Spatially contrasted response of Devonian anoxia to astronomical forcing

Abstract. The Devonian period, spanning from 419 to 359 million years ago, was marked by a warmer-than-present climate and recurring ocean anoxic events, with evidence increasingly suggesting a link between these events and astronomical forcing. Here, we explore how astronomical forcing influences ocean oxygenation by modulating the continental weathering flux of phosphate within a Late Devonian climate framework. To investigate this, we performed transient simulations spanning 1.1 Myr, crossing a 2.4 Myr eccentricity node using the cGENIE Earth system model. These simulations were driven by spatially resolved fluxes of reactive phosphorus from continents, computed using the emulator developed by Sablon et al. (2025), trained on GEOCLIM and HadSM3 outputs. Our results provide new evidence supporting eccentricity maxima as a driver of Late Devonian anoxic events. Additionally, global analysis reveals that obliquity variations can imprint a distinct signal on global ocean oxygen levels via their influence on biological productivity, offering a plausible mechanism for obliquity-driven anoxia under greenhouse conditions. Regional analysis revealed pronounced spatial heterogeneity in the biogeochemical response to astronomical forcing. Local ocean circulation emerged as a critical factor in shaping these patterns. The simulations indicate that astronomical forcing can, through its impact on continental weathering fluxes, exert a dominant influence on ocean oxygenation, with regional oxygen concentrations varying by up to 35 % and driving changes in regional anoxic volume of up to 19 %. Finally, these findings help explain why proxy records from different locations may show divergent expressions of astronomical signals, potentially leading to contrasting interpretations of their role in driving ocean anoxia.