Purpose. The purpose of the study is to determine the characteristics and trends of inter-annual variability of marine heat wave parameters off the Kamchatka Peninsula eastern coast and in the adjacent areas over the past four decades and to analyze their cause-and-effect relationships with the large-scale and regional processes in the ocean and atmosphere in the context of global warming, as well as to investigate the possible role of coastal wind upwelling in the chain of events of a large-scale environmental disaster in the study region in the fall 2020 under conditions of intensification of marine heat waves and outbreak of harmful algal blooms.

Methods and Results. Standard methods for identifying the variability of marine heat waves and for determining the amplitude-frequency parameters at the regular grid nodes were used to analyze the NOAA climate data array. The results enabled detailed characterization of the spatiotemporal variability of marine heat waves in the region under study including the frequency of events, their duration, intensity, integral indicators (cumulative intensity and composite intensity index), as well as the trends in inter-annual and seasonal variations. The cases of wind-driven upwelling of deep-sea waters in the coastal zone accompanied by a surge in chlorophyll a concentration on the ocean surface during the harmful algal bloom outbreak were also identified.

Conclusions. The marine heat wave events developed against the background of stable positive trends in sea surface temperature. During the last two decades of global warming, a significant increase in all the marine heat wave indicators has been observed. Statistically significant correlations were identified between fluctuations in various marine heat wave parameters and changes in characteristics of anomalies of the surface air temperature field, geopotential height of the 500 mbar isobaric surface as well as climate indices indicating the local and remote influence of large-scale atmospheric processes. During the outbreak of harmful algal bloom off the Kamchatka coast observed after the marine heat waves impact, an increase in wind upwelling in the coastal zone was noted that facilitated the entry of nutrients and dinoflagellates into the photic layer, and also an increase in their numbers and chlorophyll a concentration. The conducted studies confirm the assumption about the role of extreme marine heat waves in the chain of events of the environmental disaster that took place in the study region in the fall 2020.