Solid Earth forcing of Mesozoic oceanic anoxic events

Abstract

Oceanic anoxic events are geologically abrupt phases of extreme oxygen depletion in the oceans that disrupted marine ecosystems and brought about evolutionary turnover. Typi cally lasting ∼1.5 million years, these events occurred frequently during the Mesozoic era, from about 183 to 85 million years ago, an interval associated with continental breakup and widespread large igneous province volcanism. One hypothesis suggests that anoxic events resulted from enhanced chemical weathering of Earth’s surface in a greenhouse world shaped by high volcanic carbon outgassing. Here, we test this hypothesis using a combination of plate reconstructions, tectonic-geochemical analysis, and global biogeo chemical modelling. We show that enhanced weathering of mafic lithologies during con tinental breakup and nascent seafloor spreading can plausibly drive a succession of anoxic events. Weathering pulses collectively gave rise to substantial releases of the nutrient phos phorus to the oceans, stimulating biological primary production. This, in turn, enhanced organic carbon burial and caused widespread ocean deoxygenation on a scale sufficient to drive recurrent anoxia. This model complements volcanic outgassing-centred hypotheses for triggering these events by demonstrating well-quantified basaltic sources of phospho rus release during periods of intense weathering related to climate warmth. Our study highlights a close coupling between the solid Earth and biosphere during continental reor ganisation.

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Identifiers

ORCID for T.M. Gernon: orcid.org/0000-0002-7717-2092

ORCID for T.K. Hincks: orcid.org/0000-0003-4537-6194

ORCID for E.J. Rohling: orcid.org/0000-0001-5349-2158

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