Purpose. The aim of the study is to analyze the river runoff impact on density stratification in the Chukchi and Beaufort seas, and to identify the areas where the response to seasonal fluctuations in the river runoff volumes is the most pronounced.

Methods and Results. Based on the ECMWF ORAP5 reanalysis data on the monthly mean values of temperature and salinity for May – September of each year, the water density in the Chukchi and Beaufort seas was calculated. To study the river runoff impact on the density stratification of sea water, applied were the calculated maximum monthly average values of the Väisälä – Brunt frequency over depth at each grid node, and the monthly average water discharges in the closing gates of the Kolyma, Yukon and Mackenzie rivers for the period 1979–2013. The results of statistical analysis showed that density stratification of the Chukchi and Beaufort seas was most strongly affected by the Mackenzie and Yukon river runoffs for a previous month and also by the Kolyma river runoff for 3 and 6 previous months.

Conclusions. The impact of the Mackenzie runoff is found to be most pronounced from July to September. The areas of statistically significant correlation coefficients between the buoyancy frequency and the runoff volumes for the previous month are in the southeastern and central parts of the Beaufort Sea. The areas where the impact of the Yukon runoff is pronounced are in the Bering Strait area, in the northern region of the Chukchi Sea, and on the western periphery of the Beaufort gyre. The Kolyma runoff impact on the water density stratification is manifested near the western coast of the Chukchi Sea, in the Bering Strait area, the Kotzebue Bay, and on the southwestern periphery of the Beaufort gyre.