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      New isotope constraints on the Mg oceanic budget point to cryptic modern dolomite formation

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          Abstract

          The oceanic magnesium budget is important to our understanding of Earth’s carbon cycle, because similar processes control both (e.g., weathering, volcanism, and carbonate precipitation). However, dolomite sedimentation and low-temperature hydrothermal circulation remain enigmatic oceanic Mg sinks. In recent years, magnesium isotopes (δ 26Mg) have provided new constraints on the Mg cycle, but the lack of data for the low-temperature hydrothermal isotope fractionation has hindered this approach. Here we present new δ 26Mg data for low-temperature hydrothermal fluids, demonstrating preferential 26Mg incorporation into the oceanic crust, on average by ε solid-fluid ≈ 1.6‰. These new data, along with the constant seawater δ 26Mg over the past ~20 Myr, require a significant dolomitic sink (estimated to be 1.5–2.9 Tmol yr −1; 40–60% of the oceanic Mg outputs). This estimate argues strongly against the conventional view that dolomite formation has been negligible in the Neogene and points to the existence of significant hidden dolomite formation.

          Abstract

          Earth’s carbon cycle and oceanic magnesium cycle are controlled by processes such as weathering, volcanism and precipitation of carbonates, such as dolomite. Here, the authors contradict the view that modern dolomite formation is rare and suggest instead that dolomite accounts for ~40–60% of the global oceanic Mg output in the last 20 Ma.

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          Most cited references39

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          The carbonate-silicate geochemical cycle and its effect on atmospheric carbon dioxide over the past 100 million years

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            Submarine thermal sprirngs on the galapagos rift.

            The submarine hydrothermal activity on and near the Galápagos Rift has been explored with the aid of the deep submersible Alvin. Analyses of water samples from hydrothermal vents reveal that hydrothermal activity provides significant or dominant sources and sinks for several components of seawater; studies of conductive and convective heat transfer suggest that two-thirds of the heat lost from new oceanic lithosphere at the Galápagos Rift in the first million years may be vented from thermal springs, predominantly along the axial ridge within the rift valley. The vent areas are populated by animal communities. They appear to utilize chemosynthesis by sulfur-oxidizing bacteria to derive their entire energy supply from reactions between the seawater and the rocks at high temperatures, rather than photosynthesis.
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              Mid-Ocean Ridge Hydrothermal Fluxes and the Chemical Composition of the Ocean

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                Author and article information

                Contributors
                +41 44 633 67 84 , netta.shalev@erdw.ethz.ch
                Journal
                Nat Commun
                Nat Commun
                Nature Communications
                Nature Publishing Group UK (London )
                2041-1723
                11 December 2019
                11 December 2019
                2019
                : 10
                : 5646
                Affiliations
                [1 ]ISNI 0000 0001 2156 2780, GRID grid.5801.c, Department of Earth Sciences, , Institute of Geochemistry and Petrology, ETH Zürich, ; Clausiusstrasse 25, 8092 Zürich, Switzerland
                [2 ]Space Exploration Institute, Fbg de l’Hopital 68, 2002 Neuchâtel, Switzerland
                [3 ]ISNI 0000 0004 1937 0642, GRID grid.6612.3, Department of Environmental Sciences, , University of Basel, ; Klingelbergstrasse 27, Basel, Switzerland
                [4 ]ISNI 0000 0004 1936 981X, GRID grid.70738.3b, University of Alaska Fairbanks, ; PO Box 475, Moss Landing, California 95039 USA
                Author information
                http://orcid.org/0000-0002-0711-8162
                http://orcid.org/0000-0003-4917-0388
                http://orcid.org/0000-0001-8858-1310
                http://orcid.org/0000-0002-6140-6325
                Article
                13514
                10.1038/s41467-019-13514-6
                6906300
                31827091
                7b7d0ffd-b4c1-4402-8aaa-9ca61ae8c74b
                © The Author(s) 2019

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

                History
                : 1 October 2018
                : 11 November 2019
                Funding
                Funded by: FundRef https://doi.org/10.13039/501100003006, Eidgenössische Technische Hochschule Zürich (Federal Institute of Technology Zurich);
                Award ID: FEL-14 16-1
                Award Recipient :
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                © The Author(s) 2019

                Uncategorized
                element cycles,palaeoceanography,marine chemistry
                Uncategorized
                element cycles, palaeoceanography, marine chemistry

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