LINKING LAND PLANTS TO DEVONIAN MARINE ANOXIC EVENTS: INTEGRATING NUTRIENT RECORDS AND BIOGEOCHEMICAL MODELING

The evolution and expansion of land plants in the Devonian catalyzed significant biogeochemical changes in Earth’s biosphere. The development of arborescence and significant root systems revolutionized soil formation and weathering, bringing about the birth of the modern Critical Zone. Recent studies of Devonian lacustrine systems have linked these evolutionary advancements to enhanced terrestrial nutrient export into the poorly ventilated, shallow and epeiric seaways prevalent in the Devonian, reigniting the debate regarding the role of land plants in the marine anoxic events throughout the Period. While the Devonian hosted multiple marine extinctions characterized by widespread anoxia, arguably the most significant was the Late Devonian mass extinction around 375 million years ago (Ma). This biological crisis is particularly relevant with respect to plant evolution as it is concurrent with the hegemony of the earliest deeply rooting tree, Archaeopteris. Here, we use recently generated constraints from Earth’s lacustrine rock record as variable inputs in an Earth system model of the coupled C-N-P-O₂-S biogeochemical cycles in order to evaluate whether recorded changes to phosphorus fluxes linked to the evolution and expansion of land plants would be adequate to sustain Devonian marine biogeochemical perturbations and extinction dynamics. Results show that globally scaled riverine phosphorus export during the Late Devonian mass extinction generates widespread marine anoxia and produces carbon isotope, temperature, oxygen, and carbon dioxide perturbations generally consistent with the geologic record. While it is currently not possible to rule out other causal factors in Devonian extinction events, such as large-scale volcanism, these results show that biogeochemical perturbations resulting from land plant expansion and evolution may have been enough to exacerbate or perhaps even initiate marine extinction events.