Lena River Delta Research Articles

Viruses in the water column and the sediment of the eastern part of the Laptev Sea

The distribution of viruses and their impact on prokaryotes were studied using the epifluorescence and transmission electron microscopy along a transect, located at 130°E from the area adjacent to the Lena River delta next to the shelf area, the continental slope area and the deep-sea regions of the Laptev Sea in September 2015. The abundance of planktonic prokaryotes (NP) and free viral particles (NV), the frequency of visibly virus-infected prokaryotic cells (FVIC), and the viral-mediated prokaryotic mortality (VMP) varied within the following ranges: (0.1–3.1) × 106 cells mL−1, (0.1–4.4) × 106 viruses mL−1, 0.3–1.7% of NP, and 2.1–12.2% of the total mortality of prokaryotes, respectively, and reached maximum values at the inner shelf area. The percentage of viruses attached to prokaryotic cells varied from 2 to 6% of NV in the surface waters of the outer shelf and the deep-sea areas to 43–46% at the depth of 100–140 m in the continental slope area. The percentage of viruses that were attached to detrital or mineral microparticles varied from less than 1% in the waters of the deep-sea area to 27–50% in the waters of the inner shelf area adjacent to the Lena River delta. A negative correlation was found between the fraction of lysogenic prokaryotes and the FVIC values (r = – 0.60, p < 0.05).In the 20-cm bottom water layer above the sediment the NP, NV, FVIC and VMP values were (0.8–3.0) × 106 cells mL−1, (1.6–3.4) × 106 viruses mL−1, 0.5–1.2%, and 3.7–9.5%, respectively. In the surface 2-cm layer of the sediment these parameters were (1.8–4.4) × 109 cells cm−3, (0.8–2.3) × 109 viruses cm−3, 0.2–1.0%, and 1.4–7.8%, respectively. In the bottom water layer the percentage of viral particles attached to prokaryotes and to detrital and mineral particles was 10–29% and 20–79% of NV, respectively. In the surface sediments the percentage of viral particles attached to prokaryotes was considerably higher compared to the bottom water layer and ranged from 44 to 57% of NV. The capsid size of the viral particles from the pelagic zone, bottom water layer and surface sediments was on average 71 ± 14, 74 ± 7 and 63 ± 7 nm, respectively. In all these habitats, viruses from the size class of 60–100 nm prevailed.The relatively high abundance of prokaryotes and viruses, as well as the high FVIC values in the freshwater-seawater mixing zone (the highest values were recorded in the waters with a salinity of 9.6 psu) were apparently caused by the influx of considerable amounts of nutrients, and dissolved and particulate organic matter that come with the river runoff. At the same time, the high concentration of small detrital and mineral particles in the freshwaters lead to considerable adsorption of viruses by these particles and caused a decrease in the FVIC in the coastal areas adjacent to the Lena River delta.

Pojemność wodna i właściwości gleb rosyjskiej Arktyki (na przykładzie delty rzeki Leny i Półwyspu Jamalskiego)

Pojemność wodna i właściwości gleb rosyjskiej Arktyki (na przykładzie delty rzeki Leny i Półwyspu Jamalskiego)

Identifying Drivers of Seasonality in Lena River Biogeochemistry and Dissolved Organic Matter Fluxes

Warming air temperatures, shifting hydrological regimes and accelerating permafrost thaw in the catchments of the Arctic rivers is affecting their biogeochemistry. Arctic rivers monitoring is necessary to observe changes in the mobilization of dissolved organic matter (DOM) from permafrost. The Lena River is the second largest Arctic river and 71 % of its catchment is continuous permafrost. Biogeochemical parameters, including temperature, electrical conductivity (EC), stable water isotopes, dissolved organic carbon (DOC) and absorption by coloured dissolved organic matter (aCDOM) have been measured as part of a new high-frequency sampling program in the central Lena River Delta. The results show strong seasonal variations of all biogeochemical parameters that generally follow seasonal patterns of the hydrograph. Optical indices of DOM indicate a trend of decreasing aromaticity and molecular weight from spring to winter. High-frequency sampling improved our estimated fluvial flux of annual dissolved organic carbon flux (6.79 Tg C). EC and stable isotope data were used to distinguish three different source water types which explain most of the seasonal variation in the biogeochemistry of the Lena River. These water types match signatures of (1) melt water, (2) rain water and (3) subsurface water. Melt water and rain water accounted for 84 % of the discharge flux and 86 % of the DOC flux. The optical properties of melt water DOM were characteristic of fresh organic matter. In contrast, the optical properties of DOM in subsurface water revealed lower aromaticity and lower molecular weights, which indicate a shift towards older organic matter source mobilized from deeper soil horizons or permafrost deposits. The first year of this new sampling program sets a new baseline for flux calculations of dissolved matter and has enabled the identification and characterization of water types that drive the seasonality of the Lena River water properties.

New Data on the Expansion of Eurytemora Giesbrecht (Copepoda: Calanoida) in the Russian Arctic Region.

As a result of studying different populations of crustaceans of the genus Eurytemora Giesbrecht from the inland water bodies of the basins of the White Sea, the Pechora Sea, the Lena River delta, and Pacific coast of the United States, the species Eurytemora gracilicauda Akatova 1949 has been found along the entire northern border of the Russian Eurasia, while North American E. americana Williams 1906 has not been registered within these limits. Clear morphological and molecular genetic differences between E. gracilicauda and E. americana are presented.

Vertical Variability of Primary Production and Features of the Subsurface Chlorophyll Maximum in the Laptev Sea in August–September, 2015, 2017, and 2018

The vertical distribution of phytoplankton primary production (PP) and chlorophyll a (Chl) was studied based on the data carried out in August–September 2015, 2017, and 2018. The PP maximum was located at the surface or within the 0–5 m subsurface layer. The subsurface chlorophyll maximum (SCM) was recorded at 39% stations on the outer shelf and in the vicinity of the continental slope. The SCM was not detected along the northward transect (130° E) from the Lena River delta. As in other areas of the World Ocean, the SCM was located below the upper mixed layer (UML), in the nitracline, near the boundary of the euphotic zone (1% of photosynthetically active radiation). Generally, the SCM was not accompanied by an additional PP maximum. The Chl concentration at the SCM did not exceed 1 mg m–3. PP produced within the UML and SCM contributed 72 and 23%, respectively, to the integrated primary production (IPP) of the water column. Our results suggest that the influence of the SCM on IPP was insufficient due to low Chl concentration and PP colimitation by the low light and temperature at these depths.

Coloured dissolved organic matter in aquatic ecosystems of three representative regions of the Arctic according to the data obtained in year 2019

In this study the laboratory analysis of water samples from three representative regions of the Arctic for content of coloured dissolved organic matter (CDOM) – the important component of natural waters, which has a direct impact on state of aquatic ecosystems, was made. Samples were collected from water objects from the Kola Peninsula, the Yamal Peninsula and the Lena River Delta. The results of the analysis made it possible to determine CDOM concentrations in water. According to the average values, the highest values were obtained for the Yamal Peninsula and lowest – for the Kola Peninsula. The predominance of allochthonous CDOM in the water objects from all three regions was revealed. Moreover, the complete absence of photodegradation processes was determined. For the lakes and rivers from the Kola Peninsula it was also possible to follow seasonal dynamic of CDOM concentration in water and to compare it with earlier obtained data concerning seasonal CDOM dynamic in the Lena River Delta. Results are actual due to the currently existing tendency of climate change which leads to intensification of thermal denudation and thermal erosion processes in the cryolithozone, which are consequently increasing income of allochthonous CDOM in water objects.

Ice-covering hydrological and hydrochemical investigations on the Lena River delta

The study reported here was conducted on the channels of the Lena River delta in April 2019. The water temperature, specific conductivity, dissolved oxygen, PAR fluxes, and currents were measured on the cross-sections in the Olenekskaya and Bykovskaya channels, as well as in the main channel of the Lena River near Samoilov Island using the multiparameter probes CTD-48M, CTD-90M and RBR-Concerto. An analysis of the data showed that the water in the channels of the Lena River delta in winter is well saturated with oxygen (4.9-6.3 ml/l), has a very low temperature (from -0.1°C to +0.8°C). The specific conductivity of water Lena River delta channels changed from 460 to 530 )S/cm. A thick layer of snow 0.1-0.5 m with an ice thickness of more than 1.5 m prevents the penetration of solar radiation into the subglacial layer, where the PAR fluxes does not exceed 10 µmol/m2s. Current velocities reached 20–25 cm/s in the Bykovskaya channel, in Olenekskaya channel – 5-11 cm/s, and in the main channel – 12-18 cm/s. The currents data obtained made it possible to calculate the discharge in the channels during the ice-period.

Primary plant succession on freshly degraded yedoma (ice complex) in Lena delta (Eastern Siberia)

Primary plant succession was studied on freshly eroded yedoma in the southern part of Lena River Delta. Four stages of vegetation development were clearly distinguished. The first stage starts on bare ground and lasts from two-three months to one year. Its vegetation is represented only by fragmented cover of young mosses and a few seedlings of vascular plants. The most abundant moss species at this moment is Ceratodon purpureus. The second stage lasts from one to three years depending on slope steepness. Plants cover 20 to 60% of the soil surface. Main dominants are Descurainia sophioides and Tephroseris palustris. The third stage of succession presented by closed species-poor grasslands with Arctagrostis arundinacea as main dominant. This stage lasts for up to 20 years. The fourth stage is represented by species-rich herbaceous communities, which also have Arctagrostis arundinacea as main dominant but enriched with many perennial herbs. There is not enough data to determine the duration of this stage but it is at least few tens of years. This successional system requires a long time for its development. It means that IC degradation is not a recent process but accompanied yedoma deposits through all of its history.

Arctic climate variability and ice regime of the Lena River delta lakes

Climate variability in the Russian Arctic in 1991-2017 is examined based on the mesurements of the air temperature at 19 meteorological stations. The average annual air temperature at the stations fluctuated relative to the climatic baseline of 1961-1990 by 0.5-4°C in 1991-2004. Since 2005, it was higher than the climatic baseline at all stations annually. The increase in the air temperature was most pronounced in the winter months from November to February at all stations (more than 15ºC at some stations in some years). The increase in the air temperature in the summer months was noticeably smaller. The baseline level of the average monthly air temperature from November to February was exceeded most prominently at high latitude meteorological stations located at Wiese Island, Severnaya Zemlya, and Franz Josef Land (16-17ºC in some years, starting with 2005). Stations located at a distance from the ocean, such as Khatanga and Tiksi, are characterized by a smaller temperature increase compared to coastal and island stations, such as Barenzburg, Wrangel Island and others. Smaller deviations of the air temperature from the baseline level are typical in the western sector of the Russian Arctic (Murmansk, Svyatoy Nose). The influence of the Arctic climate variability on the ice regime of arctic lakes is considered according to Flake model (http://www.flake.igb-berlin.de/) for the Lena River Delta lakes.

Cold Adapted Nitrosospira sp.: A Potential Crucial Contributor of Ammonia Oxidation in Cryosols of Permafrost-Affected Landscapes in Northeast Siberia.

Permafrost-affected landscape soils are rich in organic matter and contain a high fraction of organic nitrogen, but much of this organic matter remains inaccessible due to nitrogen limitation. Microbial nitrification is a key process in the nitrogen cycle, controlling the availability of dissolved inorganic nitrogen (DIN) such as ammonium and nitrate. In this study, we investigate the microbial diversity of canonical nitrifiers and their potential nitrifying activity in the active layer of different Arctic cryosols in the Lena River Delta in North-East Siberia. These cryosols are located on Samoylov Island, which has two geomorphological landscapes with mineral soils in the modern floodplain and organic-rich soils in the low-centered polygonal tundra of the Holocene river terrace. Microcosm incubations show that the highest potential ammonia oxidation rates are found in low organic soils, and the rates depend on organic matter content and quality, vegetation cover, and water content. As shown by 16S rRNA amplicon sequencing, nitrifiers represented 0.6% to 6.2% of the total microbial community. More than 50% of the nitrifiers belonged to the genus Nitrosospira. Based on PCR amoA analysis, ammonia-oxidizing bacteria (AOB) were found in nearly all soil types, whereas ammonia-oxidizing archaea (AOA) were only detected in low-organic soils. In cultivation-based approaches, mainly Nitrosospira-like AOB were enriched and characterized as psychrotolerant, with temperature optima slightly above 20 °C. This study suggests a ubiquitous distribution of ammonia-oxidizing microorganisms (bacteria and archaea) in permafrost-affected landscapes of Siberia with cold-adapted AOB, especially of the genus Nitrosospira, as potentially crucial ammonia oxidizers in the cryosols.

A multiproxy-based reconstruction of the mid- to late Holocene paleoenvironment in the Laptev Sea off the Lena River Delta (Siberian Arctic)

Land-shelf interactions and related environmental changes were reconstructed for the past 6 cal. kyrs interpreting multiproxy records from the two AMS14C-dated sediment cores from the sites located to the north and northeast of the Lena River delta. Proxies used include terrestrial and aquatic palynomorphs, benthic/planktic foraminifers and ostracods paired with benthic δ18O and δ13C records of Haynesina orbiculare. The study focused on unravelling the relation between river runoff and the regional climate changes on the one hand, and its imprint on the shelf sea environment on timescales beyond the instrumental records on the other.The palynomorph records show that the Lena River outflow largely determined the composition of species associations and the magnitude of terrestrial matter influx from land. Pollen assemblages of the inner Laptev Sea shelf reflect complex pollen contribution of the Arctic tundra and remote taiga zones drained by the Lena River and indicate a vegetation response to warmer-than-present climatic conditions between 6.0 and 4.5 cal. ka and a subsequent gradual cooling. Fluvial influence in the records is manifested by (1) increases in sedimentation rates; (2) high influxes of pollen/spores and freshwater chlorophycean algae, wood and plant remains; (3) negative δ13C excursions due to the introduction of dissolved inorganic carbon (DIC) from river water. Episodes of enhanced freshwater influence in the surface water layers (fluvial events) correlate with positive benthic δ18O excursions and increasing representation of river-distal species among benthics. Altogether, this points to an estuarine-like reversed (north to south) bottom current activity along the submarine paleovalleys on the shelf. The most pronounced fluvial events are recognized at 5.3–5.9, 1.5 and <0.5 cal. ka. The oldest fluvial event coincides with the final stage of mid-Holocene climate warming. A fluvial event at 1.5 cal. ka is specifically strong at the northeastern site thus marking a direction change of the Lena River outflow at this time and the progressive protrusion of the delta. During the past 500 years distinct negative δ13C values at the northeastern site reflect enhanced riverine influence. It is therefore concluded that the unprecedented change in the δ13C trend corroborates the other evidence for a principal diversion of the major Lena River outflows into its present-day, easterly direction.

Hydrochemical regime of the Lena river in august 2018

The new hydrochemical data collected during August 2018 cruise from Yakutsk to Kyusyur, in the middle and lower reaches of the Lena River, are presented. Field and laboratory data were collated into a database containing 80+ parameters, notably stable water isotopes, suspended sediment concentration and dissolved organic carbon. Presented results allow the quantitative assessment of fluxes of dissolved and suspended material toward the Lena River delta, and the deduction of the regularities of transformation of these fluxes.

Dynamics of the relief and sesmotectonic activity of the modern structures in the delta of the river lena

This paper presents seismogeodynamic analysis of modern structures located in the Lena river delta. These structures are key elements in the tectonic evolution of the shelf–continent transition zone in the Arctic segment of the boundary between the Eurasian and North American lithospheric plates. The geological structure of the Lena river delta is predetermined by the junction of the ancient Siberian platform and the Mesozoic Laptev Sea plate. These two large geoblocks of the crust, which differ in age, are separated by a fragment of the Kharaulakh segment of the Verkhoyansk fold system. In our study aimed to reveal regularities in seismotectonic destruction of the crust, we analyzed the geological and geophysical data on the crustal structure, active faults, modern structural plan, dynamic characteristics of the modern relief, and hydrological features characterizing of the flow redistribution in the Lena riverbed. A system of active faults identified in the Lena river delta shows a contrasting kinematic plan of the junction zone of the main geostructures. According to the analysis results, shear faulting is a dominant factor of impact on the morphologic features and seismogeodynamic activation of the modern structures. A regional right-lateral strike-slip fault of the sublatitudinal strike is traced as a major structural boundary that cuts the Lena river delta into several geodynamic segments. Seismotectonic destruction of the crust in the segments differs in types (transpression, transtension and compression). The above-mentioned fault is not only the main element of the kinematic plan of the newest structures in the Lena river delta – it controls the general structural pattern and seismotectonic parameters of active fault zones in the entire northern sector of the Verkhoyansk marginal suture. The seismogeodynamic analysis results obtained in our study provide a reliable basis for estimating potential seismic hazard of the modern structures in the Lena river delta and updating the available seismic zoning maps of the shelf–continent transition zone in the Arctic segment of the boundary between the Eurasian and North American lithospheric plates.

Dynamics of the Relief and Seismotectonic Activity of the Modern Structures in the Delta of the River Lena

The paper presents seismogeodynamic analysis of modern structures located in the Lena river delta. These structures are key elements in the tectonic evolution of the shelf–continent transition zone in the Arctic segment of the boundary between the Eurasian and North American lithospheric plates. The geological structure of the Lena river delta is predetermined by the junction of the ancient Siberian platform and the Mesozoic Laptev Sea plate. These two large geoblocks of the crust, which differ in age, are separated by a fragment of the Kharaulakh segment of the Verkhoyansk fold system. In our study aimed to reveal regularities in seismotectonic destruction of the crust, we analyzed the geological and geophysical data on the crustal structure, active faults, modern structural plan, dynamic characteristics of the modern relief, and hydrological features characterizing of the flow redistribution in the Lena riverbed. A system of active faults identified in the Lena river delta shows a contrasting kinematic plan of the junction zone of the main geostructures. According to the analysis results, shear faulting is a dominant factor of impact on the morphologic features and seismogeodynamic activation of the modern structures. A regional right-lateral strike-slip fault of the sublatitudinal strike is traced as a major structural boundary that cuts the Lena river delta into several geodynamic segments. Seismotectonic destruction of the crust in the segments differs in types (transpression, transtension and compression). The above-mentioned fault is not only the main element of the kinematic plan of the newest structures in the Lena river delta – it controls the general structural pattern and seismotectonic parameters of active fault zones in the entire northern sector of the Verkhoyansk marginal suture. The seismogeodynamic analysis results obtained in our study provide a reliable basis for estimating potential seismic hazard of the modern structures in the Lena river delta and updating the available seismic zoning maps of the shelf–continent transition zone in the Arctic segment of the boundary between the Eurasian and North American lithospheric plates.

Evaluating closed chamber evapotranspiration estimates against eddy covariance measurements in an arctic wetland

Evapotranspiration (ET) is an important hydrological flux with a strong influence on greenhouse gas emissions from thawing permafrost. This study examines the suitability of the closed chamber method in characterising the spatial heterogeneity of ET fluxes in a typical polygonal tundra landscape in the Lena River Delta, northern Siberia. Actual evapotranspiration is compared across scales using: (1) ground-based chamber measurements to observe ET at the microsite scale; and (2) tower-based eddy covariance (EC) measurements which provide spatially averaged ET observations at the ecosystem level. Adopting an upscaling approach using EC estimates as a benchmark, the authors assess the suitability of the closed chamber method in an arctic wetland environment. A short closure time (40 s) and a linear model to describe the change in chamber headspace water vapour concentration were employed to estimate ET rates from the chamber measurements. Using a correction factor chamber fluxes were successfully scaled to the EC data. Yet, findings suggest that the performance of the closed chamber method is highly sensitive to the prevailing hydrometeorological conditions, and it is likely that the sorption and desorption of water molecules to the inside of the chamber and tubing has a strong impact on results. A number of methodological issues are presented in this paper which question the use of closed chamber measurements as a stand-alone tool for measuring ET in arctic wetland environments. However, when paired alongside a trusted benchmark, chambers can provide valuable information on ET at the microsite scale.

Geomorphological structure and neotectonics of the Lena delta

New data about geomorphological structure and neotectonic movements of the Lena Delta is presented. Thet are based on results of the Russian-German expeditions Lena-2013, Lena-2014, Lena-2015 and Lena-2018 and include geomorphological profiling with high quality satellite instruments and a number of radiocarbon dates on the Sobo-Sise, Kurungnakh, Jangylakh-Sis and Khardang-Sise islands. These islands consist of the Late Pleistocene Ice Complex (IC) remnants eroded by river and sea, and the first terrace of the Delta, which adjoins the remnants. The first terrace started to form 8,000 years ago in the western part of the Delta and was finally formed in the last millennium in the eastern part of the Delta. From the previous works, it is known that the western part of the Delta is higher than the eastern part. In our work, we explain it by the eneven movements of the Earth’s crust in this region. The aim of the paper is to study the quantitative characteristics of the tectonic movements in the Lena River Delta. For this purpose we present the geomorphological schemes and descriptions of the islands mentioned and compare the terraces heights in the different parts of the Delta. In the Late Pleistocene, according to the heights of the IC remnants, the western part of the Delta rose 1 mm per year faster than its eastern part. In the Holocene the speed difference increased to approximately 2 mm per year, which is shown by the terrace surface’s altitude. The amplitude between the western and eastern parts of this surface is about 4 m. Finally, according to 60-years observation period of the water level in the Laptev Sea, the modern speed difference of the western and eastern parts movement in the Lena Delta is 2 mm per year. As a result, we can observe changes in the main flow direction in the Delta channels from the Olenekskaya branch at the beginning of Holocene to the Bykovskaya branch today.

Scaling and balancing carbon dioxide fluxes in a heterogeneous tundra ecosystem of the Lena River Delta

Abstract. The current assessments of the carbon turnover in the Arctic tundra are subject to large uncertainties. This problem can (inter alia) be ascribed to both the general shortage of flux data from the vast and sparsely inhabited Arctic region, as well as the typically high spatiotemporal variability of carbon fluxes in tundra ecosystems. Addressing these challenges, carbon dioxide fluxes on an active flood plain situated in the Siberian Lena River Delta were studied during two growing seasons with the eddy covariance method. The footprint exhibited a heterogeneous surface, which generated mixed flux signals that could be partitioned in such a way that both respiratory loss and photosynthetic gain were obtained for each of two vegetation classes. This downscaling of the observed fluxes revealed a differing seasonality in the net uptake of bushes (−0.89 µmol m−2 s−1) and sedges (−0.38 µmol m−2 s−1) in 2014. That discrepancy, which was concealed in the net signal, resulted from a comparatively warm spring in conjunction with an early snowmelt and a varying canopy structure. Thus, the representativeness of footprints may adversely be affected in response to prolonged unusual weather conditions. In 2015, when air temperatures on average corresponded to climatological means, both vegetation-class-specific flux rates were of similar magnitude (−0.69 µmol m−2 s−1). A comprehensive set of measures (e.g. phenocam) corroborated the reliability of the partitioned fluxes and hence confirmed the utility of flux decomposition for enhanced flux data analysis. This scrutiny encompassed insights into both the phenological dynamic of individual vegetation classes and their respective functional flux to flux driver relationships with the aid of ecophysiologically interpretable parameters. For comparison with other sites, the decomposed fluxes were employed in a vegetation class area-weighted upscaling that was based on a classified high-resolution orthomosaic of the flood plain. In this way, robust budgets that take the heterogeneous surface characteristics into account were estimated. In relation to the average sink strength of various Arctic flux sites, the flood plain constitutes a distinctly stronger carbon dioxide sink. Roughly 42 % of this net uptake, however, was on average offset by methane emissions lowering the sink strength for greenhouse gases. With growing concern about rising greenhouse gas emissions in high-latitude regions, providing robust carbon budgets from tundra ecosystems is critical in view of accelerating permafrost thaw, which can impact the global climate for centuries.

The First Finding of Foliar Flora Fossils in the Section of Cenozoic Deposits of Sardakh-Sise Island (Lena River Delta)

The first findings of well-preserved foliar flora (Platanus sp., Alnus sp., Fagus sp., Salix sp., and Magnolia sp.) have been recovered from the Late Cenozoic (Neogene) deposits on Sardakh-Sise Island, in the Lena River delta. The findings, which also include remains of coniferous wood, are hosted in ferruginized sandstones at the base of the section. The floral composition suggests that mixed forests incorporating coniferous, broad- and small-leaved deciduous trees, and shrubs (moderate and subtropical thermophytes) grew in this area. The deposits contain foliar flora could forms in the Early–Middle Miocene, not in the Pliocene as is presently believed. Most likely, the basal conglomerates and sandstones of the Sardakh-Sise Island section refer to the Urasalakh Fm. The finding site of Neogene foliar flora on Sardakh-Sise Island is now the northernmost location in Eurasia.

The first data on the late pleistocene ostracodes of the Kuray depression (Gorny Altai)

During the field works in the summer of 2018, in the Lena River delta on the Sardakh-Sisse Island, prints of leaf flora belonging to species of broad and small-leaved deciduous trees were found. The prints found by us are confined to the layer of ferruginous sandstones at the base of the section. The following taxa established: Platanus sp., Alnus sp., Fagus sp., Salix sp. In addition, a fossilized fruit belonging to Magnolia sp. The findings allow to conclude that there are mixed forests in the early-middle Miocene in this region, consisting of coniferous, small- and broad-leaved deciduous species of trees and shrubs.

Partitioning net ecosystem exchange of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; on the pedon scale in the Lena River Delta, Siberia

Abstract. Arctic tundra ecosystems are currently facing amplified rates of climate warming. Since these ecosystems store significant amounts of soil organic carbon, which can be mineralized to carbon dioxide (CO2) and methane (CH4), rising temperatures may cause increasing greenhouse gas fluxes to the atmosphere. To understand how net the ecosystem exchange (NEE) of CO2 will respond to changing climatic and environmental conditions, it is necessary to understand the individual responses of the processes contributing to NEE. Therefore, this study aimed to partition NEE at the soil–plant–atmosphere interface in an arctic tundra ecosystem and to identify the main environmental drivers of these fluxes. NEE was partitioned into gross primary productivity (GPP) and ecosystem respiration (Reco) and further into autotrophic (RA) and heterotrophic respiration (RH). The study examined CO2 flux data collected during the growing season in 2015 using closed-chamber measurements in a polygonal tundra landscape in the Lena River Delta, northeastern Siberia. To capture the influence of soil hydrology on CO2 fluxes, measurements were conducted at a water-saturated polygon center and a well-drained polygon rim. These chamber-measured fluxes were used to model NEE, GPP, Reco, RH, RA, and net primary production (NPP) at the pedon scale (1–10 m) and to determine cumulative growing season fluxes. Here, the response of in situ measured RA and RH fluxes from permafrost-affected soils of the polygonal tundra to hydrological conditions have been examined. Although changes in the water table depth at the polygon center sites did not affect CO2 fluxes from RH, rising water tables were linked to reduced CO2 fluxes from RA. Furthermore, this work found the polygonal tundra in the Lena River Delta to be a net sink for atmospheric CO2 during the growing season. The NEE at the wet, depressed polygon center was more than twice that at the drier polygon rim. These differences between the two sites were caused by higher GPP fluxes due to a higher vascular plant density and lower Reco fluxes due to oxygen limitation under water-saturated conditions at the polygon center in comparison to the rim. Hence, soil hydrological conditions were one of the key drivers for the different CO2 fluxes across this highly heterogeneous tundra landscape.