THE INTERACTION BETWEEN SILICATE WEATHERING AND CLIMATE CHANGE IN THE DEVONIAN

Chemical weathering of Ca- and Mg-bearing silicate minerals and the subsequent trapping of carbon in marine carbonates act as a sink for atmospheric CO₂, driving shifts in global climate on geologic time scales. However, the role of silicate weathering in the fluctuating paleoclimate of the Devonian Period (419 to 359 Ma) is only in the early stages of investigation. Previous paleotemperature studies suggest that sub-tropical sea surface temperatures (SST) cooled considerably during the Early to Middle Devonian before warming again in the late Middle Devonian. Potential drivers for these climatic shifts that have been proposed in the literature (e.g., Chen et al., 2021) include the radiation of early rooted plants (cooling), and Acadian Orogeny degassing (warming).

This study aims to clarify the interaction between silicate weathering and the cooling and warming trends of the Early to Middle Devonian. Strontium isotopes (⁸⁷Sr/⁸⁶Sr) can act as a geochemical proxy for changing patterns in silicate weathering, both from terrestrial and submarine sources. Marine conodont apatite samples from Požáry, Czech Republic (late Silurian to Early Devonian) and Pic de Bissous, France (late Middle Devonian) had previously been analyzed for sea surface temperatures using oxygen isotopes (Joachimski et al., 2009). We are analyzing these same samples for ⁸⁷Sr/⁸⁶Sr, creating two complementary geochemical curves with no temporal uncertainty between them. We have found that ⁸⁷Sr/⁸⁶Sr inflects toward more radiogenic values within 1 My of when δ¹⁸O shifts to lower values (warmer temperature) in the mid-Givetian (ca. 383 Ma), suggesting a link between silicate weathering and climate warming. We hypothesize that higher global temperature drove increased weathering of material uplifted during the Acadian orogeny. This hypothesis is supported by forward Sr box modeling that demonstrates a 5x10^-4 increase in the riverine flux’s ⁸⁷Sr/⁸⁶Sr value can reproduce the measured seawater ⁸⁷Sr/⁸⁶Sr curve.