Description: Recent studies on permafrost organic matter (OM) suggest that a portion of previously frozen carbon will enter the active carbon cycle as high latitudes warm. Less is known about the fate of other OM components, including nutrients such as nitrogen (N). The abundance and availability of N following permafrost thaw will regulate the ability of plants to offset carbon losses. Additionally, lateral N losses could alter aquatic food webs. There is growing evidence that some N is lost vertically as N2O, a greenhouse gas 300 times stronger than CO2 over 100 years. Despite broad recognition of its role regulating both carbon and non-carbon aspects of the permafrost climate feedback, estimates of permafrost N remain uncertain. To address this knowledge gap, we quantified N content for different stratigraphic units, including yedoma, Holocene cover deposits, refrozen thermokarst deposits, taberal sediments, and active layer soils. The resulting N estimates from this one permafrost region were similar in magnitude to previous estimates for the entire permafrost zone. We conclude that the permafrost N pool is much larger than currently appreciated and a substantial pool of permafrost N could be mobilized after thaw, with continental-scale consequences for biogeochemical budgets and global-scale consequences.

Description: Fossil organic matter (OM) stored in permafrost is an important subject in climate research. Such OM represents a huge reservoir of carbon (C). Multiple studies suggest its source potential for C release into the active C cycle through permafrost thaw and subsequent microbial turnover in a warming Arctic. However, net ecosystem OM balance in the permafrost region depends on more than just carbon. The abundance and availability of nitrogen (N) following permafrost thaw will influence plant growth, nutrient delivery to aquatic and estuarine ecosystems, and N oxide (N2O) emissions. Despite its central importance to predicting permafrost impacts and feedbacks to climate change, relatively little is known about permafrost N stocks and composition. In this study, we present the most extensive dataset to date of permafrost N in the Siberian and Alaskan Yedoma domain. The Yedoma domain comprises decameter thick ice-rich silts intersected by syngenetic ice wedges, which formed in late Pleistocene tundra-steppe environments, as well as other deposits resulting from permafrost degradation during the Holocene. Together, the deposits in this region constitute a large C inventory storing several hundred Gt C, but are also known to be nutrient-rich due to rapid burial and freezing of plant remains. Hitherto, the total organic C pool of the Yedoma region was quantified, while the total N inventory is lacking so far. Based on the most comprehensive data set of N content in permafrost to date, our study aims to estimate the present pool of N stored in the different stratigraphic units of the Yedoma domain: 1) late Pleistocene Yedoma deposits, 2) in-situ thawed and diagenetically altered Yedoma deposits (taberite), 3) Holocene thermokarst deposits, 4) Holocene cover deposits on top of Yedoma, and 5) the modern active layer of soils. To quantify measurement uncertainty, we estimated nitrogen stocks with bootstrapping techniques. We show that the deposits of the Yedoma region store a substantial pool of N that is expected to get mobilized after thaw and, at least partially, affecting biogeochemical budgets of thawing warming permafrost ecosystems.

Description: The biogeochemical composition of fossil organic matter stored in permafrost is an important subject in current climate change research. Multiple studies on the quality and quantity of permafrost organic carbon suggest that there is a high potential for carbon release into the active carbon turnover cycle through permafrost thaw in a warming Arctic. Other components of organic matter that are important for biogeochemical cycling, however, are less studied so far, including the amount and distribution of nitrogen (Keuper et al., 2012; Mack et al., 2004; Rustad et al., 2001). Nitrogen from thawing permafrost could be a significant source of the greenhouse gas N2O. Given its high global warming potential (about 300 times larger than CO2 over 100 years), even small releases of N2O can affect the permafrost-climate feedback. This study focuses on the abundance and distribution of nitrogen currently freeze-locked in the Yedoma region of Siberia and Alaska. Organic matter in permafrost deposits of the northern circumpolar region accumulated over tens of thousands of years during the last glacial and interglacial periods. A part of this permafrost region, the Yedoma region, is composed of thick ice-rich silts intersected by large ice wedges, resulting from sedimentation and syngenetic freezing accompanied by ice wedge growth in polygonal tundra, which was driven by certain climatic and environmental conditions during the late Pleistocene. These unique materials are called Yedoma deposits. They constitute a large organic carbon inventory of the (sub)Arctic but are also known to be nutrient-rich due to burial and freezing of plant remains. Besides carbon inventory estimates, detailed quantification of total nitrogen (TN) stocks is lacking. Based on the most comprehensive data set of TN content in permafrost to date, our study aims to estimate the present pool of nitrogen stored in the different stratigraphic units of the Yedoma region, which are (1) late Pleistocene Yedoma deposits; (2) in-situ thawed and diagenetically altered Yedoma deposits (taberite); (3) Holocene thermokarst deposits; (4) Holocene cover deposits on top of Yedoma and (5) the modern active layer of soils. Nitrogen stock calculations are based on statistical bootstrapping techniques using resampled observed values. The total mean pool size estimate is derived for every of the 10,000 bootstrapping runs, resulting in an overall mean derived from 10,000 individual observation-based bootstrapping means. The conceptual formula for our nitrogen stock calculation is given below. We show that the deposits of the Yedoma region store a significant pool of TN. At least a portion of this nitrogen is expected to get mobilized after thaw, affecting biogeochemical budgets and cycles of thawing permafrost-affected ecosystems. Possible effects include mitigation of the current nitrogen limitation of Arctic tundra ecosystems or a contribution of additional greenhouse gases in the form of N2O. In both cases, the permafrost-climate feedback will be affected by the amount and availability of so far not accessible nitrogen. Acknowledgements: This project is integrated into the Action Group “The Yedoma Region: A Synthesis of Circum-Arctic Distribution and Thickness” (funded by the International Permafrost Association (IPA) to J. Strauss). We acknowledge the support by the European Research Council (Starting Grant #338335), the German and Russian Science Foundations (DFG and RFBR “Polygon” project, DFG-HE 3622-16-1, and RFBR-11-04-91332-NNIO-a), the German Federal Ministry of Education and Research (Grant 01DM12011, and “CarboPerm” (03G0836A)), the Initiative and Networking Fund of the Helmholtz Association (#ERC-0013) and the German Federal Environment Agency (UBA, project UFOPLAN FKZ 3712 41 106). References Keuper, F., van Bodegom, P.M., Dorrepaal, E., Weedon, J.T., van Hal, J., van Logtestijn, R.S.P. and Aerts, R., 2012. A frozen feast: thawing permafrost increases plant-available nitrogen in subarctic peatlands. Global Change Biology, 18(6): 1998-2007, doi:10.1111/j.1365-2486.2012.02663.x. Mack, M.C., Schuur, E.A.G., Bret-Harte, M.S., Shaver, G.R. and Chapin, F.S., 2004. Ecosystem carbon storage in arctic tundra reduced by long-term nutrient fertilization. Nature, 431(7007): 440-443, doi:10.1038/nature02887. Rustad, L.E., Campbell, J.L., Marion, G.M., Norby, R.J., Mitchell, M.J., Hartley, A.E., Cornelissen, J.H.C., Gurevitch, J. and Gcte, N., 2001. A Meta-Analysis of the Response of Soil Respiration, Net Nitrogen Mineralization, and Aboveground Plant Growth to Experimental Ecosystem Warming. Oecologia, 126(4): 543-562, doi:10.1007/s004420000544.

Description: The biogeochemical pools of fossil organic matter in permafrost, mainly the carbon pool, are subject in current research to estimate the quality, quantity and the potential release into the modern cycles maintained by permafrost thaw and accelerated by arctic warming. Organic matter freeze-locked in perennially frozen ground of the northern circumpolar region accumulated over tens of thousands of years during the last glacial and interglacial periods. A part of this permafrost region is composed of ice-rich silts penetrated by large ice wedges, resulting from sedimentation and syngenetic freezing accompanied by wedge-ice growth driven by certain climatic and environmental conditions during the late Pleistocene. These unique materials are called Yedoma deposits. This study focuses on the area of potential Yedoma deposit occurrence in Siberia and Alaska and on nitrogen which has mostly a subordinate role in current studies, but is also an important source of greenhouse gas N2O. Based on the most comprehensive data set of total nitrogen (TN) concentrations in permafrost, our study aims to estimate the present pool of nitrogen stored in the different stratigraphic units of the Yedoma region. Nitrogen stock calculations will be based on bootstrapping techniques using resampled observed values. The total mean pool size estimate will be derived afterward for every of the 10,000 bootstrapping runs, resulting in 1 mean calculated from 10,000 observation-based bootstrapping means. The conceptual formula for the nitrogen stock calculation is: TN budget [Gt] = (deposit thickness [m] × coverage [m²] × bulk density [g/cm³] × (100-WIV/100) × (TNwt%/100))/ 1,000,000,000; TN: total nitrogen; WIV: wedge-ice volume In conclusion, we expect a substantial amount of nitrogen sequestered in the Yedoma region, which is expected to be released after thaw, probably mitigating the current nitrogen limitation of Arctic tundra ecosystems.

Description: Das „Permafrost Young Researchers Network“ (PYRN, http://pyrn.ways.org) ist ein Netzwerk von und für junge Wissenschaftler, die sich sowohl durch ihren beruflichen Werdegang als auch aus privatem Interesse mit dem Thema Permafrost beschäftigen und mit dieser Motivation, lokale bis internationale bzw. individuelle bis organisierte Kooperation betreiben.

Description: The land-ocean transition in the Arctic is a highly sensitive environment facing severe changes due to increasing temperatures. To assess these changes, the CACOON project conducted intensive fieldwork in the Russian Arctic with four field campaigns in 2019 in the Lena and Kolyma delta region. Lena Delta: In the Lena Delta region CACOON lead a 19 day spring campaign (CACOON Ice). Using a mobile camp on sledges, we were able to collect water samples, ice cores, surface sediments, gas samples as well as CTD profiles. For getting the terrestrial endmember, a Pleistocene permafrost cliff was sampled. During the summer campaign (CACOON Sea) more than 1300 samples were retrieved along a 200 km long transect from the centre of the delta into the Laptev Sea covering the freshsalt water transition. This expedition included sampling for the CAO-EISPAC project and revisited several sampling locations from the spring expedition to investigate seasonality. Kolyma Delta: The aim of field sampling was to capture the open water season (spring, summer and autumn) from the ice breakup in early June to re-freezing in late September. During the two long campaigns with 71 field days, we were able to sample the Kolyma River and the near shore area in seven independent transects. During that period, we collected more than 1200 samples, filtered and preserved for further analysis during the coming months. The collected sample material will arrive in Potsdam in December 2019. For requests, please contact Jens.Strauss@awi.de and paul.mann@northumbria.ac.uk Modelling the comparative influence of riverine input and coastal erosion on sediments in the Laptev Sea.

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 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 (1:25,000 – 1:500,000) 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 in 50 m 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 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.

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: 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. With analyzing the natural abundance of the stable isotope composition in different form of nitrogen components, we aim to unravel the balance of transport and biological nitrogen turnover processes like remineralization or nitrification and in consequent the fate of the nitrogen. 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 and Kurunghak Island. Our aim was to determine nitrogen sources, sinks and transformation processes during transport in river and delta. Our data shows that in winter 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. The load of nitrate, during the transect cruise, increased slightly in the delta, while we observed no changes to the isotope values of DON and nitrate indicating a lack of biological activity in the winter season and the lateral transport from soils was the likely source. In summer, nitrogen was mainly transported as DON and particulate nitrogen in the suspended matter and nitrate was mainly below 1µmol/L. 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 suspended particulate matter (SPM)/sediment and DON to nitrate. These light values indicate soil nitrogen mainly originates from atmospheric nitrogen fixation. During transport and remineralization, biogeochemical recycling via nitrification and assimilation by phytoplankton led to an isotopic enrichment in summer. In the coastal waters of the Laptev Sea, the exported 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. Our data provides a baseline for isoscape analysis and can be used as an endmember signal for modeling approaches.