LIPID BIOMARKERS AND LATE QUATERNARY ORGANIC CARBON CYCLING AT LAKE ELIKCHAN, NORTHEAST SIBERIA

Sedimentary cores from Elikchan Lake, northeast Siberia, provide a continuous sequence of deposition for at least the last ~60,000 years (Lozhkin and Anderson, 1996). Palynological analysis indicates several marked shifts between forest and tundra dominated vegetation between 30,000 and 60,000 years ago (Lozhkin and Anderson, 1996). Recently, lipid biomarker concentrations of modern plants, a plankton tow, and core sediments from Elikchan Lake have been investigated to better understand organic matter sources, deposition and diagenetic effects within the catchment. Modern plants and a plankton tow were collected in 2001 and a fresh sediment core was collected from Elikchan Lake in 2002.

Higher plant leaf wax n-fatty acids (i.e., C24, C26, and C28) were present to varying degrees in all modern plants examined, including thirteen terrestrial plants and three aquatic macrophytes, and were not present in the plankton tow material. These results suggest that leaf wax n-fatty acids alone cannot distinguish between terrestrial plant and aquatic macrophyte sources. In the core sediments, shorter chained (i.e., C14, C16, C18) and unsaturated (i.e., C18) n-fatty acids decreased relative to the leaf wax n-fatty acids at all but two depths. Relative increases in shorter chained n-fatty acids were seen at ~6,000 and ~12,000 years ago. Preservation of these relatively labile compounds may reflect an increase in preservation potential of organic matter in the basin or an increase in input of aquatic sources to the site at ~6,000 and ~12,000 years ago. C/N ratios of the bulk sediments decrease initially and stabilize within the upper ~100 cm, indicating little change in preservation potential at the site through the last 30,000 years. Therefore, the increases in shorter chained n-fatty acids at 6,000 and 12,000 years ago may reflect increases in aquatic primary productivity. The n-fatty acid concentration data will eventually be coupled with d13C analysis and pollen data to further evaluate within basin shifts in carbon cycling correlated to climate change.

Reference Cited

Lozhkin, A.V., Anderson, P.M., 1996, A Late Quaternary Pollen Record From Elikchan 4 Lake, Northeast Siberia: Geology of the Pacific Ocean, v.12, p. 609-616.