Hydrochemistry and isotopic signatures of subpermafrost groundwater discharge along the eastern slope of the Lena River Delta in the Laptev Sea

•226Ra is the best tracer of groundwater discharge in the shallow Arctic seas.•Discharged groundwater is enriched in 226Ra and depleted with δ18O isotopes.•Total alkalinity increased at the groundwater discharge site.•Changes in the Ca2+/Na+ ratio are related to the groundwater composition. Geochemical processes in the Artic are changing at accelerated rates due to climate change. We present the results of a study on the features of the isotopic and hydrochemical signals of discharging submarine subpermafrost groundwaters on the transect along the underwater extension of the Lena River Delta in the Laptev Sea. This study demonstrated that the water column at submarine groundwater discharge sites is enriched with radium isotopes. A significant part of the short-lived radium isotopes depending on the season and hydrometeorological conditions can has an erosive genesis, while 226Ra activity is due to the serious contribution of groundwater. The light signal of δ18O and the increased quantities of excess deuterium can indicate that groundwater was formed when the climate was colder than today. The fraction of subpermafrost groundwater in the bottom layer of the studied transect reaches 7% at the plays of the submarine groundwater discharge. The groundwater presence was also indicated by an increase in the content of dissolved Na+ at the discharge site resulting in Ca2+/Na+ ratio decrease relative to other waters in the Buor-Khaya Bay. The higher total alkalinity value is probably also the result of submarine subpermafrost groundwater discharge.