Abnormally warm-saline alkenone signature in Lake Tuosu in centennial cold-wet periods over the late Holocene: An exceptional case for alkenone application

Highlights: • Occurrence of alkenones from Lake Tuosu over the last ∼1200 years. • Abnormal warm and saline alkenone signals in the centennial cool-wet periods. • Opposite relation between alkenone records and virtue climates in Lake Tuosu. • Specie turn-over might be the reason for the abnormal warm-saline alkenone signals. Paleoclimatic reconstructions on the arid/semi-arid northern Tibetan Plateau are important for understanding the complex interactions between the mid-latitude westerly and subtropical Asian monsoon circulations. The development of paleoclimatic reconstructions largely relies on the invention and application of proper quantitative/semi-quantitative temperature and salinity proxies. Over the last few decades, alkenones have shown great potential as indicators of the past temperatures and salinities of lakes on the northern Tibetan Plateau. Several alkenone-based temperature and salinity records have confirmed centennial warm-dry and cold-wet variations during the Holocene on the northern Tibetan Plateau. Herein, we present alkenone-based records from Lake Tuosu in the Qaidam Basin over the last ∼1200 years. The alkenone signals show similar characteristics to published alkenone records in the nearby region during centennial warm periods (the Medieval Warm Period and Current Warm Period). However, the alkenones from Lake Tuosu demonstrate abnormally warm and saline signals during centennial cold periods (mainly during the Little Ice Age), in contrast to the widely recognized cold-wet conditions in the Qaidam Basin. Accordingly, the alkenone records from Lake Tuosu provide an exceptional case for the application of alkenones. The abnormally warm and saline alkenone signals from Lake Tuosu during centennial cold periods cannot be explained by either the presence of the C_37:3 alkenone isomer or seasonal bias in alkenone production. Changes in species composition might be an alternative reason for this, which requires a further investigation of the sources of alkenones in lakes in the future.