Volcanism and basalt weathering drove Ordovician climatic cooling

Abstract Causal relationships among the major environmental and biological developments of the Ordovician Period (i.e., long-term climatic cooling, Hirnantian Glaciation, Great Ordovician Biodiversification Event, spread of bryophyte-grade land plants, and Late Ordovician Mass Extinction) remain in debate. Here, we present new data for volcanic activity, sea-surface temperatures, and chemical weathering intensity, based respectively on Hg geochemistry, conodont oxygen and strontium isotopes. This dataset documents a ~25-Myr-long interval of climatic cooling (ca. 470-445 Ma), which commenced around the Lower/Middle Ordovician boundary and intensified near the Middle/Upper Ordovician transition, ultimately culminating in the Hirnantian Glaciation. Cooling was associated with long-term intensified weathering of volcanic rocks (basalt) and drawdown of atmospheric pCO 2 , as well as periodic land plant expansion and photic-zone euxinia, during major volcanic intervals and their subsequent phases. These relationships implicate volcanic activity as the primary driver of contemporaneous environmental and climatic changes, with the spread of early land plants as a potential secondary influence, thus revealing complex modulation of life-environment coevolution during the Ordovician Period.