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Cement is a widely used construction material globally. Its manufacturing contributes to anthropogenic CO2 emissions significantly. However, its alkaline compounds can absorb CO2 from the surrounding environment and engage in a carbonation reaction, thereby functioning as a carbon sink. As a major cement producer and consumer, China has an important responsibility to rigorously investigate and accurately account for cement carbon uptake. This study presents a comprehensive analytical model of cement carbon uptake from China, revealing a substantial increase in carbon uptake from 1930 to 2021, peaking at 426.77 MtCO2 (95% Confidence Interval: 317.67–874.33 Mt CO2) in 2021. The uptake accounts for 8.10% to 45.40% of China's annual land sink and 2.51% to 4.54% of the global land sink. The cumulative carbon uptake by cement is approximately 7.06 Gt CO2 (95% CI: 5.22–9.44 Gt CO2) during this period, offsetting 50.7% of the total emissions (13.91 Gt CO2, 95% CI: 12.44–17.00 Gt CO2) from the cement industry. Notably, cement mortar contributed to most absorption (65.64%). From a life cycle perspective, the service stage of cement materials is the period where the largest CO2 sink is formed, accounting for 90.03% of the total. Therefore, the potential for carbon sequestration in cement materials and their waste is enormous. Additionally, the model improves the accuracy of cement carbon accounting, supporting both China and global carbon neutrality assessments. Thus, it is crucial for China to achieve its carbon neutrality goals sooner by prioritizing the environmental benefits of cement materials and wastes, and accelerating the development and commercialization of CO2 sequestration technologies for cement and its by-products. [ABSTRACT FROM AUTHOR]

[Display omitted] • δ13C, δ15N, and δ18O were analyzed to reveal carbon–nitrogen coupled absorption. • Stability regulation mechanism of karst reservoir was indicated by diel monitoring. • The stability promotes the biological carbon pump development of karst reservoir. • Biological carbon pump caused carbon burial in karst reservoir. While river damming has been extensively investigated, there remains unclear in the diel biogeochemical processes and carbon control mechanisms in karst reservoirs, under the influence of the biological carbon pump (BCP) effect. We investigated the diel variation of Hongjiadu (HJD) and Wujiangdu (WJD) reservoirs, which exhibit typical periodic thermal stratification, in the Wujiang River located in Southwest China. We found that diel variation of dissolved inorganic carbon (DIC) (HJD: 1668.6 ± 10.4 µmol/L; WJD: 1777.9 ± 31.5 µmol/L), δ13C DIC (HJD: −3.1 ± 0.1 ‰; WJD: −4.6 ± 0.4 ‰), and other parameters in the lentic zones were relatively stable. Moreover, the Revelle factor in the lentic zones (HJD: 44.3-49.0; WJD: 44.3-53.9) were substantially higher than those of the fluvial zones (HJD: 24.4-33.4; WJD: 14.2-35.1). The stable diel variations indicate that the HJD and WJD reservoirs may have distinct stability regulatory mechanisms. In the lentic zones, δ13C DIC , nitrogen–oxygen isotope (δ15N and δ18O), and the correlation of C-N indicated that the conversion of DIC and NO 3 – is primarily influenced by primary production, and there was coupled absorption of carbon and nitrogen nutrients during photosynthesis. Meanwhile, the C/N weight ratio (6.0-10.1) and the δ13C POC (−30.0 ‰ to −24.7 ‰) also revealed a gradual transition from soil organic matter (OM) in the fluvial zone to phytoplankton source in the intermediate-lentic zone. Thus, two reservoirs had a significant BCP effect and converted a significant amount of DIC to autochthonous organic carbon (AOC) burial in the lentic zones. The BCP effect in subtropical deep karst reservoirs buried lots of carbon, increased carbon sequestration and decreased CO 2 emissions in the lentic zone. Simultaneously, the stability of reservoirs promotes BCP effect and intensifies carbon sequestration, which is of great significance for the study of the global carbon sources-sinks pattern. [ABSTRACT FROM AUTHOR]