Ground ice is a distinctive feature of permafrost terrain, and could be a potential water source and a proxy index of past climates, which has great impacts on the local hydrological process and is also sensitive to climate change. 

In recent years, due to the warming climate, the ground ice near the permafrost table is thawing, which influences water and heat exchange, energy budget, and greenhouse gases release. 

Consequently, it is of great significance to understand ground ice recharge and cycling near the permafrost table on the Qinghai-Tibet Plateau (QTP). 

However, there is little knowledge on ground ice hydrology near permafrost table under a warming climate. 

Recently, scientists from the Northwest Institute of Eco-Environment and Resources (NIEER) of the Chinese Academy of Sciences, together with their colleagues from Lanzhou University, explored the ground ice recharge near permafrost table on the central QTP by using chemical and isotopic data. 

They quantified the sources of ground ice near permafrost table in continuous permafrost regions of the central QTP by using stable tracers (isotopes and chloride) and hydrograph separation model. 

The results indicate that the ground ice near permafrost table is mainly supplied by active layer water and permafrost water, accounting for 58.9 to 87.0% and 13.0 to 41.1%, respectively, which imply that the active layer was the dominant source. 

Besides, the alpine ecosystems are notably affecting ground ice sources near permafrost table in permafrost regions under a warming climate. 

The study also shows that the effects of evaporation and freeze-out fractionation on the soil water and ground ice are evident. 

The objectives of this study are expected to fill the fundamental knowledge gap on the sources of ground ice near permafrost table, and provide theoretical foundation for understanding the hydrological processes in permafrost regions of the QTP. 

The study entitled "Exploring the Ground Ice Recharge near Permafrost Table on the Central Qinghai-Tibet Plateau Using Chemical and Isotopic Data" was published in a paper in Journal of Hydrology. 

 The conceptual diagram on the sources and cycling of the ground ice near permafrost table (The influence of lateral groundwater flow on ground ice near permafrost table in the QTP was not considered in this diagram). (Image by WU Tonghua)