Exploring the mechanisms of Devonian oceanic anoxia: impact of ocean dynamics, palaeogeography, and orbital forcing
<p>The Devonian is a warmer-than-present geological period spanning from 419 to 359 million years ago (Ma) characterized by multiple identified ocean anoxic/hypoxic events. Despite decades of extensive investigation, no consensus has been reached regarding the drivers of these anoxic events....
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Copernicus Publications
2025-01-01
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| Series: | Climate of the Past |
| Online Access: | https://cp.copernicus.org/articles/21/239/2025/cp-21-239-2025.pdf |
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| author | J. Gérard L. Sablon J. J. C. Huygh A.-C. Da Silva A. Pohl C. Vérard M. Crucifix |
| author_facet | J. Gérard L. Sablon J. J. C. Huygh A.-C. Da Silva A. Pohl C. Vérard M. Crucifix |
| author_sort | J. Gérard |
| collection | DOAJ |
| description | <p>The Devonian is a warmer-than-present geological period spanning from 419 to 359 million years ago (Ma) characterized by multiple identified ocean anoxic/hypoxic events. Despite decades of extensive investigation, no consensus has been reached regarding the drivers of these anoxic events. While growing geological evidence has demonstrated a temporal correlation between astronomical forcing and anoxia during this period, underlying physical mechanisms remain unknown, hence questioning causality. Here, we perform multiple sensitivity experiments, using an Earth system model of intermediate complexity (cGENIE), to isolate the influences of specific Devonian climate and palaeogeography components on ocean oxygen levels, contributing to the better understanding of the intricate interplay of factors preconditioning the ocean to anoxia. We quantify the impact of continental configuration, ocean–atmosphere biogeochemistry (global mean oceanic <span class="inline-formula">PO<sub>4</sub></span> concentration and atmospheric <span class="inline-formula"><i>p</i></span><span class="inline-formula">O<sub>2</sub></span>), climatic forcing (<span class="inline-formula"><i>p</i></span><span class="inline-formula">CO<sub>2</sub></span>), and astronomical forcing on background oceanic circulation and oxygenation during the Devonian. Our results indicate that continental configuration is crucial for Devonian ocean anoxia, significantly influencing ocean circulation and oxygen levels while consistently modulating the effects of other Devonian climate components such as oceanic <span class="inline-formula">PO<sub>4</sub></span> concentration, atmospheric <span class="inline-formula"><i>p</i></span><span class="inline-formula">O<sub>2</sub></span> and <span class="inline-formula"><i>p</i></span><span class="inline-formula">CO<sub>2</sub></span>, and orbital forcing. The evolution of continental configuration provides a plausible explanation for the increased frequency of ocean anoxic events identified during the Middle and Late Devonian periods, as it contributed to the expansion of oxygen-depleted zones. Our simulations also show that both the decreased atmospheric <span class="inline-formula"><i>p</i></span><span class="inline-formula">O<sub>2</sub></span> and increased oceanic <span class="inline-formula">PO<sub>4</sub></span> concentration exacerbate ocean anoxia, consistent with established knowledge. The variation of <span class="inline-formula"><i>p</i></span><span class="inline-formula">CO<sub>2</sub></span> reveals a wide range of ocean dynamics patterns, including stable oscillations, multiple convection cells, multistability, and hysteresis, all leading to significant variations of the ocean oxygen levels and therefore strongly impacting the preconditioning of the ocean to anoxia. Furthermore, multistability and important hysteresis (particularly slow ocean time response) offer different mechanisms to account for the prolonged duration of some ocean anoxic events. Finally, we found that astronomical forcing substantially impacts ocean anoxia by altering ocean circulation and oxygen solubility, with obliquity consistently emerging as the primary orbital parameter driving ocean oxygen variations.</p> |
| format | Article |
| id | doaj-art-e140b51e854e44c8898580f1f4e539c7 |
| institution | Kabale University |
| issn | 1814-9324 1814-9332 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | Copernicus Publications |
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| series | Climate of the Past |
| spelling | doaj-art-e140b51e854e44c8898580f1f4e539c72025-01-28T11:05:18ZengCopernicus PublicationsClimate of the Past1814-93241814-93322025-01-012123926010.5194/cp-21-239-2025Exploring the mechanisms of Devonian oceanic anoxia: impact of ocean dynamics, palaeogeography, and orbital forcingJ. Gérard0L. Sablon1J. J. C. Huygh2A.-C. Da Silva3A. Pohl4C. Vérard5M. Crucifix6Earth and Life Institute (ELI), Université catholique de Louvain (UCLouvain), 1348 Louvain-la-Neuve, BelgiumEarth and Life Institute (ELI), Université catholique de Louvain (UCLouvain), 1348 Louvain-la-Neuve, BelgiumDepartment of Geology, University of Liège, Sart Tilman, 4000 Liège, BelgiumDepartment of Geology, University of Liège, Sart Tilman, 4000 Liège, BelgiumBiogéosciences, UMR 6282 CNRS, Université de Bourgogne, 21000 Dijon, FranceDepartment of Earth Sciences, University of Geneva, 13 Rue des Maraîchers, 1205 Geneva, SwitzerlandEarth and Life Institute (ELI), Université catholique de Louvain (UCLouvain), 1348 Louvain-la-Neuve, Belgium<p>The Devonian is a warmer-than-present geological period spanning from 419 to 359 million years ago (Ma) characterized by multiple identified ocean anoxic/hypoxic events. Despite decades of extensive investigation, no consensus has been reached regarding the drivers of these anoxic events. While growing geological evidence has demonstrated a temporal correlation between astronomical forcing and anoxia during this period, underlying physical mechanisms remain unknown, hence questioning causality. Here, we perform multiple sensitivity experiments, using an Earth system model of intermediate complexity (cGENIE), to isolate the influences of specific Devonian climate and palaeogeography components on ocean oxygen levels, contributing to the better understanding of the intricate interplay of factors preconditioning the ocean to anoxia. We quantify the impact of continental configuration, ocean–atmosphere biogeochemistry (global mean oceanic <span class="inline-formula">PO<sub>4</sub></span> concentration and atmospheric <span class="inline-formula"><i>p</i></span><span class="inline-formula">O<sub>2</sub></span>), climatic forcing (<span class="inline-formula"><i>p</i></span><span class="inline-formula">CO<sub>2</sub></span>), and astronomical forcing on background oceanic circulation and oxygenation during the Devonian. Our results indicate that continental configuration is crucial for Devonian ocean anoxia, significantly influencing ocean circulation and oxygen levels while consistently modulating the effects of other Devonian climate components such as oceanic <span class="inline-formula">PO<sub>4</sub></span> concentration, atmospheric <span class="inline-formula"><i>p</i></span><span class="inline-formula">O<sub>2</sub></span> and <span class="inline-formula"><i>p</i></span><span class="inline-formula">CO<sub>2</sub></span>, and orbital forcing. The evolution of continental configuration provides a plausible explanation for the increased frequency of ocean anoxic events identified during the Middle and Late Devonian periods, as it contributed to the expansion of oxygen-depleted zones. Our simulations also show that both the decreased atmospheric <span class="inline-formula"><i>p</i></span><span class="inline-formula">O<sub>2</sub></span> and increased oceanic <span class="inline-formula">PO<sub>4</sub></span> concentration exacerbate ocean anoxia, consistent with established knowledge. The variation of <span class="inline-formula"><i>p</i></span><span class="inline-formula">CO<sub>2</sub></span> reveals a wide range of ocean dynamics patterns, including stable oscillations, multiple convection cells, multistability, and hysteresis, all leading to significant variations of the ocean oxygen levels and therefore strongly impacting the preconditioning of the ocean to anoxia. Furthermore, multistability and important hysteresis (particularly slow ocean time response) offer different mechanisms to account for the prolonged duration of some ocean anoxic events. Finally, we found that astronomical forcing substantially impacts ocean anoxia by altering ocean circulation and oxygen solubility, with obliquity consistently emerging as the primary orbital parameter driving ocean oxygen variations.</p>https://cp.copernicus.org/articles/21/239/2025/cp-21-239-2025.pdf |
| spellingShingle | J. Gérard L. Sablon J. J. C. Huygh A.-C. Da Silva A. Pohl C. Vérard M. Crucifix Exploring the mechanisms of Devonian oceanic anoxia: impact of ocean dynamics, palaeogeography, and orbital forcing Climate of the Past |
| title | Exploring the mechanisms of Devonian oceanic anoxia: impact of ocean dynamics, palaeogeography, and orbital forcing |
| title_full | Exploring the mechanisms of Devonian oceanic anoxia: impact of ocean dynamics, palaeogeography, and orbital forcing |
| title_fullStr | Exploring the mechanisms of Devonian oceanic anoxia: impact of ocean dynamics, palaeogeography, and orbital forcing |
| title_full_unstemmed | Exploring the mechanisms of Devonian oceanic anoxia: impact of ocean dynamics, palaeogeography, and orbital forcing |
| title_short | Exploring the mechanisms of Devonian oceanic anoxia: impact of ocean dynamics, palaeogeography, and orbital forcing |
| title_sort | exploring the mechanisms of devonian oceanic anoxia impact of ocean dynamics palaeogeography and orbital forcing |
| url | https://cp.copernicus.org/articles/21/239/2025/cp-21-239-2025.pdf |
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