A molecular and stable carbon isotopic study of lipids in late Quaternary sediments from the Arabian Sea

The distribution of apolar and polar lipids and their stable carbon isotopic compositions were determined for a number of sediment samples from different sites in the Arabian Sea. Lipids are mainly derived from planktonic Archaea and a range of algae, including Haptophytes, Eustigmatophytes and diatoms. The stable carbon isotopic compositions of compounds from diatoms, highly branched isoprenoids, fall into distinct groups suggesting other sources beside the diatom species Rhizosolenia setigera for these compounds. High amounts of sterol ethers, which may be derived from diatoms, were also detected. A recently identified triterpenoid, malabaricatriene, was also present in high abundance in these samples. The terrestrial input of lipids consists of n-alkanes and their carbon isotopic compositions show that they are derived from aeolian dust input from the Arabian Peninsula. The isotopic compositions of C37 alkenones from two cores during the last 15 ka is relatively constant and suggests that growth conditions for Haptophyte algae (averaged over 500 years) did not change significantly over this period.