Phosphorus-cycle disturbances during the Late Devonian anoxic events

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 ©2019, Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http:// creativecommons.org/licenses/by-nc-nd/4.0/ 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 (osmiumisotope, silicon/aluminum, and titanium/aluminum 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.

Roles of Phosphate Solubilizing Microorganisms from Managing Soil Phosphorus Deficiency to Mediating Biogeochemical P Cycle

“…The P cycle exists within individual ecosystems including soil, stream, forest, and marine, which are closely related to key security issues of surrounding environment and human society [6,[8][9][10]. P cycle differs from the N and C biogeochemical cycles since it does not form any stable gaseous species at Earth temperatures and atmospheric pressures [11,12]. Only small amounts of phosphoric acid (H 3 PO 4 ) may enter the atmosphere and contribute to acid rain in some cases [13].…”

“…P cycle differs from the N and C biogeochemical cycles since it does not form any stable gaseous species at Earth temperatures and atmospheric pressures [ 11 , 12 ]. Only small amounts of phosphoric acid (H 3 PO 4 ) may enter the atmosphere and contribute to acid rain in some cases [ 13 ].…”

Significant Fluctuation in the Global Sulfate Reservoir and Oceanic Redox State During the Late Devonian Mass Extinction

“…2E, Table S2). The rise in P contents at this time is recorded in other sections worldwide such as the Appalachian basin (USA) 33 and Steinruch Schmidt (Germany) 34 , making a case for increased P availability at this time (Fig. S3).…”

“…The observed trend in the measured isotopic composition may have, instead, been the result of low-sulfate condition and or reoxidation of sul de 20,30 . Speci cally, in the low-sulfate seawaters, the sulfate produced by abiotic oxidation of parent H 2 S is depleted in 34 S by 4 − 5‰, which leads to the 34 S enrichment in sul de compare to sulfate, owing to Rayleigh distillation effect 20,30 . However, the fraction of H 2 S re-oxidized in reduced environments is considered to be low (0.11-0.42) 31 , implying an unlikely role of the re-oxidation of sul de in driving the observed isotopic trend during the UKH.…”

“…2D). At transition B in the interval IIa, δ34 S Kero and Δ 34 S Kero−Py show coupled positive shifts alongside a decrease in δ 34 S Py . Further upwards within interval IIb, δ 34 S Kero , δ 34 S Py , and Δ 34 S Kero−Py show increasing trends, and δ 34 S CAS shows a decrease towards the FFB.…”