Diagenetic environments indicated by key metal element systems in cold seep sediments

Cold seep activity is a significant manifestation of seafloor methane seepage, playing a crucial role in global carbon cycling and the geochemical processes of extreme marine environments. Reconstructing early diagenetic environments using metal element systems in cold seep sediments is the key for understanding the biogeochemical processes and revealing the characteristics and historical evolution of methane seepage activities. This review systematically expounds on the biogeochemical behaviors of main metal element systems (Fe, Mn, Ni, Cu, Zn, Cd, As, Hg, Mo, W, U, Ba, and REE) in cold seep environment and synthesizes the applications of their representative proxies in cold seep research. Current research focuses primarily on two scientific aspects: revealing the evolution of complex redox conditions dominated by methane seepage and tracing the specific biogeochemical processes closely linked to the cold seep systems, particularly microbial metabolic activities. This study emphasizes that due to the multiple impacts of different diagenetic processes within cold seep systems, the application of any single element proxy has its limitations. Therefore, the integrated application of multi-proxy systems in combination with detailed analysis of the geological background is crucial for accurate interpretation of environmental information. Future research shall focus on the application of high-resolution in-situ microanalytical techniques and metal stable isotope systems.