The latest Devonian glaciation represents a significant climatic cooling event in the Late Paleozoic, characterized by a rapid decline in global temperatures and an expansion of ice sheets, accompanied by marine mass extinction event (Hangenberg Crissis). However, a systematic understanding of marine biogeochemical cycling during the Devonian-Carboniferous boundary and its response to climatic changes remains elusive. Here, we focus on the Long’an, Qilinzhai, and Malanbian sections in South China, which was depostied in the shallow water environment. Through high-resolution bulk nitrogen (δ¹⁵N_bulk), carbonate-associated sulfur (δ³⁴S_CAS) isotopic analyses, and iodine-to-calcium ratios (I/Ca), our findings indicate significant changes in isotopic compositions during the Hangenberg Crisis interval, accompanied by a sharp negative shift in δ¹⁵N_bulk, δ³⁴S_CAS, and carbonate I/Ca values. These geochemical indicators collectively suggest a marked intensification of oceanic anoxia, with the expansion of the oxygen minimum zone (OMZ) in response to the global cooling. These studies will provide new insights into the evolution of marine biogeochemical cycles in response to global cooling events.
 

Nitrogen cycle; Sulfur cycle; Paleo-Tethys Ocean; Mass extinction; Glaciation