ORIGINS AND SIMULATED THERMAL ALTERATION OF STEROLS AND KETO-ALCOHOLS IN DEEP-SEA MARINE-SEDIMENTS OF THE OKINAWA TROUGH

Compositional data on the sterol and alcohol fractions isolated from deep-sea marine sediments from the Okinawa Trough were obtained to determine the relative contribution from marine and terrestrial inputs. Following extraction, the total saponified neutral fraction was derivatized with BSTFA and then analysed by capillary GC and GC-MS. A suite of C26-C29 stenols and stanols and C30-C32 keto-alcohols were identified in the sediments. Major sterols included 27-nor-24-methylcholesta-5,22E-dien-3beta-ol and cholest-5-en-3beta-ol, which are most likely from marine fauna, and the C28 sterols 24-methylcholesta-5,22E-dien-3beta-ol and 24-methylcholesta-5,24(28)-dien-3beta-ol, both of which are common in diatoms. C29 sterols were dominated by sterols with 24-ethyl substitution of higher plant origin, but 23,24-dimethyl sterols which are found in some marine phytoplankton were also quite abundant. The major 4-methyl sterol was 4alpha,23,24-trimethyl-5alpha-cholest-22E-en-3beta-ol which is considered a common indicator of dinoflagellates. Each sterol co-occurred with the corresponding 5alpha-stanol. Other indicators of terrestrial input such as alpha- and beta-amyrin were also identified. The sediments also contained significant amounts of the C30 keto-alcohol triacontan-15-one-1-ol, as well as smaller amounts of C31 and C32 keto-alcohols. These unusual lipids are found in many marine sediments, and they may be formed by the oxidation of the corresponding C30-C32 alkyl diols found in some marine microalgae. The thermal stability of the compounds in these sediments was studied by heating portions of the surface sediment in glass tubes for 16 h at temperatures ranging from 100-degrees-C to 200-degrees-C. The C27 stanol/stenol ratio increased with increasing temperatures up to 140-degrees-C, as did the corresponding C28 and C29 stanol/stenol ratios. The keto-alcohols were more stable than sterols under these conditions.