Marine Anoxia and Ocean Acidification During the End-Permian Extinction: An Integrated View From δ²³⁸U and δ^44/40Ca Proxies and Earth System Modeling

The largest mass extinction event in the Phanerozoic, known as the end-Permian mass extinction (or EPME, ca. 252 Ma) is coincident with the main eruption phase of Siberian Traps volcanism (ca. 252 to 250 Ma), a large igneous province (LIP). This LIP is estimated to have a volume larger than 2 × 10⁶ km³ and to have released both mantle carbon dioxide (CO₂) through extrusions and thermogenic methane (CH₄) and carbon dioxide (CO₂) through intrusions. The climatic consequences of these greenhouse gases is detrimental to both marine and terrestrial life and may have delayed the recovery of ecosystems after the extinction. Quantitatively, the amount of CO₂ released can be estimated using global carbon (C) cycle model or plant and soil-based proxies with varying time resolution. In light of the recent advances in geochemical proxies of ocean anoxia and acidification, we review the latest uranium isotopes (δ²³⁸U) and calcium isotope (δ^44/40Ca) records and Earth system modeling results to summarize the environmental response to the forcing of increased atmospheric CO₂ concentrations. The extent of increase in oceanic anoxic area can be estimated by δ²³⁸U, and the δ^44/40Ca records may be used to evaluate ocean acidification. This evidence suggests that excessive nutrient load in the ocean (decreased strength of meridional overturning circulation) and ocean acidification in poorly buffered seawater (potentially triggered by the Siberian Traps LIP) worked together to create the most severe biological crisis and delayed recovery of life in the Earth’s history.