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 isotopi c compositions were determined for a number of sediment samples from differ ent sites in the Arabian Sea. Lipids are mainly derived from planktonic Arc haea and a range of algae, including Haptophytes, Eustigmatophytes and diat oms. The stable carbon isotopic compositions of compounds from diatoms, hig hly branched isoprenoids, fall into distinct groups suggesting other source s beside the diatom species Rhizosolenia setigera for these compounds. High amounts of sterol ethers, which may be derived from diatoms, were also det ected. A recently identified triterpenoid, malabaricatriene, was also prese nt in high abundance in these samples. The terrestrial input of lipids cons ists of n-alkanes and their carbon isotopic compositions show that they are derived from aeolian dust input from the Arabian Peninsula. The isotopic c ompositions of C-37 alkenones from two cores during the last 15 ka is relat ively constant and suggests that growth conditions for Haptophyte algae (av eraged over 500 years) did not change significantly over this period. (C) 2 000 Elsevier Science Ltd. All rights reserved.