ALBERT

Description: Soils of the permafrost zone store globally relevant reservoirs of frozen matter, such as organic matter, mineral elements as well as other biogeochemical relevant compounds like contaminants. Besides well-studied organic carbon (OC), other compounds can become available in active biological and hydrological element cycling as global climate change is warming northern permafrost regions nearly four times faster than the global average. Current heating in Siberia is unprecedented during the past seven millennia, triggering widespread permafrost degradation and collapse. This is especially relevant for our study region, the Yedoma domain. In this region, a large amount of belowground ice is present and the ground can become unstable with warming, allowing the mobilisation of previously frozen sediments with their geochemical element contents. With this presentation, we want to synthesise recent studies, which have improved the understanding of various frozen stocks. Here, we estimated that the Yedoma domain contains 41.2 Gt of nitrogen, which increases the previous estimate for the circumpolar permafrost zone by ~46%. The highest element stock within the Yedoma domain is estimated for r Si (2739 Gt), followed by Al, Fe, K, Ca, Ti, Mn, Zr, Sr, and Zn. The stocks of Al and Fe (598 and 288 Gt) are in the same order of magnitude as OC (327–466 Gt). Concerning contaminants, we focused on mercury. Using the ratio of mercury to OC (RHgC, our found value: 2.57 μg Hg g C−1) and the OC levels from various studies for a first rough estimation of the Hg reservoir, we estimate the Yedoma mercury pool to be ~542000 tons. In conclusion, we find that deep thaw of the Yedoma permafrost domain and its degradation will bear the potential to change the availability of various elements in active biogeochemical and hydrological cycles, which will have the potential to change crucial ecosystem variables and services.

Description: Permafrost-affected soils around the Arctic Ocean contain a large reservoir of organic matter including nitrogen, which partly reach the river after thawing, degradation and erosion of permafrost. After mobilization, reactive remineralised nitrogen is either used for primary production, microbial processing or is simply transported to coastal waters. We have analyzed soil, suspended matter and dissolved inorganic and organic nitrogen for their contents and 15N stable isotope composition to create a baseline for a nitrogen inventory of the Lena River Delta in 2019/2020. We used samples from two transect cruises through the delta in March and August 2019, a monitoring program at Samoylov Island in the central delta (2019/2020), and different soil type samples from Samoylov Island. Our data shows that the nitrogen transported from the delta to the Laptev Sea were dominated by dissolved organic nitrogen (DON) and nitrate, which occur in similar amounts of approx. 10 μmol/L. DON was available during the whole year. Nitrate showed a clear seasonal pattern: increase from late summer until the spring flood, during summer the nitrate concentration are close to zero. During the spring flood the nitrogen concentration are higher with up to 100 μmol/L. The nitrogen stable isotope values of the different nitrogen components ranges mainly between 0.5 and 4.5‰, and were subsequently enriched from the soils via suspended particulate matter (SPM)/sediment and DON to nitrate. During the spring flood, the stable isotope signature of nitrate suggested a strong source of atmospheric deposition. The 15N values are depleted with appox. -8‰ and the 18O values are enriched up to 60‰. Our data provides a baseline for isoscape analysis and can be used as an endmember signal for modeling approaches.

Description: 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.

Description: Rapid Arctic warming accelerates permafrost thaw releasing aged organic matter (OM) to inland aquatic ecosystems and ultimately, after transport via estuaries or deltas, to the Arctic Ocean nearshore. Despite the importance of Arctic deltas, their functioning is still poorly studied. Here, we examined seasonal fluctuations and spatial differences in the quantity and composition of OM in the Lena Delta, measuring dissolved and particulate organic carbon (DOC and POC) concentrations, carbon isotopes (δ13C and Δ14C), and total suspended matter (TSM). We compared deltaic POC to the POC in the Lena River main stem over a ~1600 km transect, from Yakutsk to the Lena Delta. We further examined and compared dynamics of DOC and POC in summer and winter across a ~140 km transect in the Lena Delta. TSM and POC concentrations decreased by 75 % during transit from Yakutsk to the Lena Delta. 18 % of deltaic and 5 % of river main stem POC originated from Yedoma deposits. Thus, despite lower concentrations of POC in the delta, amount of POC from Yedoma deposits in deltaic waters were almost twice as large as in the main stem (0.07 ±0.02 and 0.04 ±0.02 mg L-1, respectively). Deltaic POC was strongly depleted in 13C due to significant phytoplankton contributions (~-68 ±6 %). Strong differences between winter and summer samples in DOC and POC concentrations and their properties in the Lena Delta were also found. Combined analyses of DOC and POC revealed that Pleistocene-aged Yedoma deposits were still actively degrading in winter influencing the quantity and composition of OM of the Lena Delta and exported OC loads. Deltaic processes control the type and amount of OM exported to the Arctic Ocean and require deeper investigations as crucial processes for the riverine and oceans pathways in a warming Arctic.

Description: Permafrost-affected soils around the Arctic Ocean contain a large reservoir of organic matter including nitrogen, which partly reaches the riverine system after thawing, degradation and erosion of permafrost. After mobilization, reactive nitrogen in form of dissolved organic nitrogen (DON) ordissolved inorganic nitrogen (DIN: ammonium and nitrate) is either used for primary production, microbial turnover and/or is transported to coastal waters where it serves as a key source of nutrition for the marine food web. In this study, we have followed the nitrogen released from permafrost soil via the Lena River into the Laptev Sea and used the natural abundance of 15N stable isotopes to identify sources, sinks and processes. Therefore, we have investigated different soil. We present a comprehensive data set from two transect cruises (03/08 2019) through the delta, and the outcome of a monitoring program (2018 - 2021) at Samoylov Island in the central delta. High-frequency monitoring and cruise data shows that the nitrogen transported from the river to the Laptev Sea was dominated by DON and nitrate, which occurred in similar amounts of approx. 10 μmol L–1 in the river water. The nitrate concentration decreased during the early summer and increased from late summer throughout the winter until the spring flood. During the spring flood, the nitrogen concentration was up to ten times higher. Thus, spring floods transport approx. 20 % of the annual load of reactive nitrogen into the Laptev Sea just at the onset of the growing season. The nitrogen stable isotope values of the different nitrogen components ranged mainly between 0.5 and 4.5‰, and were subsequently enriched from the permafrost soils via suspended particulate matter/sediment and DON to nitrate, which indicate an oligotrophic ecosystem. Using a Bayesian mixing model, the stable isotope signature of nitrate suggested a strong source of atmospheric deposition during the spring flood. During the rest of the year, soils are the main source of the reactive nitrogen, which is transported to the marine realm.

Description: Soils of the permafrost zone store globally relevant reservoirs of frozen matter, such as organic matter, mineral elements as well as other biogeochemical relevant compounds like contaminants. Besides the well-studied organic carbon (OC), other compounds can become available in active biological and hydrological element cycling as global climate change is warming northern permafrost regions nearly four times faster than the global average. Current heating in Siberia is unprecedented during the past seven millennia, triggering widespread permafrost degradation and collapse. This is especially relevant for our study region, the Yedoma domain. In this region, a large amount of belowground ice is present and the ground can become unstable with warming, allowing the mobilisation of previously frozen sediments with their geochemical element contents. With this presentation, we synthesise recent studies, which have improved the understanding of various frozen stocks. Here, we estimated that the Yedoma domain contains 41.2 Gt of nitrogen (N), which increases the previous estimate for the circumpolar permafrost zone by ~46 %. The highest element stock within the Yedoma domain is estimated for Si (2739 Gt), followed by Al, Fe, K, Ca, Ti, Mn, Zr, Sr, and Zn. The stocks of Al and Fe (598 and 288 Gt, respectively) are in the same order of magnitude as OC (327-466 Gt). Concerning contaminants, we focused on mercury. Using the ratio of mercury to OC (R(HgC), value based on own measurements: 2.57 μg Hg g C−1) and the OC levels from various studies for a first rough estimation of the Hg reservoir, we estimate the Yedoma mercury pool to be ~542,000 tons. In conclusion, we find that deep thaw of the Yedoma permafrost domain and its degradation will bear the potential to change the availability of various elements in active biogeochemical and hydrological cycles in northern regions, which will have the potential to change crucial ecosystem variables and services.

Description: Nutrient and carbon dynamics within the river-estuary-coastal water systems are key processes to understand the matter fluxes from the terrestrial environment to the ocean. In a large-scale study we analysed those dynamics with the focus of the prevailing low water conditions by following a sampling approach based on the travel time of water. We started with a nearly Lagrangian sampling along the River Elbe (German part; 580 km within 8 days travel time). After a subsequent investigation of the estuary, the plume of the river was followed by raster sampling the German Bight (North Sea) using three ships simultaneously. In the river, intensive growth of phytoplankton was determined connected with high oxygen saturation and pH values as well as under-saturation of CO2, whereas concentrations of dissolved nutrients declined. In the estuary, the Elbe shifted from an autotrophic to a heterotrophic system: Phytoplankton died off upstream of the salinity gradient causing minima in oxygen saturation and pH, supersaturation of CO2, and a release of nutrients. In the coastal region, phytoplankton and nutrient concentrations were low, oxygen close to saturation, and pH in a typical marine range. We detected a positive relationship between pH values and oxygen saturation and a negative one between pCO2 and oxygen saturation. Corresponding to the significant particulate nutrient flux via phytoplankton, flux rates of dissolved nutrients from the river into the estuary were low and determined by depleted concentrations. In contrast, fluxes from the estuary to the coastal waters were higher and the pattern was determined by tidal currents. Overall, the presented observation approach is appropriate to better understand land-ocean fluxes, particularly if it is performed under different hydrological conditions including extremes and seems to be suitable to investigate the impact of such events in freshwater on coastal systems in future. The study was conducted within the frame of the Helmholtz MOSES initiative (Modular Observation Solutions for Earth Systems) targeting processes and impacts of hydrological extremes.

Description: 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 as assess 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 (1:25 000–1:500 000) current and historical nautical maps of the Lena Delta and the Kolyma Gulf region in northeastern Siberia. We present the first detailed and seamless digital models of coastal zone bathymetry for both delta and gulf regions in 50 and 200 m spatial resolution. 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 they may be useful for a range of other studies related to Arctic delta and near-shore dynamics such as modeling 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 for the Lena Delta (https://doi.org/10.1594/PANGAEA.934045; Fuchs et al., 2021a) and Kolyma Gulf region (https://doi.org/10.1594/PANGAEA.934049; Fuchs et al., 2021b), respectively. Likewise, the depth validation data are available on PANGAEA as well (https://doi.org/10.1594/PANGAEA.933187; Fuchs et al., 2021c).

Description: Organic carbon (OC) stored in Arctic permafrost represents one of Earth’s largest and most vulnerable terrestrial carbon pools. Amplified climate warming across the Arctic results in widespread permafrost thaw. Permafrost deposits exposed at river cliffs and coasts are particularly susceptible to thawing processes. Accelerating erosion of terrestrial permafrost along shorelines leads to increased transfer of organic matter (OM) to nearshore waters. However, the amount of terrestrial permafrost carbon and nitrogen as well as the OM quality in these deposits is still poorly quantified. We define the OM quality as the intrinsic potential for further transformation, decomposition and mineralisation. Here, we characterise the sources and the quality of OM supplied to the Lena River at a rapidly eroding permafrost river shoreline cliff in the eastern part of the delta (Sobo-Sise Island). Our multi-proxy approach captures bulk elemental, molecular geochemical and carbon isotopic analyses of Late Pleistocene Yedoma permafrost and Holocene cover deposits, discontinuously spanning the last ~52 kyr. We showed that the ancient permafrost exposed in the Sobo-Sise cliff has a high organic carbon content (mean of about 5 wt %). The oldest sediments stem from Marine Isotope Stage (MIS) 3 interstadial deposits (dated to 52 to 28 cal ka BP) and are overlaid by last glacial MIS 2 (dated to 28 to 15 cal ka BP) and Holocene MIS 1 (dated to 7–0 cal ka BP) deposits. The relatively high average chain length (ACL) index of n-alkanes along the cliff profile indicates a predominant contribution of vascular plants to the OM composition. The elevated ratio of iso and anteiso-branched fatty acids (FAs) relative to mid- and long-chain (C�20) n-FAs in the interstadial MIS 3 and the interglacial MIS 1 deposits suggests stronger microbial activity and consequently higher input of bacterial biomass during these climatically warmer periods. The overall high carbon preference index (CPI) and higher plant fatty acid (HPFA) values as well as high C=N ratios point to a good quality of the preserved OM and thus to a high potential of the OM for decomposition upon thaw. A decrease in HPFA values downwards along the profile probably indicates stronger OM decomposition in the oldest (MIS 3) deposits of the cliff. The characterisation of OM from eroding permafrost leads to a better assessment of the greenhouse gas potential of the OC released into river and nearshore waters in the future.