Forced changes in a Tibetan lake ecosystem over the past millennium.

Aquatic ecosystems have changed dramatically, but the relative roles of external forcings and internal atmospheric variability remain unclear. Here, using Tibetan lake ecological reconstructions and Earth system simulations, we reveal how shared external forcings shaped Tibetan Plateau limnoecology over the past millennium through two distinct pathways. In the temperature-centric pathway, cooling episodes driven by volcanic activity and internal variability likely regulated preindustrial lake conditions. This baseline was disrupted as recent forced warming has shortened lake ice-cover and increased meltwater input, altering lake resources and triggering unprecedented diatom shifts. In the freshening-centric pathway, salinity-tolerant diatoms tracked monsoon-driven precipitation changes and lake freshening, both governed by shifts in the intertropical convergence zone. Preindustrial shifts likely reflected hemispherically asymmetric orbital and volcanic forcings, whereas modern changes have been altered remarkably by Northern Hemisphere industrial aerosol fluctuations and warming-induced meltwater. As multifaceted stressors intensify, Tibetan lake ecosystems may continue diverging from their natural variability.