Large methane emission during ice-melt in spring from thermokarst lakes and ponds in the interior Tibetan Plateau.

• Significant CH 4 accumulation in winter were found in thermokarst lakes on the TP. • The ice-melt period is critical for evaluating thermokarst lake CH 4 and CO 2 fluxes. • Lake depth determines the magnitude of methane flux during ice-melt period. • Snowfall events may accelerate gas release during the ice-melt period. The magnitudes of annual CO 2 and CH 4 emissions from thermokarst lakes and ponds are uncertain due to scarce measurements on the Tibetan Plateau (TP) and limited data on emissions during ice-melt. To evaluate the importance of CO 2 and CH 4 emissions during late winter and spring among the whole year, surface water CO 2 and CH 4 concentrations were measured with the headspace method in ten thermokarst lakes and ponds in 2020–2021 on the TP. The concentrations of CH 4 and CO 2 under ice in winter (CH 4 , 1.05–127.16 μmol/L, CO 2 , 13.24–95.57 μmol/L) were 3–4 orders of magnitude and several times higher than those in summer (CH 4 , 0.02–2.34 μmol/L, CO 2 , 7.26–49.18 μmol/L), respectively. The CH 4 concentrations and fluxes during ice-melt increased with as the depth of the thermokarst lakes and ponds increased. However, the variation in CO 2 concentration was not significant in depth. Snowfall events played an important role in influencing gas exchange during ice-melt. In the ten lakes researched, 42.2% and 19.2% of the annual CH 4 and CO 2 fluxes occurred during ice-melt, respectively. Our results indicated that CH 4 and CO 2 accumulation in winter should be considered when evaluating annual carbon budgets in thermokarst lakes and ponds on the TP and similarly high fluxes during ice-melt might occur in other thermokarst lakes and ponds. [ABSTRACT FROM AUTHOR]