Molybdenum isotope behaviour accompanying weathering and riverine transport in a basaltic terrain
Molybdenum isotope behaviour accompanying weathering and riverine transport in a basaltic terrain
The application of the molybdenum (Mo) isotope system as a proxy for determining changes in the redox state of the oceans is predicated on the assumption that the composition of continental input can be characterised from crustal rock types, and remains constant. However, it has recently been shown that the ?98/95Mo composition of global rivers varies between 0.15‰ and 2.4‰ and is therefore systematically heavier than the average composition of the continental crust (not, vert, similar 0‰). In order to understand the processes that control Mo-isotope fractionation during weathering this study presents ?98/95Mo and Mo abundance data for rivers (and estuarine samples) from Iceland that drain predominantly basaltic terrains. Resolvable differences are observed in the isotopic composition of the riverine Mo sources; ice (?98/95Moice > 1.8‰), basaltic bedrock (?98/95Mobedrock not, vert, similar 0.0‰) and hydrothermal waters (?98/95Mohydrothermal not, vert, similar?3.4‰). Systematic changes in the dissolved Mo-isotope composition are also observed within river catchments, with ?98/95Mo values increasing from not, vert, similar 0‰ in glacial rivers (close to the source) to not, vert, similar 1‰ downstream, consistent with Mo-isotopes being fractionated during weathering. Analysis of other riverine phases (bedload, colloids and iron-precipitates) demonstrates that these phases preferentially incorporate light Mo-isotopes, and remain coupled to the dissolved load during riverine transportation. A ?98/95Mo profile through the Borgarfjörður estuary exhibits a predominantly conservative mixing behaviour, but suggests that the release of isotopically light Mo from the particulate and/or colloidal phases may occur in the low salinity part of the estuarine mixing zone.
molybdenum (Mo) isotopes, basaltic weathering, riverine inputs, estuarine mixing
104-114
Pearce, Christopher R.
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Burton, Kevin W.
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Pogge von Strandmann, Philip A.E.
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James, Rachael H.
79aa1d5c-675d-4ba3-85be-fb20798c02f4
Gíslason, Sigurður R.
1fba4984-5465-43cc-b3c1-f73cbaa829e0
15 June 2010
Pearce, Christopher R.
3d683112-72dc-444f-ae06-da9c571d799a
Burton, Kevin W.
b17a2651-0697-4369-bfa7-ece9a9f0a3f1
Pogge von Strandmann, Philip A.E.
2de2f498-427b-4dcd-a435-ae9253ef20a3
James, Rachael H.
79aa1d5c-675d-4ba3-85be-fb20798c02f4
Gíslason, Sigurður R.
1fba4984-5465-43cc-b3c1-f73cbaa829e0
Pearce, Christopher R., Burton, Kevin W., Pogge von Strandmann, Philip A.E., James, Rachael H. and Gíslason, Sigurður R.
(2010)
Molybdenum isotope behaviour accompanying weathering and riverine transport in a basaltic terrain.
Earth and Planetary Science Letters, 295 (1-2), .
(doi:10.1016/j.epsl.2010.03.032).
Abstract
The application of the molybdenum (Mo) isotope system as a proxy for determining changes in the redox state of the oceans is predicated on the assumption that the composition of continental input can be characterised from crustal rock types, and remains constant. However, it has recently been shown that the ?98/95Mo composition of global rivers varies between 0.15‰ and 2.4‰ and is therefore systematically heavier than the average composition of the continental crust (not, vert, similar 0‰). In order to understand the processes that control Mo-isotope fractionation during weathering this study presents ?98/95Mo and Mo abundance data for rivers (and estuarine samples) from Iceland that drain predominantly basaltic terrains. Resolvable differences are observed in the isotopic composition of the riverine Mo sources; ice (?98/95Moice > 1.8‰), basaltic bedrock (?98/95Mobedrock not, vert, similar 0.0‰) and hydrothermal waters (?98/95Mohydrothermal not, vert, similar?3.4‰). Systematic changes in the dissolved Mo-isotope composition are also observed within river catchments, with ?98/95Mo values increasing from not, vert, similar 0‰ in glacial rivers (close to the source) to not, vert, similar 1‰ downstream, consistent with Mo-isotopes being fractionated during weathering. Analysis of other riverine phases (bedload, colloids and iron-precipitates) demonstrates that these phases preferentially incorporate light Mo-isotopes, and remain coupled to the dissolved load during riverine transportation. A ?98/95Mo profile through the Borgarfjörður estuary exhibits a predominantly conservative mixing behaviour, but suggests that the release of isotopically light Mo from the particulate and/or colloidal phases may occur in the low salinity part of the estuarine mixing zone.
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Published date: 15 June 2010
Keywords:
molybdenum (Mo) isotopes, basaltic weathering, riverine inputs, estuarine mixing
Organisations:
Marine Geoscience, National Oceanography Centre,Southampton
Identifiers
Local EPrints ID: 172253
URI: http://eprints.soton.ac.uk/id/eprint/172253
ISSN: 0012-821X
PURE UUID: 3830380b-3d5a-4768-b49d-7f456c6cf62e
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Date deposited: 24 Jan 2011 16:01
Last modified: 14 Mar 2024 02:53
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Author:
Christopher R. Pearce
Author:
Kevin W. Burton
Author:
Philip A.E. Pogge von Strandmann
Author:
Sigurður R. Gíslason
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