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The results of complex research carried out in the East Siberian Sea on board of RV “Professor Levanidov” in September 2019 are presented. The formation of positive air temperature anomalies over the sea, the expansion of the zone of river flow influence in the central and southeastern parts of the shelf, and an abnormal decrease in sea ice cover were noted. Arctic water masses and the waters of the East Siberian Sea were dominant on the shelf. At depths of more than 180 m, waters of Atlantic origin were well traced by salinity more than 34.5 ‰, positive temperature and silicon content less than <10 μM. Photosynthesis processes were limited by nitrogen, whose concentrations in the photic layer were reduced to analytical zero. Summer phase of phyto- and zooplankton development was observed in most of the sea. The main contribution to the total biomass of mesoplankton was made by copepods and chaetognaths. Plankton biomass on the inner shelf was twice as high as on the outer shelf. The average benthic biomass in trawl catches was 15 kg per mile, of which up to 74 % was echinoderms and 9 % crustaceans.17 fish species from 6 families were registered in trawl catches. The dominant species was the polar cod Boreogadus saida found in small numbers almost everywhere at depths 33 to 250 m with bottom temperatures from –1.7 to 0.47 °C, kept sparse, without forming dense aggregations. Maximum concentrations were observed in the southeastern part of the study area. High intensity of fish feeding was noted. Diets of polar cod and snailfishes (Liraridae) consisted mostly of hyperiids, gammarids, and copepods. The diet of capelin Mallotus villosus was dominated by copepods. Polychaetes and gammarids formed the bulk of the diet of sculpins (Cottidae). Microplastics are found in small quantities in the southeastern and central part of the sea only. Tissue samples were collected for population-genetic analysis, DNA‑barcoding studies, and analysis of aquaDNA.

In September 2019, the R/V “Professor Levanidov” carried out comprehensive studies in the Laptev Sea from 140 ° to 110 ° E at depth range of 60–950 m. High positive anomalies of air and surface water temperatures were noted up to + 2 + 3 °C and +1.5 °C respectively with an abnormally low sea ice cover. Cold Arctic and desalinated waters of the river flow dominated in the upper 200 m layer. Atlantic waters were traced in the layer from 180–300 m to the bottom, and their core — at a maximum temperature of + 1.6 + 1.92 °C at 240–280 m. By the time of the survey, the active vegetation of phytoplankton had finished. Oxygen saturation in the almost the entire surface layer was below 100 %. Primary production was limited by mineral nitrogen concentration. Low concentrations of phosphates, nitrates and silicates in the intermediate waters indicated the penetration of Atlantic waters. The average biomass of plankton on the shelf was 239,8 mg/m3, on the slope — 374,2 mg/m3. Copepods and chaetognaths with considerable contribution of hyperiids and euphausiids dominated in plankton by weight. The bulk of zooplankton was large organisms, while small and medium fractions were 22 and 10 %. Brittle star, starfish, and shrimp dominated in trawl benthos. 25 demersal fish species of 14 families were found in bottom trawl catches. Zoarcidae, Liparidae and Gadidae were the most diverse. Polar cod was recorded along the entire route with highest concentrations in Atlantic waters at depths of 217–460 m. Copepods dominated in the diet of Polar cod juveniles, while that of adults was supplemented by large pelagic crustaceans and fish with high level of cannibalism. Greenland halibut was found along the entire continental slope at 270–750 m while the largest catches were in its central and western parts. The increase of halibut number and occurrence was due to the wide distribution of Atlantic waters on the slope. The main component of its diet was Polar cod.