Lena River Delta Research Articles

Geochemical Markers of Organic Matter Transformation in the Eastern Part of the Laptev Sea

The sources of supply and transformation of organic matter (OM) during the transition from the dissolved form to suspension, fluffy and bottom sediments on the meridional transect from the Lena River delta to the continental slope were described (depths from 10 to 2390 m, cruise 63 of the R/V Akademik Mstislav Keldysh, September 2015). The results of the study of OM molecular markers showed that dissolved and suspended OM of marine and terrigenous origin biodegrades in the water column and practically does not accumulate in bottom sediments. Thus, OM of the Lena river runoff does not contribute to the formation of OM in the bottom sediments in the summer period. On the outer shelf, an area of influence of ice bloom on the sedimentation process was revealed.

The structure of the upper part of the Earth’s crust in the area of the Lena River delta: the first magnetotelluric data

The structure of the upper part of the Earth’s crust in the area of the Lena River delta: the first magnetotelluric data

РАСПРЕДЕЛЕНИЕ БИОГЕННЫХ ЭЛЕМЕНТОВ НА ГРАНИЦЕ ВОДА–ДНО В ПОРОВЫХ И НАДДОННЫХ ВОДАХ КАРСКОГО МОРЯ И МОРЯ ЛАПТЕВЫХ

The paper presents data from the 63rd cruise of the R/V “Akademik Mstislav Keldysh” in August–October 2015. The main areas of work included the western part of the Kara Sea, the bays of Novaya Zemlya (Sedova, Oga and Tsivolki), a transect through the Voronin Trench, a transect from the Lena River delta to the continental slope of the Laptev Sea. During the cruise, a chemical analysis of pore and bottom waters was carried out for the content of nitrite, nitrate nitrogen, silicon, phosphates, total alkalinity and pH. The patterns of distribution of silicon and phosphorus concentrations at the water-bottom interface are considered. In the Kara Sea analysis of the data showed that the maximum concentrations of nutrients are located in the upper 10 cm sediment layer, below that concentrations gradually decrease. In all studied bays of Novaya Zemlya, the concentrations of nutrients in the silt waters were lower than on the adjacent shelf. In the Laptev Sea, the content of nitrates in silt waters is higher, and phosphates are lower than in the Kara Sea. Differences in the content of nutrients in the bottom and silt water are associated both with external factors (river runoff) and physical and geological features of the upper sediment layer of the studied areas.

The Importance of Riverine Nutrient Supply for the Marine Silica Pump of Arctic Shelves: Evidence From the Laptev Sea

AbstractArctic shelves receive a large load of nutrients from Arctic rivers, which play a major role in the biogeochemical cycles of the Arctic Ocean. In this study, we present measurements of dissolved silicon isotopes (δ30Si(OH)4) around the Laptev Sea and surface waters of the Eurasian shelves collected in October 2018 to document terrestrial silicon modifications on shelves and their contribution to the Arctic basin. Nitrogen was found to be depleted in surface waters and the limiting nutrient to primary production in the Laptev Sea, allowing excess silicon export to the central Arctic Ocean. Heavy δ30Si(OH)4 in the water column was linked to the strong biological removal of DSi on shelves, enabled by vigorous N recycling. From isotopically constrained processes, we estimate that >50% of the silicon from riverine inputs is removed within the Lena River delta and on the Laptev Sea shelf. Extrapolating this to major Siberian rivers, this leads to an export of 2.5 ± 0.8 kmol/s of riverine silicon through the Transpolar Drift. An updated isotopic budget of the Arctic Ocean reproduces the observed δ30Si(OH)4 signatures out of the Arctic Ocean and underlines the importance of biological processes in modulating silicon export. Given that opal burial fluxes on Artic shelves are controlled by denitrification and N‐limitation, these processes are sensitive to ongoing climate change. As a consequence of higher riverine DSi inputs and shelf denitrification responding to productivity, it is inferred that silicon export from the Arctic Ocean could increase in the future, accompanied by lighter δ30Si(OH)4 signatures.

THERMAL STATE OF THE LITHOSPHERE BENEATH THE LAPTEV SEA: GEODYNAMIC IMPLICATIONS FROM GEOMAGNETIC DATA

The Laptev Sea is a unique region, representing a transition zone from the spreading Gakkel Ridge to the rift system, located on the continental margin of Eurasia. In this study, we construct high-resolution distributions of the depths to the top and bottom of the lithospheric magnetic layer (LML) for the Laptev Sea using the centroid method and the EMAG2v3 model of the lithospheric magnetic field. Maximum bottom depths of the LML (45–48 km) are observed under the Siberian Platform, in the north of the Verkhoyansk Range, and under the Lena River delta and Buor-Khaya Bay, while the shallowest bottom depths (<34 km) are attributed to the Eurasia Basin and eastern Laptev Sea. Our results indicate that the coldest lithosphere is attributed to the Siberian Platform. The lithospheric heating is observed under the Eurasia Basin and eastern Laptev Sea; the western part of the shelf, Buor-Khaya Bay, and Lena River delta are characterized by the colder lithosphere. The eastern segment of the Khatanga-Lomonosov Fracture is characterized by a local temperature minimum, evidencing for the spreading axis of the Gakkel Ridge does not continue to the shelf. An area of relatively high temperatures in the east of the shelf passes to the continent through the Yana Bay and covers the Yana-Indigirka lowland. This fact along with the crustal thinning and extension allow us to suggest rifting processes in the considered area.

Structure of the Upper Part of the Earth’s Crust in the Area of the Lena River Delta: The First Magnetotelluric Data

Structure of the Upper Part of the Earth’s Crust in the Area of the Lena River Delta: The First Magnetotelluric Data

Carbon Stocks and Potential Greenhouse Gas Production of Permafrost‐Affected Active Floodplains in the Lena River Delta

AbstractArctic warming increases the degradation of permafrost soils but little is known about floodplain soils in the permafrost region. This study quantifies soil organic carbon (SOC) and soil nitrogen stocks, and the potential CH4 and CO2 production from seven cores in the active floodplains in the Lena River Delta, Russia. The soils were sandy but highly heterogeneous, containing deep, organic rich deposits with &gt;60% SOC stored below 30 cm. The mean SOC stocks in the top 1 m were 12.9 ± 6.0 kg C m−2. Grain size analysis and radiocarbon ages indicated highly dynamic environments with sediment re‐working. Potential CH4 and CO2 production from active floodplains was assessed using a 1‐year incubation at 20°C under aerobic and anaerobic conditions. Cumulative aerobic CO2 production mineralized a mean 4.6 ± 2.8% of initial SOC. The mean cumulative aerobic:anaerobic C production ratio was 2.3 ± 0.9. Anaerobic CH4 production comprised 50 ± 9% of anaerobic C mineralization; rates were comparable or exceeded those for permafrost region organic soils. Potential C production from the incubations was correlated with total organic carbon and varied strongly over space (among cores) and depth (active layer vs. permafrost). This study provides valuable information on the carbon cycle dynamics from active floodplains in the Lena River Delta and highlights the key spatial variability, both among sites and with depth, and the need to include these dynamic permafrost environments in future estimates of the permafrost carbon‐climate feedback.

SEISMICITY of YAKUTIA in 2018–2019

According to the information received from 20 stationary digital seismic stations of the Yakutia Branch of Geophysical Survey of the Russian Academy of Sciences, two-year (2018–2019) seismic monitoring of the territory of the Republic of Sakha (Yakutia) was carried out. During this time interval, more than 730 earthquakes with an energy class of KR≥7.2 (magnitude M≥1.8) were registered. During the previous two years, their number was 801. Manifestations of seismicity fixed the spatial position of the contact zones and their constituent blocks of known lithospheric plates: the Eurasian and North American plates in the northeastern and arctic regions, as well as the Eurasian and Amur plates – in the southern areas of Yakutia. The epicentral fields traced individual relief lineaments and identified active boundary structures combined into two large-scale seismic belts – BaikalStanovoy and Arctic-Asian. Their outlines are seen as bands of earthquake epicenters, elongated from the Olekma River to the Sea of Okhotsk in the south and as ensembles of separate groups and chains of earthquakes between the Laptev and Okhotsk Seas in the northeast and in the Arctic. Significant seismic activity has been detected in the northeast of the region – in the Olekminsk region and the Aldan Highlands (South Yakutia), as well as in the Yano-Oymyakon Highlands, the Chersky Ridge and the Laptev Sea. A map of epicenters was constructed for the entire territory of the region, where 12 districts were identified and an analysis of the seismotectonic situation in each of them was given. The map of Arctic earthquakes in the Lena River delta is considered separately. It is compiled according to the processing of digital seismograms obtained at 25 autonomous field stations installed in accordance with the Russian-German project "Seismicity and Neotectonics of the Laptev Sea Region" (SIOLA). In this area during 2016–2019 more than 2 thousand shocks of small energy classes KR≥7.2–10.7 (M≥1.8–3.7) were recorded within the depth interval of 1–36 km of the Earth's crust. The characteristics of the most seismically active local tectonic structures developed in this region are given.

Climate change impacts on streamflow, sediment load and carbon fluxes in the Lena River delta

Water and sediment supply are essential to the health of deltaic ecosystems. Diverse datasets were integrated to better understand how climate change is shifting the supply of water and sediment to the largest polar distributary channel pattern – the Lena River Delta. Here the increase in warming rate from an average air temperature is from 4.1 °C for the period 1950–99 to 6.1 °C during 2000–21, which is higher than in the adjacent polar regions. Streamflow and sediment yield entering the Lena Delta have increased since 1988 by 56.3 km3 and 6.1×106 t, respectively; meanwhile, the Lena River’s increases in water temperature in June, July–August and September were found to be as much as 1.1, 0.6 and 0.05 °C. These changes have a pronounced effect on sediment regimes in particular parts of the delta. Based on analyses of correlations between various hydroclimatic drivers and sediment concentration changes across particular distributaries of the Lena Delta extracted from Landsat datasets, bank degradation driven by thermal erosional processes (which are in turn related to air and soil temperature increases) is proved to be the primary factor of the sediment regime in the delta. The study also highlights that sediment load changes are sensitive to wind speed due to remobilization of bottom sediment. Sums of daily air temperature and wind speed over 3 days are correlated with sediment concentration changes in the delta. The results also indicate that carbon transport across the delta (both POC and DOC) depends on sediment transport conditions and water discharge and might increase by up to 10 %. We conclude that the Lena Delta can be recognized as the global hot spot in terms of the hydrological consequences of climate change, which is altering sediment regimes, stream hydromorphology and carbon transport.

Investigating the thermal state of permafrost with Bayesian inverse modeling of heat transfer

Abstract. Long-term measurements of permafrost temperatures do not provide a complete picture of the Arctic subsurface thermal regime. Regions with warmer permafrost often show little to no long-term change in ground temperature due to the uptake and release of latent heat during freezing and thawing. Thus, regions where the least warming is observed may also be the most vulnerable to permafrost degradation. Since direct measurements of ice and liquid water contents in the permafrost layer are not widely available, thermal modeling of the subsurface plays a crucial role in understanding how permafrost responds to changes in the local energy balance. In this work, we first analyze trends in observed air and permafrost temperatures at four sites within the continuous permafrost zone, where we find substantial variation in the apparent relationship between long-term changes in permafrost temperatures (0.02–0.16 K yr−1) and air temperature (0.09–0.11 K yr−1). We then apply recently developed Bayesian inversion methods to link observed changes in borehole temperatures to unobserved changes in latent heat and active layer thickness using a transient model of heat conduction with phase change. Our results suggest that the degree to which recent warming trends correlate with permafrost thaw depends strongly on both soil freezing characteristics and historical climatology. At the warmest site, a 9 m borehole near Ny-Ålesund, Svalbard, modeled active layer thickness increases by an average of 13 ± 1 cm K−1 rise in mean annual ground temperature. In stark contrast, modeled rates of thaw at one of the colder sites, a borehole on Samoylov Island in the Lena River delta, appear far less sensitive to temperature change, with a negligible effect of 1 ± 1 cm K−1. Although our study is limited to just four sites, the results urge caution in the interpretation and comparison of warming trends in Arctic boreholes, indicating significant uncertainty in their implications for the current and future thermal state of permafrost.

New data on the transformation of water and sediment runoff into the Lena river delta based on the results of expedition measurements in August 2022

Field hydrological measurements were performed in the Lena River delta from the 10th to the 16th of August 2022. 25 values of water discharge and 58 suspended sediment concentrations (SSC) were measured, multiple chemical composition water samples were taken, along with samples of bottom and bank river sediments, and thermal abrasion coasts were highlighted. Particle size and chemical composition analyses of the sediment samples were carried out. The aim of the study was to estimate the water flow distribution in the delta and to determine the directional SSC, sediment particle size and chemical composition changes along the delta and inside the depth of the river flow, and define the roles of the local hydrological and morphological factors of river flow transformation. Moreover, field measurements are crucial for SSC estimation and monitoring based on satellite image data. The laboratory analyses included particle size definition in suspended and bottom sediment samples, organic matter and SSC definition. The August 2022 expedition results were compared to the previous surveys. It was established that the flow distribution around the Stolb island corresponds with that of 2016: the Bykovsky, Trophimovsky, Tumatsky and Oleneksky branches receive 24.9–25.5, 58–59.2, 6 and 6.6 % of the water discharge from the Kusur gauging station on the Lena River, respectively. However, the role of the Main channel was slightly overestimated. The new data includes water discharges in the branches around the Samoilovsky island and in the channel systems of the Oleneksky and Tumatsky branches. SSC was relatively low and amounted to around 12–24 mg/l, rising from the water surface to the bottom 1.2–2 times. SSC decreased along the course of the Oleneksky and Tumatsky branches (1.5 and 1.1 times, respectively) due to the ratio between SSC and the potential stream transport capacity. SSC rose along the course of the Bykovsky branch, even though it wasn’t shown by the Landsat-8 satellite image (16th of August 2022). A significant sediment source in the delta are eroded and thermo eroded shores of the edoma island systems. The average sediment size proved to be from 0.011 to 0.019 mm. SSC does not vary much around the main channel and the nearest branches. Important relations between SSC, optical turbidity and ADCP backscatter intensity were estimated. The coarse diameter of 30 bottom sediment samples was 0.46 mm. The largest sediments were discovered in the Bykovsky branch, while the smallest sediments were found in the smaller transverse branches. Along the Tumatsky and Oleneksky branches the bottom sediments alternate from fine to medium sands.

Study of the relationship between agrochemical indicators of soils and species composition of plants in some sites of the Lena River Delta, Northern Yakutia

In connection with climate change and the development of natural resources in the Arctic, increasingly relevant is the problem of revealing the response of tundra vegetation to various natural and anthropogenic impacts, as well as the search for indicators for developing a system of monitoring the state of ecosystems in the Far North. The aim of this work was to describe the floristic composition and structure of plant communities, as well as to search for relationships between agrochemical indicators of soils and the species composition of plants in certain key sites of the Lena River Delta. A total of ten key sites of the Lena delta were studied. Agrochemical analysis of the soil samples was performed using standard methods. The content of biogenic and abiogenic elements was measured using an emission spectrometer. The relationship between the soil parameters and floristic composition was studied using cluster analysis. It was shown that the clustering of sites by standard agrochemical indicators was weakly expressed, while in terms of the content of elements in the mineralized samples and in water extracts the sites were grouped into two clusters at the level of 40 %÷60 % of the differences. The clustering of sites by plant species composition was very weak, and it was not possible to identify clusters with high or medium level of similarity, nor was it possible to detect similarity between cluster diagrams constructed by soil parameters and by plant species composition. As a result of the study, it is shown that the species composition of vascular plants weakly correlates with the properties of the soils of the key sites. The individual features identified manifest themselves in the form of trends and no clear patterns of interrelation of vegetation and soil parameters are discerned.

Trees on the tundra: warmer climate might not favor prostrate Larix tree but Betula nana shrub growth in Siberian tundra (Lena River Delta)

Tundra is primarily a habitat for shrub growth, not trees, but growth of prostrate forms of trees has been reported occasionally from the subarctic tundra region. In the light of on-going climate change, climate sensitivity studies of these unique trees are essential to predict vegetation dynamics and potential northward expansion of boreal forest tree species into tundra. Here we studied one of the northernmost Larix Mill. trees and Betula nana L. shrubs (72°N) from the Siberian tundra for the common period 1980-2017. We took advantage of the discovery of a single cohort of prostrate Larix trees within a tundra ecosystem, i.e., ca. 60 km northwards from the northern treeline, and compared climate-growth relationships of the two species. Both woody plants were sensitive to the July temperature, however this relationship was stable across the entire study period (1980-2017) only for Betula nana chronology. Additionally, radial growth of Larix trees became negatively correlated to temperatures during the previous summer. In recent period moisture sensitivity between Larix trees and Betula nana shrubs was contrasting, with generally wetter soil conditions favoring Larix trees growth and dryer conditions promoting Betula nana growth. Our study indicates that Larix trees radial growth in recent years is more sensitive to moisture than to summer air temperatures, whereas temperature sensitivity of Betula nana shrub is stable over time. We provide first detailed insight into the annual resolution on Larix tree growth sensitivity to climate in the heart of the tundra. The potentially higher Betula nana shrub resistance to warmer and drier climate versus Larix trees on a tundra revealed in our study needs to be further examined across habitats of various soil, moisture and permafrost status.

Features of Formation of the Lena Polynya on the Estuarine Coast of the Bykovsky Arm in the Summer

Based on the results of the global oceanic reanalysis (GLORYS12.v.1), materials of hydrometeorological observations of the Roshydromet network in the Laptev Sea and the mouth of the Lena River, reviews of the ice processes in the Arctic Ocean by the Arctic and Antarctic Research Institute, this paper considers the features of the evolution of the Lena Polynya on the estuarine coast of the Bykovsky Arm in the warm period 1993–2019. The relationship between the timing of the formation of a polynya on the seashore of this arm with the dates of the beginning of the flood at the top of the Lena River delta has been revealed. The assumption is confirmed that the average growth rate of the Lena polynya in summer is determined by the timing of its formation – the earlier the flood begins, the earlier the polynya forms on the coast of the Bykovsky arm and the smaller the average rate its growth. It has been established that the process of warming in the mouth area of the Lena in 2008–2019 stabilized, as there are no significant trends in the characteristics of water and ice regimes. These regularities may be invariant for other mouths of the rivers of the Laptev Sea basin, and the obtained dependences can be used to improve the forecast of the dates of cleansing of the water area at the estuary seashore of the Lena from ice and planning icebreaking navigation along the route Tiksi port–Lena River.

Particulate organic matter in the Lena River and its delta: from the permafrost catchment to the Arctic Ocean

Abstract. Rapid Arctic warming accelerates permafrost thaw, causing an additional release of terrestrial organic matter (OM) into rivers and, ultimately, after transport via deltas and estuaries, to the Arctic Ocean nearshore. The majority of our understanding of nearshore OM dynamics and fate has been developed from freshwater rivers despite the likely impact of highly dynamic estuarine and deltaic environments on the transformation, storage, and age of OM delivered to coastal waters. Here, we studied particulate organic carbon (POC) dynamics in the Lena River delta and compared them with POC dynamics in the Lena River main stem along a ∼ 1600 km long transect from Yakutsk, downstream to the delta. We measured POC, total suspended matter (TSM), and carbon isotopes (δ13C and Δ14C) in POC to compare riverine and deltaic OM composition and changes in OM source and fate during transport offshore. We found that TSM and POC concentrations decreased by 70 % during transit from the main stem to the delta and Arctic Ocean. We found deltaic POC to be strongly depleted in 13C relative to fluvial POC. Dual-carbon (Δ14C and δ13C) isotope mixing model analyses indicated a significant phytoplankton contribution to deltaic POC (∼ 68 ± 6 %) and suggested an additional input of permafrost-derived OM into deltaic waters (∼ 18 ± 4 % of deltaic POC originates from Pleistocene deposits vs. ∼ 5 ± 4 % in the river main stem). Despite the lower concentration of POC in the delta than in the main stem (0.41 ± 0.10 vs. 0.79 ± 0.30 mg L−1, respectively), the amount of POC derived from Yedoma deposits in deltaic waters was almost twice as large as the amount of POC of Yedoma origin in the main stem (0.07 ± 0.02 and 0.04 ± 0.02 mg L−1, respectively). We assert that estuarine and deltaic processes require consideration in order to correctly understand OM dynamics throughout Arctic nearshore coastal zones and how these processes may evolve under future climate-driven change.

Species Diversity and Driving Factors of Benthic and Zooplanktonic Assemblages at Different Stages of Thermokarst Lake Development: A Case Study in the Lena River Delta (Middle Siberia)

Global climate change might result in permafrost thaw and the formation of thermokarst landscapes that release long-term carbon stocks as greenhouse into the atmosphere, thereby initiating a positive climate feedback. These processes are mediated by biological activity, including by microbes, vascular plants and animals, whereas the role of invertebrates in thermokarst ecosystems remains poorly understood. We investigated the diversity and assemblage structures of zooplankton (mainly Copepoda, Cladocera), microbenthos (testate amoebae) and meio- (Copepoda and Cladocera) and macrozoobenthos (mollusks, crustaceans, insects and annelids) from a range of water bodies representing different stages of thermokarst lake formation in the southern part of the Lena River Delta (Central Siberia). Altogether, 206 species of testate amoeba, mollusk, crustacean, insect and annelid taxa were identified. A total of 60 species of macrozoobenthos (mainly insects) and 62 species of testate amoebae were detected in the water bodies of the Lena River Delta for the first time. The species richness of zooplankton and meio- and macrozoobenthos was greater in the large thermokarst lakes than in the polygonal ponds due to the freezing of the latter in the winter. In contrast, the species richness of protists was higher in the polygonal ponds, which was related to the habitat preferences of testate amoebae. Fish grazing strongly affected the macrobenthos assemblages but not the smaller-sized organisms. Water acidity and temperature were the main environmental drivers of the assemblage structure of testate amoeba and microcrustacean. The species structure of the macroinvertebrate assemblages was significantly explained by water acidity, permafrost depth and size of the water area. It means that small size organisms with their short generation times are sensitive to more dynamic factors such as temperature and may serve as indicators of ecosystem changes due to global climate warming. In contrast, large size organisms are affected by driven factors that appear during thermokarst lakes formation and permafrost degradation.

Eurytemora gracilicauda (Copepoda: Calanoida) in the Russian Arctic

As a result of studying the populations of Eurytemora genus crustaceans from the internal reservoirs of the drainage basin of the White, Pechora Seas, the Lena deltas, Island of Wrangel and Kamchatka peninsula was set that the species Eurytemora gracilicauda is common along the entire northern border of Russian Eurasia. It was shown that the species distribution for populations from the rockpools of the Kandalaksha Bay of the White Sea, from Lake on Kashin Island in the Pechora Sea and from the Lena River Delta was sequentially along the coast of the Arctic. Studies are based on genetic (parts of CO1 and ITS1 genes) and morphological analyzes of the studied populations. The synonymy of the Kamchatka species E. kurenkovi and E. gracilicauda was confirmed by the morphological analysis. Variation coefficients (CV), calculated for the populations of females from the White Sea, the Lena River delta and from the Kamchatka do not exceed 10%, which indicates a low morphological variability of the species. The most widely represented in the genetic analysis, the White Sea population has a low level of genetic variability, which, together with significant tolerance to the fluctuations of salinity in the rockpools in which it lives, may indicate its recent introduction to the region. A phylogenetic reconstruction was not revealed reliable topology for the species E. gracilicauda. It was shown that E. gracilicauda is not related to the affinis group species. Molecular Clocks with use part of CO1 gene and paleontological calibration revealed the speciation of E. gracilicauda species on the Paleocene – Late Cretaceous boundary. We also can hypothesize a Laurasian origin of the Eurytemora genus.

SEISMICITY of YAKUTIA in 2016–2017

According to the data of 23 seismic stations of the Yakutia branch of GS RAS, the seismicity monitoring of the territory of the Republic of Sakha (Yakutia) was carried out for 2016–2017. During this period, more than 800 earthquakes with an energy class of KR≥7.1 (magnitude M≥1.7) were registered. This is somewhat more than in 2015 (N=567) and is due to the extension of the time interval of work up to 2 years. The epicenters were located in the zones of interaction between large lithospheric plates: the Eurasian and North American in the Northeastern and Arctic regions, as well as the Eurasian and Amur in the southern regions of Yakutia. The clusters of these events comprised two extended (Arctic-Asian and Baikal-Stanovoy) seismic belts. On the map of epicenters, these zones are displayed as a continuous strip of earthquakes from the Olekma River to the Sea of Okhotsk in the south and in the form of separate groups and clusters of earthquakes between the Laptev and Okhotsk Seas – in the northeast and in the Arctic. The highest seismic activity was noted in the Olekma area, the Stanovoy Ridge and the Aldan Highlands (Southern Yakutia) and the Chersky Ridge and Laptev Sea (in the North-East). Information on the manifestations of local seismicity in the Lena River Delta, where from August 2016 to December 2017 is given. 25 temporary field automatic stations under the joint Russian-German project "Seismicity and neotectonics of the Laptev Sea region" (SIOLA) in 2016–2018 operated. The first results of the distribution of Arctic earthquakes in the lower reaches of the Lena River in space, time, by depth and their connection with active tectonics are considered.

STUDYING POLYNYA OCCURRENCE TERMS AND DURATION ON THE SHIPPING ROUTES IN THE LAPTEV SEA

The dynamics of the development of the Lena polynya formed on the shipping routes of the Northern Sea Route in the Laptev Sea and its influence on the conditions of navigation in the Arctic are studied. During the period of winter-spring navigation in the Laptev Sea, the Great Siberian polynya, which is located near the fast ice border and creates good opportunities for winter navigation on the Northern Sea Route, is formed. This problem is important to ensure year-round navigation in the Eastern Sector of the Northern Sea Route. The hypothesis that the terms of a polynya occurrence can significantly affect the average rate of its growth is tested in the study. When checking, the results of the GLORYS12v1 global reanalysis and standard methods of mathematical statistics are used. On the example of the polynya section located on the estuary seashore of the largest navigable channel of the Lena River Delta - Bykovskaya, the validity of the hypothesis is confirmed. Steady trends in the change in the polynya formation terms towards earlier dates in the modern period are revealed. A high probability of improving the conditions of navigation in this region in 2020-2040 is noted. At the same time, with further warming of the Siberian climate, the opposite process, namely, the freezing of a polynya that formed too early, which will lead to a cooling of the climate in the region and a deterioration in navigation conditions, is possible. Comparing the results obtained with other studies that are devoted to the construction of general routes for ships in various ice conditions, it is possible to identify trends that the actual routes during independent navigation pass along the forming polynyas, regardless of the physical principle of their formation, then the choice of general routes for ships in the areas of polynya distribution will be promote more intensive and safe shipping. What requires accurate forecasts of its size and position. The relevance of the research results for forecasting year-round navigation, both for independent navigation of ships with a high ice class, and in the development of plans for using icebreaking escort of ships, is noted.

Results of local seismological monitoring in the Lena delta region

Refinement of the geodynamic situation in the area of the Lena River delta is relevant for understanding local geological processes. Previously, source seismology for this area was provided only by remote regional seismic stations. This paper shows the results of processing data from detailed seismological observations for 2018–2021. The distribution of earthquake hypocenters and their focal mechanisms are presented. The results of processing largely confirm the a priori geological data and do not contradict the results of regional observations. The accumulation of earthquakes in the area of the Kharaulakh Range most likely refers to the Primorsky Fault, which extends along the coast of the Bykovskaya channel. According to geological studies, the Primorsky Fault is a fault, which is confirmed by the focal mechanisms of earthquake sources in this area.