Using radium isotope fingerprinting to trace hydrogeochemistry change and permafrost water cycle in cold regions

Glaciers and permafrost, as core hydrological components of cold regions, are sensitive to climate change and the response in turn affects regional water resources. The ablation of glaciers and permafrost has caused severe environmental problems, including sea level rise, the release of greenhouse gases and further global warming. One poorly understood part that has so far remained underdeveloped is the change natural radioactivity related to ablation processes in cold regions. Radium isotope (²²³Ra, ²²⁴Ra, ²²⁶Ra and ²²⁸Ra) has been considered as an effective tracer for submarine groundwater discharge into coastal and estuarine environments over years. Unlike the coastal environments, Ra activities and activity ratios seem to show a unique distribution in cold regions. Ra will accumulate with glaciers and permafrost ablation and the activity ratios of ²²⁴Ra/²²⁸Ra (＜1 in cold regions and ＞1 in coastal regions) indicate that the radioactive equilibrium of short-time Ra isotopes has not yet been reached, which seems to be closely related to glaciers and permafrost thawing. The results of laboratory experiments show that Ra distribution between ice and water will change during freezing, and Ra exchange will occur at the ice-water interface with interaction time increasing. This study aims to explore how natural radioactivity varies in cold regions, and to provide a new tracing method for hydrological investigation in cold regions.