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Rapid warming in Subarctic areas releases large amounts of frozen carbon which can potentially result in large CO₂ and CH₄ emissions to the atmosphere. In Northern Norway vast amount of carbon are stored in peat plateaus, but these landscape elements have been found to decrease laterally since at least the 1950s. Peat plateaus are very sensitive to climate change as the permafrost is relatively warm compared to permafrost found in the arctic. So far, only limited information is available about potential degradation kinetics of organic carbon in these ecosystems. We sampled organic matter from depth profiles along a well-documented chronosequence of permafrost degradation in Northern Norway. After thawing over-night, we incubated permafrost and active layer for up to 3 months at 10°C. To determine factors constraining degradation, we measured gas kinetics (O₂, CO₂, CH₄) under different conditions (oxic/anoxic, loosely packed/stirred suspensions in water, with altered DOC content and nutrient amendments) and related them to pH, DOC, element (C, N, P, S) and δ¹³C and δ¹⁵N signatures of the peat. Organic matter degradation was strongly inhibited in the absence of oxygen. By contrast, CH₄ production or release seemed to be related to soil depth rather than incubation conditions and was found to be highest in samples from the transition zone between active layer and permafrost. Degradation rates and their dependencies on peat characteristics will be compared with permafrost characteristics along the chronosequence and additional experiments exploring the role of O₂, DOC and other nutrients for carbon degradation will be discussed.

How to cite: Kjær, S. T., Nedkvitne, N., Westermann, S., Althuizen, I., and Dörsch, P.: Carbon degradation in Subarctic organic permafrost (peat plateaus) after thawing – what constraints CO2 and CH4 production?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11121, https://doi.org/10.5194/egusphere-egu21-11121, 2021.

The East Siberian Arctic Shelf is an integrated coastal sea system with complex biogeochemical processes influenced by underlying subsea permafrost, hydrates and thermogenic compartments. Methane is released from the marine sediments to the water column, which serves as an interphase between the lithosphere and the atmosphere. Before escaping into water column and atmosphere, methane has potentially experienced extensive aerobic and anaerobic oxidation by microbes in the marine sediment. In particular, the aerobic process is assumed to be dominant in the surface oxic/suboxic marine sediment (upper 1cm) after anaerobic processes in deeper zones. However, these processes are insufficiently understood in sediments of the Arctic Ocean. To probe these, we investigated the microbial lipids and their stable carbon composition in surface marine sediment (upper 1 cm) from two active methane seep areas in the Laptev Sea and the East Siberian Sea.

The microbial fatty acids (C12 to C18 fatty acids) were relatively enriched in ¹³C (δ¹³C -18.8 to -31.2‰) compared to that of dissolved CH₄ in nearby bottom water (-54.6 to -29.7‰). This contrasts to previous reports of strongly depleted δ¹³C signals in microbial lipids (e.g., -100‰) at active marine mid-ocean ridges and mud volcanoes, from quite different ocean areas. The absence of a depleted δ¹³C signal in these general microbial biomarkers suggest that these reflect substrates other than methane such as other parts of the sediment organic matter, indicated by the stronger correlation of δ¹³C between fatty acids and bulk organic carbon than that between fatty acid and CH₄. However, the putatively more specific biomarkers for aerobic methanotrophic bacteria (mono-unsaturated C16 and C18 fatty acids) show a distinct pattern in the Laptev Sea and East Siberian Sea: C16:1 and C18:1 were enriched in ¹³C (up to 4.5 ‰) relative to their saturated analogs in the Laptev Sea; whereas, C18:1 was depleted in ¹³C (up to 4.5 ‰) compared to C18 in the East Siberian Sea. This could be because the relative populations of Type I and II methanotrophs were different in the two areas with different carbon assimilation pathways. Our results cannot exclude a slowly active aerobic methanotrophs at methane seeps in the East Siberian Arctic Ocean and thus call for more information from molecular microbiology.

How to cite: Wu, W., Holmstrand, H., Wild, B., Shakhova, N., Kosmach, D., Semiletov, I., and Gustafsson, Ö.: Methane oxidation processes in sediment of the Laptev and East Siberian Seas indicated from microbial lipids and carbon isotope composition, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13428, https://doi.org/10.5194/egusphere-egu21-13428, 2021.

Ongoing warming of the Northern high latitudes has intensified abrupt thaw processes throughout the permafrost zone. The resulting terrain disturbances are prone to release large amounts of particulate organic matter (OM) from deeper permafrost soils with thus far poorly constrained decay kinetics. Organo-mineral interactions may inhibit OM decomposition, thereby mediating the release of carbon to the atmosphere. Yet how these interactions evolve upon release and during transport along the fluvial continuum is still insufficiently understood. Here we investigate the mobilization of particulate OM from disturbed permafrost soils to the aquatic environment in the Zackenberg watershed in Northeastern Greenland. We collected soil samples in a thermo-erosion gully and a retrogressive thaw slump, as well as suspended solids and stream sediments along the glacio-nival Zackenberg River, including its tributaries, and a small headwater stream (Grænselv) affected by abrupt permafrost thaw. To evaluate the organic and mineral material transported, we compare mineral element and organic carbon (OC) concentrations, bulk carbon isotopes (¹³C and ¹⁴C), together with source-specific molecular biomarkers (plant-wax lipids and branched glycerol dialkyl glycerol tetraethers, brGDGTs) for the suspended load with their soil and sediment counterparts.

Preliminary results show large contrasts in OC concentrations as well as Δ¹⁴C between the glacio-nival river and the headwater stream, as well as between the different thaw features. The retrogressive thaw slump mobilizes relatively OC-poor material with very low Δ¹⁴C signatures suggesting a petrogenic contribution, while soil samples from the thermo-erosion gully had higher OC concentrations and Δ¹⁴C values. For Grænselv, Δ¹⁴C values of the particulate OC were lower close to the eroding stream bank, whereas the Zackenberg main stem displayed fairly constant Δ¹⁴C values, with some of the Zackenberg tributaries delivering relatively organic-rich particles low in Δ¹⁴C.

Molecular biomarker analyses will provide additional information on specific OM sources, while X-ray Diffraction (XRD) and X-ray Fluorescence (XRF) analyses on the soils, sediments and suspended mineral load will give more detailed insights into the composition of the mineral matrices. By combining these analytical methods, we aim to improve our understanding of the interactions between minerals and OM and thereby help to constrain the fate of mobilized OM upon permafrost thaw.

How to cite: Bröder, L., Hirst, C., Opfergelt, S., Lattaud, J., Haghipour, N., Eglinton, T., Vonk, J., and Fouché, J.: Mobilization of particulate organic matter and minerals in Zackenberg valley, Greenland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11539, https://doi.org/10.5194/egusphere-egu21-11539, 2021.

A vast amount of global mercury is believed to be stored in the Arctic, much of which is frozen in permafrost. Increasing temperatures in the Subarctic, leading to permafrost thaw, alter the global mercury cycle by mobilizing and releasing stored mercury. This is of concern since it allows mercury to spread though air- and waterways. Moreover, mobilized mercury in combination with increased microbial activity can increase the production of methyl mercury (MeHg), a highly potent neurotoxin which readily bioaccumulates throughout food webs. We report current levels of total mercury (HgT) and MeHg for permafrost cores, ambient surface waters, and active layer pore waters across a gradient of sporadic permafrost (peat plateaus) ranging from coastal-mild to inland-cold climate in the northernmost part of continental Europe (Finnmark, Norway). To investigate the effect of microbial activity on mercury methylation, permafrost samples were thawed and subjected to long-term incubation under oxic, and oxic/anoxic conditions, with and without additional native DOC and extraneous C, N, P, S, and Hg additions. Microbial activity was monitored by CO₂ and CH₄ production. Our field samples indicate that the %MeHg of HgT are higher in the outlet of the peat plateau than in the inlet and that streams have a significantly higher %MeHg of HgT than ponds. In contrast, thermokarst ponds (collapsed peat plateaus) have a significantly higher concentration of HgT than streams. In the incubation experiments, presence or absence of oxygen had the largest impact on DOC and dissolved HgT accumulation; soil slurries incubated under anoxic conditions yielded higher concentrations of both DOC and dissolved HgT compared to oxic conditions. Selected results from ongoing experiments will be presented.

How to cite: Nedkvitne, N., Trier Kjær, S., de Wit, H., Westermann, S., and Dörsch, P.: Mercury in permafrost landscapes in the Norwegian Subarctic – current status and potential for increased release and methylation by permafrost thaw, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11126, https://doi.org/10.5194/egusphere-egu21-11126, 2021.

Recent decades have shown phases of very rapid warming in the Canadian Arctic. This raises a concern, also in reference to potential changes in permafrost active layer deepening, enhancing the fact that seawater, snow and soils are becoming important secondary sources remobilizing persistent organic pollutants (POPs). This work investigates the potential influence of permafrost on POPs distribution in the soils of two small coastal catchments at the Canadian Beaufort coast. One catchment is located south of Herschel Island on the mainland and was covered by the Laurentide ice sheet during the last glacial maximum (LGM), the second catchment is located westerly at Komakuk Beach and was ice-free during the LGM.

Soils were sampled by horizon in the Active Layer from an open soil pit and by coring into the permafrost, near the top of the permafrost table and at 90 cm depth from the soil surface (99 samples form Ptarmigan Bay and 89 from Komakuk Beach). The total sampling depth was 1,0 m (including Active Layer and Permafrost). A random distribution of the points over the areas guaranteed the sampling over different Landforms, aiming to understand the contaminant concentration and distribution. Quantification of PAHs, PCBs, HCB was performed using GC-MS technique, a 7890A gas chromatographer coupled with a 5975C MSD System, Agilent Technologies, at CNR-ISP Venice, Italy.

Preliminary results confirm that the mechanism responsible for the transport of POPs into the soil are believed to be gravity drainage and capillary suction into fissures and cracks. An accumulation of PAHs has been detected in the permafrost transient layer. It is probably related, as demonstrate in literature, to the accumulation and transport of soil organic carbon influence, as well as the changing in hydraulic barriers. The role of cryoturbation in the vertical transport and accumulation of POPs is also considered and discussed.

The study has been conducted thanks to Grant Agreement number: 773421 — Nunataryuk — H2020-BG-2016-2017/H2020-BG-2017-1 ‘Permafrost thaw and the changing arctic coast: science for socio-economic adaptation — Nunataryuk’

How to cite: Lodi, R., Wagner, J., Hugelius, G., Martin, V. S., Speetjens, N., Richter, A., Gabrieli, J., and Barbate, C.: Persistent organic pollutants distribution of small coastal catchments at the Canadian Beaufort coast., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10165, https://doi.org/10.5194/egusphere-egu21-10165, 2021.

The Action Group called ‘Standardized methods across Permafrost Landscapes: from Arctic Soils to Hydrosystems’ (SPLASH), funded by the International Permafrost Association, is a community-driven effort aiming to provide a suite of standardized field strategies for sampling mineral and organic components in soils, sediments, surface water bodies and coastal environments across permafrost landscapes. This unified approach will allow data to be shared and compared, thus improving our understanding of the processes occurring during lateral transport in circumpolar Arctic watersheds. This is an international and transdisciplinary effort aiming to provide a fieldwork “tool box” of the most relevant sampling schemes and sample conservation procedures for mineral and organic permafrost pools.

With climate change, permafrost soils are undergoing drastic transformations. Both localized abrupt thaw (thermokarst) and gradual ecosystem shifts (e.g., active layer thickening, vegetation changes) drive changes in hydrology and biogeochemical cycles (carbon, nutrients, and contaminants). Mineral and organic components interact along the “lateral continuum” (i.e., from soils to aquatic systems) changing their composition and reactivity across the different interfaces. The circumpolar Arctic region is characterized by high spatial heterogeneity (e.g., geology, topography, vegetation, and ground-ice content) and large inter-annual and seasonal variations in local climate and biophysical processes. Common sampling strategies, applied in different seasons and locations, could help to tackle the spatial and temporal complexity inextricably linked to biogeochemical processes. This unified approach developed in permafrost landscapes will allow us to overcome the following challenges: (1) identifying interfaces where detectable changes in mineral and organic components occur; (2) allowing spatial comparison of these detectable changes; and (3) capturing temporal (inter-/intra-annual) variations at these interfaces. In order to build on the great effort to better assess the permafrost feedback to climate change, there is an urgent need for a set of community-based protocols to capture changes the dynamics of organics and minerals during their lateral transport.

Here, we present the first results from an online survey recently conducted among researchers from different disciplines. The survey inputs provide valuable information about the common approaches currently applied along the “soil-to-hydrosystems” continuum and the specific challenges associated with permafrost studies. These results about the ‘WHAT, WHERE, WHEN, and HOW’ of field sampling (e.g., sample collection, filtration, conservation...) allow for identifying the most relevant sampling strategies and also the current knowledge gaps. Finally, we present examples of the protocols available to investigate organic and mineral components from soils to marine environments, on which a synoptic sampling strategy can be built. All forthcoming contributions from our community are still welcome, helping the SPLASH team to fill up the most adapted tool box to Arctic permafrost landscapes.

How to cite: Fouche, J., Shakil, S., Hirst, C., Bröder, L., Agnan, Y., Sjöberg, Y., and Bouchard, F.: The SPLASH Action Group – Towards standardized sampling strategies along the soil-to-hydrosystems continuum in permafrost landscapes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11184, https://doi.org/10.5194/egusphere-egu21-11184, 2021.

Coastal erosion rates are increasing along the Alaskan Beaufort Sea coast due to increases in wave action, the increasing length of the ice-free season, and warming permafrost. These eroding permafrost coastlines transport organic matter and inorganic nutrients to the Arctic Ocean, likely fueling biological production and CO₂ emissions. To assess the impacts of Arctic coastal erosion on nearshore carbon and nitrogen cycling, we examined geochemical profiles from eroding coastal bluffs and estimated annual organic matter fluxes from 1955 to 2018 for a 9 km stretch of coastline near Drew Point, Alaska. Additionally, we conducted a laboratory incubation experiment to examine dissolved organic carbon (DOC) leaching and biolability from coastal soils/sediments added to seawater.

Three permafrost cores (4.5 – 7.5 m long) revealed that two distinct horizons compose eroding bluffs near Drew Point: Holocene age, organic-rich (~12-45% total organic carbon; TOC) terrestrial soils and lacustrine sediments, and below, Late Pleistocene age marine sediments with lower organic matter content (~1% TOC), lower carbon to nitrogen ratios, and higher δ¹³C-TOC values. Organic matter stock estimates from the cores, paired with remote sensing time-series data, show that erosional TOC fluxes from this study coastline averaged 1,369 kg C m⁻¹ yr⁻¹ during the 21^st century, nearly double the average flux of the previous half century. Annual TOC flux from this 9 km coastline is now similar to the annual TOC flux from the Kuparuk River, the third largest river draining the North Slope of Alaska.

Experimental work demonstrates that there are distinct differences in DOC leaching yields and the fraction of biodegradable DOC across soil/sediment horizons. When core samples were submerged in seawater for 24 hours, the Holocene age organic-rich permafrost leached the most DOC in seawater (~6.3 mg DOC g^-1 TOC), compared to active layer soils and Late-Pleistocene marine-derived permafrost (~2.5 mg DOC g^-1 TOC). Filtered leachates were then incubated aerobically in the dark for 26 and 90 days at 20°C to examine biodegradable DOC (i.e. the proportion of DOC lost due to microbial uptake or remineralization). Of this leached DOC, Late Pleistocene permafrost was the most biolabile over 90 days (31 ± 7%), followed by DOC from active layer soils (24 ± 5%) and Holocene-age permafrost (14% ± 3%). If we scale these results to a typical 4 m tall eroding bluff at Drew Point, we expect that ~341 g DOC m^-2 will rapidly leach, of which ~25% is biodegradable. These results demonstrate that eroding permafrost bluffs are an increasingly important source of biolabile DOC, likely contributing to greenhouse gas emissions and marine production in the coastal environment.

How to cite: Bristol, E., Connolly, C., Lorenson, T., Richmond, B., Ilgen, A., Choens, R. C., Bull, D., Kanevskiy, M., Iwahana, G., Jones, B., Spencer, R., and McClelland, J.: Land-to-ocean fluxes and biolability of organic matter eroding along the Beaufort Sea coast near Drew Point, Alaska, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9260, https://doi.org/10.5194/egusphere-egu21-9260, 2021.

Until two decades ago, ancient carbon was regarded as non-bioavailable substrate for organisms because it was synthesised, deposited, and once before (partially) degraded thousands to millions of years ago. Such aged organic matter is stored in terrestrial permafrost deposits or sedimentary bedrock, where it is locked up and remains disconnected from the active global carbon cycle. However, with changing climatic conditions, these organic matter reservoirs are being remobilised at faster rates by receding glaciers or permafrost thaw. During transport and after redeposition in newly formed sediments, the ancient carbon can be accessed by micro-organisms, but whether or not the micro-organisms can utilize the ancient carbon is highly debated.

Using a combined approach of lipid biomarker analysis, lipidology, and radiocarbon dating of bulk organic matter as well as single compounds targeting intact polar lipid fatty acids (IPL-FAs), our research demonstrates that microbial communities utilise supposedly non-bioavailable ancient carbon for biosynthesis in Arctic marine fjord sediments. The availability of ancient carbon to the sub-surface microbes represents a carbon source that has not been accounted for in today’s climate models. These implications are of major importance concerning the increased thawing of high latitude permafrost soils, permafrost mobilization and coastal erosion due to anthropogenic climate change, catalysing associated positive feedback loops. In future research, we will use this approach to study the utilization of ancient carbon derived from North American and Siberian permafrost soils in Arctic shelf sediments to assess its importance in the global carbon budgets.

How to cite: Ruben, M., Schubotz, F., Marchant, H., Hefter, J., Grotheer, H., Forwick, M., Szczuciński, W., and Mollenhauer, G.: Microbial utilization of terrigenous ancient carbon released to marine environments traced by compound specific radiocarbon dating, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1030, https://doi.org/10.5194/egusphere-egu21-1030, 2021.

Climate warming is accelerating erosion rates along permafrost-dominated Arctic coasts. To study the impact of erosion on marine microbial community composition and growth in the Arctic coastal zone, dissolved organic matter (DOM) from three representative glacial landscapes (fluvial, lacustrine and moraine) along the Yukon coastal plain, are provided as substrate to marine bacteria using a chemostat setup. Our results indicate that chemostat cultures with a flushing rate of approximately a day provide comparable DOM bioavailability estimates to those from bottle experiments lasting weeks to months. DOM composition (inferred from UV-Visible spectroscopy) and biodegradability (inferred from DOC concentration, bacterial production and respiration) significantly differed between the three glacial deposit types. DOM from fluvial and moraine deposit types shows more terrestrial characteristics with lower aromaticity (S_R: 0.63 (±0.02), SUVA₂₅₄: 1.65 (±0.06) respectively S_R: 0.68 (±0.00), SUVA₂₅₄: 1.17 (±0.06)) compared to the lacustrine deposit type (S_R: 0.71 (±0.02), SUVA₂₅₄: 2.15 (±0.05)). The difference in composition of DOM corresponds with the development of three distinct microbial communities, with a dominance of Alphaproteobacteria for fluvial and lacustrine deposit types (relative abundance 0.67 and 0.87 respectively) and a dominance of Gammaproteobacteria for moraine deposit type (relative abundance 0.88). Bacterial growth efficiency (BGE) is 66% for moraine-derived DOM, while 13% and 28% for fluvial-derived and lacustrine-derived DOM respectively. The three microbial communities therefore differ in their net effect on DOM utilization. The higher BGE value for moraine-derived DOM was found to be due to a larger proportion of labile colourless DOM. The results from this study, therefore indicate a substrate control of marine microbial community composition and activities, suggesting that the effect of permafrost thaw and erosion in the Arctic coastal zone will depend on subtle differences in DOM related to glacial deposit types. These differences further determines the speed and extent of DOM mineralization and thereby carbon channelling into biomass in the microbial food web. We therefore conclude that marine microbes strongly respond to the input of terrestrial DOM released during coastal erosion of Arctic glacial landscapes.

How to cite: Bruhn, A. D., Stedmon, C. A., Comte, J., Matsuoka, A., Speetjens, N. J., Tanski, G., Vonk, J. E., and Sjöstedt, J.: Permafrost-derived dissolved organic matter character controls microbial community composition in Arctic coastal waters, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13069, https://doi.org/10.5194/egusphere-egu21-13069, 2021.

Understanding optical characteristics, composition and source of dissolved organic matter (DOM) in rivers is important for region and global carbon cycle, especially in the inland rivers of the Qinghai-Tibet Plateau. In order to understand the impact of permafrost degradation on river DOM output under the background of climate warming, we selected 34 typical sub-basins in the upper reaches of the Heihe River basin on the Qinghai-Tibet Plateau according to the different proportion of permafrost area in the basin. Water samples were collected at the outlet of each sub-basin in October 2018, January, April and July 2019, respectively. The variations of DOM structure and source identification in different permafrost basin were investigated using UV–visible absorbance and fluorescence spectroscopy. The results showed that: (1) The concentration of C1 and C2 components and the values ​​of SUVA₂₅₄, HIX and FI increased with the decrease of the percentage of permafrost area. , Indicating that with the degradation of frozen soil, the runoff path deepens, and more terrestrial organic matter is dissolved into the water body, which increases the terrestrial DOM in the river water, which in turn leads to the increase of DOM concentration, humification degree and aromaticity; (2) As the proportion of permafrost area decreases, the S_R value shows a decreasing trend, indicating that the DOM of rivers in permafrost regions has the characteristics of low molecular weight and low humic acid, while the DOM of rivers in seasonally frozen soil regions is the opposite, indicating a frozen soil Melting may lead to the increase of terrestrial DOM in river water, and the increase in the depth of freeze-thaw cycle may release aromatic substances containing fused ring structure in frozen soil, which will enter the river with runoff, resulting in increased aromaticity and molecular weight of DOM in river water; (3) The concentrations of C1 and C2 components are positively correlated with vegetation coverage, and vegetation coverage is negatively correlated with the percentage of permafrost area. It shows that the degradation of frozen soil will increase the coverage of vegetation, thereby increasing the DOM from terrestrial sources. This study shows that the optical characteristics, composition and source of DOM have important indications for the degradation of permafrost under the background of global warming.

How to cite: Pan, Y. and Sun, Z.: The effect of permafrost area and types on flux and composition of dissolved organic matter in stream from alpine catchments, northeastern Qinghai-Tibet Plateau, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4288, https://doi.org/10.5194/egusphere-egu21-4288, 2021.

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.

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.

We measured organic and inorganic nitrogen and the ¹⁵N stable isotopes composition of all three sample types to determine sources, sinks and processes of nitrogen transformation during transport.

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.

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.

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.

How to cite: Sanders, T., Fiencke, C., Fuchs, M., Haugk, C., Mollenhauer, G., Ogneva, O., Palmtag, J., Strauss, J., Tuerena, R., and Dähnke, K.: Seasonal variations in the transport and biogeochemical turnover of mainly dissolved organic nitrogen from the Lena Delta to the nearshore Laptev Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8191, https://doi.org/10.5194/egusphere-egu21-8191, 2021.

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 ∼2,61×10⁶ km²  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 δ¹³C and ∆¹⁴C values in water samples collected along a ∼1500 km long Lena River transect from Yakutsk downstream to the river outlet into the Laptev Sea.

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 ¹³C relative to fluvial POC, and that its ¹⁴C 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 ¹⁴C 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.

How to cite: Ogneva, O., Mollenhauer, G., Fuchs, M., Palmtag, J., Sanders, T., Grotheer, H., Mann, P., and Strauss, J.: Particulate and dissolved organic carbon composition in the Lena River and its Delta, from Yakutsk to the Arctic Ocean., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8005, https://doi.org/10.5194/egusphere-egu21-8005, 2021.

River biogeochemistry at any location integrates environmental processes over a definable upstream area of the river watershed. Therefore, biogeochemical parameters of river water are powerful indicators of the climate change impact on the entire watershed and smaller parts of it.

The current warming of the Siberian Arctic is changing atmospheric forcing, precipitation, subsurface water storage, and runoff from rivers to the Arctic Ocean. A number of studies predict an increase of organic carbon export by rivers into the Arctic Ocean with further warming of the Arctic. Major potential drivers for this increase are the rise of river discharge and permafrost thaw, which mobilizes organic matter.

Here, we present results of high frequency monitoring program of the Lena River waters in the central part of its delta at the Laptev Sea. For the first time, a number of biogeochemical parameters such as dissolved organic carbon (DOC), coloured dissolved organic matter, electrical conductivity, temperature, and d¹⁸O isotopes were measured at an interval of every few days throughout the entire season. Currently, the data set comprises two complete years from the spring 2018 until the spring 2020, which were characterized by extremely high and low summer discharges, respectively. While 2018 to 2019 was the fourth highest on record from 1936 to present, resulting in an annual DOC flux of 6.8 Tg C yr^-1, 2019 was the sixth lowest discharge year with a significantly lower DOC flux of 4.5 Tg C yr^-1. Endmember analysis using electrical conductivity and d¹⁸O isotopes showed that rainwater transported less DOC in 2019 (1.5 Tg C) than in 2018 (2.9 Tg C) although the winter base flow and the snow and ice meltwater transported similar amounts.

The biogeochemical response of the Lena River water provides us with new insights into the catchment processes, including permafrost thaw and potential mobilization of previously frozen organic carbon. Our new monitoring program will serve 1) as a baseline to measure future changes and 2) as a training dataset to project changes under future climate scenarios.

How to cite: Juhls, B., Morgenstern, A., and Overduin, P. P.: Lena River biogeochemistry resolved by a high frequency monitoring: comparing a wet and a dry year, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14501, https://doi.org/10.5194/egusphere-egu21-14501, 2021.

There is the significant progress in recent decades in the quantification of terrigenous carbon release to the rivers of the Arctic Ocean basin and characterization of its chemical properties, origin and age (e.g. Amon et al., 2012, Holmes et al., 2012). As warming accelerates the thawing permafrost may potentially increase the release the ancient carbon (Wild et al., 2019, Estop-Aragonés et al., 2020). However, more detailed analysis is still needed particularly in regard of the age of carbon exported from the diverse landscapes of large Arctic rivers and its transformation during the transport to the Arctic ocean.

In this study we analyzed D14C in dissolved organic carbon (DOC) and particulate organic carbon (POC) of the Yenisei River main channel and its major tributaries between 56oN and 68oN at freshet, summer and fall seasons. D14C was measured in Max Planck Institute for Biogeochemistry (Germany) by the accelerator mass spectrometry (AMS) system based on a 3MV Tandetron accelerator as described earlier (Steinhof et al., 2017).

 The oldest DOC in the Yenisei main stem was detected right after the Krasnoyarsk dam (56oN) and varied during a year without clear seasonal pattern in the range of the fraction of modern C (fMC) from 0.868 to 1.028. At freshet the fMC increased down stream up to 1.12 at 60oN and then remained relatively stable between 61o and 67.4oN (1.097±0.014). The major tributaries released DOC with fMC ranging from 1.0869 (Angara, 58oN) to 1.1046 (Kurejka (66.5oN), demonstrating more modern C with latitude. During the summer-fall season the Yenisei main channel and main Eastern tributaries contained older DOC (fMC = 0.968-1.054 and 0.949-1.045, respectively).

The POC of the Yenisei River was sufficiently older (fMC = 0.83-0.92) than DOC at all seasons and showed similar latitudinal pattern, i.e. the youngest POC was detected near 60-61oN (fMC > 0.90). The D14C-POC values in analyzed tributaries were increasing with latitude at freshet (R2 = 0.53) and summer lowflow (R2 = 0.33), except the largest Eastern tributaries, demonstrating the slight opposite pattern. On the other hand, increasingly more ancient POC was releasing by permafrost-dominated Eastern tributaries with increasing basin size. In opposite, D14C-POC of Western tributaries showed increased input of more recently fixed carbon. Our findings provided new data on the formation of terrigenic carbon fluxes to the Arctic Ocean from one of the largest river basins in the Arctic. This study was supported by RFBR grants #18-05-60203-Arktika. The radiocarbon analyses were kindly supported by Max-Plank Institute for biogeochemistry (ZOTTO project).

How to cite: Polosukhina, D., Prokushkin, A., and Steinhof, A.: Radiocarbon patterns of dissolved and particulate organic carbon in the Yenisei River and its major tributaries, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9734, https://doi.org/10.5194/egusphere-egu21-9734, 2021.

Climate change is expected to affect the release of organic carbon (OC) from Arctic permafrost systems and other terrestrial deposits. In addition to greenhouse gas emissions on land, a fraction of the organic matter is liberated to the aquatic cycle and migrates to the Arctic Ocean where it is either degraded or buried in sediments, foremost on the vast continental shelves.

The Arctic Ocean basin represents a large footprint for contemporary and past land-ocean transport of terrestrial OC. To this end, the Circum-Arctic Sediment CArbon DatabasE (CASCADE; https://doi.org/10.5194/essd-2020-401) was established to curate and harmonize data on OC and total nitrogen concentrations, carbon isotopes (δ¹³C, Δ¹⁴C) and terrestrial biomarkers (long-chain n-alkanes, n-alkanoic acids and lignin phenols) in an openly accessible data collection. CASCADE was populated using carbon data from both published records and unpublished data from a large community collaboration. The first release of CASCADE includes observations at thousands of oceanographic stations distributed over the shelves and the central basins of the Arctic Ocean, and also includes hundreds of sediment cores, representing a range of time scales (decadal to orbital).

Mapping CASCADE data provides an overview to start deducing sources, pathways and deposition of carbon in different regions of the Arctic Ocean. Dual-isotope (δ¹³C, Δ¹⁴C) source apportionment of OC and ²¹⁰Pb dating of centennial-scale sediment cores permit quantitative analysis of sequestration of carbon transported from permafrost systems and other deposits to the Arctic Ocean. Preliminary results suggest that surface soils (incl. permafrost active layer) are the dominating terrestrial carbon source to Circum-Arctic shelf sediments. The second largest terrestrial source are Pleistocene ice-rich permafrost compartments (Ice Complex Deposits), which stretch along coastlines of the Laptev, East Siberian, Chukchi and Beaufort Seas and are highly vulnerable to coastal erosion and thermal collapse in a warming climate.

Climate change is likely to cause permafrost thawing by further deepening of the seasonal active layer and accelerated coastal erosion of permafrost, as well as disturbance of the vast boreal peatlands. CASCADE provides an integrated perspective and benchmark for lateral carbon remobilization and will fuel further empirical and modelling studies of Arctic biogeochemical cycles.

How to cite: Martens, J., Wild, B., Semiletov, I., Dudarev, O. V., and Gustafsson, Ö.: Patterns of terrestrial carbon distribution in the Arctic Ocean deduced from the Circum-Arctic Sediment CArbon DatabasE (CASCADE), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5401, https://doi.org/10.5194/egusphere-egu21-5401, 2021.

It is consensus that the deglacial changes in ocean carbon storage and circulation play a role in regulating atmospheric CO₂. However, emerging evidence suggests that the rapid deglacial CO₂ rises can in part be attributed to large quantities of pre-aged carbon being released from degrading permafrost. In this study, we apply a radiocarbon approach on both terrestrial compounds (high molecular weight fatty acids; HWM-FA) and bulk organic carbon from a well-studied core ARA04C/37 from the Canadian Beaufort Sea. Based on our records, substantial amounts of ancient carbon were supplied from land to the ocean during the mid-late deglaciation (14.5-10 cal. kyr BP) by frequent high sediment flux events. Because the core location is strongly influenced by the Mackenzie River discharge, sediments only contain minor contributions from marine organic matter, allowing to consider mainly two terrestrial sources to explain the characteristics of bulk sedimentary organic matter. The terrestrial HMW-FA are taken to represent the biospheric carbon, and their age differences from the bulk organic carbon are explained by petrogenic carbon input. During the Younger Dryas, ice-sheet melting and meltwater outbursts enhanced petrogenic carbon contributions, suggesting a major source in the hinterland drainage system. During the rapid sea-level rise (meltwater pulses 1a and 1b), the very old organic carbon and comparable ages between biospheric carbon and bulk organic carbon indicate the occurrence of permafrost carbon remobilization primarily via coastal erosion while petrogenic carbon from the drainage system was found negligible. Remobilized ancient permafrost carbon is commonly regarded to be highly bioavailable, while petrogenic carbon is likely more recalcitrant to biological degradation. Our records thus suggest that the release of ancient carbon to the Beaufort Sea had the strongest impact on the atmospheric CO₂ level and contributed to its rapid increases during the B/A and Pre-Boreal when permafrost deposits along the coast were eroded.

How to cite: Wu, J., Mollenhauer, G., Stein, R., Hefter, J., Fahl, K., Grotheer, H., Wei, B., and Nam, S.-I.: Mobilization of aged carbon via meltwater floods and coastal erosion in the Canadian Arctic during the last deglaciation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-448, https://doi.org/10.5194/egusphere-egu21-448, 2021.

The thawing of permafrost in the polar regions has important implications for climate on Earth. Indeed, permafrost degradation results in a positive climate feedback which is currently aggravated by human action. The dynamic character of Earth’s climate means that past trends and variability can be examined to improve future projections of this effect. Notably, the permafrost zone that covered parts of Europe during the Last Glacial Maximum (LGM) is currently absent, indicating that this region is a crucial area for the study of permafrost carbon remobilization during the last deglacial warming. Here, we investigate the mobilization of permafrost material to the Bay of Biscay, off the English Channel. Although this location has been shown to have experienced an enhanced deposition of terrigenous material during the last deglaciation, the contribution of permafrost thaw is unknown. We have established an accurate and robust chronological framework for this deposition, showing enhanced rates of sediment accumulation from approximately 20.2 to 15.8 kcal BP. Biomarker analysis has revealed periods of marked increases in terrigenous input, namely from approximately 20.5 to 19 and from 19 to 16.5 kcal BP. Moreover, by performing compound specific radiocarbon dating on n-alkanoic acids isolated from the sedimentary archive, we have been able to determine the origin of organic matter deposited at the core location. Our results will help researchers to assess to what extent permafrost thaw contributed to the peak of organic matter deposition present in the marine sediment, allowing us to sharpen our understanding of the mechanisms of permafrost carbon mobilization.

How to cite: Queiroz Alves, E., Wang, Y., Hefter, J., Grotheer, H., A. F. Zonneveld, K., and Mollenhauer, G.: Uncovering the contribution of permafrost thaw to the enhanced terrestrial organic matter input into the Bay of Biscay during the last deglaciation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3398, https://doi.org/10.5194/egusphere-egu21-3398, 2021.