Net carbon dioxide sequestration by large alkaline lakes dominates the carbon exchange of Qinghai-Tibet Plateau lakes

Alpine lakes on the Qinghai-Tibet Plateau (QTP) are rapidly expanding under climate change, yet their role in the regional carbon budget remains unclear. Here we analyze carbon flux data from 156 alpine lakes of varying sizes and find that these lakes acted as a net carbon sink of 6.7 Tg C yr−1 during 2011–2022, approximately one-fifth of the terrestrial carbon sink over the QTP. This sink is dominated by alpine large alkaline lakes that sequester substantial carbon dioxide far outweighs carbon emissions from smaller lakes. Projected lake expansion under Shared Socioeconomic Pathway (SSP) scenarios indicates an increase in the lake carbon sink by 2100, with the magnitude of this increase varying inversely with scenario level due to the effect of rising water temperatures. When combined with reduced terrestrial carbon sequestration by inundated grasslands, the overall impact of lake expansion on regional carbon budgets depends on future warming rates. Our results highlight alpine lakes act as an important carbon sink and stress the need to account for carbon uptake by large alkaline lakes in regional carbon budget assessments. Carbon flux data from 156 Qinghai-Tibet Plateau lakes reveal a net sink of around 7 Tg carbon per year during 2011–2022, about one-fifth of the regional terrestrial carbon sink, with projections indicating future changes under lake expansion and warming.