The application progress of BHT-x as biomarker to marine hypoxia

Marine hypoxia is one of the major ecological and environmental problems at present as it has important impact on marine organisms, chemical element cycle, and global climate. Bacteriohopanepolyols (BHPs) are a group of pentacyclic triterpenoid compound derived from bacterial cell membranes, and also the biological precursor of hopane that are ubiquitous in geological records. BHPs have been widely used as a biomarker in tracing terrestrial organic matter and indicating aerobic methane oxidation. By focusing on bacteriohopanetetrol (BHT)-x, an important member of BHPs that could be used to indicate anaerobic ammonia oxidation and water hypoxia, we reviewed its biological origination and the verification, and briefly introduced the application of the BHT-x ratio (the ratio of BHT-x over total BHT) as a proxy of water column hypoxia for different marine environments, including samples of suspended particles and sediments. The application of BHT-x could help us reconstruct marine hypoxia evolution, and predict and protect the modern marine environment with richer theoretical evidence.