Diversification to extinction: oceanic and climatic context of the Ordovician

The Ordovician (470–443 Ma) witnessed an epic evolutionary trajectory, from the Great Ordovician Biodiversification Event (GOBE) to the Late Ordovician Mass Extinction (LOME), marking an unprecedented rise and fall in biodiversity. Complex interactions among climate, ocean, and geological events, drove fluctuations in the carbon cycle and environmental heterogeneity. Here, we review key developments within this interval pertaining to biological evolution, elemental cycling, climate change, atmospheric composition, and marine redox structure and their mutual interactions. We employ the Community Earth System Model (CESM) to explore the factors underpinning the biotic turnover with a resolution of 10-Myrs time slice. Our simulations suggest that increased organic carbon burial triggered long-term cooling culminating in the Hirnantian ice age, carbon isotopic perturbations, alongside rising atmospheric oxygen and declining CO₂. On a secular scale, oxic oceanic water masses expanded worldwide, while the continental seas of the low-latitude landmasses remained oxygen-depleted. The results correspond to a destabilization of oceanic structure with La Niña-like enhanced upwelling in the equatorial region of western flank of Gondwana. This heterogeneous redox structure and reorganization of oceanic currents potentially marked the consequence of one of the most fundamental oceanic oxygenation processes throughout Earth history. This environmental heterogeneity also explains and reconciles discrepancies in estimates of the GOBE duration derived from different palaeobiological databases. Our review and simulations consistently support a dynamic interplay between environmental changes and biotic evolution during the Ordovician.