<b>MZ section AMS</b>^{<strong>14</strong>}<b>C age and proxy record data set</b>

The Holocene climatic optimum has been widely documented in northern China and eastern Central Asia. In this study, we present evidence for twin climatic optima since the Last Deglaciation (LD) in the northern Qinghai–Tibet Plateau (QTP). Based on a newly obtained lake sediment record from the Shule River Basin, located on the northern margin of the QTP, we reconstructed the lake evolution history through a combination of proxy indicator analysis, paleoclimate simulations, lake hydrological modeling, and synthesis of regional paleoclimate records. This integrated approach clarifies the spatial distribution of the bimodal lake-level pattern across the QTP, evaluates multiple hypotheses for the elevated lake levels during the LD, and identifies previously unrecognized driving mechanisms. The results indicate that the Shule River Basin experienced pronounced lake expansion during both the LD and the Middle Holocene (MH). This twin-peak climatic pattern was widespread across the QTP and adjacent regions. Enhanced summer monsoon precipitation was the primary driver of the MH climatic optimum, whereas the LD optimum was shaped by the combined effects of glacial meltwater input, increased summer solar radiation, and reduced evaporation.