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Molybdenum isotope behaviour in groundwaters and terrestrial hydrothermal systems, Iceland

Molybdenum isotope behaviour in groundwaters and terrestrial hydrothermal systems, Iceland
Molybdenum isotope behaviour in groundwaters and terrestrial hydrothermal systems, Iceland
Molybdenum (Mo) isotopes have proved useful in the reconstruction of paleoredox conditions. Their application generally relies upon a simplified model of ocean inputs in which rivers dominate Mo fluxes to the oceans and hydrothermal fluids are considered to be a minor contribution. To date, however, little attention has been paid to the extent of Mo isotope variation of hydrothermal waters, or to the potential effect of direct groundwater discharge to the oceans. Here we present Mo isotope data for two Icelandic groundwater systems (Mývatn and Þeistareykir) that are both influenced by hydrothermal processes. Relative to NIST 3134 = +0.25‰, the cold (<10 °C) groundwaters (δ98/95MoGROUNDWATER = −0.15‰ to +0.47‰; ) show little, if any, fractionation from the host basalt (MoBASALT = +0.16‰ to −0.12‰) and are, on average, lighter than both global and Icelandic rivers. In contrast, waters that are hydrothermally influenced (>10 °C) possess isotopically heavy δ98/95MoHYDROTHERMAL values of +0.25‰ to +2.06‰ with the possibility that the high temperature endmembers are even heavier. Although the mechanisms driving this fractionation remain unresolved, the incongruent dissolution of the host basalt and both the dissolution and precipitation of sulfides are considered. Regardless of the processes driving these variations, the δ98Mo data presented in this study indicate that groundwater and hydrothermal waters have the potential to modify ocean budget calculations.
0012-821X
108-118
Neely, Rebecca A.
93aa734c-4fb8-4f93-b6d4-ef84cca76eb8
Gislason, Sigurdur R.
031aa1d2-b345-4e99-9e15-c73f29215e19
Ólafsson, Magnus
1e5e05d3-624e-4a16-a9ed-ab5109ea565c
Mccoy-west, Alex J.
3ab426c2-3df6-4d80-8e6a-cc8de87237fb
Pearce, Christopher R.
c83b6228-0b64-4f5a-a8ad-e5cd33a11de3
Burton, Kevin W.
b17a2651-0697-4369-bfa7-ece9a9f0a3f1
Neely, Rebecca A.
93aa734c-4fb8-4f93-b6d4-ef84cca76eb8
Gislason, Sigurdur R.
031aa1d2-b345-4e99-9e15-c73f29215e19
Ólafsson, Magnus
1e5e05d3-624e-4a16-a9ed-ab5109ea565c
Mccoy-west, Alex J.
3ab426c2-3df6-4d80-8e6a-cc8de87237fb
Pearce, Christopher R.
c83b6228-0b64-4f5a-a8ad-e5cd33a11de3
Burton, Kevin W.
b17a2651-0697-4369-bfa7-ece9a9f0a3f1

Neely, Rebecca A., Gislason, Sigurdur R., Ólafsson, Magnus, Mccoy-west, Alex J., Pearce, Christopher R. and Burton, Kevin W. (2018) Molybdenum isotope behaviour in groundwaters and terrestrial hydrothermal systems, Iceland. Earth and Planetary Science Letters, 486, 108-118. (doi:10.1016/j.epsl.2017.11.053).

Record type: Article

Abstract

Molybdenum (Mo) isotopes have proved useful in the reconstruction of paleoredox conditions. Their application generally relies upon a simplified model of ocean inputs in which rivers dominate Mo fluxes to the oceans and hydrothermal fluids are considered to be a minor contribution. To date, however, little attention has been paid to the extent of Mo isotope variation of hydrothermal waters, or to the potential effect of direct groundwater discharge to the oceans. Here we present Mo isotope data for two Icelandic groundwater systems (Mývatn and Þeistareykir) that are both influenced by hydrothermal processes. Relative to NIST 3134 = +0.25‰, the cold (<10 °C) groundwaters (δ98/95MoGROUNDWATER = −0.15‰ to +0.47‰; ) show little, if any, fractionation from the host basalt (MoBASALT = +0.16‰ to −0.12‰) and are, on average, lighter than both global and Icelandic rivers. In contrast, waters that are hydrothermally influenced (>10 °C) possess isotopically heavy δ98/95MoHYDROTHERMAL values of +0.25‰ to +2.06‰ with the possibility that the high temperature endmembers are even heavier. Although the mechanisms driving this fractionation remain unresolved, the incongruent dissolution of the host basalt and both the dissolution and precipitation of sulfides are considered. Regardless of the processes driving these variations, the δ98Mo data presented in this study indicate that groundwater and hydrothermal waters have the potential to modify ocean budget calculations.

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More information

Accepted/In Press date: 28 November 2017
e-pub ahead of print date: 28 January 2018
Published date: 15 March 2018

Identifiers

Local EPrints ID: 420396
URI: http://eprints.soton.ac.uk/id/eprint/420396
ISSN: 0012-821X
PURE UUID: b2283edf-2036-45cd-99eb-19b8f3751e21

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Date deposited: 04 May 2018 16:31
Last modified: 27 Apr 2022 04:26

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Contributors

Author: Rebecca A. Neely
Author: Sigurdur R. Gislason
Author: Magnus Ólafsson
Author: Alex J. Mccoy-west
Author: Christopher R. Pearce
Author: Kevin W. Burton

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