Significant winter CO2 uptake by saline lakes on the Qinghai‐Tibet Plateau

Abstract Direct measuring of CO 2 flux remains challenging for global lakes. The traditional sampling and gas transfer models used to estimate lake CO 2 fluxes are variable and uncertain, and ice‐covered periods are often excluded from the annual carbon budget. Here, the first longtime (2013−2017) direct measurement of CO 2 flux by eddy covariance system over the largest saline lake (Qinghai lake) in the Qinghai‐Tibet Plateau (QTP) revealed that ice‐covered period draws large amounts of CO 2 from the atmosphere (−0.87 ± 0.38 g C m −2 d −1 ), a value more than twice the CO 2 flux rate during the ice‐free period (−0.41 ± 0.35 g C m −2 d −1 ). The total CO 2 uptake by all saline lakes on the QTP was estimated to −10.28 ± 1.65 Tg C yr −1 , an equivalent to approximately one third of the net terrestrial ecosystems carbon sink in QTP. Our results indicate large sink for CO 2 in winter is controlled by both seasonal hydrochemistry processes and lake ice absorption in saline lakes. This research also demonstrates decreasing CO 2 uptake from the atmosphere by saline lakes on the QTP, which may turn carbon sinks to carbon sources with future warming.