Middle-late Devonian warming and land plant evolution drive changes in silicate weathering: A new 87Sr/86Sr conodont record paired with δ18O

The Devonian Period (419 to 359 Ma) is marked by a shift from cooling in the Early Devonian to warming in the Middle-Late Devonian. Previous studies have hypothesized that an increase in metamorphic degassing during the Acadian Orogeny caused the late Givetian warming. Alternatively, a reduction in physical erosion leading to reduced silicate weathering could have increased pCO2 and contributed to warming. Previous studies show that the 87Sr /86Sr curve of the Middle Devonian (late Givetian) increases (i.e., more granitic) around the same time as warming based on δ18O using brachiopod calcite. We present new Middle to Late Devonian 87Sr /86Sr and δ18O data from conodont apatite and confirm this link between warming and rising 87Sr /86Sr using paired analyses from a single measured section whereas previous studies relied on compiling data from different sections that did not individually capture the baseline values and subsequent shifts in proxies. We integrate these datasets into the SCION climate-biogeochemical model and determine that the hypothesized magnitude of metamorphic degassing could neither reproduce the seawater 87Sr/86Sr ratio nor explain the extent of low-latitude warming (δ18O) observed in the geologic record. An alternative warming mechanism is rising atmospheric pCO2 due to reduced physical erosion and silicate weathering related to land plant colonization. Regional uplift of high 87Sr/86Sr rocks in the Acadian orogeny may have driven the increasing seawater 87Sr /86Sr ratio.