Monthly average sea surface temperatures (SSTs) in the region of the northern Kuril Islands for 1998–2022 are analyzed. Based on a 25-year observation series, the norms—average long-term distributions—are constructed for each month. It is shown that a cold spot with very low temperatures (around 6°C) and small annual variations (around 3°C) forms in the coastal waters from the island of Simushir to the Fourth Kuril Strait during the summer. Seasonal variations are characterized by an annual cycle with maximum values in August–September and minimum values in February–March. For the region as a whole, they are well described by a combination of annual and semiannual harmonics with amplitudes of 4.9 and 1.1°C, respectively. Interannual variability is reflected in variations in summer maxima with a period of approximately 6 years. During the summer–fall period, a steady upward temperature trend is observed outside the cold spot, most significantly in the northwestern Pacific Ocean (approximately 1°C over 25 years). In the winter–spring, the opposite trend is observed in the Sea of Okhotsk, with a downward trend in thermal indicators. Calculating deviations of average monthly temperatures from normal values has revealed that large-scale zones with significant temperature anomalies, predominantly below freezing, may form in the Northern Kuril Islands, potentially posing a serious threat to aquatic life.
Shevchenko et al. (Mon,) studied this question.