Carex delongii (Cyperaceae), a new sedge from Russia

While performing vegetation surveys in the southern part of the Lena delta, a new species of Carex from section Phacocystis has been found. Morphologically, Carex delongii sp. nov. is most close to C. cespitosa and C. minuta but differs from the former in smaller inflorescences, shorter pistillate spikes, narrow and soft leaves, oblong-ovoid (vs. ovoid) utricles; from the latter, it is distinguished by having smaller spikes and larger utricles. This relationship is also confirmed by molecular data. A detailed description of Carex delongii, its comparison with related species, illustrations, characteristics of habitat and phylogenetic position are reported.

Monitoring the Spring Flood in Lena Delta with Hydrodynamic Modeling Based on SAR Satellite Products

Due to the remote location and the extreme climate, monitoring stations in Arctic rivers such as Lena in Siberia have been decreasing through time. Every year, after a long harsh winter, the accumulated snow on the Lena watershed melts, leading to the major annual spring flood event causing heavy transport of sediments, organic carbon, and trace metals, both into as well as within the delta. This study aims to analyze the hydrodynamic processes of the spring flood taking place every year in the Lena Delta. Thus, a combination of remote sensing techniques and hydrodynamic modeling methodologies is used to overcome limitations caused by missing ground-truth data. As a test site for this feasibility study, the outlet of the Lena River to its delta was selected. Lena Delta is an extensive wetland spanning from northeast Siberia into the Arctic Ocean. Spaceborne Synthetic Aperture Radar (SAR) data of the TerraSAR-X/TanDEM-X satellite mission served as input for the hydrodynamic modeling software HEC-RAS. The model resulted in inundation areas, flood depths, and flow velocities. The model accuracy assessed by comparing the multi-temporal modeled inundation areas with the satellite-derived inundation areas ranged between 65 and 95%, with kappa coefficients ranging between 0.78 and 0.97, showing moderate to almost perfect levels of agreement between the two inundation boundaries. Modeling results of high flow discharges show a better agreement with the satellite-derived inundation areas compared to that of lower flow discharges. Overall, the remote-sensing-based hydrodynamic modeling succeeded in indicating the increase and decrease in the inundation areas, flood depths, and flow velocities during the annual flood events.

High-resolution bathymetry models for the Lena Delta and Kolyma Gulf coastal zones

Arctic river deltas and deltaic near-shore zones represent important land-ocean transition zones influencing sediment dynamics and nutrient fluxes from permafrost-affected terrestrial ecosystems into the coastal Arctic Ocean. To accurately model fluvial carbon and freshwater export from rapidly changing river catchments, as well assessing impacts of future change on the Arctic shelf and coastal ecosystems, we need to understand the sea floor characteristics and topographic variety of the coastal zones. To date, digital bathymetrical data from the poorly accessible, shallow and large areas of the eastern Siberian Arctic shelves are sparse. We have digitized bathymetrical information for nearly 75,000 locations from large-scale current and historical nautical maps of the Lena Delta and the Kolyma Gulf Region in Northeast Siberia. We present the first detailed and seamless digital models of coastal zone bathymetry for both delta/gulf regions. We validated the resulting bathymetry layers using a combination of our own water depth measurements and a collection of available depth measurements, which showed a strong correlation (r > 0.9). Our bathymetrical models will serve as an input for a high-resolution coupled hydrodynamic-ecosystem model to better quantify fluvial and coastal carbon fluxes to the Arctic Ocean but may be useful for a range of other studies related to Arctic delta and near-shore dynamics such as modelling of submarine permafrost, near-shore sea ice, or shelf sediment transport. The new digital high-resolution bathymetry products are available on the PANGAEA data set repository (Fuchs et al. 2021a, b). Likewise the depth validation data is available on PANGAEA as well (Fuchs et al., 2021c).

Paleo-Ecology of the Yedoma Ice Complex on Sobo-Sise Island (EasternLena Delta, Siberian Arctic)

Late Pleistocene permafrost of the Yedoma type constitutes a valuable paleo-environmental archive due to the presence of numerous and well-preserved floral and faunal fossils. The study of the fossil Yedoma inventory allows for qualitative and quantitative reconstructions of past ecosystem and climate conditions and variations over time. Here, we present the results of combined paleo-proxy studies including pollen, chironomid, diatom and mammal fossil analyses from a prominent Yedoma cliff on Sobo-Sise Island in the eastern Lena Delta, NE Siberia to complement previous and ongoing paleo-ecological research in western Beringia. The Yedoma Ice Complex (IC) cliff on Sobo-Sise Island (up to 28 m high, 1.7 km long) was continuously sampled at 0.5 m resolution. The entire sequence covers the last about 52 cal kyr BP, but is not continuous as it shows substantial hiatuses at 36–29 cal kyr BP, at 20–17 cal kyr BP and at 15–7 cal kyr BP. The Marine Isotope Stage (MIS) 3 Yedoma IC (52–28 cal kyr BP) pollen spectra show typical features of tundra–steppe vegetation. Green algae remains indicate freshwater conditions. The chironomid assemblages vary considerably in abundance and diversity. Chironomid-based TJuly reconstructions during MIS 3 reveal warmer-than-today TJuly at about 51 cal kyr BP, 46-44 and 41 cal kyr BP. The MIS 2 Yedoma IC (28–15 cal kyr BP) pollen spectra represent tundra-steppe vegetation as during MIS 3, but higher abundance of Artemisia and lower abundances of algae remains indicate drier summer conditions. The chironomid records are poor. The MIS 1 (7–0 cal kyr BP) pollen spectra indicate shrub-tundra vegetation. The chironomid fauna is sparse and not diverse. The chironomid-based TJuly reconstruction supports similar-as-today temperatures at 6.4–4.4 cal kyr BP. Diatoms were recorded only after about 6.4 cal kyr BP. The Sobo-Sise Yedoma record preserves traces of the West Beringian tundra-steppe that maintained the Mammoth fauna including rare evidence for woolly rhinoceros’ presence. Chironomid-based TJuly reconstructions complement previous plant-macrofossil based TJuly of regional MIS 3 records. Our study from the eastern Lena Delta fits into and extends previous paleo-ecological Yedoma studies to characterize Beringian paleo-environments in the Laptev Sea coastal region.

Particulate and dissolved organic carbon composition in the Lena River and its Delta, from Yakutsk to the Arctic Ocean.

<p>Rapid climate warming in the Arctic intensifies permafrost thaw, increases active layer depth in summer and enhances riverbank and coastal erosion. All of these cause additional release of organic matter (OM) into streams and rivers. OM will be (1) transformed and modified during transport and subsequently discharged into the Arctic Ocean, or (2) removed from the active cycling by sedimentation. Here, the nearshore zone (which includes deltas, estuaries and coasts) is of great importance, where the major transformation processes of terrestrial material take place. Despite the importance of deltas for the biogeochemical cycle, their functioning is poorly understood. For our study we examined the Lena River nearshore, which represents the world’s third largest delta and supplies the second highest annual water and sediment discharge into the Arctic Ocean. Running through almost the entirety of East Siberia from Lake Baikal to the Laptev Sea, the Lena River drains an area of ∼2,61×10<sup>6</sup> km<sup>2</sup>  with approximately 90% underlain by permafrost. Our aims were to investigate the spatial variation of OM concentration and isotopic composition during transit from terrestrial permafrost source to the ocean interface, and to compare riverine and deltaic OM composition. We measured particulate and dissolved organic carbon (POC and DOC) concentrations and their associated δ<sup>13</sup>C and ∆<sup>14</sup>C values in water samples collected along a ∼1500 km long Lena River transect from Yakutsk downstream to the river outlet into the Laptev Sea.</p><p>We find significant qualitative and quantitative differences between the OM composition in the Lena River main channel and its delta. Further, we found suspended matter and POC concentrations decreased during transit from river to the Arctic Ocean.  DOC concentrations in the Lena delta were almost 50% lower than OM from the main channel. We found that deltaic POC is depleted in <sup>13</sup>C relative to fluvial POC, and that its <sup>14</sup>C signature suggests a modern composition indicating phytoplankton origin. This observation likely reflects the difference in hydrological conditions between the delta and the river main channel, caused by lower flow velocity and average water depth. We propose that deltaic environments provide favorable growth conditions for riverine primary producers such as algae and aquatic plants. Deltaic DOC is depleted in <sup>14</sup>C compared to riverine, especially in samples taken from the water surface, which indicates contributions from an additional old carbon stock source, specific for the Lena Delta. We suggest that this C is released from deltaic bank erosion and partly stays floating on the surface. In conclusion, we found a strong impact of deltaic processes on the fate and dominant signatures of OM discharged into the Arctic Ocean.</p>

Landscape-level remote sensing for upscaling of land cover, above ground biomass and above ground carbon fluxes in the Lena River Delta (Northern Yakutia, Russia)

<p>Vegetation biomass is a globally important climate-relevant terrestrial carbon pool. Landsat, Sentinel-2 and Sentinel-1 satellite missions provide a landscape-level opportunity to upscale tundra vegetation communities and biomass in high latitude terrestrial environments. We assessed the applicability of landscape-level remote sensing for the low Arctic Lena Delta region in Northern Yakutia, Siberia, Russia. The Lena Delta is the largest delta in the Arctic and is located North of the treeline and the 10 °C July isotherm at 72° Northern Latitude in the Laptev Sea region. We evaluated circum-Arctic harmonized ESA GlobPermafrost land cover and vegetation height remote sensing products covering subarctic to Arctic land cover types for the central Lena Delta. The products are freely available and published in the PANGAEA data repository under https://doi.org/10.1594/PANGAEA.897916, and https://doi.org/10.1594/PANGAEA.897045.</p><p>Vegetation and biomass field data (30 m x 30 m plot size) and shrub samples for dendrology were collected during a Russian-German expedition in summer 2018 in the central Lena Delta. We also produced a regionally optimized land cover classification for the central Lena Delta based on the in-situ vegetation data and a summer 2018 Sentinel-2 acquisition that we optimized on the biomass and wetness regimes. We also produced biomass maps derived from Sentinel-2 at a pixel size of 20 m investigating several techniques. The final biomass product for the central Lena Delta shows realistic spatial patterns of biomass distribution, and also showing smaller scale patterns. However, patches of high shrubs in the tundra landscape could not spatially be resolved by all of the landscape-level land cover and biomass remote sensing products.</p><p>Biomass is providing the magnitude of the carbon flux, whereas stand age is irreplaceable to provide the cycle rate. We found that high disturbance regimes such as floodplains, valleys, and other areas of thermo-erosion are linked to high and rapid above ground carbon fluxes compared to low disturbance on Yedoma upland tundra and Holocene terraces with decades slower and in magnitude smaller above ground carbon fluxes.</p>

Features of the Lena River runoff influence on the adjacent Laptev Sea shelf

<p>The annual runoff of river water into the Laptev Sea is 745 km<sup>3</sup>, most of the runoff belongs to the Lena River - 525 km<sup>3</sup>.  Long-term variability in the volume of the Lena River runoff play a significant role in the variability of the scale of distribution of freshwater lenses in the Laptev Sea. The processes that take place in the area of ​​intense river runoff have an impact both in the shelf zone and in the open part of the sea due to the transfer of large-area lenses of freshened water. The influence of river runoff is considered from the Lena Delta to the continental slope of the Laptev Sea.</p><p>The data on physical and chemical properties of the Laptev Sea shelf used in this investigation was obtained during the expeditions of the Shirshov Institute of Oceanology in 2015 and 2017 and the Pacific Oceanological Institute in 2018-2020.</p><p>The distribution of hydrochemical parameters in the Lena Delta area in 2019 was typical for the river-sea mixing zone. The distribution of silicate was mixed, i.e. horizontal stratification prevailed in the near-surface layers, and vertical stratification in the bottom layers. The maximum values ​​were observed in the near-mouth area, reaching indicators over 30 µM / L, which generally coincides with the values ​​of this indicator in 2015 and more than in 2017.</p><p>When considering the distribution of specific alkalinity (total alkalinity-salinity ratio), which serves as a proxie of riverine water, it is worth noting the deepening of the boundary by 0.07 units. In 2019, this border was at depths of 20 to 40 meters, which is an atypical indicator for this water area. Apparently, this has happened owing to an increase in the supply of carbonate ions, which is noticeable from an increase in the values ​​of carbonate alkalinity in the Lena River waters (Arctic Great Rivers Observatory data).</p><p>The calculation of the parts of fresh water, based on salinity data in 2019, showed that the maximum values ​​were observed near the Lena River delta and amounted to 30-35%. Northward, the part of riverine water was up to 10% only in the surface layer. Comparing with similar calculations performed for the 2015 and 2017 sections, it should be noted that the part of fresh water has decreased. Perhaps this is due to the inflow of continental runoff in 2019 was the lowest over the considered period.</p><p>Funding: The work was carried out within the framework of the Shirshov Institute of Oceanology state assignment (theme No. 0149-2019-0008), with funding of the Russian Scientific Foundation (project No. 19-17-00196) and the grant of the President of the Russian Federation MK-860.2020.5.</p>

Seasonal variations in the transport and biogeochemical turnover of mainly dissolved organic nitrogen from the Lena Delta to the nearshore Laptev Sea

<p>Pan-arctic rivers transport a huge amount of nitrogen to the Arctic Ocean. The permafrost-affected soils around the Arctic Ocean containe a large reservoir of organic matter including carbon and nitrogen, which partly reach the river after permafrost thaw and erosion.</p><p>Our study aims to estimate the load of nitrogen supplied from terrestrial sources into the Arctic Ocean. Therefore, water, suspended particulate matter (SPM) and sediment samples were collected in the Lena Delta along a (~200 km) transect from the center of the Lena Delta to the open Laptev Sea in late winter (April) and in summer (August) 2019. In winter, 21 sample from 13 stations and in summer, 51 samples from 18 stations were taken. 9 of these sampling stations in the outer delta region were sampled in both seasons.</p><p>We measured organic and inorganic nitrogen and the <sup>15</sup>N stable isotopes composition of all three sample types to determine sources, sinks and processes of nitrogen transformation during transport.</p><p>In winter, the nitrogen transported from the delta to the Laptev Sea were mainly dissolved organic nitrogen (DON) and nitrate, which occur in similar amounts. The load of nitrate increased slightly in the delta, while no changes to the isotope values of DON and nitrate were observe indicating a lack of biological activity in the winter season. However, lateral transport from soils was a likely source. In summer, nitrogen was mainly transported as DON and particulate nitrogen in the SPM fraction, including phytoplankton.</p><p>The nitrogen stable isotope values of the different nitrogen components ranges between 0.5 and 4.5 ‰, and were subsequently enriched from the soils via SPM/sediment and DON to nitrate. This indicates that nitrogen in the soils mainly originates from nitrogen fixation from the atmosphere. During transport and remineralisation, biogeochemical recycling via nitrification and assimilation by phytoplankton led to an isotopic enrichment in summer from organic to inorganic components. In the coastal waters of the Laptev Sea, the river waters are slowly mixed with marine nitrate containing waters from the Arctic Ocean, and a part of the riverine organic nitrogen is buried in the sediments.</p><p>We assume that the ongoing permafrost thawing and erosion will intensify and increase the transport of reactive nitrogen to coastal waters and will affect the biogeochemical cycling, e.g. the primary production.</p>