Calibration of alkenone unsaturation index with growth temperature for a lacustrine species, Chrysotila lamellosa (Haptophyceae)

Although long chain alkenones (LCKs) occur widely in lacustrine sediments, their origin is not clear. Here, we report a lacustrine source, the non-calcifying species Chrysotila lamellosa Anand (Haptophyceae), collected and isolated from an inland saline water body, Lake Xiarinur (Inner Mongolia, China). Its alkenone pattern is similar to those of coastal marine strains of C. lamellosa,but the relationship between U37K′ index and culture temperature for the lacustrine species is quite different from that of the coastal species. A significant feature of the alkenones in this strain of C. lamellosa is a lack of C38 methyl alkenones, which might be used to distinguish the species from the marine haptophyte species Emiliania huxleyi and Gephyrocapsa oceanica. The higher C38 tetraunsaturated compound abundance might be another important feature for distinguishing the C. lamellosa alkenone producer from the coastal species Isochrysis galbana. This alkenone distribution pattern has been detected in many lakes, which suggests that C. lamellosa or a closely related species might be a very common alkenone precursor in lacustrine systems. We examined U37K′ and U37K values for C. lamellosa as a function of culture temperature in a batch culture experiment. The calibration for U37K′ vs. culture temperature (T) was U37K′=0.0011×T2-0.0157×T+0.1057(n=14,r2=0.99) from 10 °C to 22 °C or U37K′=0.0257×T-0.2608(n=9,r2=0.97) from 14 °C to 22 °C. U37K vs. culture temperature was U37K=0.0377×T-0.5992(n=14,r2=0.98) from 10 °C to 22 °C. Our experiments show that the alkenone unsaturation index (U37K′) is strongly controlled by culture temperature and can be used for palaeoclimate reconstruction.