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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 re-active phosphorus from continents, computed using the em-ulator developed by Sablon et al. (2025), trained on GEO-CLIM 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 leave an imprint on global ocean oxygen levels via their influence on biological productivity , suggesting a potential pathway for obliquity-driven anoxia under greenhouse conditions. Regional analysis revealed pronounced spatial heterogeneity in the biogeochemi-cal 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.
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Gérard, J., Pohl, A., Sablon, L., Huygh, J., Da Silva, A.-C., & Crucifix, M. (2026). Spatially contrasted response of Devonian anoxia to astronomical forcing. Climate of the Past, 22, 1003-1021. https://doi.org/10.5194/cp-22-1003-2026 (Original work published 2026)