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Hydrothermal and Cold Spring Water and Primary Productivity Effects on Magnesium Isotopes: Lake Myvatn, Iceland

Pogge von Strandmann, Philip A.E.; Burton, Kevin W.; Opfergelt, Sophie; Eiríksdóttir, Eydís S.; Murphy, Melissa J.; Einarsson, Arni; Gislason, Sigurdur R.

Hydrothermal and Cold Spring Water and Primary Productivity Effects on Magnesium Isotopes: Lake Myvatn, Iceland Thumbnail


Authors

Philip A.E. Pogge von Strandmann

Sophie Opfergelt

Eydís S. Eiríksdóttir

Melissa J. Murphy

Arni Einarsson

Sigurdur R. Gislason



Abstract

Lake Myvatn, Iceland, is one of the most biologically productive lakes in the northern hemisphere, despite seasonal ice cover. Hydrothermal and groundwater springs make up the dominant source to this lake, and we investigate their Mg isotope ratio to assess the effect of mid-ocean ridge hydrothermal springs, which are the primary modern sink of seawater magnesium. We also examine a time series in the only outflow from this lake, the Laxa River, to assess the effects of seasonal primary productivity on Mg isotopes. In the hydrothermal waters, there is a clear distinction between cold waters (largely unfractionated from primary basalt) and relatively hot waters, which exhibit over 1‰ fractionation, with consequences for the oceanic mass balance if the hydrothermal removal of Mg is not fully quantitative. The outflow Mg isotopes are similar to basalts (δ26Mg = −0.2 to −0.3) during winter but reach a peak of ∼0‰ in August. This fractionation corresponds to calcite precipitation during summer in Lake Myvatn, preferentially taking up light Mg isotopes and driving the residual waters isotopically heavy as observed, meaning that overall the lake is a CO2 sink.

Journal Article Type Article
Acceptance Date Mar 24, 2020
Online Publication Date Apr 30, 2020
Publication Date 2020
Deposit Date May 27, 2020
Publicly Available Date May 27, 2020
Journal Frontiers in Earth Science
Publisher Frontiers Media
Peer Reviewed Peer Reviewed
Volume 8
Article Number 109
DOI https://doi.org/10.3389/feart.2020.00109
Public URL https://durham-repository.worktribe.com/output/1301369

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Published Journal Article (2.1 Mb)
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Publisher Licence URL
http://creativecommons.org/licenses/by/4.0/

Copyright Statement
Copyright © 2020 Pogge von Strandmann, Burton, Opfergelt, Eiríksdóttir, Murphy, Einarsson and Gislason. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.






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