text: Bacteria such as green sulfur bacteria and purple sulfur bacteria, which exist where the photic zone overlaps with euxinic water masses, leave pigments behind in sediments. These pigments can be used to identify past euxinic conditions. The pigments used to identify past presence of green sulfur bacteria are chlorobactane and isorenieratene. The pigments used to identify past presence of purple sulfur bacteria is okenane.