252-9 Investigating Environmental Controls on Extinction Selectivity During the Late Devonian Kellwasser Events using Proxy-Constrained Earth System-Ecophysiological Modeling

Session: Climate Transitions in the Paleozoic

Presenting Author:

Ashley Prow-Fleischer

Authors:

Prow-Fleischer, Ashley¹, Lu, Zunli², Blättler, Clara³, Al Aswad, Jood Al⁴, Pohl, Alexandre⁵, Ridgwell, Andy⁶, Penn, Justin⁷, Payne, Jonathan L.⁸

(1) Earth and Planetary Sciences, Stanford University, Stanford, Cal, USA; Earth and Environmental Sciences, Syracuse University, Syracuse, NY, USA, (2) Syracuse Univ Earth Sciences, Syracuse, NY, USA, (3) University of Chicago, Chicago, IL, USA, (4) Stanford University, Stanford, CA, USA, (5) Université Bourgogne Franche-Comté, Dijon, France, USA, (6) University of California Riverside, Riverside, Cali, USA, (7) Princeton University Department of Geosciences, Princeton, NJ, USA, (8) Stanford University, Stanford, CA, USA,

Abstract:

The Kellwasser Events, biodiversity crises near the Late Devonian Frasnian-Famennian boundary, led to extinctions among both tropical reef-builders and pelagic taxa. Geochemical proxies (e.g., δ²³⁸U) and sedimentary indicators (e.g., black shales) suggest that widespread ocean deoxygenation was a major driver of these extinctions. However, uncertainties in key environmental parameters, including atmospheric O₂ and CO₂ levels as well as marine PO₄ inventories, limit our ability to reconstruct the spatial extent of anoxia and the broader changes in oxygen availability. Additionally, increasing evidence that the Kellwasser Events coincided with climate cooling has shifted focus toward understanding how circulation changes under cooling scenarios could intensify oxygen depletion while remaining consistent with geochemical proxies and extinction patterns.

To address these challenges, we use a proxy-constrained Earth system–ecophysiological modeling approach to examine links among temperature change, deoxygenation, and aerobic habitat loss during the Kellwasser Events. We present new I/Ca ratio data, a proxy for shallow-marine hypoxia, from four globally distributed sites. These data constrain dissolved oxygen patterns in the cGENIE Earth system model across a parameter space of varying PO₄, pO₂, and pCO₂. Paired simulations were selected based on criteria such as a required 5-15% increase in benthic anoxic extent during the Kellwasser Events consistent with published δ²³⁸U estimates (White et al., 2018).

Model results suggest that Kellwasser-state conditions expanded the area of shallow-water anoxia in the tropics, increased O₂ at high northern latitudes, and caused moderate deoxygenation near the southern pole. To evaluate extinction selectivity, we applied a trait-based ecophysiological model to the subset of plausible transitions and quantified species' aerobic habitat loss in response to temperature and oxygen stress. Most scenarios predicted heightened extinction intensity in the mid-southern latitudes relative to the tropics.

We then compared these model predictions to reconstructed extinction gradients derived from cleaned and spatio-temporally binned and standardized fossil occurrence data in the Paleobiology Database. Observed extinction was highest in the northern tropics and southern mid-latitudes relative to the southern tropics. Achieving general agreement between fossil data and model predictions required greater than 3 °C of cooling and/or intensified shallow-water anoxia via increased nutrient input or shallower remineralization in the simulations.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6184

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