A MESOZOIC PRELUDE TO THE ANTHROPOCENE: INTENSIFICATION OF THE HYDROLOGICAL CYCLE DRIVEN BY CAMP-INDUCED CO2 INJECTION

Global climate models of increasing pCO₂ predict an enhanced hydrological cycle coupled with warming, and amplification of the effects of orbitally-paced precipitation cycles. High-pCO₂ warm intervals during the hothouse Mesozoic world should display these effects and be analogues to our future greenhouse world. We present Late Triassic and Early Jurassic lithological, plant physiognomic, δ¹³C, soil carbonate pCO₂, and leaf wax n-alkane hydrogen isotopic (δD) data from both marine and non-marine records in eastern North America, Peru, and England, with an emphasis on the end-Triassic mass extinction (ETE).

Pre-ETE Rhaetian cyclicity is muted at all scales, consistent with a damped hydrological cycle under lower pCO₂ (<2,500 ppm) compared to the preceding Norian, whereas cyclicity is strongly enhanced during the ETE pCO₂ zenith (~5,000 – 6,000 ppm) caused by emissions from the Central Atlantic Magmatic Province (CAMP). Cyclicity variance drops again as pCO₂ declines (<2,000 ppm) during the earliest Jurassic Period, less than 1 million years after the extinction. Marine ⁸⁷Sr/⁸⁶Sr records suggest the Rhaetian pCO₂ minimum was driven by exposure and weathering of the volcanic Wrangellia oceanic plateau, whereas the increase in radiogenic Sr across the ETE was driven by globally enhanced continental weathering associated with the extreme high pCO₂, followed by Jurassic declines as weathering of CAMP basalts drove down ⁸⁷Sr/⁸⁶Sr and pCO₂. In some tropical rift valleys flooded by these basalts, lacustrine limestones were deposited after major CAMP pulses due to transient extreme local weathering. Pronounced variability in leaf wax δD across the ETE records variations in relative evaporation, tracking other environmental perturbations across the extinction interval, all suggesting strong coupling among the hydrological cycle, carbon pools and expression of orbitally paced cyclicity. Conifer leaf area and cuticular morphology show trends consistent with the changes in the hydrological cycle. Collectively, these data help confirm climate model predictions of an enhanced hydrological cycle with increasing pCO₂.