LONG-TERM RISE AND FALL OF LEVEL OF ICE-COVERED OKHOTSK SEA NEAR THE COAST OF MORDVINOV BAY

The analysis of the causes of sea level rise and fall under the ice was carried out using sea level time series obtained by measurements performed in the coastal zone of the southeastern coast of Sakhalin island in 2019–2021. The analysis of all the events of sea level rising and falling showed that they are not associated with tidal waves, the minima of sea level correspond to different phases of tide and the duration of the events is several times longer than the period of the daily tidal wave. Analysis of the causes of six detected events of sea level fall showed that they are the result of long-lasting winds of the western direction. The fast ice field breaks away from the shore due to these winds and at the place of formed polynya a small set-down appears under the influence of the same winds. Instruments recorded this sea set-down as a decrease of sea level. The analysis of the seven selected events associated with sea level rise showed their connection with a decrease of atmospheric pressure during the cyclones passage near the observation area. The comparison of sea level behaviour and regression coefficients for an ice-covered sea with similar ones for an ice-free sea showed that for an ice-free sea, the level rises are about twice longer in time and occur later than the atmospheric pressure minima. At the same time, the absolute values of the regression coefficient for an ice-free sea are on average almost four times less than for an ice-covered one. The assumption that atmospheric pressure fluctuations can saturate the continental shelf waves has been verified using the Buchwald and Adams shelf wave model. Shelf wave periods of 37.7 hours calculated from spectra confirmed the possibility of transmission to sea level rise, and the shelf waves themselves can be saturated by atmospheric pressure fluctuations from passing cyclones.