PROGLACIAL LAKE SEDIMENT RECORDS OF CONTEMPORARY CLIMATE CHANGE IN LAKE SHALLAP, CORDILLERA BLANCA, PERU

Tropical glaciers are particularly responsive to climatic changes and have experienced rapid retreat in the last century. In the Cordillera Blanca range of the Peruvian Andes, glacier retreat poses risks to over 2 million people who rely on glacial meltwater for their potable water supply. While most paleoclimatic records from the region emphasize large-scale changes over the Holocene, few authors have specifically examined the paleoclimatic record of the last century and its effect on glacial processes. Moreover, the effect of the El Niño Southern Oscillation (ENSO) on tropical glaciers is poorly understood, owing largely to its place-specificity. We examined a 100-year sediment record obtained from the proglacial Lake Shallap in the Cordillera Blanca to evaluate the effects of recent climate change and ENSO on glacial activity and meltwater quality. X-ray fluorescence analysis of cored sediment indicates that geochemical proxies for terrigenous sediment, iron, and sulfure content have risen in the last century, with a significant increase in both magnitude and variability from the 1980s to present. The drastic increase in terrigenous sediment input suggests rapid glacial retreat since the 1980s, which aligns with a period of greater frequency and intensity of warm, dry El Niño conditions. A strengthening of El Niño conditions can exacerbate glacial retreat by reducing precipitation required for snow accumulation and raising ablation rates. We interpret the associated rise in iron and sulphur content as a function of increased weathering of the pyritic bedrock exposed by the retreating glacier, which acidifies and contaminates meltwater. Our findings suggest that recent climate change, exacerbated by ENSO events, has resulted in rapid glacial retreat in the Cordillera Blanca, particularly since the 1980s. This retreat has also caused meltwater runoff and water quality to decrease and threatens the sustainability of water resources for nearby communities.