Tritium records to trace groundwater recharge and mixing in the western Russian Arctic

The Arctic regions are characterized by widespread development of permafrost. We studied a sandy aquifer used for water supply in the talik zone of the Pechora River valley. It has been found that groundwater has TDS values from 75 mg/L far from the river bank to 200 mg/L in the coastal zone. This indicates a predominantly atmospheric recharge of groundwater far from the river and the significant contribution of river water in the composition of groundwater in the coastal zone. The 3H age of groundwater in onshore wells was 20–25 years, on the basis of which it was concluded that the groundwater entering the aquifer before 1995–2000 was almost completely replaced. Mean water residence time, sampled from wells far from the river bank, ranges from 20 to 50 years. However, unlike onshore wells, this groundwater contains “bomb water” and old water that entered the aquifer before 1952. The age of the old water reaches 12.9 ± 2.5 ka. The use of information on the distribution of tritium isotopes made it possible to clarify the conditions of groundwater recharge and end-member ratios of young water, “bomb water” and old water in different parts of the aquifer.