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Permafrost in northern Norway is characterized by peat plateaus and palsas and is among the fastest degrading permafrost areas in the world. Changes in these ecosystems with sporadic permafrost can be viewed as possible future states for currently stable permafrost regions. The thawing of permafrost at large scale has the potential to release stored carbon into atmospheric cycling and becomes a source of greenhouse gases. Lateral export of dissolved organic matter (DOM) from thawing permafrost could be an important pathway for loss of formerly stable organic matter (OM), and is controlled by temperature, soil moisture and local hydrology. We aim to study thermokarst ponds and the lateral flux of water, heat, organic carbon and greenhouse gases from a rapidly thawing permafrost peat plateau using high-frequency sensors, floating chambers, measurements of dissolved gases and water chemistry, and assessment of DOM. We analyzed water chemistry and extracted gas samples on 5 sampling campaigns of the Iškoras peat plateau located in the Finnmarksvidda in northern Norway between Sept 2020 and Oct 2021. We investigated production and consumption rates of gases at 3 campaigns by dark incubations between 36-50 hours. We present early data of the peat plateau and the hydrologically connected adjacent wetland.

We explore three hypotheses to better understand the role of hydrology and biogeochemistry in lateral transport of organic matter from the active peat plateau area to the larger catchment. First, there is seasonal changes in the lability of DOM in thermokarst ponds. Second, there is seasonal connection and transport of OM from the peat plateau to the wetland stream that connects to the catchment. Finally, we focus on identifying the areas in the landscape that are hotspots for greenhouse gas production and transport.

The thermokarst ponds were very acidic and high in dissolved gases and TOC compared with the wetland stream system. High emissions from the thermokarst ponds are a key source of CO₂ and CH₄. Aquatic processing of DOM and turbulence in streams both affect level of GHG emissions. There are also differences in parameters such as CO₂ evasion and DIC concentration when there is connection of the wetland stream to the peat plateau. The early data indicate high rates of DOM processing and GHG production in the thermokarst ponds and high variability in DOM export from the peat plateau.

How to cite: Knutson, J., Clayer, F., Dörsch, P., Westermann, S., and de Wit, H. A.: Investigating hydrology and carbon cycling connections in peatland permafrost, northern Norway., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9445, https://doi.org/10.5194/egusphere-egu22-9445, 2022.

Cold-regions contain a vast pool of organic carbon in permafrost, which is currently immobilized. As the global air temperatures rise, permafrost active layer depths are increasing. The deepening of the active layer reactivates groundwater transport processes, leading to the release of solutes such as dissolved carbon to streams and the atmosphere. In order to make predictions of the rates of permafrost thaw based upon numerical modeling, we need accurate data on active layer thermal properties.

Active layer thermal properties, thermal conductivity and heat capacity, are strongly coupled to geological properties such as water content, and organic matter content and are therefore highly heterogenous in natural systems. Furthermore, the effective thermal properties vary as a function of temperature through ice-content, especially across the freeze-thaw interval near 0 ^oC. Direct in-situ observations of active-layer thermal properties are rare because in-situ measurements involves sampling of frozen samples and analysis in a laboratory.

This study uses soil column (1 m high x 0.31 m diameter) experiments to investigate the relation between soil physical properties and thermal properties. A total of nine samples were synthesized using a range of grain sizes and organic matter contents, and were fully saturated with water. The columns were insulated on the sides and top, aiming to create a fully 1D thermal system allowing only vertical heat transport. The columns are subjected to one freeze-thaw cycle, lasting about 20 weeks. Resulting temperature observations were analyzed using a numerical heat transfer model. By fitting the temperature observations to the heat transfer model, thermal properties can be inferred. Initial data shows differences in heat propagation through the soil column, indicating differences in thermal conductivity and heat capacity as a result of varying soil grain size and organic matter content. This research will help to link permafrost soil physical properties to thermal properties, and increase understanding at the dynamic freeze-thaw interval.

How to cite: de Bruin, J., Bense, V., and van der Ploeg, M.: Inferring permafrost thermal properties from freeze-thaw column experiments and numerical modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12968, https://doi.org/10.5194/egusphere-egu22-12968, 2022.

Thermokarst lakes of permafrost peatlands in Western Siberia are among the most important sources of greenhouse gases (GHG) such as CO₂ and CH₄ because of current permafrost thawing due to climate change. Field measurements demonstrated the increase of dissolved GHG concentrations with the decreasing lake size due to higher concentration of coastal-derived organic C in water of small lakes. However, the size-dependent mechanisms of the GHG production and consumption (e.g. CH₄ oxidation) in the sediments of these lakes remain poorly known. We estimated aerobic CO₂ production and CH₄ oxidation potentials based on natural ¹³C abundance and ¹³C labeling in two layers of upper 20 cm sediments of three thermokarst lakes: small (~ 300 m²), medium (~ 3000 m²) and large (~ 1 km²). We hypothesized that i) specific CO₂ production (per gram of sediment) decreases with increasing lake size, but CH₄ oxidation increases, and ii) both processes are more intensive in the upper 10 cm of sediments than in deeper 10–20 cm, due to naturally occurring O₂ gradients and the available C. As expected, CO₂ production in the upper layer was 1.4–3.5 times higher than in the deeper layer and the rate of production increased from large (170 nmol CO₂ g^-1 d.w. h^-1) to medium (182) and small (234) lakes. In contrast to CO₂, CH₄ oxidation in the uppermost sediment layer was similar between lakes, while the deeper layer in the large lakes had 12- and 73-fold higher oxidation rates (5.1 nmol CH₄-derived CO₂ g^-1 d.w. h^–1) than in small and medium lakes, respectively. This was attributed to the fact that the O₂ concentration in the water of large lakes is higher than in smaller lakes due to the intense turbulence caused by wind and waves. Due to the ongoing and future thawing of permafrost, smaller lakes will increase in size, so that a large part of the CH₄ produced in the sediments will be oxidized. However, this process can be (over)compensated by the increased formation of new small lakes. From an ecological perspective, the sediments of shallow thermokarst lakes in the discontinuous permafrost zone of Western Siberia could oxidize up to 0.48 Tg C as CH₄ in the summer period, with the largest contribution coming from the large lakes. This confirms the key role of the thermokarst lake ecosystems as a global hotspot of GHG turnover.

Acknowledgement. This work was supported by RSF grant No. 21-77-10067 and the German Academic Exchange Service (DAAD).

How to cite: Dorodnikov, M., Manasypov, R., Fan, L., Pokrovsky, O., Dippold, M. A., and Kuzyakov, Y.: The size matters: aerobic methane oxidation in thermokarst lake sediments in Western Siberia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11190, https://doi.org/10.5194/egusphere-egu22-11190, 2022.

Previous research was addressed to carbon emissions after permafrost thaw, but less attention was paid to changes in nitrogen availability and N₂O emissions and in particular data from the Russian Arctic are scarce. Rise in water temperature and sea-level contribute to coastal erosion accelerating thaw rates and the release of dissolved nitrogen. Already 78% of the coastal regions of the Laptev Sea are affected by rapid permafrost thaw. This study estimates whether eroded Arctic coasts are hotspots for N availability and N₂O emissions and to further understand the impact of NO₃^- leaching. Therefore, we estimated N-transformation rates and greenhouse gas (GHG) production (CO₂, CH₄, N₂O) by incubating non-vegetated and revegetated soil samples from a retrogressive thaw slump in the Lena River Delta, Siberia. Within the thaw slump we found at exposed thaw mounds a domination of DIN over DON and an accumulation of NO₃^- with up 110 µg N (g DW)^-1 within the growing season and in the presence of vegetation. Those results are contracting to what is normally reported in Arctic regions. Our incubations indicate that thaw mounds are hotspots for N-mineralization and N₂O release (up to 390 ng N₂O-N (g DW)^-1) via denitrification while at the slump floor denitrification was substrate limited. Substrate limitation is rather caused by soil moisture and pH value than by functional limitation, since in our incubation N-mineralization could proceed in all samples. Simulated NO₃^- leaching removed the substrate limitation of the denitrification and converted the slump floor to a significant N₂O hotspot (410 ng N₂O-N (g DW)^-1).

Our results emphasise that it is necessary to consider geomorphology and landscape processes to identify hotspots of gaseous and dissolved N loss. A higher availability of inorganic nitrogen in coastal zones will have effects on marine ecosystems and more in depth-studies are needed to characterise seasonality of nitrogen leaching by melt water and eroded sediments.

How to cite: Wegner, R., Fiencke, C., Knoblauch, C., Sauerland, L., and Beer, C.: Rapid Permafrost Thaw Removes Nitrogen Limitation Rising the Potential of N2O Emissions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11181, https://doi.org/10.5194/egusphere-egu22-11181, 2022.

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.  

How to cite: Sanders, T., Fiencke, C., Juhls, B., Ogneva, O., Strauss, J., Tuerena, R., and Dähnke, K.: Nitrogen isotopic inventory of the Lena River Delta, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12454, https://doi.org/10.5194/egusphere-egu22-12454, 2022.

Rapid warming of the Arctic is accelerating thaw of permafrost, which mobilizes organic carbon (OC). Remineralization of this carbon can contribute to further climate warming. The Peel River watershed is underlain by continuous and discontinuous permafrost and covers a diverse set of landscapes from wetlands to barren mountainous areas. Part of the watershed undergoes abrupt permafrost thaw that releases particulate OC (POC) to the fluvial system. In this study, we couple landscape characteristics to river POC to better understand its spatial variability and the changes imposed on the watershed by permafrost thaw. We sampled POC in July-August 2019 in the Peel River main stem and its tributaries (total n=~120) and used carbon isotopes and lipid biomarkers to characterize its composition and trace its sources. Our first results indicate a compositional diversity within the watershed as POC ranges between <0.1 and 2.1 mg L^-1, δ¹³C-POC from -36.7 to -26.5‰ and Δ¹⁴C-POC from -906.4 to -43.5‰. Ongoing changes in the watershed can be traced within its waters, and may help us to decipher how it is changing and may change in the future.

How to cite: Keskitalo, K., Speetjens, N., Overduin, P., Westermann, S., Miesner, F., Sachs, T., Nitze, I., Bröder, L., Haghipour, N., Eglinton, T., and Vonk, J.: Particulate organic carbon composition and landscape characteristics in the Peel River Watershed, Canada, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9657, https://doi.org/10.5194/egusphere-egu22-9657, 2022.

The Arctic is undergoing accelerated changes in response to ongoing alterations to the climate system (Arctic report card 2019), and there is a need for local to regional scale records of past climate variability in order to put these changes into historical context. The Mackenzie Delta region (Northwestern Territories, Canada) is populated by numerous small shallow lakes. They are classified as no-, low- and high-closure lakes, reflecting varying degrees of connection to the river main stem, and as a result, have different sedimentation characteristics. As for much of the Arctic region, the Mackenzie Delta is expected to undergo marked environmental perturbations such as earlier melting of river ice. As a consequence, the annual flood pulse (freshet) may decline, potentially resulting in the disconnection of some lakes from the river, leading to their subsequent desiccation (Lesack et al., 2014; Lesack & Marsh, 2010). In contrast, abrupt permafrost thaw and enhanced thermokarst-related processes might lead to additional lake formation and deepening of already formed lakes.

In this study, we used sediment cores originating from several lakes within the Mackenzie Delta, representing the three types of connectivity to the river (Lattaud et al., 2021). Radiocarbon and stable carbon isotopic signatures of two groups of compounds - fatty acids and isoprenoid and branched glycerol dialkyl glycerol tetraethers (GDGTs) - are employed as tracers of carbon supply to, and cycling within the different lakes. Short-chain fatty acids as well as GDGTs serve as putative tracers of microbial production while long-chain fatty acids originate from higher terrestrial plants. The carbon isotopic signatures are used to distinguish between the relative importance of carbon inputs derived from in situ production, as well as from proximal (lake periphery) and distal (Mackenzie River) sources to the different lakes in the context of their degree of connectivity. Down-core molecular ¹⁴C measurements provide insights into the temporal evolution of the lakes, providing context for their response to past and future climate change.

How to cite: Lattaud, J., Bröder, L., Haghipour, N., Giosan, L., and Eglinton, T.: Radiocarbon and Stable Isotope Constraints on the Sources and Cycling of Organic Carbon in Mackenzie Delta Lakes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1095, https://doi.org/10.5194/egusphere-egu22-1095, 2022.

The Canadian Beaufort Sea coastline consists of permafrost, permanently frozen soils, that store large amounts of organic carbon (OC). Rising temperatures in the Arctic will lead to thaw of these permafrost soils as well as enhanced coastal erosion. The trajectory of thawing coastal carbon upon thaw will determine the degree of breakdown and greenhouse gas emission, impacting climate warming. However, we still have a poor understanding of the marine fate of sediments and OC from eroding arctic coastlines.

In order to obtain more insight into the fate of the eroding material, we will use hydrodynamic fractionation on a variety of actively eroding coastal cliffs (parent material). Hydrodynamic fractionation accounts for the sediment sorting of particles when exposed to different energy conditions such as waves. With this technique we will fractionate based on density and grainsize to mimic the route in the marine system. Current estimates of sediment and OC input from arctic coastal erosion are only based on bulk measurements.

Samples were collected from eight sites (n=5 at each site) with a wide spatial and geological variation across the Canadian Beaufort Sea. These sites range from peaty and flat islands to muddy slumps and sandy locations. For all sites, parent material was collected onshore, fractionated and separated in five fractions based on density (cut-off 1.8 g/mL) and grainsize (cut-offs 38, 63, and 200mm). All fractions will be analysed for geochemical properties (total OC, total nitrogen, δ¹³C, and D¹⁴C, biomarkers and lipids) in order to determine the quantity and quality of the organic matter. Distribution of sediment fractions based on weight shows large variability between sites (e.g. low density fraction between 2-13% and high density between 9-50% with grainsize 63-200mm) as well as within sites, depending on the characteristics of the coast. Using the spatial variability of these fractions in combination with coastal characteristics assessed with GIS techniques we will attempt to upscale for the Canadian Beaufort Coast. This will hopefully improve our insights on the type and composition of parent material which is released into the marine system as a source of carbon.

How to cite: van Crimpen, F., Madaj, L., Whalen, D., Tesi, T., and Vonk, J.: The hydrodynamic potential of eroding arctic permafrost coasts: fractionation of permafrost parent material in the Canadian Arctic to determine its fate in the marine system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11429, https://doi.org/10.5194/egusphere-egu22-11429, 2022.

The Canadian Beaufort Sea receives large quantities of sediment, organic carbon and nutrients from rapid coastal erosion and permafrost degradation. In addition, the Mackenzie River, the largest North American Arctic river, discharges great amounts of freshwater, dissolved solids and suspended sediments to the Beaufort Sea. Current changes in these fluxes in response to the warming climate have uncertain consequences for the carbon budget on the shelf and in the deep ocean. To investigate the movement and transformation of organic matter along the land-ocean continuum, we collected water and surface sediment samples along five major transects across the Beaufort Sea during the 2021 expedition of the Canadian Coast Guard Ship Amundsen. Sampling locations span from shallow, coastal, sites with water depths ≤ 20 m, to shelf-break and deep-water settings on the continental slope (water depths of ≥1000 m). For this study, we use stable and radiocarbon isotopic (δ¹³C and Δ¹⁴C) analyses of dissolved inorganic (DIC), dissolved organic (DOC) and particulate organic carbon (POC) for surface and bottom waters, as well as surface sediments, in order to compare, contrast and constrain the relative source contributions and ages of these different forms of carbon. Our results will help to better understand the fate of permafrost organic matter in the marine environment and to ultimately improve assessments of the Canadian Beaufort Sea shelf as a carbon source or sink and its potential trajectory with ongoing environmental changes.

How to cite: Bröder, L., Lattaud, J., Juhls, B., Eulenburg, A., Priest, T., Fritz, M., Matsuoka, A., Pellerin, A., Bossé-Demers, T., Rudbäck, D., O'Regan, M., Whalen, D., Haghipour, N., Eglinton, T., Overduin, P., and Vonk, J.: Tracing the footprint of permafrost carbon supply to the Canadian Beaufort Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8694, https://doi.org/10.5194/egusphere-egu22-8694, 2022.

Around 65% of the Arctic coastline consists of permafrost soils which are currently thawing on an accelerating rate due to rising global air temperatures. The uncontrolled and rapid thaw of permafrost soils leads to increased coastal erosion and input of large amounts of organic carbon (OC) into the coastal ocean. Here, the OC can either be degraded (leading to production and emission of greenhouse gases that strengthen climate warming) or be sequestered over short or long timescales (attenuating climate warming). A major proportion of permafrost-derived OC quickly settles upon coastal release and therefore the sediment-water interface is the crucial zone for determining the trajectory of thawed OC and whether it deposits or remains in suspension. However, there is little data available from these so-called flocculation (i.e. nepheloid) layers, particularly in the Arctic shelf seas.

Here, we investigate the composition of suspended sediment within the flocculation layer at the sediment-water interface as well as the shallow surface sediments to shed light on the degradation state and fate of terrestrial OC, and additionally, characterize its lateral and vertical variability upon transport offshore. All samples were collected during ISSS-2020 expedition in late summer (Sept-Oct) of 2020 onboard R/V Akademik Msistlav Keldysh in the Kara Sea (n=2), Laptev Sea (n=8), and East Siberian Sea (n=4). We present first results of elemental, isotopic, and sedimentological analyses of suspended and surface sediments (C/N values, δ¹³C, Δ¹⁴C, surface area). With these data, we want to better understand how transport and degradation processes of terrestrial OC vary across the vast Siberian shelves.

How to cite: Madaj, L., Keskitalo, K., Gustafsson, Ö., Tesi, T., Semiletov, I., Dudarev, O., Martens, J., and Vonk, J.: Transport and Composition of Terrestrial Organic Matter at the Sediment-Water Interface of the Kara, Laptev and East Siberian Shelf Seas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9760, https://doi.org/10.5194/egusphere-egu22-9760, 2022.