中国科学院南京地质古生物研究所机构知识库

The Hirnantian carbon isotopic excursion (HICE) was characterized by a positive delta C-13 excursion (up to similar to + 7 parts per thousand) of oceanic dissolved inorganic carbon (DIC). However its mechanism remains controversial, impeding our understanding of this global event and its environmental significance. Here, we conducted a comprehensive analysis of global carbon-isotope records, based on 65 paleogeographically-widely distributed sections (4612 carbon-isotope data), documenting a steep oceanic DIC delta C-13 water-depth gradient (e.g., a 4.6 parts per thousand offset in the HICE excursion magnitude within Laurentia) during the Hirnantian Stage. We propose a hybrid hypothesis that the HICE records a shift toward more positive values owing to a large glacio-eustatic fall (>100 m) under the herein-identified steep delta C-13 water-depth gradient, with potential contributions from global-ocean delta C-13(DIC) changes and authigenic carbonates. This study provides the first large-data evidence for a widely density-stratified ocean during the Hirnantian Glaciation, with implications for reconstructions of ocean circulation and the carbon cycle during the Early Paleozoic.