Occurrence of extended chain length C41 and C42 alkenones in hypersaline lakes

The chain length of long chain alkenones (LCAs) in ocean and lake sediments commonly ranges from C37 to C39. Alkenones > C40 are extremely rare: C41 and C42 alkenones have only been reported in a Cretaceous black shale (Cenomanian, ca. 95 Ma) from the Blake Bahama Basin, western North Atlantic (DSDP Leg 76, site 534). The significance of these exceptionally long chain alkenones is, however, unclear. We have conducted a systematic survey of LCAs in surface sediments from 12 lakes with a wide range of salinity (0.7-146.3 g/l) from arid northwestern China. They showed a general trend of increasing maximum chain length with increasing salinity. In particular, C41 and C42 LCAs occurred only in the surface sediments of hypersaline lakes (113.6-146.3 g/l), but were absent from lakes with lower salinity, indicating that these compounds may be produced by an unknown haptophyte species living in hypersaline environments.