The Tibetan Plateau (TP) is essential for evaluating global ecological impact through tracing the mercury (Hg) source and transformation in its lake sediments. Cuona Lake, situated at the transition zone of the Indian summer monsoon (ISM) and the westerlies, provides an ideal natural archive for understanding long-term interactions between Hg deposition and climate change. Our results show that temporal variations of Hg accumulation in a sediment core CN12/01 are influenced by distinct atmospheric patterns since 13 cal ka BP. During similar to 13-8 cal ka BP, elevated triangle Hg-200 and higher smectite/illite ratios indicate that intensified summer monsoon rainfall enhanced atmospheric Hg contributions (41 +/- 7%). Increased Zr/Rb ratios coupled with decreased total Hg concentrations (THg) suggest that fine particulates carrying soil-eroded mercury preferentially export downstream. In contrast, during 6-3 cal ka BP, the climatic pattern of the studied area is mainly controlled by the westerlies, showing relatively weakened precipitation associated with depleted triangle Hg-200 and lower smectite/illite ratios. However, enhanced accumulation of fine particulates (low Zr/Rb ratios) and THg concentrations during this period indicates increased terrestrial mercury retention in the lake sediments. This study proposes that Cuona Lake shifts from functioning as a Hg "transporter" to a "sink" at approximately 6 cal ka BP, coinciding with the climatic transition of ISM-westerlies patterns. This shift represents an important process in regulating the mercury cycle of the terrestrial ecosystems in the TP.