Remote Sensing Evidence for the Harmful Algal Bloom Explanation of the Ecological Situation in Kamchatka in Autumn of 2020

In this study, we investigated the remote sensing evidence of the harmful algal bloom at the coast of Kam-chatka, a widely reported ecological disaster in the autumn of 2020. We analyzed time series of relative chlorophyll concentration anomaly maps derived from Sentinel-3 OLCI and Sentinel-2 MSI data and historical sea surface temperature data from Sentinel-3 SLSTR. Significant chlorophyll concentration anomaly values were observed during September and October of 2020. There was also a notable increase in sea surface temperature compared to earlier years. Both of these effects are indirect evidence for the presence of an algal bloom. Without any in situ measurements, our results do not constitute an irrefutable case by themselves, but in conjunction with extensive on-site investigation reports, leave a harmful algal bloom as the only plausible explanation.