Carbon Isotope and Abundance Systematics Reveal an Insignificant Crustal Sink of Mantle‐Derived CO 2 in On‐Land Rift Zone Geothermal Systems
Year: 2025
Type: article
Abstract: Rift zones, both on land and submarine, are key pathways for mantle‐derived CO 2 degassing to the Earth's surface. Fixation of CO 2 as carbonates plays a critical role in regulating these emissions. This study examines carbon abundance and isotope compositions in hydrothermal fluids, altered rocks, and carbonates from geothermal systems in both Iceland rift and off‐rift. Hydrothermal fluids exhibit wide CO 2 concentrations (6.1–70.4 mmol kg −1 ) but narrow δ 13 C values (−4.8 to −2.5‰) assuming limited to no fractionation between vapor and liquid phases, in contrast to the broader δ 13 C range of carbonates (−14.5 to +0.5‰). Altered rocks contain up to 4.33 wt.% carbon, with enrichment in the upper 1,000 m of geothermal systems. Isotopic and geochemical modeling indicate that carbon is sourced from the mantle. Decompression boiling and water‐rock interaction drive carbonate formation, but only 1%–10% of mantle‐derived CO 2 is sequestered in on‐land rift carbonates, with the majority emitted via hydrothermal fluids. In contrast, Icelandic off‐rift low‐temperature systems represent significant CO 2 sinks due to limited boiling processes. This study suggests that submarine rift zones, lacking prominent boiling processes, may sequester mantle‐derived CO 2 more effectively into oceanic crust, facilitating long‐term recycling into the mantle. These findings highlight the limited capacity of on‐land rift systems to retain mantle‐derived CO 2 , underscoring the contrasting roles of terrestrial and submarine environments in global carbon cycling.
DOI: 10.1029/2025gc012219
Authors: Barbara I. Kleine‐Marshall, Maud J. Smit, Diego I. Toro Vivanco, Emilie Thomassot, Nico Müller, Ann Marie di Stefano, Emily Pope, Tod E. Waight, Heejin Jeon, Martin J. Whitehouse, Kevin Padilla, Frauke Wiese, Thráinn Fridriksson, Halldór Ármansson, Sveinborg H. Gunnarsdóttir, Kiflom G. Mesfin, Ásgerður K. Sigurðardóttir, Jens Fiebig, Andrea Ricci, Jóhann Gunnarsson‐Robin, Sæmundur A. Halldórsson, Shuhei Ono, Árný E. Sveinbjörnsdóttir, Andri Stefánsson
Institutions: University of Iceland, Friedrich-Alexander-Universität Erlangen-Nürnberg, Institute of Earth Sciences, University of Bern, Centre de Recherches Pétrographiques et Géochimiques, Université de Lorraine, University of Copenhagen, Swedish Museum of Natural History, New Mexico Institute of Mining and Technology, Europa-Universität Flensburg, Reykjavík Energy (Iceland), Iceland GeoSurvey, Landsvirkjun (Iceland), Goethe University Frankfurt, University of Pisa, INGV Sezione di Palermo, Massachusetts Institute of Technology
Language: English
Subfield: Geophysics
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Climate action
Open Access status: gold
Estimated APC paid: $3,000
OpenAlex ID: W4414779274