THE INFLUENCE OF VOLCANICALLY DRIVEN CLIMATE CHANGE ON PHANEROZOIC BIODIVERSITY

Prominent shifts in baseline climate states can have dramatic effects on the biosphere. These climatic shifts are driven by changes in the partial pressure of atmospheric carbon dioxide (pCO₂), which on multimillion year timescales is controlled by the long-term carbon cycle: whereas silicate weathering and the burial of organic matter serve as the principal CO₂ sinks, metamorphic and volcanic degassing are the primary sources. Whether it is the sources or sinks of the long-term carbon cycle that exert the dominant control on pCO₂ remains a topic of debate. Continental magmatic arc systems, in particular, can produce large CO₂ fluxes by releasing CO₂ from bedrock reservoirs in the upper crust; accordingly, we evaluate the spatial distribution of continental arcs over the last ~720 Myr—as evidenced in the zircon record—in relation to major icehouse-greenhouse transitions and biodiversity. We demonstrate a first-order correlation between continental arc distribution and shifts in Earth’s climate state, which profoundly influenced biodiversity. Intervals of spatially reduced continental arcs correspond with major icehouse climates, including the Cryogenain snowball Earth events, glaciations associated with the end-Ordovician extinction, and the late Paleozoic Ice Age. Intervals of extensive continental arcs correspond with greenhouse climates characterized by periods of environmental stress with expansive oceanic anoxia and mass extinctions (e.g., the early Paleozoic and Mesozoic), and to a lesser extent, relatively brief global-scale magmatic flare-ups may influence end-Permian biological crises. While arc volcanism does not directly cause all individual extinction events, the large CO₂ fluxes from continental arcs increase atmospheric CO₂ and baseline climate such that the effects of perturbations to the Earth surface system (e.g. Large Igneous Province eruptions) may be amplified to trigger mass extinctions. Quantitative carbon cycle modeling (using LOSCAR) provides support for the model that variation in the volcanic CO₂ flux plays a major role in shaping Earth’s climatic evolution.