Source characterisation of Sedimentary organic matter in mangrove ecosystems of northern Kerala, India: Inferences from bulk characterisation and hydrocarbon biomarkers

Surface sediment samples from five mangrove ecosystems along the Kerala coast, north of Kochi were analysed for elemental ratios, stable isotopes of carbon and hydrocarbon biomarkers (n-alkanes, n-alkenes and hopanes) to assess the sources and early diagenesis of sedimentary organic matter. The elemental and isotopic ratios along with sedimentary chlorophyll a content, suggested substantial contribution of planktonic organic matter apart from mangrove/terrestrial derived organic matter. The sources of organic matter showed variability in relation with the geographical setting of mangrove systems as well as with seasons. The n-alkanes in mangrove sediments consist of organic matter derived from varying contributions of planktonic, bacterial and terrestrial sources. The distributional features of n-alkanes with low molecular weight (