Discharge of Salt Groundwater in the Estuary of the Razdol’naya River (Amur Bay) in February 2020

In February 2020, geochemical tracers along with hydrochemical and hydrological characteristics were used to reveal a discharge site of salt groundwaters in the head of the Razdol’naya R. estuary at a distance of 22 km from its mouth bar. The elevated activity of 224 Ra isotopes from 11.1 ± 0.1 to 2.2 ± 0.05 Bq/m 3 in the bottom water layer over a distance of 15 km indicates to the propagation of slightly saline waters from a pool 8 m in depth toward the receiving basin. The distribution of stable water isotopes (δ 18 O and δD) and ions of basic salt composition showed that water of the top aquifer at the site of discharge area can suffer the effect of seawater. The major cause of the observed phenomenon is supposed to be the penetration of seawater into the top aquifer within the estuary during winter low-water season and the seepage of this water in the region with largest depth. The contrast of the temperature of ground and surface water was accompanied by a positive temperature anomaly in the zone of their interaction and a decrease in ice thickness along the mixing zone.