oa Bacteriohopanepolyols Track Environmental Transitions in the Black Sea

Bacteriohopanepolyols (BHPs) are structurally diverse compounds produced by a wide range of bacteria making them ideal candidates as chemotaxonomic biomarkers and indicators of bacterially driven biogeochemical processes in the geological record. In this study, we characterize BHP distribution changes in the Black Sea over the past 20 ka. Changes in BHP abundances follow four distinct periods, corresponding to previously defined phases of the Black Sea: (1) an oxic lacustrine phase where the Black Sea was disconnected from the global ocean (19.5 - 9.6 ka) and is characterized by nucleoside BHPs associated with high terrigenous inputs. (2) This is followed by a transition period during the initial influx of marine water into the basin (9.6 - 7.2 ka) and the presence of ubiquitous BHPs. Finally, the marine phase where the basin is permanently euxinic that is further divided into an (3) early marine phase (7.2 - 5 ka) where there is evidence of methanotrophs BHPs near the oxycline and (4) a late marine phase (5 ka to present) that is characterized by a decline of methanotroph-associated BHPs. This offers new insights into changes in microbial communities and biogeochemical processes in the Black Sea in response to hydrologic changes and oxygen conditions.