Narrowing the Gap Between Early Deccan Traps CO2 Outgassing and pre-KPB Global Climate

A 2-4 °C warming episode that preceded the Cretaceous Paleogene boundary (KPB) mass extinction has been linked with the opening phases of Deccan Traps volcanism. Here, we use measurements of trace elements and CO₂ in melt inclusions to test the hypothesis that early Deccan magmatism triggered the Late Cretaceous warming interval. Using glassy, bubble-bearing melt inclusions hosted in magnesian olivines from early picritic basalts, we report CO₂ concentrations from NanoSIMS analysis of glass and Raman spectroscopy on vapor bubbles. Trace element proxies for CO₂, such as Ba and Nb, yield estimates of initial CO₂ prior to degassing. In conjunction with our melt inclusion data, trace element ratios support a range of CO₂ concentrations to higher values than prior estimates, with strong degassing beginning at the Moho or in the lower crust. However, our revised estimates of magmatic carbon inventories narrow but do not eliminate the gap between volcanic carbon outgassing and the carbon emissions. Based on scalings from carbon cycle modeling and estimates of preserved lava volumes from the Kalsubai and Lonavala subgroups of ~120,000 km³, we find that volcanic CO₂ outgassing alone remains insufficient to account for the magnitude of observed Late Cretaceous warming. Possible explanations for this 'missing' carbon include: (1) cryptic degassing, (2) degassing of sedimentary rocks, or (3) magma volumes not included in estimates based on preserved, onshore lavas. Unlike other Large Igneous Provinces, Deccan country rocks are not known to host significant masses of carbon-rich sedimentary lithologies. Consequently, we suggest that cryptic degassing or unaccounted-for magma volume constitute the best available explanations. Our results allow us to reconstruct the depths of carbon saturation and degassing histories in early Deccan magmas.