全球主要河流流域碳酸盐岩风化碳汇评估

碳酸盐岩风化吸收的大气CO₂主要以HCO₃ ^-形式连续地经由河流从大陆输送到海洋,成为陆地生态系统的重要碳汇。目前主要河流流域的碳酸盐岩风化碳汇估算存在不确定性,分布格局尚不清晰。基于GEMS-GLORI全球河流数据库提供的全球10万km ²以上主要河流流域多年平均监测数据,利用水化学径流法估算出全球主要河流流域碳酸盐岩对CO₂的吸收速率为0.43±0.15 Pg CO₂ yr ^-1,平均CO₂吸收通量为7.93±2.8 t km ^-2 yr ^-1。CO₂吸收通量在不同气候带下差异显著,热带和暖温带CO₂年吸收速率占全球主要河流流域年吸收速率的62.95%。冷温带CO₂年吸收速率占全球主要河流流域的33.05%,仅次于热带地区。本文划分出全球CO₂吸收通量的9个关键带,关键带的交汇处CO₂吸收通量较高。喀斯特出露流域碳酸盐岩对CO₂吸收通量的均值为8.50 t km ^-2 yr ^-1,约为非喀斯特流域的3倍。全球喀斯特出露流域碳酸盐岩风化碳汇在全球碳循环、水循环及碳收支平衡估算研究方面占据重要地位。

Estimation of carbonate rock weathering-related carbon sink in global major river basins

Atmospheric CO₂ uptake by carbonate rock weathering is continuously transported from the land to the ocean by rivers in the form of HCO₃ ^-, and it has become an important carbon sink of terrestrial ecosystems. In the existing research, the estimation and distribution of carbonate weathering-related carbon sink in global major river basins are still unclear. In this study, we collect hydrochemical and discharge data of multiyear average (runoff modulus, main ion concentration, and dissolved inorganic carbon) in large river basins over 100, 000 km ². By using hydrochem-discharge method, we estimate that the CO₂ uptake rates (F_v) of carbonate weathering in global major river basins is 0.43 ± 0.15 Pg CO₂ yr ^-1 and the average CO₂ uptake flux(F) is 7.93 ± 2.8 t km ^-2 yr ^-1. The CO₂ uptake F and uptake F_v are substantially different under various climatic zones. The annual uptake F_v of tropical and warm regions accounts for 62.95% of the total annual F_v. The cold temperate zone is widely distributed, and its CO₂ uptake F_v accounts for 33.05%, which is second only to the tropics. We also propose the nine critical zones of global CO₂ uptake F (four in the middle and low latitudes, two in the western hemisphere and three in the eastern hemisphere). The CO₂ uptake F in the intersection of the critical zones is high. The average CO₂ uptake F in the karst-outcropped basins is 8.50 t km ^-2 yr ^-1, which is approximately three times that in the non-karst basins. Carbonate weathering carbon sinks in global karst-outcropped basins play an important role in the study of global carbon cycle, water cycle, and carbon budget balance estimation. On the basis of river basin scales, various factors (e.g., carbonate composition, exogenous acid, and climatic environment) for carbonate weathering carbon sinks should be considered. The hydrochem-discharge method should be further improved in future research. Moreover, the effects of the photosynthesis of river aquatic organisms on rock weathering carbon sinks should be considered, and carbonate rock weathering carbon sinks should be refined and extrapolated to the world.