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Abstract
Abstract Continuous annual carbon dioxide (CO2) flux, encompassing ice‐covered periods, has been monitored in Ngoring Lake, the largest freshwater lake on the Qinghai‐Tibet Plateau (QTP). By utilizing continuous eddy system data, the characteristics and mechanisms influencing CO2 flux at various temporal scales in the lake were investigated. Findings revealed that Ngoring Lake was predominantly acting as a carbon sink year‐round. The average annual CO2 sink value was maximum in 2016, about −1.46 g C m−2 d−1. There were two CO2 absorption peaks in spring and autumn, respectively. The multi‐year average monthly mean CO2 absorption peaks occurred in April (−1.70 g C m−2 d−1) and October (−1.75 g C m−2 d−1), respectively. These peaks were associated with the freeze‐thaw process and were caused by the mixing process due to water cooling. The continuous warming during the ice‐covered period led to a high‐water temperature, and the maximum value reached 6°C. In spring, mixing occurred upon ice melt, and the water temperature at 2 m depth decreased rapidly to 4°C because it was about 5°C higher than the air temperature. In autumn, cooling and mixing were induced by decreasing air and water temperatures alongside strong wind. These cooling processes facilitated significant CO2 absorption. The CO2 absorption process was controlled by wind speed, lake ice, lake mixing and stratification.
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