Phosphorus-cycle disturbances during the Late Devonian anoxic events

Percival, Lawrence; Bond, D. P.G.; Rakociński, M.; Marynowski, L.; Hood, A. V.S.; Adatte, T.; Spangenberg, J. E.; Föllmi, K. B.

Abstract

The Late Devonian was marked by repeated faunal crises and episodes of geographically widespread marine anoxia, and featured one of the ‘Big Five’ mass extinctions of the Phanerozoic Aeon during the Frasnian–Famennian transition. However, the processes responsible for causing the numerous anoxic events remain unclear. This study highlights the occurrence of disturbances to the phosphorus cycle during several Late Devonian crises by investigating sedimentary concentrations of the element (Ptot) as a tracer of nutrient influx, as well as its ratio with total organic carbon (TOC) to infer the recycling of the element from marine sediments. Increased TOC/Ptot ratios in the Frasnian–Famennian Lower and Upper Kellwasser horizons and upper Famennian Annulata and Hangenberg levels suggest that such nutrient recycling occurred across extensive areas of the marine shelf in Laurentia and both Rheic Ocean margins at those times, helping to sustain reducing conditions in those environments. Elevated Ptot values in the Upper Kellwasser, Annulata, and Hangenberg levels are consistent with an enhanced nutrient influx as the initial trigger for the anoxia. Correlation of phosphorus trends with other geochemical indicators of weathering/detrital influx (osmium-isotope, silicon/aluminum, and titanium/aluminium ratios) support a scenario in which terrestrial runoff provided these nutrients both to marine shelves and the oceanic inventory. Upwelling of oceanic deep-water bodies may have then brought the phosphorus to areas that had not featured major direct inputs of terrigenous material. The exception is the Lower Kellwasser Event, during which there was no increase in phosphorus delivery to marine areas and no evidence for terrestrial influx at the studied sections, invoking a different mechanism for the development of water-column anoxia. Clearly, the Late Devonian marine realm was unusually susceptible to becoming anoxic through various possible triggers, including nutrient influx from land and/or deep-water upwelling, and the recycling of phosphorus from newly deposited sediments.

Citation

Percival, L., Bond, D. P., Rakociński, M., Marynowski, L., Hood, A. V., Adatte, T., …Föllmi, K. B. (2020). Phosphorus-cycle disturbances during the Late Devonian anoxic events. Global and planetary change, 184, Article 103070. https://doi.org/10.1016/j.gloplacha.2019.103070

• Journal Article Type: Article
• Acceptance Date: Oct 29, 2019
• Online Publication Date: Oct 31, 2019
• Publication Date: 2020-01
• Deposit Date: Oct 30, 2019
• Publicly Available Date: Nov 1, 2020
• Journal: Global and Planetary Change
• Print ISSN: 0921-8181
• Electronic ISSN: 1872-6364
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 184
• Article Number: 103070
• DOI: https://doi.org/10.1016/j.gloplacha.2019.103070
• Keywords: Phosphorus; Late Devonian; marine anoxia; nutrient recycling; Frasnian–Famennian extinction
• Public URL: https://hull-repository.worktribe.com/output/3029059
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S0921818119305557