Radium fingerprinting traces hydrology of the global cryosphere under climate warming

Dynamic changes in the cryosphere have profound implications for global warming. This study, through case studies of seasonal ice lakes and glacier-originated rivers, complemented by global data, offers novel insights into radium (Ra) isotopes' characteristic in the cryosphere. It elucidates the quantification of the “Ra quartet” as tracers in frozen hydrological processes across various timescales. (1) Theoretical case studies. Significant differences in water chemistry and Ra activities were observed, highlighting distinct Ra supply and depletion mechanisms. The improved Ra mass model was utilized to estimate the freezing duration of the lakes and the groundwater discharge beneath the ice, while also elucidating the recharge dynamics of groundwater along glacial rivers. (2) Global scale theoretical discoveries. The low ²²⁴Ra/²²⁸Ra ratio, including the case studies presented, may be a significant characteristic of the non-subterranean cryosphere. This phenomenon can be attributed to various processes, including decay, particulate scavenging, groundwater discharge, upwelling, and glacial meltwater. In contrast, the ratio observed in permafrost is more complex, potentially influenced by diverse hydrogeological conditions and intricate sampling protocols. While Ra isotopes are well-traced in the ocean cryosphere—covering groundwater discharge, water exchange, and composition-particle interactions—their application in terrestrial and atmospheric cryospheric studies remains underexplored. Our study provides novel perspectives on Ra isotopes in the cryosphere, offering crucial theoretical and practical implications for addressing ongoing climate warming.