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

Direct measuring of CO₂  flux remains challenging for global lakes. The traditional sampling and gas transfer models used to estimate lake CO₂  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 CO₂  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 CO₂ from the atmosphere (-0.87 ± 0.38 g C m^-2 d^-1 ), a value more than twice the CO₂  flux rate during the ice-free period (-0.41 ± 0.35 g C m^-2 d^-1 ). The total CO₂ 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 CO₂ in winter is controlled by both seasonal hydrochemistry processes and lake ice absorption in saline lakes. This research also demonstrates decreasing CO₂ uptake from the atmosphere by saline lakes on the QTP, which may turn carbon sinks to carbon sources with future warming.