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

Compositional data on the sterol and alcohol fractions isolated from d eep-sea marine sediments from the Okinawa Trough were obtained to dete rmine the relative contribution from marine and terrestrial inputs. Fo llowing extraction, the total saponified neutral fraction was derivati zed 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-5,2 2E-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 com mon in diatoms. C29 sterols were dominated by sterols with 24-ethyl su bstitution of higher plant origin, but 23,24-dimethyl sterols which ar e found in some marine phytoplankton were also quite abundant. The maj or 4-methyl sterol was pha,23,24-trimethyl-5alpha-cholest-22E-en-3beta -ol which is considered a common indicator of dinoflagellates. Each st erol co-occurred with the corresponding 5alpha-stanol. Other indicator s of terrestrial input such as alpha- and beta-amyrin were also identi fied. 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 sedi ments, and they may be formed by the oxidation of the corresponding C3 0-C32 alkyl diols found in some marine microalgae. The thermal stabili ty of the compounds in these sediments was studied by heating portions of the surface sediment in glass tubes for 16 h at temperatures rangi ng from 100-degrees-C to 200-degrees-C. The C27 stanol/stenol ratio in creased with increasing temperatures up to 140-degrees-C, as did the c orresponding C28 and C29 stanol/stenol ratios. The keto-alcohols were more stable than sterols under these conditions.