Using sterol biomarkers in paleoecological studies

Sediments from five contrasting stations in the western Mexican margin (Pacific Ocean) were investigated for sterol distribution and organic-walled dinoflagellate cysts (dinocysts). Sub-samples were taken from depths of 3-6cm and 16-27cm, representing different environmental conditions. In general, the sterol concentrations examined from these sites showed more advanced degradation in the deeper sediments compared to samples near the sediment-water interface. Using a molecular-level gas chromatography (GC) approach, 23 sterols of marine and terrigenous sources were identified in the natural samples. The major sterol components detected in most of these sediments were cholest-5-en-3β-ol (cholesterol), 24-methylcholesta-5,22E-dien-3β-ol (brassicasterol or dihydrobrassicasterol) and 24-Ethylcholesta-5,22E-dien-3β-ol (stigmasterol). This method also enabled the identification of a specific biomarker of a eukaryotic organism, 4{460},23,24-trimethyl-5{460}-cholest-22 E-en-3β-ol (dinosterol), indicating dinoflagellate inputs to marine sedimentary organic matte