Photosynthetic pigments in marine sediments provide useful information concerning water column and benthic plants and microbial communities in marine accumulated sediments. They are important chemical biomarkers which can characterize certain biotic sources and retain their source information after burial in sediments, even after some alteration.
Pigments in marine sediments mainly come from pelagic and benthic algae communities, phototrophic bacteria and aquatic higher plants, and others come from terrestrial environment. Exposure to direct light, warm temperatures (>0℃), pH extremes, and enzymes should be avoided because pigments are labile and can degrade fast in the above environments. All sediment samples should be frozen at -20℃ or colder as soon as possible after sampling and stored at this temperature without additional treatment (e.g., freeze-drying) until just before the analysis of pigments. Since no extraction method is suitable to all kinds of sediments, it is necessary to optimize the extraction method according to the properties of sediment samples. Since 1980, High Performance Liquid Chromatography (HPLC) analyses have become the method of choice for rapid, quantitative determinations of carotenoid, chlorophyll and derivative content in aquatic ecosystems and their sediments.
Pigments can degrade both in water column and sediment. The degradation rates of pigments can be affected by both their inherited natures and external factors. Usually, pigments undergo different phases of degradations, while they deposit from water columns to sediment-water interfaces, and till to the deep sediments. The degradation products of chlorophylls are more stable than their parents; the carotenoids with 5,6-epoxide function are more labile than those without this function.
As biomarkers, sedimentary pigments can be used to ①characterize the composition and abundance of phytoplankton communities and their historical changes; ②reflect the primary production and status of eutrophication; ③trace the sources and fates of organic matter; and ④indicate hypoxia events. It is a good choice to combine sedimentary pigments with other marine environmental parameters, such as, biogenic silica, total organic carbon, total nitrogen, ratio of C/N, δ13C and δ15N. These kinds of multiproxy studies have been shown to be a reliable way of describing ecological status changes within a system. The researches on sedimentary pigments have implications for ①understanding the processes of biogeochemical cycles of carbon in marine sediments;②reconstructing the records of palaeoenvironment, paleoceanography, palaeoclimatology, palaeoecology; and ③formulating reasonable ocean management policies.