Characteristics of Carbon Sink and the Influencing Factors in Ngoring Lake, Qinghai‐Tibet Plateau

Abstract Continuous annual carbon dioxide (CO 2 ) 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 CO 2 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 CO 2 sink value was maximum in 2016, about −1.46 g C m −2 d −1 . There were two CO 2 absorption peaks in spring and autumn, respectively. The multi‐year average monthly mean CO 2 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 CO 2 absorption. The CO 2 absorption process was controlled by wind speed, lake ice, lake mixing and stratification.