Aral Sea's Rapid Drying Shifts from Carbon Sink to Source

Drying of the Aral Sea has released more than 200 teragrams of carbon from exposed lake-bed sediments, transforming the region from a carbon sink into a carbon source, according to a new study. The findings reveal the importance of recognizing carbon fluxes from drying lakes in global carbon inventories and suggest that restoring shrinking lakes could become an important tool to limit future greenhouse gas emissions. Lakes store substantial amounts of organic carbon in their sediments, while also releasing greenhouse gases such as carbon dioxide and methane. These processes play an important role in regulating Earth's climate. However, widespread lake expansion and, more notably, lake drying driven by water diversion, dam construction, and climate change are altering this balance. As lakebeds dry, sediments that once securely stored carbon are exposed to air, allowing previously buried organic matter to decompose and release carbon dioxide back into the atmosphere, potentially reversing a long-term natural carbon sink. How large-scale lake desiccation transforms regional carbon storage and emissions remains poorly understood. Situated between Kazakhstan and Uzbekistan, the Aral Sea – once the world's fourth-largest inland lake – has become the world's largest exposed dry lake bed after the diversion of its feeder rivers for irrigation, making it an exceptional natural laboratory for studying these dynamics. Rafael Marcé and colleagues used a space-for-time substitution approach that combined sediment core analysis, in situ CO₂ flux measurements, and remote sensing to quantify carbon losses from the exposed sediments of the Aral Sea between 1960 and 2022. Marcé et al. estimate that the desiccated lake-bed sediments have released an average of roughly 204 ± 53 teragrams of carbon since 1960. New vegetation growth on the dry lakebed has only offset less than 1% of those emissions. The findings show that the Aral Sea basin's land-use carbon balance has shifted from a net carbon sink to a significant carbon source over the last 50 years. According to the authors, reflooding the lake could not only improve the region's socioeconomic health but also help to halt continued carbon loss. Moreover, the study further proposes that these avoided emissions and renewed carbon storage could generate high-quality carbon credits in voluntary carbon markets, creating a substantial financial incentive for restoration.