Seasonal Variability of CO2 Exchange in a High-Altitude, Freshwater Lake on the Tibetan Plateau: Insights from Eddy Covariance-based Observations

High-mountain lakes are sentinels of climate change, yet their carbon cycling mechanisms remain poorly understood due to extreme conditions and data scarcity. This study investigates the air-water CO₂ exchange and its driving mechanisms in Taro Co (4566 m a.s.l.), a large, freshwater, and dimictic lake on the central Tibetan Plateau. In 2023, an eddy covariance observation station was established on an island in the lake, yielding a 21-month continuous observation record of the air-water CO₂ exchange flux at the lake surface.

The results illustrate that the lake acts as a carbon sink year-round. CO₂ absorption is at its lowest during the summer and increases during the overturning periods in autumn and winter. The results also reveal a sudden change consistent with the formation of the lake ice sheet. The increased CO₂ absorption during the overturning period is partially driven by enhanced primary productivity due to strong solar radiation in this low-latitude, high-altitude region, as evidenced by increased chlorophyll concentrations observed via satellite imagery.