Purpose. The purpose of the work is to summarize information on the features of spatial variability of the ²²⁶Ra and ²²⁸Ra concentration fields and the factors influencing these features in the surface water layer of the Black Sea.

Methods and Results. The data on spatial variability of the ²²⁸Ra and ²²⁶Ra concentrations in the surface (0.3–3.0 m) layer of the Black Sea obtained during four expeditions were used. The ²²⁸Ra and ²²⁶Ra isotopes were recovered from the seawater samples using the MnO₂-based fiber. Their activity was measured by a UMF-2000 alpha-beta radiometer. The data on the content of main elements of the basic biogenic cycle were obtained photometrically.

Conclusions. The concentrations of ²²⁸Ra and ²²⁶Ra varied in a range of 17.2 to 172.2 dmp/m³ and from 38.0 to 270.1 dmp/m³, respectively. It is shown that in the region under study, the influence of submarine sources and, presumably, sewage is of a local character and is manifested in an increase of concentrations of these radionuclides or one of them by 1.5–2.3 times. The mesoscale eddies observed in the region of the Southern Coast of Crimea are assumed to affect spatial variability of the radium isotope concentration fields that results in a local decrease or increase in their concentrations by 2.3–2.8 times. It is shown that propagation of the Azov Sea waters in the Black Sea is traced by the ²²⁸Ra and ²²⁶Ra concentration fields: the increased (by 2.3–2.6 times) values of the contents of both isotopes are observed in these areas. It is established that in the areas subjected to the affect of river runoff, the concentration of long-lived radium isotopes is observed to increase with distance from the coast. The spatial scales, on which the influence of a particular source is manifested, are expected to be proportional to its power (flow rate and radionuclides concentration): the higher the power, the greater the distance at which its influence is monitored.