Coastal Polynya Disrupts the Acoustic Backscatter Diurnal Signal Over the Eastern Laptev Sea Shelf

The diel vertical migration (DVM) of zooplankton is one of the largest species migrations to occur globally and is a key driver of regional ecosystems and the marine carbon pump. The dramatic changes in the Arctic environment in recent years, mainly associated with sea-ice decline, may have wide significance for the Arctic shelf ecosystems including DVM. Observations have revealed the occurrence of DVM in ice-covered Arctic waters, however, there have yet to be observations of DVM from the extensive Siberian shelves in the Eurasian Arctic and no analysis of how the sea-ice decline may affect DVM. Here, 2 yearlong time series of acoustic backscatter, collected by moored acoustic Doppler current profilers in the eastern Laptev Sea from August 1998 to August 1999, were used to examine the annual cycle of acoustic scattering, and therefore the annual cycle of DVM in the area. The acoustic time series were used along with atmospheric and oceanic reanalysis and satellite data. Our observations show that DVM did not occur during polar night and polar day, but is active during the spring and fall transition periods when there is a diurnal cycle in light conditions. DVM began beneath the fast ice at the end of polar night and increased in intensity through spring. However, the formation of a large polynya along the landfast ice edge in late March 1999 caused DVM to abruptly cease near the fast ice edge, while DVM persisted through spring to the start of polar day at the onshore mooring. We associate this cessation of synchronized DVM ∼1 month ahead of polar day with a predator-avoidance behavior of zooplankton in response to higher polar cod abundance near the polynya. During polar day, the intensity of acoustic scattering was attributed to the riverine suspended particles. Overall, our results highlight the occurrence of DVM on the Siberian shelves, the cessation of synchronized DVM when a polynya opens up nearby, and the potential impact of significant trends toward a more extensive Laptev Sea polynya as part of changing ice conditions in the Eurasian Arctic and their impact on the Arctic shelf ecology.

Bryozoa of the Laptev and East Siberian seas: modern research

The new data about bryozoan fauna of the Siberian seas (Laptev Sea and East Siberian Sea) are obtained. 48 species of Bryozoa were identified in the samples, collected in the MMBI RAS expedition (2014) at 50 stations: 45 – in the Laptev Sea and 16 – in the East Siberian Sea. The taxonomic and biogeographic composition, the features of distribution of Bryozoa are analyzed. A comparative analysis of the studies of the end of the 20th century (1986, 1987 and 1993–1998) based on literature data is carried out (Gontar, 1990, 1994, 2004, 2015а,б, 2016). There was a significant increase 60 in the share of boreal-arctic species due to a significant decrease of arctic species (by almost a third), which probably reflects the climate change towards warming , observed at the beginning of the 21st century.

Spatial distribution of Icelus bicornis (Reinhardt, 1840) and Icelus spatula Gilbert & Burke, 1912 in the russian Arctic seas

This article provides data on distribution of two circumpolar species – twohorn sculpin Icelus bicornis and spatulate sculpin Icelus spatula in the Russian Arctic seas (Barents Sea, Kara Sea, Laptev Sea, East Siberian Sea) in the period from 2014 to 2019. The abundance of the twohorn sculpin varied from 2 to 18 ind/km2, and the biomass varied within 0.002–0.089 kg/km2. For the spatulate sculpin, these parameters were 2–21 ind/km2 and 0.002–0.699 kg/km2. The maximum and minimum values of these parameters for Icelus bicornis were recorded in the Laptev Sea, and for Icelus spatula in the East Siberian Sea. Information on the vertical spatial distribution of these species is also given, confirming the information given earlier that the spatulate sculpin occurs at shallower depths in contrast to the twohorn sculpin.

Bioindication of the water salinity dynamics by the microalgae communities in the Lena River Delta, Laptev Sea, Russian Arctic

The Lena River in the Laptev Sea forms a vast delta, one of the largest in the world. The Ust-Lensky State Nature Reserve saves biodiversity on the Lena Delta territory beyond the Arctic Circle, in the zone of continuous permafrost. In recent years, large-scale plans for the development of extractive industries are implemented in this Russian Arctic sector. In this regard, the study of biodiversity and bioindication properties of aquatic organisms in the Lena River estuary area is becoming more and more relevant. This study aims to identify the species composition of microalgae in lotic and lentic water bodies of the Lena River Delta and use their indicator property for water salinity. It was a trace indicator of species distribution over the delta and their dynamics along the delta main watercourses to assess the impact of river waters on the Laptev Sea coastal areas. For this, all previously published materials on algae and chemical composition of the region waters as well as data obtained in recent years for the waters of the lower Lena reach were involved. In total, 700 species considered to 10 phyla were analyzed: Cyanobacteria (83), Euglenozoa (13), Ochrophyta (Chrysophyta, Xanthophyta) (41), Eustigmatophyta (4), Bacillariophyta (297), Miozoa (20), Cryptophyta (3), Rhodophyta (1), Chlorophyta (125), and Charophyta (111). The available materials of the field and reference observations were analyzed using several statistical methods. The study results indicate that hydrological conditions are the main factor regulating the spatial structure of the species composition of the microalgae communities in the Lena River Delta. The distribution of groups of salinity indicators across flowing water bodies reflects the effect of water salinity, and this allows suggesting possible sources of this effect. The mechanism of tracking the distribution of environmental indicators itself is a sensitive method, that reveals even their subtle changes in them; therefore, as an integral method, it can be helpful for further monitoring.