In this work, IBSS materials on seawater bioluminescence intensity changes in the Atlantic sector of the Antarctic Ocean (the Weddell Sea area) with an interval of almost 20 years are presented. Data were obtained using a single instrument, the hydrobiophysical system Salpa‐M, in the area of 50–63°S, 62–49°W in March 2002 (183 soundings at 45 stations during cruise 7 on RV Gorizont) and in February 2020 (122 soundings at 18 stations during cruise 79 on RV Academic Mstislav Keldysh). The bioluminescence studies were coupled with the simultaneous measurement of temperature, electrical conductivity, and photosynthetically active radiation, and they were compared with the data from processing plankton samples. Over the past 20 years, as a consequence of the appearance of a large number of gelatinous organisms and the resulting changes in the structure of the plankton community, the bioluminescence of Antarctic waters in the euphotic layer of this region has decreased almost two‐fold, currently being in the range 8.4 × 10−12 to 104.42 × 10−12 W·cm−2·L−1.

Large‐scale surveys represented by 5800 bathymetric casts in the western Indian Ocean (0–22oN, 54–58oE), elucidated the 10‐fold variation of the bioluminescent potential (BP) in the upper mixed layer, during the winter (north‐east) monsoon season. The mesoscale survey in February 2017 consisted of 26 drift stations (4oN–3oS, 65–68oE) on which 5–10 bathymetric casts were deployed down to 60 m. The maximal BP was associated with the periphery of a cyclonic eddy. The two‐fold to three‐fold variation of BP characterized the spatial heterogeneity modulated by a detected eddy. High‐frequency casts on drift stations resembled the fine‐scale heterogeneity in which the three‐fold variation was observed within the BP maximum at a 37 ± 13 m depth. The latter one was located above the deep chlorophyll maximum at a 80 m depth. A general decline of the BP variance from the large scale through mesoscale to fine scale, fits that of the zooplankton biomass.

Vertical distribution of ctenophores near the boundary of oxygen-depleted waters of the Black Sea redoxcline was studied by use of video observations with real-time water sampling, horizontal MultiNet towing, and soundings using bathyphotometers with simultaneous vertical plankton net sampling. The results of the study showed for the first time that the daytime accumulation of ctenophores above the upper boundary of the suboxic zone changes the biophysical properties of the medium, causing an increase in the daytime intensity of bioluminescence near the redoxcline.The dynamics of this glow is in antiphase to that in the surface layers, where it is associated with the bioluminescence of phytoplankton. Therefore, in the deep-sea areas, two types of bioluminescence peaks differ in the light generation sources: the nighttime glow of phytoplankton in surface layers and the daytime glow of zooplankton in layers of oxygen-depleted waters at the redoxcline. The discovery of this new phenomenon allows the use of bioluminescent methods for the rapid assessment of the depth of the daytime zooplankton layers for the subsequent hauls of plankton nets. This significantly expands the possibilities of studying the structure and functioning of the pelagic ecosystem of the Black Sea and other marine basins with a redoxcline.

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