91 / 2025-03-31 17:21:45

Terrestrial arid climate and soil nitrate fluxes in South China during the phanerozoic: New evidence from shale nitrate isotopes

nitrate isotopes,nitrogen cycle,arid paleoclimate,Black shale

Theme 4: Microbial and Biogeochemical Evolution through Time > Session 4b: Roles of Microbes in Shaping Our Habitable Earth

Climate changes are known to have been a key regulator of the structure and function of terrestrial ecosystems in Earth's history. Although sedimentary records such as plant fossils, coal, and evaporites qualitatively indicate climate variability, the arid-humid degrees and alternating patterns throughout the Phanerozoic remain largely unconstrained. Moreover, nitrogen (N) cycling is crucial information for understanding responses of biota to arid climates. However, it remains unclear whether and how key soil N-cycling processes respond to aridity under arid paleoclimates. This study established a method for analyzing the nitrate (NO₃^-) content and isotope (δ¹⁵N, δ¹⁸O, and ∆¹⁷O) in black shale using the denitrifier method (Sigman et al., 2001; Liu et al., 2018) and applied it to the Early Cambrian Niutitang Formation at the Pingyin section of South China (Fan et al., 2024). By constructing an oxygen-isotope-based model to reconstruct paleo-aridity degrees and a N-isotope-based quantitative model to evaluate soil NO₃^- production-consumption processes (microbial nitrification, denitrification, and assimilation), we quantified the aridity degrees of South China during the Phanerozoic with 10-million-year resolution and investigated the relationship between soil NO₃^- flux and the aridity degrees under arid paleoclimates. This provides the basis for simulating N cycles in current and future arid climates and enriching the understanding of the co-evolution of climate and surface processes in Earth's history.