PERSISTENT LATE PERMIAN TO EARLY TRIASSIC WARMTH LINKED TO ENHANCED REVERSE WEATHERING

Chemical weathering and reverse weathering are two critical processes controlling biogeochemical cycles of silicon and carbon. Geochemical and stratigraphic records suggest that these processes might have varied considerably during the Permian to Early Triassic period influencing biogeochemical cycles during this critical interval of Earth’s history. Here we present newly derived seawater lithium and strontium isotope records of bulk carbonates and fossil brachiopods spanning the Permian to Early Triassic period (300 Ma to 247 Ma). The lithium isotope composition of seawater remained constant for most of the Permian until a sharp decrease in the Changhsingian (~ 254 – 252 Ma), reaching a minimum value of around 5‰ near the Permian-Triassic boundary (PTB, ~ 251.92 Ma). This decline occurred several million years prior to the PTB but low seawater Li isotope values (~10‰) persisted throughout the Early Triassic. Based on steady-state box modeling of the marine Li isotope budget, changes in the fluxes and isotopic composition of Li inputs alone (i.e., chemical weathering and hydrothermal) are unable to explain the abrupt decline in seawater Li isotopes. Rather, increased reverse weathering rates could explain the failure of chemical weathering to drawdown atmospheric CO₂ levels during the Early Triassic leading to protracted biotic recovery from the Permian-Triassic mass extinction.