Carbonate-associated sulfate (CAS) refers to trace sulfate structurally substituted into carbonate lattices and serves as a faithful archive of ancient seawater sulfate, regulating the biogeochemical cycles of sulfur, oxygen, and carbon. High-dimensional isotopic compositions, particularly massindependent fractionation effects, have established CAS as a premier proxy for reconstructing ancient atmospheric and oceanic conditions. Here I review the fundamentals of CAS formation and preservation, persistent analytical and interpretive challenges, and advances in applications of highdimensional isotope systematics. I argue that integrating sequential extraction protocols with multiisotope measurements allows for robust screening of diagenetic overprints and contamination.Methodological and conceptual developments have propelled CAS research through three critical transitions: from isolated data points to continuous chemostratigraphic records; from single-proxy reliance to integrated multi-isotope frameworks; and from qualitative interpretations toward rigorous, quantitatively constrained models. By synthesizing high-dimensional isotopic data with biogeochemical modeling and complementary geochemical proxies, CAS emerges as a powerful tool for deciphering Earth's oxygenation history, atmosphere-ocean redox feedbacks, and the coevolution of life and planetary habitability.
Yongbo Peng (Sun,) studied this question.