe isotopes in ferromanganese deposits and their applications to paleoceanography

The prime foci of this study have been to investigate two new potential tracers, the Hf and Fe isotopic systems, and their applications to marine environmental studies.  My work has focussed on a suite of ferromanganese crusts from the Pacific Ocean (Central Pacific and Izu-Bonin back-arc basin), encompassed different geographic and geologic settings, to obtain new insights into the present and past sources of Hf and Fe in seawater.

First, a Hf isotope analytical method has been established for multi-collection Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS, Chu et al, 2002).  This refined method has led to the determination of a new set of ytterbium (Yb) isotopic ratios benefiting from improved isobaric interference corrections and offering a promising future application:  in situ Laser ablation analyses.

The present-day profile of 176Hf/177Hf ratios in the Pacific Ocean has been inferred by analysing surface scrapings of Fe-Mn crusts collected at various water-depths in the Central Pacific.  In these samples, Nd isotope and rare earth element distributions correlate well with hydrological properties inferred from WOCE data, demonstrating the applicability of this approach.  The Hf isotopic composition does not display any significant variations with depth, throughout the water column, confirming that its oceanic residence time (τHf) is most probably longer than that of Nd and similar to that of the thermohaline circulation (˜1500 yr).  Estimated Hf isotopic compositions for Pacific Intermediate Water and Pacific Deep Water masses are suggested, based upon this vertical distribution.

Isotopic depth-profiles for Hf, Nd and Pb drilled into three Fe-Mn crusts have been measured to help decipher the radiogenic isotope budget of the Central Pacific and Izu-Bonin back-arc basin throughout the Late Neogene.  Isotopic records for Central Pacific crusts match those from the literature, showing no significant variations over the last 10 Myr.  For the Izu-Bonin area, by contrast, Pb-isotope variations suggest mixing between dissolved inputs from aeolian loess and volcanic island arcs.  A decoupling of the Hf and Nd isotope records is observed in both Izu-Bonin crusts at ˜4Ma.

University of Southampton
Chu, Nan-Chin
8bdef7b1-3345-471e-819a-26b588b2f93a
Chu, Nan-Chin
8bdef7b1-3345-471e-819a-26b588b2f93a

Chu, Nan-Chin (2003) An investigation into Hf and Fe isotopes in ferromanganese deposits and their applications to paleoceanography. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The prime foci of this study have been to investigate two new potential tracers, the Hf and Fe isotopic systems, and their applications to marine environmental studies.  My work has focussed on a suite of ferromanganese crusts from the Pacific Ocean (Central Pacific and Izu-Bonin back-arc basin), encompassed different geographic and geologic settings, to obtain new insights into the present and past sources of Hf and Fe in seawater.

First, a Hf isotope analytical method has been established for multi-collection Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS, Chu et al, 2002).  This refined method has led to the determination of a new set of ytterbium (Yb) isotopic ratios benefiting from improved isobaric interference corrections and offering a promising future application:  in situ Laser ablation analyses.

The present-day profile of 176Hf/177Hf ratios in the Pacific Ocean has been inferred by analysing surface scrapings of Fe-Mn crusts collected at various water-depths in the Central Pacific.  In these samples, Nd isotope and rare earth element distributions correlate well with hydrological properties inferred from WOCE data, demonstrating the applicability of this approach.  The Hf isotopic composition does not display any significant variations with depth, throughout the water column, confirming that its oceanic residence time (τHf) is most probably longer than that of Nd and similar to that of the thermohaline circulation (˜1500 yr).  Estimated Hf isotopic compositions for Pacific Intermediate Water and Pacific Deep Water masses are suggested, based upon this vertical distribution.

Isotopic depth-profiles for Hf, Nd and Pb drilled into three Fe-Mn crusts have been measured to help decipher the radiogenic isotope budget of the Central Pacific and Izu-Bonin back-arc basin throughout the Late Neogene.  Isotopic records for Central Pacific crusts match those from the literature, showing no significant variations over the last 10 Myr.  For the Izu-Bonin area, by contrast, Pb-isotope variations suggest mixing between dissolved inputs from aeolian loess and volcanic island arcs.  A decoupling of the Hf and Nd isotope records is observed in both Izu-Bonin crusts at ˜4Ma.

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Published date: 2003

Identifiers

Local EPrints ID: 465221
URI: http://eprints.soton.ac.uk/id/eprint/465221
PURE UUID: 559166ed-ee62-424b-adf8-ddcc9d137498

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Date deposited: 05 Jul 2022 00:29
Last modified: 23 Jul 2022 01:13

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Author: Nan-Chin Chu

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