Climate driven Holocene variations in lipid biomarkers from Shenmihu Lake, Northeastern Taiwan

Lake sediment provides information on hydrogeological and environmental conditions. It contains a wide range of physical, chemical, and biological archives that could be used to reconstruct paleoclimatic trends and shifts. Applying lipid biomarker proxies to lake sediment is widely used to reconstruct past conditions. However, it is also essential to consider the stages of lake evolution. In particular, a lake that is surrounded by steep slope topography potentially has a mix of watershed and water body organic material sources. In this study, we aim to disentangle terrestrial and aquatic organic matter sources using a range of lipid biomarker proxies.

Shenmihu Lake is located in the mountains near Yilan, northeastern Taiwan, about 1000 meters above sea level, and surrounded by steep slopes and ephemeral creeks containing loose gravel that may be transported to the lake by rain or extreme weather (torrential rain, typhoon, etc.). A 9,78m long composite core was retrieved from the lake using a Russian corer, and sub-samples were taken every 20 cm from the core. The bottom part of the core was radiocarbon dated to about 10700 BP, and the age model suggests continuous sedimentation spanning the entire Holocene. The Carbon Preference Index (CPI) and Paq ratio can be used to distinguish organic material sources from terrestrial, emergent, or submerged macrophytes. The preliminary result showed that organic materials of around 8000 and 6700 BP were dominated by floating macrophytes, indicating that water fully covered the lake. A better understanding of lake succession and lake internal processes is necessary to allow extracted paleoenvironmental archives to be compared to regional and global climate records.

Keywords: Lipid biomarker, lake sediment, Russian core, Asian monsoon