Preliminary biogeochemical characterization of sediments from Lake Sibinacocha, Peruvian Andes

High-elevation regions are particularly vulnerable to the physical and ecological consequences of global climate change. The high Andes are at the forefront of these changes due to their sensitivity to fluctuations in glacial mass and energy balance. In this study, we present a preliminary biogeochemical characterization of sediment cores from Lake Sibinacocha, Peru, which sits at 5,000m asl in a rapidly deglaciating catchment adjacent to the Quelccaya Ice Cap. Due to its remote location and large size, Sibinacocha's sediments have not been well studied to gain a paleoclimatological or paleoenvironmental understanding of the region. Gravity cores spanning 25 cm and roughly 300 years of sedimentation were taken in 2017 and 2018 from the northern section of the lake close to its glacial source. Initial investigations found that diatom populations have significantly changed throughout the past several centuries. We analyzed the sediment cores for bulk carbon and nitrogen content as well as isotope ratios using EA-IRMS to characterize geochemical changes. We find that bulk carbon, nitrogen, and δ¹³C are fairly constant until the mid-1800's. Around 1850, δ¹³C became more negative, and the concentrations of carbon and nitrogen increase, indicating substantial changes in productivity. Additionally, concentrations of sedimentary chlorophyll a (including its main diagenetic products) were found to be constant until the mid-1800's when they started to rapidly increase, also possibly indicating an increase in productivity. To contextualize these trends, we also present initial biomarker data, including analyses of fatty acids from plant waxes for their δD content and chain lengths in order to reveal variations in precipitation and flora over time, and fecal sterols in the sediment which shed light on the regional history of human and animal population change in the high Andes. Our results provide proof-of-concept for future reconstructions of the climate, flora, and fauna of the high Peruvian Andes over the past 300 years.