| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 4704998 | Geochimica et Cosmochimica Acta | 2005 | 19 Pages |
Long-chain alkenones (LCK) of lacustrine surface sediments were analyzed in 37 lakes from China. The results obtained were complemented by published data from 13 other Chinese lakes. These lakes are located across large temperature and precipitation gradients, therefore allowing for an assessment of the distribution pattern of LCK and their temperature dependency. Different distribution patterns of LCK (C37 predominant pattern and C38 predominant pattern) were detected in the surface sediment samples. The ratio of C37:4 methyl ketone to the sum of C37 alkenones observed in the different lakes is highly variable (5%–96%, with mean value of 55%), and more than that seen in marine systems. The finding that some of the ocean LCK precursor algae (Gephyrocapsa oceanica, Coccolithus pelagicus) were also present in the limnic systems suggested that both systems might have similar biosynthetic sources. Empirical relationships between the alkenone unsaturation index U37k′ and different temperature sets (mean annual air temperature, mean annual air temperature in different seasons, and lake surface water temperature of July) were tested. The best correlation between U37k′ and temperature was obtained using mean annual air temperature. A general linear regression of U37k′ and MAAT can be expressed as U37k′ = 0.0328 × T + 0.126 (n = 38, r2 = 0.83). Although questions such as species-uncertainty and other unknown factors for U37k′ temperature dependence still remain, the equation might be representative of the average contribution of LCK to sediments for these data over a wide range of surface temperatures, water chemistry and different alkenones-producer algal populations. The general relationship of U37k′ and mean annual air temperature is consistent with that in marine systems. It supports the suggestion that the biosynthetic pathway of alkenones and the mechanism of their temperature signal may be similar in both marine and limnic systems. LCK might be used as an important paleotemperature proxy in limnic environment.
