Volume and rate of volcanic CO₂ emissions governed the severity of past environmental crises

The emplacement of large igneous provinces (LIPs) has been linked to catastrophic mass extinctions in Earth's history, but some LIPs are only associated with less severe oceanic anoxic events, and others have negligible environmental effects. Although it is widely accepted that massive magma outpouring can affect the environment through volatile degassing, it remains debated what controls the severity of environmental crises. Here, we demonstrate that the second-most-voluminous Phanerozoic LIP, the Kerguelen LIP, may have contributed to the early Aptian oceanic anoxic event 1a, a global event previously believed to have been caused by the Ontong Java LIP. Geochronological data show that the earliest eruptions of the Kerguelen LIP preceded the onset of oceanic anoxic event 1a by at least ∼5 million years. Analyses of CO₂ abundances in melt inclusions combined with Monte Carlo simulations reveal that the volume and degassing rate of CO₂ emissions from the Kerguelen LIP are an order of magnitude lower compared to LIPs that caused severe mass extinctions. We propose that the severity of volcanism-related environmental and biotic perturbations is positively correlated with the volume and rate of CO₂ emissions. Our results highlight the significant importance of reducing and slowing down CO₂ emission in preventing future disastrous environmental consequences.