Detection and Analysis of the Causes of Intensive Harmful Algal Bloom in Kamchatka Based on Satellite Data

Abstract

In this paper, the causes of the anomalous harmful algal bloom which occurred in the fall of 2020 in Kamchatka have been detected and analyzed using a long-term time series of heterogeneous satellite and simulated data with respect to the sea surface height (HYCOM) and temperature (NOAA OISST), chlorophyll-a concentration (MODIS Ocean Color SMI), slick parameters (SENTINEL-1A/B), and suspended matter characteristics (SENTINEL-2A/B, C2RCC algorithm). It has been found that the harmful algal bloom was preceded by temperature anomalies (reaching 6 °C, exceeding the climatic norm by more than three standard deviation intervals) and intensive ocean level variability followed by the generation of vortices, mixing water masses and providing nutrients to the upper photic layer. The harmful algal bloom itself was manifested in an increase in the concentration of chlorophyll-a, its average monthly value for October 2020 (bloom peak) approached 15 mg/m3, exceeding the climatic norm almost four-fold for the region of interest (Avacha Gulf). The zones of accumulation of a large amount of biogenic surfactant films registered in radar satellite imagery correlate well with the local regions of the highest chlorophyll-a concentration. The harmful bloom was influenced by river runoff, which intensively brought mineral and biogenic suspensions into the marine environment (the concentration of total suspended matter within the plume of the Nalycheva River reached 10 mg/m3 and more in 2020), expanding food resources for microalgae.

Unprecedented Outbreak of Harmful Algae in Pacific Coastal Waters off Southeast Hokkaido, Japan, during Late Summer 2021 after Record-Breaking Marine Heatwaves

“…Moreover, our particle-tracking simulations revealed that the Pacific Ocean to the east of the Kamchatka Peninsula could be the other potential source. This possibility is consistent with the outbreaks of K. selliformis in September-October 2020 [18,19]. These observations lead to the hypothesis that different algal species may have been separately transported from the three potential source areas and contributed simultaneously to the occurrence of the HABs off the southeast coast of Hokkaido in late summer of 2021.…”

“…In the second step, 87,616 particles were initially set at each of three depths (1, 5, and 10 m) below the sea surface east of the Kamchatka Peninsula and tracked forward in time for 360 days. Initial conditions of the particles were updated at intervals of five days from 30 September to 20 October 2020, which corresponded to the period of occurrence of the HABs off the east coast of the Kamchatka Peninsula [18].…”

“…It took about 4 months, at least, for the particles to be transported retrospectively from coastal waters off southeast Hokkaido to the area east of the Kamchatka Peninsula (Figure 10d-f). Next, we examined whether harmful algae could have been passively transported by ocean currents to the focal region from the Pacific Ocean east of the Kamchatka Peninsula, where a massive bloom of the dinoflagellate K. selliformis occurred during September-October 2020 [18], with a focus on wider area and longer tracking time (Figure 10). Particles that were transported retrospectively to the northeast along the Oyashio and the East Kamchatka Current travelled the longest distance.…”

“…It is very instructive to remember that the massive HABs in the Pacific Ocean near the east coast of the Kamchatka Peninsula in the late summer of 2020 followed extreme marine heatwaves that occurred in both June and July of 2020, when the maximum anomalies of sea surface temperature reached about 6 • C [18]. The magnitude and timing of the second marine heatwave and the time lag between the second marine heatwave and the HABs were very consistent with the sequence of events in this study.…”

“…In general, blooms of K. mikimotoi have been frequently reported from Japanese and Chinese coastal waters south of 40 • N (e.g., [6]), whereas K. selliformis [16,17] was massively identified in Japanese waters for the first time. Devastating damage to marine ecosystems by K. selliformis was reported to have occurred to the east of the Kamchatka Peninsula during September-October 2020, just a year before the HABs off southeast Hokkaido [18,19]. Likewise, along with outbreaks of harmful algae, serious damages to coastal ecosystems and fisheries were reported off southeast Hokkaido (green bold lines in Figure 1b): sea urchins experienced mass die-offs, chum salmon died in fixed nets, and fish juveniles died in rearing facilities.…”