Responses of lake diatoms to rapid 21st century warming on the southeastern Tibetan Plateau

Many paleolimnological studies from the Northern Hemisphere have shown how diatom assemblages preserved in dated lake sediment cores have responded to anthropogenic climate warming over the past ~100 years. In contrast, diatom records from lakes in the southeastern Tibetan Plateau have typically registered minimal compositional change during this recent period of warming. Site-specific conditions can dampen the biological response to regional climate change in this topographically complex mountain landscape. In this study, we used a 210Lead/137Cesium-dated sedimentary diatom record collected in 2018 from a remote, oligotrophic, alpine lake (Cuomujiri Lake) in the southeastern Tibetan Plateau to track environmental changes during the past ~100 years. Change-point analysis on air temperature trends from the nearby Nyingchi meteorological station and from across the Tibetan Plateau (composite of 150 stations) showed exceptionally rapid and statistically significant warming since 2004 CE, although localized variations exist in this heterogeneous region. Concurrent with this pronounced temperature rise, the Cuomujiri diatom record registered an abrupt shift from a benthic to a planktonic-dominated assemblage for the first time in the record, with a clear increase in Lindavia ocellata since ca. 2004 CE. Despite substantial warming in the southeastern Tibetan Plateau over the past several decades, diatom assemblages in Cuomujiri Lake did not register a notable response until the significantly high temperatures experienced during the past ~14 years. These results from Earth's highest plateau signify that, with sustained anthropogenic warming, exceedance of ecological thresholds will continue in lakes throughout the Tibetan Plateau and likely in other high latitude regions of the world.