The end-Triassic extinction (ETE) is one of the most severe biotic crises in the Phanerozoic. This event was synchronous with volcanism of the Central Atlantic Magmatic Province (CAMP), the ultimate cause of the extinction and related environmental perturbations. However, the continental weathering response to CAMP-induced warming remains poorly constrained. Strontium isotope stratigraphy is a powerful correlation tool that can also provide insights into the changes in weathering regime but the scarcity of 87Sr/86Sr data across the Triassic-Jurassic boundary (TJB) compromised the use of this method. Here we present new high-resolution 87Sr/86Sr data from bulk carbonates in Csővár, a continuous marine section that spans 2.5 Myrs across the TJB. We document a continuing decrease in 87Sr/86Sr the from the late Rhaetian to the ETE, terminated by a 300 kyr interval of no trend and followed by a transient increase in the early Hettangian that levels off. We suggest that the first in the series of perturbations is linked to the influx of non-radiogenic Sr from the weathering of freshly erupted CAMP basalts, leading to a delay in the radiogenic continental weathering response. The subsequent rise in 87Sr/86Sr after the TJB is explained by intensified continental crustal weathering from elevated CO2 levels and reduced mantle-derived Sr flux. Using Sr flux modeling, we also find support for such multiphase, prolonged continental weathering scenario. Aggregating the new dataset with published records employing an astrochronological age model results in a highly resolved Sr isotope reference curve for an 8.5 Myr interval around the TJB.

A document by Yoshiki Kanzaki. Click on the document to view its contents.

Significant interest and capital are currently being channeled into techniques for durable carbon dioxide removal (CDR) from Earth’s atmosphere. A particular class of these approaches — referred to as enhanced weathering (EW) — seeks to modify the surface alkalinity budget to store CO2 as dissolved inorganic carbon species. Here, we use SCEPTER — a reaction-transport code designed to simulate EW in managed lands — to evaluate the throughput and storage timescales of anthropogenic alkalinity in agricultural soils. Through a series of alkalinity flux simulations, we explore the main controls on cation storage and export from surface soils in key U.S. agricultural regions. We find that lag times between alkalinity modification and climate-relevant CDR can span anywhere from years to many decades locally but can aggregate to shorter timescales depending on deployment region. Background soil cation exchange capacity, agronomic target pH, and fluid infiltration all impact the timescales of CDR relative to the timing of alkalinity input. There is likely scope for optimization of weathering-driven alkalinity transport through variation in land management practice. However, shifting management practices to reduce lag times will likely decrease total CDR from weathering and lead to non-optimal nutrient use efficiencies and soil nitrous oxide (N2O) fluxes. Although CDR lag times will be more of an issue in some regions than others, these results have significant implications for the technoeconomics of EW and the integration of EW into voluntary carbon markets, as there may often be a large temporal disconnect between deployment of EW and climate-relevant CDR.