Displays

The rivers of the Arctic permafrost region discharge about 11% of the global volumetric river water flux into oceans, doing so into an ocean (the Arctic) with 1% of global ocean water volume and a very high surface area: volume ratio, making it comparatively sensitive to influxes of terrestrially derived matter. This river flux is sourced from precipitation as either rain or snow, which, upon initial contact with the landscape has the immediate potential to interact with carbon(C) in one of two ways: Water running over carbonate or silicate –bearing rocks will cause a reaction whose reactant requires the uptake of atmospheric CO₂, which is subsequently transported in river water. This ‘inorganic’ C derived from interaction of water, atmosphere and lithosphere thus represents a C storage or ‘sink’ vector.   In addition, water interacting with organic matter in tree canopies, litter or soil can dissolve C contained therein, and transfer it via surface and subsurface water flows into rivers, whereupon it may either be metabolised to the atmosphere or exported to the sea. Recent improvements in understanding of terrestrial C dynamics indicate that this hydrologic transfer of organic matter represents the dominant fate of organic carbon, after plant and soil respiration are accounted for. In the context of amplified Arctic anthropogenic warming, the thermal exposure imposed on the permafrost C stock with expectations of enhanced future precipitation point toward substantial shifts in the lateral flux-mediated organic and inorganic C cycle. However, the complex totality of the processes involved make prediction of this shift difficult.

Here, we build upon previous advances in earth system modelling to include the production and lateral transport of dissolved organic C (DOC), respiration-derived CO₂, and rock-weathering derived alkalinity in a global land surface model (ORCHIDEE) previously developed to specifically resolve permafrost-region processes.   By subjecting the resulting model to state of the art soil, water, vegetation and climatology datasets, we are able to reproduce existing lateral transport processes and fluxes, and project them into the future.   In what follows, we show that while Pan-Arctic alkalinity exports and attendant CO₂ uptake increase over the 20^th and 21^st Centuries under warming, DOC fluxes decline largely as a result of deeper soil water flow-paths and the resulting changes in carbon-water interactions. Rather than displaying a clear continuous (linear or non-linear) temperature sensitivity, future Arctic DOC release can increase or decrease with temperature depending on changes in the thermal state and hydrologic flow paths in the deep soil. The net marine effect of these fluxes is to decrease future terrestrially derived seawater acidification.   Conversely, our simulations show that CO₂ uptake from chemical weathering exceeds its evasion from river water, meaning that when weathering is considered, the inland water carbon cycle shifts from being a net C-source to a sink. Further, this sink increases into the 21^st C, partially buffering soil C loss from permafrost thaw.

How to cite: Bowring, S., Lauerwald, R., Guenet, B., Jornet-Puig, A., and Ciais, P.: How Permafrost-Affected Arctic Rivers May Become Net Carbon Sinks Over the 21st Century , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2214, https://doi.org/10.5194/egusphere-egu2020-2214, 2020.

Soil temperatures in permafrost (i.e. perennially frozen ground) are rising globally. The increasing temperatures accelerate permafrost thaw and release of organic carbon, that has been locked in permafrost soils since the last glacial period, to the contemporary carbon cycle. The potential remineralisation of organic carbon to greenhouse gases can contribute to further climate warming. Particulate organic carbon (POC) in the Kolyma River is older than dissolved organic carbon (DOC) thus serves as a good tracer for abrupt permafrost thaw (i.e. river bank erosion and thermokarst) that dominantly releases old POC. While dissolved organic carbon (DOC) mobilised from the old Yedoma outcrops on the banks of the Kolyma River is shown to be highly labile, vulnerability of POC to biodegradation is not yet known. In this study we aim to constrain degradation rates for POC in the Kolyma River. To capture seasonal variability of the POC pool and its degradation rate the incubation was conducted both during the spring freshet and in late summer (2019 and 2018, respectively). We incubated whole-water samples over 9 to 15 days and quantified POC (and DOC) loss over time, as well as dissolved inorganic carbon (DIC). The incubation was carried out in the dark. We also tracked changes in POC composition and age with carbon isotopes (d¹³C-OC, d¹³C-DIC, ∆¹⁴C). Preliminary results from 2018 suggest a decrease in POC concentrations of up to 30 % while those of DOC decrease by up to 11 %. The rate of POC degradation is nearly three times faster than DOC though the absolute amounts of DOC are in turn higher than those of POC (< 1 mg L^-1 for POC and ~3 mg L^-1 for DOC). Furthermore, the changes in d¹³C of POC, DOC and DIC suggest ongoing microbial degradation and conversion of organic carbon into inorganic carbon. These first estimates show that POC degrades fairly rapidly while transported in the Kolyma River. A better understanding of POC degradation along lateral flow paths is critical for improving our knowledge of permafrost thaw and its possible climate impacts in the future.

How to cite: Keskitalo, K., Bröder, L., Jong, D., Zimov, N., Davydova, A., Davydov, S., Tesi, T., Mann, P., Haghipour, N., Eglinton, T., and Vonk, J.: Degradation of permafrost carbon in the Kolyma River , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8311, https://doi.org/10.5194/egusphere-egu2020-8311, 2020.

Arctic rivers will be increasingly affected by the hydrological and biogeochemical effects of thawing permafrost. During transport, permafrost thaw-derived organic carbon (OC) can be degraded into greenhouse gases and potentially add to further climate warming, or transported to the shelf seas and buried in marine sediments, attenuating this ‘permafrost carbon feedback’. To assess the transport pathways and fate of permafrost-OC, we focus on the river-shelf continuum of the Kolyma River, the largest river on Earth completely underlain by continuous permafrost. Three pools of riverine OC were investigated: dissolved OC (DOC), suspended particulate OC (POC), and river sediment OC (SOC). Preliminary results of bulk carbon isotopes (δ¹³C, Δ¹⁴C) and molecular biomarkers (lignin phenols, leaf wax lipids) show contrasts in composition and degradation state for these carbon pools. Old permafrost-OC seems to be mostly associated with SOC, and less dominant in POC. However, while SOC shows the oldest Δ¹⁴C signal, lignin phenol results (e.g., acid to aldehyde ratios) suggest this material is the least degraded. In contrast, DOC shows more degraded signal, even at the outflow of an active permafrost thaw site. Our study serves as a terrestrial extension to earlier investigated marine sediments from the Kolyma paleoriver transect in the East Siberian Sea. It also highlights the value of connecting terrestrial and marine observations to gain insight into the complete pathway of permafrost-OC, from the moment of thaw, via aquatic transport and degradation, towards storage in marine sediments.

How to cite: Jong, D., Bröder, L., Keskitalo, K., Kloostra, O., Tesi, T., Zimov, N., Davydova, A., Haghipour, N., Eglinton, T., and Vonk, J.: Permafrost organic carbon transport and degradation on a transect from the Kolyma River to the East Siberian Shelf, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7206, https://doi.org/10.5194/egusphere-egu2020-7206, 2020.

Increasing air and sea surface temperatures at high latitudes lead to accelerated thaw, destabilization, and erosion of perennially frozen soils (i.e., permafrost), which are often rich in organic carbon. Coastal erosion leads to an increased mobilization of organic carbon into the Arctic Ocean that can be converted into greenhouse gases and may therefore contribute to further warming. Carbon decomposition can be limited if organic matter is efficiently deposited on the seafloor, buried in marine sediments and thus removed from the short-term carbon cycle. Basins, canyons and troughs near the coastline can serve as sediment traps and potentially accommodate large quantities of organic carbon along the Arctic coast. Here we use biomarkers (source-specific molecules), stable carbon isotopes (δ¹³C) and radiocarbon (Δ¹⁴C) to identify the sources of organic carbon in the nearshore zone of the southern Canadian Beaufort Sea. We use an end-member model based on the carbon isotopic composition of bulk organic matter to identify sources of organic carbon. Monte Carlo simulations are applied to quantify the contribution of coastal permafrost erosion to the sedimentary carbon budget. The models suggest that 40% of all carbon released by coastal erosion is efficiently trapped and sequestered in the nearshore zone. We conclude that permafrost coastal erosion releases huge amounts of sediment and organic matter into the nearshore zone. Rapid burial removes large quantities of carbon from the carbon cycle in depositional settings.

How to cite: Fritz, M., Grotheer, H., Meyer, V., Riedel, T., Pfalz, G., Mathieu, L., Hefter, J., Gentz, T., Lantuit, H., and Mollenhauer, G.: Burial and origin of permafrost organic carbon in the Arctic nearshore zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4244, https://doi.org/10.5194/egusphere-egu2020-4244, 2020.

Increase of methane concentration in atmosphere due to emission from Arctic shelf subsea deposits can play considerable role in climate change [1-2]. Methane seeps in East-Siberian and Laptev Seas were investigated in frames of complex research cruise АМК-78 onboard R/V «Akademik Mstislav Keldysh», (September 17 - October 22, 2019).

In the seep areas gas was collected to study its molecular and stable isotopes composition and reveal the genesis of discharging methane. Sediments were collected using box-corer for detailed lithological investigations and characterization of mineral inclusions. At the sampling station within methane seep in the Northern Laptev Sea, dark grey to black clays with hydrotroilite were collected.  They contained rounded inclusions of light grey carbonates with size up to 3x4cm.

Methane that migrates to the seafloor surface is characterized by wide range of stable isotopes composition values with predominance of ¹³C depleted biogenic component [3-4].

Stable carbon and oxygen isotopes composition of carbonate inclusions was measured. The carbonates are strongly depleted in ¹³C up to -32,4 ‰VPDB. δ¹⁸О varies in wide range between -3 and +4,4 ‰VPDB. Depletion of the carbonates in ¹³C indicates its formation as a result of bacterial oxidation of methane in anaerobic conditions. Anaerobic oxidation of methane is an important biogeochemical process in the areas of methane emissions. The size and isotopes data of the authigenic methane-derived carbonates provide information on the intensity and time of methane discharge, geochemical characteristics of the fluids, including water. Enrichment of the carbonate inclusions in ¹⁸O can be explained by the migration of isotopically heavy water from dissociating gas hydrates [5].

Obtained results of the complex study of discharging fluids and authigenic minerals allow to characterize the biochemogenic processes in seep sediments, local variations in the environmental conditions and methane flux and isotopic effects during bacterial oxidation of methane.

Literature:

1. Shakhova N., Semiletov I., Chuvilin E. Understanding the permafrost-hydrate system and associated methane releases in the East Siberian Arctic Shelf // Geosciences, 2019, 9, 251.
2. Shakhova N.E., Sergienko V.I., Semiletov I.P. Contribution of East-Siberian shelf to the modern methane cycle // RAS bulletin, 2009, vol. 79, №6, pp. 507-518.
3. Whiticar, M.J. Correlation of natural gases with their sources. In: Magoon, L., Dow, W. Eds., The Petroleum System — From Source to Trap. AAPG Memoir 60, 1994, pp. 261–284.
4. Sapart, C. J., Shakhova, N., Semiletov, I., Jansen, J., Szidat, S., Kosmach, D., Dudarev, O., van der Veen, C., Egger, M., Sergienko, V.,; Salyuk, A., Tumskoy, V., Tison, J.L., Rockmann, T. The origin of methane in the East Siberian Arctic Shelf unraveled with triple isotope analysis // Biogeosciences, 14, 9, 2283-2292, 2017.
5. Bohrman G., Suess E., Greinert J., Teichert B., Naehr T. Has hydrate carbonates from Hydrate ridge, Cascadia convergent margin: indicators of near-seafloor clathrate deposits // Fourth Int. Conf. Gas Hydrates: Yokohama, Japan, 19023:102-107. 2002.

How to cite: Yurchenko, A., Krasnova, E., Semiletov, I., Shakhova, N., and Spasennykh, M.: Bacterial oxidation of methane within seeps in the northern Laptev Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22421, https://doi.org/10.5194/egusphere-egu2020-22421, 2020.

Mercury (Hg) is a pollutant of great concern for indigenous populations in the Arctic, which are exposed to high dietary Hg from fish and marine mammal consumption. Hg in marine biota can be derived from direct atmospheric deposition to the Arctic Ocean or from terrestrial sources by river runoff. Permafrost soils thereby play a pivotal role in the Arctic Hg cycle by storing atmospheric Hg deposition and providing a reservoir for later mobilization to the Arctic Ocean. The stability of Hg in permafrost soils depends on the pathway of atmospheric Hg deposition and Hg release processes, i.e. reduction and re-emission to the atmosphere and transfer to river runoff. We combined Hg stable isotope with Hg flux measurements in a field study on the Arctic Coastal Plain in northern Alaska. We could show that gaseous elemental Hg uptake by vegetation represents 70% of total atmospheric Hg deposition. Atmospheric Hg uptake by vegetation results in a characteristic Hg isotope fingerprint. This fingerprint dominates Hg signatures in permafrost soils measured across the Arctic coastal plain and is also imprinted in marine mammals and Ocean sediments, suggesting that Hg from Arctic permafrost soils represent a major source to the Arctic Ocean. Knowing the pool and spatial distribution of Hg in permafrost soils is therefore essential to assess current Hg mobilization to aquatic ecosystems and potential future changes due to permafrost thaw and climate change. Two recent studies have used Hg to carbon (C) ratios, R_HgC, measured in Alaskan permafrost mineral and peat soils, together with a northern soil carbon inventory, to estimate that these soils contain large amounts, 184 to 755 Gg of Hg in the upper 1 m. In a second part, we present new Hg and C data for six peat cores, down to mineral horizons, across a latitudinal permafrost gradient in the Western Siberian lowlands. Hg concentrations increase from south to north in all soil horizons, reflecting enhanced net accumulation of atmospheric gaseous elemental Hg by the vegetation Hg pump. We reviewed and estimate pan-arctic organic and mineral soil R_HgC to be 0.19 and 0.77 Gg Pg^-1, and use a soil C budget to revise the northern soil Hg pool to be 67 Gg (37-88 Gg, interquartile range (IQR)) in the upper 30 cm and 225 Gg (102-320 Gg, IQR) in the upper 1 m. Finally, we discuss how climate change may affect the mobilization of Hg from permafrost soils to the atmosphere and the Arctic Ocean.

How to cite: Jiskra, M., Sonke, J. E., Lim, A. G., Loiko, S. V., Kosykh, N., Pokrovsky, O., Agnan, Y., Helmig, D., and Obrist, D.: The role of permafrost soils in Arctic mercury cycling: source tracing with Hg stable isotopes and revised soil pool estimate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5734, https://doi.org/10.5194/egusphere-egu2020-5734, 2020.

Soils and sediments in the Lena Delta in Northeast Siberia store large amounts of organic matter including organic bound nitrogen. This nitrogen is not directly available for plants and primary production, but can be remineralised in the soils or in sediments after erosion to the Lena River. Our study aims to estimate the load of reactive nitrogen from terrestrial sources into the Arctic Ocean. Therefore, water and sediment samples were collected along a transect (~200 km) from the centre of the Delta to the open Laptev Sea in summer 2019. On the collected samples, we will measure dissolved organic and inorganic nitrogen, particulate nitrogen and CN ratio. In addition, the ¹⁵N stable isotope values of these components will be determined to identify nitrogen sources, sinks and processes of nitrogen transformation. Additionally, we carried out incubation experiments in the field to determine the potential remineralisation rates of various soil types in Lena water and nutrients fluxes of the sediments. The load of dissolved inorganic nitrogen in the Lena water in the delta was very low and low nitrate and silicate concentration indicate uptake by phytoplankton. Outside the Lena Delta, a lens of nutrient depleted freshwater covered the salty Arctic Ocean water, which had higher loads of reactive nitrogen. The organic matter content of the soils and sediment is highly variable and ranges from 1 to 45 %. This organic matter is the source of reactive nitrogen, which is determined in incubation experiments and using nitrogen stable isotopes. We found that especially the unvegetated soils and sediment are sources of reactive nitrogen in the end of vegetation period, and are potentially sources of nitrous oxide emissions.

How to cite: Sanders, T., Fuchs, M., and Dähnke, K.: Fate and transport of nitrogen in soils, sediment and water of the Lena Delta, Northeast Siberia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21011, https://doi.org/10.5194/egusphere-egu2020-21011, 2020.

Influence of thawing permafrost on the chemical properties of the sea water was studied in 2 experiments organized in Svalbard in 2017 and 2018. Permafrost samples were collected at an abrasive cliff 10 km west of Longyearbyen. Experiments were focused on identifying the possible changes in concentrations of nutrients, carbonate system parameters and pollutant composition related to permafrost thawing. During the experiment, the samples of permafrost were added to the seawater. The solution was exposed to natural conditions for 24 hours in 2017 and 5 days in 2018 while water samples from the solution were taken at specified time intervals. The results of the experiment show that the sea water composition changes are connected to the permafrost thawing. Data from this experiment allowed us to estimate the total annual supply of nutrients to the Arctic from permafrost thawing by multiplying the change in concentration from this study by the annual eroded permafrost total volume in Siberia.

How to cite: Pogojeva, M., Yakushev, E., Petrov, I., Yaeski, E., and Polukhin, A.: Study of sea water chemistry changes due to thawing permafrost, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-736, https://doi.org/10.5194/egusphere-egu2020-736, 2020.

The carbon export by rivers to the Arctic Ocean is expected to increase in response to the rapidly changing climate in the Arctic (Camill, 2005; Freeman et al., 2001; Frey and Smith, 2005). This is in part due to thawing permafrost and mobilization of particulate and dissolved organic matter (DOM). The Lena River delivers approximately one fifth of the total river discharge to the Arctic Ocean and is the main source of DOM in the Laptev Sea shelf (Thibodeau et al., 2014). To date river fluxes of DOM have been based on sparse coverage of sample across the hydrograph about 700 km upstream (Cooper et al 2005; Raymond et al 2007; Stedmon et al 2011; Amon et al 2012). The effects of low frequency sampling on load estimates are unknown and potentially large for systems such as these where there are considerable changes across the hydrograph.   Here we present results from a unique high frequency sampling program and evaluate its viability to monitor export fluxes of DOM and its biogeochemistry in the Lena River. The sampling takes place close to the river mouth at the research station Samoylov in the central Lena River Delta. The Samoylov research station allows a unique chance for continuous sampling since it operates throughout the year. The sampling program includes measurements of several water parameters, such as temperature, electric conductivity, dissolved organic carbon (DOC), spectral CDOM absorption (aCDOM), fluorescent dissolved organic matter (FDOM) and water stable isotopes.
The data facilitated the identification of the main drivers behind the seasonality of DOM concentration and biogeochemistry of the Lena River. Three main water sources could be identified (1) (snow) melt water, (2) rain water and (3) subsurface water. Melt and rain water are found to be the prevailing water sources that combined transport 5.8 Tg C dissolved organic matter (~ 85 % of annual flux (6.8 Tg C)) into the Lena River. The high number of samples throughout the whole year allowed flux calculations that are independently from load models that likely lead to a large variation of earlier studies.
The absorption properties of DOM revealed changing composition and sources of DOM throughout the year. Decreasing SUVA values during the summer point towards an increasing fraction of old DOM which potentially originates from degrading permafrost. In contrast, during the spring freshet, high SUVA indicate mostly fresh organic matter with high molecular weight and high aromaticity.
This dataset represents the first year of a planned long-term monitoring program at the Research Station Samoylov Island and provides a baseline data set against which future change of this large integrative system may be measured. A continuous sampling of Arctic River water will facilitate to identify intra and inter-annual trends with ongoing climate change.

How to cite: Juhls, B., Overduin, P. P., Stedmon, C. A., Morgenstern, A., Meyer, H., Heim, B., Hölemann, J., and Povazhnyi, V.: Seasonality in Lena River biogeochemistry and dissolved organic matter , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5253, https://doi.org/10.5194/egusphere-egu2020-5253, 2020.

Cold-regions hold a pool of organic carbon that has accumulated over many thousands to millions of years and which is currently kept immobile by permafrost. However, in a warming climate, a deepening of the active layer results in the release of greenhouse gasses CO₂ and CH₄ into the atmosphere from this carbon pool. Additionally, due to the degradation of deeper permafost, soil hydraulic properties and associated groundwater flow paths are shifting rapidly as a result of which also organic carbon in deeper permafrost is being dissolved into groundwater, which can then reach the surface environment via groundwater flow.  This provides an additional mechanism by which permafrost carbon can be mobilized in  a warming climate, and one which is likely increasingly important for progressive surface warming.

Although the process of carbon leaching from thawing organic rich permafrost layers into the groundwater is an increasingly important part of the carbon cycle of cold-regions, it is notoriously difficult to measure in situ or incorporate into numerical model assessments due to the highly heterogeneous properties of the permafrost, and lack of process knowledge. In particular, the crucial understanding of the influence of different soil physical properties such as soil grain size and organic matter content on permafrost thawing processes is missing, as well the precise release mechanisms  of organic matter into pore waters in thawing soils.

This study employs lab soil column experiments to investigate the interplay between soil physical properties and thawing dynamics of permafrost. One meter high soil columns are frozen to create controlled permafrost conditions. A range of sand grain sizes (0.1 to 0.8mm) and organic matter contents (1 to 10 wt%) representative for sedimentary permafrost are used. The column is thermally insulated on the sides and top, exposing only one face to ambient temperature in the climate chamber. In this way one-dimensional heat flow conditions are created. So far, the columns are equipped with arrays of temperature sensors. Experiments consist of a cycle of freezing and thawing. Our initial data and analysis illustrate how a fast evolving thawing front develops through the frozen soil column  including the effects of latent heat at the thawing front. Numerical modeling allows to infer the soil thermal properties relevant to model the permafrost thawing process.

How to cite: de Bruin, J., Bense, V., and van der Ploeg, M.: Freeze-thaw dynamics in synthetic permafrost soil columns with variable organic carbon content, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7532, https://doi.org/10.5194/egusphere-egu2020-7532, 2020.

With Arctic warming, both gradual and abrupt thaw of permafrost may trigger a positive feedback loop, since large amounts of organic matter (OM) are released into rivers and thus exposed to mineralization along the fluvial continuum. Both dissolved (DOM) and particulate organic matter (POM) mineralization during lateral transport generates greenhouse gases that may fuel further global warming. In addition to glacier retreat, the extent of permafrost thaw is predicted to increase across the Arctic, which will change the release of DOM and POM to aquatic environments. However, the fate of DOM and POM will likely differ during transport in surface waters due to POM-DOM exchange and biodegradation control from organo-mineral interactions. The contrasting behavior between POM and DOM may affect the strength of the permafrost-carbon feedback to climate but is currently afflicted with high uncertainties.

This study characterizes the export of DOM and POM along the fluvial continuum at time of maximum thaw depth and investigates the impacts of permafrost thaw on OM composition and age in the Zackenberg watershed (Northeastern Greenland). In August 2019, streams were sampled twice, before and after a rain event. We collected water and suspended sediments from rivers, the river delta, snow patches and permafrost ice from thermokarst features. Besides in situ river chemistry, we analyzed stable water isotopes (δ¹⁸O, δ²H) and dissolved organic carbon (DOC) concentrations. The composition of DOM was characterized using absorbance and fluorescence spectroscopy and both DOM and POM were analyzed for radiocarbon (Δ¹⁴C).

DOC concentrations increase from 3.1 mg L^-1 upstream to 15.6 mg L^-1 after the confluence with the main tributaries, which are characterized by a nival river regime, and decreased to 4.3 mg L^-1 at the outlet. Optical properties of DOM highlight that low molecular weight microbial-derived organic compounds contribute most to the fluorescent DOM (fDOM) in the upstream part of the river, likely originating from glacial waters. The contribution of soil and plant derived fDOM increases downstream, and corresponding Δ¹⁴C_DOC values increase from upstream (-240‰, i.e. ~2200 yr) to downstream (-30‰, i.e. ~200 yr) resulting from the increasing tributary inputs. Interestingly, POM displays more depleted Δ¹⁴C (older ages) than DOC.

We observed contrasting patterns in river chemistry before and after the rain event with temperature decreasing and pH and EC increasing. δ¹⁸O and δ²H compositions were less depleted after the rain event, DOC concentrations were lower and DOM displayed a greater contribution of soil and plant derived fDOM. This evidence illustrates the increasing contribution of rain fed streams draining organic-rich top soil and the dilution of the glacial inputs after the rain event. We conclude that, in this glacio-nival Arctic watershed, affected by both permafrost degradation and glacier retreat, old DOM and POM is released and evolves differently in the fluvial continuum.

How to cite: Fouche, J., Hirst, C., Opfergelt, S., Vonk, J., Bonneville, S., Haghipour, N., Eglinton, T., and Bröder, L.: Characterization of dissolved and particulate organic matter exported during late summer from a glacio-nival river, Zackenberg, Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9776, https://doi.org/10.5194/egusphere-egu2020-9776, 2020.

The East Siberian Arctic shelf (ESAS), the world’s largest continental shelf, receives substantial input of terrestrial organic carbon (TerrOC) both from increasing river discharge and from amplifying coastal erosion. Increasing TerrOC supply directly affects the Arctic marine carbon cycle, and, therefore, the fate of TerrOC upon its translocation to the Arctic continental margin has been the subject of growing interest in recent decades. Previous studies reported a strong decrease in sedimentary bulk TerrOC and terrestrial biomarkers with increasing distance from the coast during cross-shelf transport with much higher extent of degradation in the ESAS nearshore zone. Despite major progress has been made in estimating TerrOC inputs and quantifying its degradation rates in the Arctic land-shelf system, there are still important pieces insufficiently understood. Rock-Eval (RE) pyrolysis contributes to the traditional geochemical interpretations, based on elemental, isotopic and biomarker analyses and provides additional insight into the distribution, source and degradation state of organic carbon compounds of sedimentary organic matter.

In this study, the analytical approach included the characterization of marine and terrestrial carbon compounds using RE data coupled with organic carbon stable isotope composition. Rock-Eval analyses was performed on over 80 surface sediments samples from the Laptev Sea and western part of the East Siberian Sea collected during Arctic expeditions in 2011-2019. A track of rapidly degrading terrOC in shallow deposits may be traced using the ratios between hydrogen and oxygen indices and from the distribution of labile organic carbon fraction. Our results indicated high content of heavily degraded material with low hydrogen index, high oxygen index and a high content of residual carbon in sediments on the outer shelf of the western Laptev Sea and on the continental slope. Sharp decreasing of oxygen content in the eastern part of Laptev Sea and the western East Siberian Sea marked intensive dilution of degraded carbon with fresher material exported from New Siberian Islands. Furthermore, the RE data indicated a relatively high content of residual carbon (up to 87 %) stored in the studied surface sediments.

This research is supported by Russian Science Foundation, project # 19-77-00067.

How to cite: Gershelis, E., Kashapov, R., Ruban, A., Grin'ko, A., Dudarev, O., Shakhova, N., and Semiletov, I.: Tracing terrestrial organic matter in surface sediments in Laptev Sea and East Siberian Sea: a Rock-Eval pyrolysis approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13091, https://doi.org/10.5194/egusphere-egu2020-13091, 2020.

Accelerating coastal erosion and enhancing river sediment discharge are expected to greatly increase the delivery of terrestrial organic carbon (terrOC) to the Arctic Ocean. Remobilized terrOC may be buried in shallow or outer shelf sediments, degraded and translocated to the deeper basins, or remineralized in the water column causing a positive feedback to amplified global warming. The East Siberian Arctic Shelf (ESAS), represented by the Laptev Sea, the East Siberian Sea, and the Russian part of the Chukchi Sea, is the widest and shallowest continental shelf of the World Ocean. In the current study, we investigated surface sediment samples collected across the Laptev Sea shelf (from the coastline to the outer shelf) during the Arctic expedition onboard the Russian R/V Academician M. Keldysh during fall 2018.

We analyzed 16 samples for bulk (TOC, δ13C) and molecular (distribution and concentration of n-alkanes and PAHs) parameters. We also performed Rock-Eval (RE) analysis in order to compare its results with the signatures provided by traditional geochemical tracers and thereby to gain new insights into the sources of organic matter in modern surface sediments. In addition, a grain-size analysis was carried out to reveal hydrodynamic control on the organic carbon transport across the studied transect. Using a combination of traditional molecular interpretations (performed in this study and published earlier) and RE parameters (Hydrogen index, Oxygen index and T_peak) we attempted to distinguish riverine input and coastal erosion and disentangle processes of terrOC degradation and its replacement with fresh/marine OC during cross-shelf transport. Overall, a strong decrease of terrigenous contribution to the sedimentary organic carbon was observed on molecular level with increasing distance from the coast. According to the RE data, intensive terrOC degradation takes place in the shallow and mid-shelf sediments which is traced by sharply increasing oxygen index. The clear correlation between OI and the clay content points toward the perception that mineral matrix do not seem to be such good protector as expected, and intensive microbial degradation of the sedimentary organic matter contained in fine particles occurs during repeated resuspension.

This research is supported by Russian Science Foundation, project # 19-77-00067.

How to cite: Oberemok, I., Gershelis, E., Grin’ko, A., Ruban, A., Klevantseva, E., Zhivotova, N., Dudarev, O., Shakhova, N., and Semiletov, I.: Characteristics of organic carbon in surface sediments of Laptev Sea shelf, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13305, https://doi.org/10.5194/egusphere-egu2020-13305, 2020.

Widespread accelerated permafrost thawing is predicted for this century and beyond. This threatens to remobilize the large amounts of Mercury (Hg) currently ‘locked’ in Arctic permafrost soils to the Arctic Ocean and thus potentially lead to severe consequences for human and wildlife health. Future risks of Arctic Hg in a warmer climate are, however, poorly understood. One crucial knowledge gap to fill is the fate of Hg once it enters the marine environment on the continental shelves. Arctic rivers are already today suggested to be the main source of Hg into the Arctic Ocean, with dissolved and particulate organic matter (DOM and POM, respectively) identified as important vectors for the land to sea transport.

In this study, we have investigated total Hg (HgT) and monomethylmercury (MeHg) concentrations in surface sediments from the East Siberian Arctic Shelf (ESAS) along a transect from the Lena river delta to the Laptev Sea continental slope. The ESAS is the world’s largest continental shelf and receives large amounts of organic carbon by the great Arctic Russian rivers (e.g., Lena, Indigirka and Kolyma), remobilized from continuous and discontinuous permafrost regions in the river catchments, and from coastal erosion. Data on HgT and MeHg levels in ESAS sediments is however limited. Here, we observed concentrations of Hg ranging from 30 to 96 ng Hg g^-1 d.w. of HgT, and 0.03 to 9.5 ng Hg g^-1 d.w. of MeHg. Similar concentrations of HgT were observed close to the river delta (54 ± 19 ng Hg g^-1 d.w.), where >95 % of the organic matter is of terrestrial origin, and the other section of the transect (42 ± 7 ng Hg g^-1 d.w.) where the terrestrial organic matter is diluted with carbon from marine sources. In contrast, we observed higher concentrations of MeHg close to the river delta (0.72 ± 0.71 ng Hg g^-1 d.w. as MeHg) than further out on the continental shelf (0.031 ± 0.71 ng Hg g^-1 d.w. as MeHg). We also observed a positive correlation between the MeHg:Hg ratio and previously characterized molecular markers of terrestrial organic matter (Bröder et al. Biogeosciences (2016) & Nature Com. (2018)). We thus suggest riverine inputs, rather than in situ MeHg formation, to explain observed MeHg trends.

How to cite: Nguyen, V. L., Wild, B., Gustafsson, Ö., Semiletov, I., Dudarev, O., and Jonsson, S.: Mercury and methylmercury along a transect from the Lena river estuary across the Laptev Sea Shelf, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13727, https://doi.org/10.5194/egusphere-egu2020-13727, 2020.

The thawing of permafrost is leading to increased export of organic matter into aquatic ecosystems that was previously stored within frozen peatland soils. This organic matter has been found to be reactive to microbial and photochemical processes, so that permafrost thaw is expected to lead to an increased production of greenhouse gases. Being able to predict the fate of these increased loads of terrestrial organic carbon in aquatic systems is therefore important from a climate change perspective. In a previous study we suggest that terrestrial organic compounds susceptible to photodegradation are also prone to adsorb to mineral particles. Whereas photodegradation stimulates CO₂ production, adsorption has the potential to remove organic matter from the water column and store it in the sediment. Warming at high latitudes involves both permafrost thaw and glacial melt. Glacial runoff streams often contain high loads of suspended sediment. As these minerogenic particles are transported downstream the aquatic continuum, they can eventually mix with water containing high concentrations of freshly released organic matter, and act as an adsorbent.

In order to predict CO₂ production from mobilized permafrost organic matter, we need to study the bioavailability of this material before and after alteration by physical and chemical processes such as photodegradation and adsorption to mineral particles. In this study, we compared the effect of adsorption to glacial suspended sediment to that of photodegradation on the dissolved organic matter composition of surface water collected from a thawing peat plateau in northern Sweden. We used optical measurements and mass spectrometry to evaluate changes in the composition of the organic matter and employed a three-month incubation to determine its bioavailability. Initial results from optical measurements indicate that while chromophoric compounds in general were removed by both photodegradation and adsorption, humic-like fluorescent compounds were more susceptible to photodegradation than adsorption. UV-irradiation increased bioavailability of the organic matter, whereas pre-treatment by adsorption to mineral particles slightly decreased bioavailability compared to the control. Results from this study will help advance our understanding of interactive effects between physico-chemical processes and microbial degradation at an increasingly relevant interface where melting permafrost meets glacial meltwaters.

How to cite: Groeneveld, M., Jakobsson, E., Hawkes, J., Tittel, J., Kothawala, D., and Tranvik, L.: When mobilized organic matter and glacial suspended sediment meet: effects of adsorption, photo- and biodegradation , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17679, https://doi.org/10.5194/egusphere-egu2020-17679, 2020.

Warming-induced permafrost thawing is expected to intensify the remobilization of terrigenous organic matter (terrOM) to the East Siberian Arctic Shelf (ESAS) via increasing river discharge and coastal erosion. Earlier studies have focused on source apportionment and transport of terrOM, with less emphasis on its degradation state during cross-shelf transport. Since degradation of terrOM is the link between permafrost thawing and release of GHGs such as CO₂, this study focuses on the degradation characteristics. Hence, the main objective of this study is to assess the patterns of terrOM degradation across the East Siberian Arctic Shelf using molecular proxies that are specific to terrOM.

Lignin phenols and high molecular weight (HMW) n-alkanes and n-alkanoic acids are only produced by terrestrial plants which make them suitable biomarkers to assess degradation of terrestrial material throughout the ESAS. The lignin-based proxies acid to aldehyde ratios of vanillyl (Vd/Vl) and syringyl (Sd/Sl) structural units, as well as the ratio of 3,5-dihydroxybenzoic acid over vanillin (3,5-Bd/V) are expected to increase during degradation under oxic conditions. Fresh terrestrial plant material is predominated by long odd-numbered (>C₂₅) and even-numbered (>C₂₄) carbon chain length of n-alkanes and n-alkanoic acids, respectively. This dominance is described in the Carbon Preference Index (CPI). When degradation takes place, CPI values decrease accordingly, describing how much of the original material was preserved. Ratios of HMW n-alkanoic acids to HMW n-alkanes are also expected to decrease during microbial degradation owing to preferential loss of functional groups.

The data show increasing Vd/Vl, Sd/Sl and 3,5-Bd/V ratios, and decreasing HMW n-alkanes CPI values toward the outer shelf, consistent with continuous degradation of terrOM across the ESAS. While Vd/Vl and HMW n-alkane CPI did not show strong differences between east and west, Sd/Sl ratios were highest in the outer western ESAS, and 3,5-Bd/V ratios were highest in the outer east. These differences may reflect different terrOM pools along the ESAS due to differences in vegetation zones releasing the input material through river discharge and coastal erosion. In contrast, HMW n-alkanoic acid to HMW n-alkane ratio and HMW n-alkanoic acid CPI showed inconsistent patterns across the ESAS; reasons for it are currently being investigated. These results will also be complemented by additional biomarkers to better understand the degradation of terrOM during cross-shelf transport.

How to cite: Matsubara, F., Wild, B., Martens, J., Wennström, R., Tesi, T., Dudarev, O., Shakhova, N., Semiletov, I., and Gustafsson, Ö.: Degradation of terrigenous organic matter on the East Siberian Arctic Shelf assessed by lipid and lignin oxidation products, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19668, https://doi.org/10.5194/egusphere-egu2020-19668, 2020.

Inland waters can be significant sources of greenhouse gases (GHGs; CO₂, CH₄ and N₂O) to the atmosphere, yet they are often excluded from terrestrial GHG balances. Vast stocks of carbon stored in Arctic tundra permafrost soils are vulnerable to mobilisation due to permafrost thawing accelerated by the amplified effects of climate warming at high latitudes. The carbon that is released becomes available to (partial) degradation producing GHGs which inland waters emit to the atmosphere, thus forming a positive feedback to climate warming. Rising temperatures, longer summers and increased precipitation in the Arctic tundra are expected to increase permafrost thaw and degradation rates, therefore the contribution of inland waters to the tundra terrestrial GHG budgets needs to be better understood to assess the strength and timing of the feedback effect in the future.

Field data from lakes, ponds and streams throughout the summer season of three years and from floodplain water present in one of the years was collected. This data was used to calculate CO₂ equivalent diffusive fluxes from inland freshwaters, and combined with eddy covariance flux tower measurements and with satellite remote sensing to calculate total GHG emissions of the study area.

The results indicate that ponds are the largest contributors to upscaled inland water GHG emissions (around 50%) followed by streams and finally lakes. Streams had the highest emission rates followed by lakes and ponds the lowest, however due to the large surface area coverage of ponds (15% of the study area) they become the largest contributor to the upscaled freshwater GHG emissions. Upscaling of CH₄ and CO₂ fluxes shows that while the study region remains a GHG sink, inclusion of freshwater emissions reduces its sink capacity by 28% during our reference month July. Assuming that 10% of the study area is flooded in this month, it reduces the terrestrial GHG sink estimate to 45% instead of 28%, partially due to N₂O oversaturation in the flood water in relation to the atmosphere whereas N₂O concentrations in lakes, streams and ponds are close to zero. Overall the results show that if the Siberian Arctic tundra becomes wetter or more frequently flooded due to climate warming it will significantly affect the total terrestrial GHG balance.

How to cite: Martyn, M., Dean, J., Dolman, H., and Vonk, J.: The role of inland freshwaters in summer CO2, CH4 and N2O emissions from northeast Siberian Arctic tundra, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20028, https://doi.org/10.5194/egusphere-egu2020-20028, 2020.

Arctic and sub-arctic regions contain a globally significant reservoir of easily degradable glacial organic carbon (GOC) held within glacier ice, subglacial sediments, and proglacial sediments and soils. 21st century warming will result in global glacier retreat with the potential to expose and release GOC, degradation of which can produce CO₂ and/or CH₄ through physical, chemical or biological processes. Newly-exposed nutrient rich glacial landscapes may develop soils and ecosystems. However, current understanding of the nature of glacial carbon cycling is very weak. In this study, sources and transformations of organic carbon (OC) within proglacial environments were determined using a combination of organic biomarkers, DNA sequencing and elemental concentrations.

Soil development was characterised in three contrasting glacial systems (Oræfajökull ice cap in Iceland, Tarfala in Sweden and Zackenberg in Greenland) in order to understand the main source of OC in soils exposed after glacier retreat and soil development along downstream transects from the glacier front. Water, soil and sediment samples were collected during four successful field campaigns (Iceland and Sweden in summer 2018, Greenland and Iceland in summer 2019). Soil and sediment samples were analysed for organic carbon and nitrogen concentrations, bacteriohopanepolyol biomarkers (BHPs), a group of membrane lipids that can be used to trace major microbial groups, DNA sequencing and major elements (using ICP-OES and IC).  

Soil samples from moraines showed highest OC concentrations (up to 5.5% in Iceland), while fluvial sediment samples from all study areas had low to no OC. BHPs were rare in fluvial sediments, observed in riverbank soils and most common in moraines. Both total BHP concentration and R’soil index (up to 50.5 µg/g ΣBHPs in a Little Ice Age and 0.41 R’soil in a 2500-year-old Icelandic moraines) show development of soils over time along the downstream transect from the glacier front. DNA concentrations in soil extracts are much higher than fluvial sediment samples. Particulate OC concentration in glacial meltwater streams and proglacial lakes was low (up to 0.03 mg/L), perhaps due to the high total suspended sediment concentrations (up to 0.96 mg/L) in most of the streams. Water chemistry analyses showed significant Ca, S, Na, Fe, Mg and Al concentrations, that potentially would fertilise the Arctic Ocean.

Based on these preliminary data, it can be concluded that direct glacial output of organic carbon is low, but soil and ecosystem development in front of retreating glaciers leads to the build-up of new terrestrial OC stores. Erosion of OC from these pro-glacial landscapes by glacial meltwater might highly affect estimates of GOC. Future glacier retreat in deglaciating systems in the Arctic (Greenland and Sweden) and sub-arctic (Iceland) regions might increase terrestrial OC productivity and carbon export, as well as seeding biological production downstream.

How to cite: Akhmetkaliyeva, S., Sparkes, R., Clarke, L., Dean, A., and Cook, S.: Quantifying and characterising organic carbon in newly-developed soils following glacier retreat in northern latitudes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20836, https://doi.org/10.5194/egusphere-egu2020-20836, 2020.

Ongoing climate warming in the western Canadian Arctic is leading to thawing of permafrost soils and subsequent mobilization of its organic matter (OM) pool. Part of this mobilized terrestrial OM enters the aquatic system as dissolved organic matter (DOM) and is laterally transported from land to sea. Mobilized DOM is an important source of nutrients for ecosystems as it is available for microbial breakdown, the consequent turnover of the dissolved organic carbon (DOC) fraction of DOM serving as a potential source of greenhouse gases. We are beginning to understand spatial controls on the release of DOM as well as the quantities and fate of this material in large arctic rivers, but these processes remain systematically understudied in small, high-arctic watersheds, despite the fact that these particular watersheds experience strongest warming.

We sampled soil (active layer and permafrost) and water (porewater and stream water) from two small catchments along the Yukon coast, Canada, during the summers of 2018 and 2019. We assessed the organic carbon quantity (using DOC and soil OC content), quality (d¹³C-DOC, C/N ratios and optical properties including components modelled with EEMs-PARAFAC), the turnover of DOM through incubation experiments as well as nutrients and stable water isotopes. We classify and compare different landscape units by quantitative and qualitative change across gradients from soil stocks down to the catchment outflow.

Our results show that substantial variation in DOC concentrations exists among various landscape units as well as between active layer and permafrost. We find high soil carbon stocks and leaching potentials from these coastal tundra soils. Moreover, we find that permafrost DOM is utilized rapidly upon thaw. Using remote sensing-based landscape classification, we are planning to upscale carbon and nutrient fluxes for the panarctic coastal zone to account for small yet numerous high-arctic watersheds in lateral terrestrial OM transfer from land to sea Under current climate projections and with continued permafrost thaw altered lateral fluxes may have profound impacts on the arctic aquatic ecosystem and arctic carbon cycling.

How to cite: Speetjens, N., Tanski, G., Martin, V., Wagner, J., Richter, A., Hugelius, G., Lodi, R., Knoblauch, C., Koch, B., Stedmon, C., and Vonk, J.: Landscape-driven carbon export from small coastal permafrost watersheds , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21915, https://doi.org/10.5194/egusphere-egu2020-21915, 2020.

Permafrost-region lakes are dynamic landscape systems and play an important role for climate change feedbacks. Lake processes such as mineralization and flocculation of DOC, one of the main carbon fraction in lakes, contribute to the global carbon cycle. These processes are in focus of climate research but studies have been limited in geographic extent. We synthesized published datasets and unpublished datasets from the author team totaling 1,691 water samples from 1,387 lakes across the Subarctic and Arctic in permafrost regions of Alaska, Canada, Siberia, and Greenland to provide first insights for linkages between DOC concentration to the basin. In our synthesis, we find regional differences in DOC concentration of permafrost-region lakes. We focussed on relations between lake DOC concentration and latitude, permafrost zones, ecoregions, lake surrounding deposit type, and ground ice classification of each lake basin. Additionally, we analysed the lake surrounding soil organic carbon content from 0-100 cm depth and 0-300 cm depth. Individual lake DOC concentrations of our dataset range from below detection limit assigned to 0 mg L^-1 (North Slope, Alaska) to 1,130 mg L^-1 (Yukon Flats, Alaska). We found regional median lake DOC concentrations of 18.8 mg L^-1 (Greenland, n=25), 12.2 mg L^-1 (Alaska, n= 1,135), 9.6 mg L^-1 (Siberia, n=252), and 7.2 mg L^-1 (Canada, n=279). Lakes in the isolated permafrost zone had the highest median DOC concentration compared to lakes in the sporadic, discontinuous, and continuous permafrost zones. Our synthesis shows increasing lake DOC concentration with decreasing latitude and, due to a larger availability of biomass and organic carbon, a significant relationship of lake DOC concentration and ecoregion of the lake. We found higher lake DOC concentrations in boreal permafrost sites compared to tundra sites. About 22 % of lakes in our dataset are located in regions with ice-rich syngenetic permafrost deposits (yedoma). Because yedoma contains large amounts of organic carbon, we assumed to find higher DOC concentrations in yedoma lakes compared to non-yedoma lakes. Our analysis shows a significant relationship of lake DOC concentration and surrounding deposit type but not a higher DOC concentration in yedoma lakes compared to non-yedoma lakes. Finally, we found a relationship of soil organic carbon content from 0-100 cm depth and lake DOC concentration. In contrast, a comparison of soil organic carbon content from 0-300 cm depth and lake DOC concentration shows no significant correlation. This was also found for ground-ice content and lake DOC concentration. Our dataset of lakes across the Arctic shows that the DOC concentration of a lake strongly depends on its environmental properties. This dataset will be fundamental to establish a pan-Arctic lake DOC pool for estimations of the impact of lake DOC on the global carbon cycle and further on climate change.

How to cite: Stolpmann, L., Morgenstern, A., Boike, J., Fritz, M., Herzschuh, U., Dvornikov, Y., Heim, B., Lenz, J., Coch, C., Larsen, A., Walter Anthony, K., Arp, C., Jones, B., Frey, K., and Grosse, G.: First Pan-Arctic Assessment of Dissolved Organic Carbon Concentration in Permafrost-Region Lakes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8174, https://doi.org/10.5194/egusphere-egu2020-8174, 2020.

Permafrost-affected soils contain a large quantity of soil organic carbon (SOC). Two processes control the amount of carbon stored in soils. The photosynthetic activity of plants produces biomass that may accumulate in the soil, while microorganism’s respiration leads to a depletion of the soil carbon stocks through decomposition. The carbon balance defines whether a soil acts as a source or sink of carbon. In recent decades, many researchers observed and analyzed the carbon balance of permafrost soils. In most cases, the focus lays on observations of the vertical carbon flux (CO₂ and CH₄) to estimate the carbon balance. However, there is lack of information regarding the lateral losses of carbon via dissolved organic carbon (DOC) or dissolved inorganic carbon (DIC) in ground- or rainwater.

In this study, we estimate the lateral carbon fluxes from a permafrost-affected site in north-eastern Siberia, Russia. Long-term measurements of vertical carbon fluxes have been conducted at this study site. By considering both, the vertical and the lateral carbon fluxes, we estimate the complete carbon balance for one growing season in 2014 and discuss the contribution of the lateral carbon flux to the overall carbon balance.

The results show that the vertical CO₂ fluxes dominate the carbon balance during the growing season from June 8^th – September 8^th (-19 ± 1.2 kg-C m^-2). The lateral fluxes of DOC and DIC reached values of +0.1 ± 0.01 and +1.4 ± 0.09 kg-C m^-2, respectively, whereas the vertical fluxes of CH₄ had values of +0.7 ± 0.02 kg-C m^-2 integrated over this time. By considering the lateral carbon export, the net ecosystem carbon balance of the study area was reduced by 8%. On shorter time scales of days, the relationship between lateral and vertical flux changes within the growing season. Early in the growing season, the lateral carbon flux outpaces the weak vertical CO₂ uptake for a few days and converts the estimated carbon balance from a sink to a source.

We conclude that lateral carbon fluxes have a larger influence on the carbon balance of our study site on time scales of days (early and late growing season) and that this influence decreases with annual time scales. Therefore, the vertical carbon flux can be seen as a good approximation for the carbon balance of this study site on annual time scales.

How to cite: Beckebanze, L., Walz, J., Runkle, B. R. K., Holl, D., Fedorova, I. V. F., Helbig, M., and Kutzbach, L.: Lateral carbon export from polygonal tundra catchments on Samoylov Island, Lena River Delta, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8991, https://doi.org/10.5194/egusphere-egu2020-8991, 2020.

Thawing of permafrost in the Mackenzie Delta region of northern Canada, coupled with an increase in river discharge, prompts the release of particulate and dissolved organic matter from the largest Arctic drainage basin in North America into the Arctic Ocean. While this ongoing process is well-recognized and its rate is accelerating, the fate of the newly-mobilized organic matter as it transits from the watershed through the delta and into the marine system remains poorly understood. In the framework of the H2020 Nunataryuk project, and in partnership with ArcticNet and Sentinel North, we conducted intensive field expeditions in the Mackenzie Delta from April to September 2019. The temporal sampling scheme of this project allowed the investigation of ambient conditions in the coastal waters under a full ice cover prior to the spring freshet, during the ice break-up, in summer, as well as in fall prior to the freeze-up period. In order to capture the fluvial-marine transition zone and with specific challenges related to shallow waters and changing seasons, the field sampling was conducted using several platforms: helicopters, snowmobiles and small boats. Water column profiles of physical and optical variables were measured on site, and water and sediment samples were collected and preserved for the determination of the composition and sources of particulate and dissolved organic matter, as well as its biogeochemical cycling in the coastal environment. Beyond improving our understanding of the origin and fate of this re-mobilized organic matter, the data gathered will serve as a new basis for the ground truthing of remotely sensed images in a changing arctic environment. Finally, the tuned satellite data will be incorporated into numerical models, providing better predictions of the impacts of permafrost thaw on local biogeochemical cycling and ultimately on sea-air fluxes of carbon dioxide and global climate.

How to cite: Lizotte, M. and the Nunataryuk WP4 team: From pre-freshet to pre-freeze: a field survey of the fate of organic matter remobilized from the thawing permafrost to the coastal waters of the Mackenzie Delta region , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11944, https://doi.org/10.5194/egusphere-egu2020-11944, 2020.

A complex multydisciplinary oceanographic research was carried out along 358 km transect along the Lena Delta coastline (DCL): 58 stations were accomplished in 7 days in early September 2009. Our study focuses on structure of bottom sediments, dynamics of suspended particulate matter (SPM), content of particulate organic carbon (POC), total nitrogen (ON), C/N value, stable carbon (δ¹³С) and nitrogen isotopes (δ¹⁵N). It has been found a close connection between channels morthology, tectonic features and distribution of bottom sediments, SPM, water runoff along the DCL.

Neotectonic movements happened about 6,000 yr BP led to uplift of the DCL western part, which caused  redistribution of river runoff to the eastern channels of the DCL. The boundary between these “tectonic” parts of the DCL is the submeridional fault, to which the Tumatsky Channel is currently confined. Shelf waters with salinity (S) > 20‰ penetrated to the channel mouth, causing formation of a frontal hydrological zone with increased gradients of thermohaline characteristics. Almost fresh river waters (S<1 ‰) are distributed along the eastern part of the DCL (EDCL), and brackish water are distributed to the west of Tumatsky Channel (WDCL). The differences in the SPM average content between EDCL and WDCL are only 1.5 times, but the density of the river net in EDCL is almost 3 times higher. The reason is a more intense sedimentation of the SPM, causing the DCL progradation to the east and northeast of Laptev Sea. This is supported by 2-fold decrease by SPM from the inlets of Sardakhskaya, Bykovskaya and Trofimovskaya Channels to their mouths. Only fine SPM remain in transfer from the central DCL to the mixing water zone “river-sea”. A circumterral narrow strip of sand-silt sediments formed along the DCL’s edge, and a vast field of relict sands is distributed near the northwestern elevated ledge of the delta (WDCL). Seaward direction from DCL sand-silt sediments are quickly replaced by silt-mud. The average POC content in EDCL and WDCL, respectively, is 1.6 and 2.7%; average C-13 isotopic signal is -26.5 and -26.0 ‰; average C/N values are 9.8 and 9.3. That is confirmed by similar terrestrial geochemical signature in the nearshore sediments adjacent to EDCL and WDCL

Acknowledgements. This study was supported by Ministry of Science and Education of Russia (project № АААА-А17-117030110039-2), the Russian Science Foundation (grants № 19-17-00058), the Russian Foundation for Basic Research (grants №№ 18-05-70047, 18-05-00559, 19-77-00016, 20-05-00545).

How to cite: Oleg, D., Alexander, C., Aleksey, R., Irina, P., Svetlana, P., Birgit, W., Andrey, L., Tomasso, T., Jannik, M., Igor, S., Natalia, S., and Örjan, G.: Elemental and isotopic signatures of terrestrial organic matter along the Delta coastline of Lena River (Laptev Sea), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12326, https://doi.org/10.5194/egusphere-egu2020-12326, 2020.

Permafrost thaw leads to the formation of shallow water bodies in which large quantities of terrestrial organic carbon are mobilized as dissolved organic matter (DOM), partly turned into greenhouse gases (GHG). DOM comes from ancient carbon pools trapped in frozen soils for hundreds to thousands of years but also from present-day primary producers. Determining the fate of these pools is fundamental to evaluate the potential of these water bodies to amplify climate warming through their GHG emissions. In addition to the microbial degradation pathways producing CO₂ and CH₄, DOM can be directly mineralized into CO₂ by sunlight. The CO₂ production rates from photodegradation vary extensively across Arctic regions. The controlling factors and interactions with the microbial communities are not well understood, while photodegradation is likely to rise as the open-water season extends. Determining the photo- and bio-lability of the carbon pools available on thawing permafrost landscapes is needed to predict to what extent these systems can affect the global carbon cycle.

Various DOM and environmental characteristics are considered in my PhD project, including mixing regime, seasonal exposure and light attenuation, as well as the microbial community response to photo-induced chemistry changes in DOM. Study sites include subarctic and arctic peatland areas of Eastern Canada, rich in thaw ponds and where organic matter started to accumulate between 3700 and 5600 years BP. These are non-Yedoma systems that have been poorly studied despite the large amount of organic carbon they store. This presentation will show the results of a lab experiment using a solar simulator where DOM of various origins and ages were tested: thaw pond water and leachates from plants, permafrost active layer, and previously unthawed permafrost. Short term incubations were carried out under five treatments: exposure to light without bacteria (0.2 µm filtration), exposure to light followed by a dark incubation with a bacterial inoculum, dark incubation with a bacterial inoculum, dark incubation with the whole bacterial community (2.7 µm filtration), and dark control without bacteria. A set of optical, biological and chemical characteristics were measured at the beginning and end of incubation. DOM losses (DOC, CDOM, and FDOM) and CO₂ production vary extensively among treatments and DOM pools. They were the highest in dark bacterial incubations of plants leachates. DOM of the subarctic area was quite refractory to degradation in general, except for the biodegradation of the unthawed permafrost leachate (- 50%). Photodegradation was observed in all water types, with DOM losses faster than biodegradation ones for the Arctic soils leachates and all the ponds waters. The highest CO₂ photoproduction was measured in Arctic unthawed permafrost leachates. Finally, the enhancement of DOM lability to microbes caused by photodegradation was generally observed for unthawed permafrost leachates. Incoming biological and 14C data, along with multivariate analyses, will improve the characterisation of the trends.

How to cite: Mazoyer, F., Laurion, I., and Rautio, M.: The role of photodegradation on the mineralization of permafrost DOM, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1144, https://doi.org/10.5194/egusphere-egu2020-1144, 2020.

The Canadian Beaufort Sea is experiencing coastal erosion at unprecedent rates due to waves impacts and permafrost thaw. Water derived from permafrost thaw has profound impacts on coastal hydrogeology and carbon dynamics. The quality and volume of permafrost water (as surficial and groundwater) discharging to the ocean controls on coastal water chemistry and turbidity. These disturbances alter coastal ecosystems and endanger species with ecological, cultural, and economic value. Robust estimates of these solute and solid inputs are needed on a site-specific scale to obtain accurate regional and global estimations. However, the determination of appropriate endmembers to estimate these fluxes is not straightforward; and yet, little is known about the chemical composition and reactivity of carbon, nutrients and metals of water in coastal permafrost settings. The main objective here is to trace permafrost-derived solutes and study their transport and transformation to coastal water. Several coastal permafrost slumps were visited last summer in the Tuktoyaktuk Peninsula region. Melting-ice, surficial and groundwater were collected to systematically measure short-live isotopes (Rn-222, Ra-223, Ra-224), the stable isotopes of water (δ¹⁸O, δD), dissolved organic and inorganic carbon (DOC and DIC), chromophoric component of the organic matter (CDOM), total and non-carbonate alkalinity. In front of these systems, surface seawater samples were collected to 1 to 2 km from the shore to trace these chemical inputs to the coastal ocean. Preliminary results will be presented with a specific focus on the geochemical signature of waters at the nearshore. This project is a part of the WP4 Nunataryuk Program, in collaboration with Natural Resources Canada

How to cite: Chaillou, G., Kipp, L., Bélanger, F., and Whalen, D.: Detecting the signature and transformations of water from coastal permafrost thaw in the Beaufort Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3094, https://doi.org/10.5194/egusphere-egu2020-3094, 2020.

About one-third to half of the global soil carbon is held in the top 1-3 m of tundra+taiga permafrost PF (~1000 Pg-C) with deeper layers below as Deep-PF (~400 Pg-C) and in Pleistocene Ice Complex Deposit permafrost (ICD-PF, ~400 Pg-C), lining 4000 km of the East Siberian Arctic coast.  In order to overcome the landscape heterogeneity and the stochastic nature of e.g. erosional release processes, we use the East Siberian Arctic Shelf (ESAS) in an inverse approach – as a natural integrator of the TerrOM releases from both the river drainage basins and from the erosion of ICD-containing bluffs. We are exploring how source-dependent transport and translocated degradation affect the released TerrOM.

The sources of released terrOM have been increasingly constrained using great rivers and the ESAS as natural integrators through a combination of biomarkers and δ¹³C/Δ¹⁴C on bulk-C and on compound level. There are significant gradients in sources both E-W and S-N across each shelf sea and between water column DOM, POM and sedimentary OM. The largest source of OC to ESAS sediments is not rivers or marine plankton – it is coastal erosion of old ICD.  Our initial limited dataset has now been much expanded, as has the end-member database while the statistical source apportionment method has been refined. They combine to show more efficient cross-shelf transport of river-borne “topsoil-PF” compared to ICD-PF and a clear distinction in sources of TerrOM between western and eastern ESAS regimes separated roughly along 165E, consistent with the local oceanography.

There have been good strides also in understanding degradation of TerrOM exported to ESAS. Studies are demonstrating continuous offshoreward degradation of all TerrOM, yet with large differences between compound classes. Physical association of TerrOM with different sediment components, and sorting of the sediments exert first-order control on TerrOM distribution and degradation. An expanded dataset on specific surface area (SSA) and CuO oxidation products reveals spatial patterns across ESAS. The combination of compound-specific radiocarbon analysis of terrestrial biomarkers with SSA-normalized TerrOM signals constrains the ambient degradation rates and fluxes during the 3-4000 year timescale of cross-shelf transport. The degradation of TerrOM also causes severe ocean acidification of the ESAS.

Investigations of sources and fate of TerrOM on the ESAS – the World’s largest shelf sea– provides a window to constrain permafrost-C remobilization and to study mechanisms of transport and degradability of different components of released terrestrial organic matter.

How to cite: Gustafsson, Ö., Semiletov, I., Shakhova, N., Dudarev, O., Vonk, J., van Dongen, B., Eglinton, T., Tesi, T., Bröder, L., Andersson, A., Wild, B., Matsubara, F., and Martens, J.: Transport and fate of different components of terrestrial organic matter across the Siberian-Arctic shelves, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17595, https://doi.org/10.5194/egusphere-egu2020-17595, 2020.

Subsea permafrost contains a potentially large and vulnerable organic carbon pool that might be or become a source of greenhouse gases to the atmosphere. While organic carbon stocks and vulnerability of terrestrial permafrost are increasingly well constrained, the dynamics of subsea permafrost remain highly uncertain due to limited observational data from these hard-to-access systems. Based on a unique set of drill cores from the near-coastal Laptev Sea, we here assess the vulnerability of subsea permafrost organic matter to degradation after thaw. To that end, we combine biomarker analyses of organic matter above and below the in-situ thaw front with incubation of subsea permafrost material in the laboratory. Biomarker degradation proxies based on the lignin phenol composition of organic matter (acid/aldehyde ratios of syringyl and vanillyl phenols; 3,5-dihydroxybenzoic acid/vanillyl ratio) suggest an overall low degradation state of lignin compared to terrestrial permafrost deposits and marine sediments in the region, and no systematic change across the thaw front. These lignin-based proxies are mostly sensitive to degradation under oxic conditions, i.e. before organic matter burial in subsea permafrost deposits, and less to degradation under anoxic conditions that prevail at the thaw front of subsea permafrost. Lignin phenol proxies will therefore be complemented by other biomarker degradation proxies sensitive to degradation under anoxic conditions, as well as by first data from incubation of subsea permafrost material under cold, anoxic conditions. Together, these data will enhance our understanding of organic matter in subsea permafrost, its vulnerability to degradation after thaw and the potential for greenhouse gas emissions from this system.

How to cite: Wild, B., Shakhova, N., Dudarev, O., Ruban, A., Kosmach, D., Tumskoy, V., Tesi, T., Joß, H., Alexanderson, H., Jakobsson, M., Mazurov, A., Semiletov, I., and Gustafsson, Ö.: Vulnerability of subsea permafrost organic matter to degradation after thaw, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17935, https://doi.org/10.5194/egusphere-egu2020-17935, 2020.

Permafrost contains 1400-1660 Gt of organic carbon (OC), from which 5-15% will likely be emitted as greenhouse gases (GHG) by 2100. The soil organic carbon stock is distributed between a pool of particulate organic matter (POM), and a pool of mineral-associated OM (MOM). POM can be free, i.e., more readily available for microbial decomposition, or occluded within soil aggregates (involving clay minerals or Fe-Al (hydr)oxides), i.e., spatially inaccessible for microorganisms. MOM includes OC sorbed onto mineral surfaces (such as clay minerals or Fe-oxides) and OC complexed with metal cations (e.g., Al, Fe, Ca), i.e., stabilized OC. The interactions between OC and minerals influence the accessibility of OC for microbial decomposition and OC stability and are therefore a factor in controlling the C emissions rate upon thawing permafrost.

In the warming Arctic, there is growing evidence for soil disturbance such as coastal erosion, thermokarst and soil drainage as a consequence of abrupt and gradual permafrost thaw. These disturbances induce changes in the physico-chemical conditions controlling mineral solubility in permafrost soils which directly affect the stability of the MOM and of the occluded POM. As a consequence, a portion of OC can be unlocked and transferred into the free POM. This additional pool of freely available OC may be degraded and amplify C emissions from permafrost to the atmosphere. Conversely, the concomitant release of metal cations upon permafrost thaw may partly mitigate permafrost C emissions by stabilization of OC via complexation or sorption onto mineral surfaces and return a portion of freely available OC to the MOM. The majority of C is emitted as CO₂ but 1.5 and 3.5% of the total permafrost C emissions will be released as CH₄, with implications for the atmospheric radiative forcing balance. Importantly, the proportion CH₄ emitted relative to CO₂ is likely to increase with increasing abrupt thaw and associated anoxic conditions, but a portion of CH₄ emissions could be mitigated by the anoxic oxidation of methane mediated by the presence of Fe-oxides exposed by abrupt thaw of deep permafrost.

This contribution aims at assessing how changing soil physico-chemical conditions affect interactions between mineral surfaces and OC in thawing permafrost. Scenarios of mineral-organic interactions during gradual thaw, including changes in water drainage and talik formation, and abrupt thaw including shifting redox conditions associated with thermokarst will be presented. Approaches to quantify changes in mineral-organic interactions will be discussed. By integrating the most recent studies from the permafrost carbon community with soil mineralogy, soil chemistry and soil hydrology, this contribution demonstrates that the fate of mineral-organic interactions upon thawing must be considered given their potential implications for GHG emissions. If we do not include the role of mineral-organic interactions in this puzzle, the complexities involved in soil carbon decomposition may propagate large uncertainties into coupled soil carbon-climate feedback predictions.

How to cite: Opfergelt, S., Hirst, C., Monhonval, A., Mauclet, E., and Thomas, M.: Integrating mineral interactions with organic carbon in thawing permafrost to assess climate feedbacks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19501, https://doi.org/10.5194/egusphere-egu2020-19501, 2020.

The Arctic ocean receives 11% of the global river discharge and the Arctic rivers drain large permafrost rich catchments. Where these rivers outflow into the marginal shelf seas of the Arctic ocean the terrestrial dissolved organic matter (tDOM) which they transport has an important role to play in the coastal ecosystem. This tDom is derived from inland permafrost and as it thaws under future climate scenarios there are expected to be changes to both the composition and quantity of riverine tDOM. At the same time there will be changes to the seasonality and magnitude of river discharge, due to increased precipitation and earlier snow melt, and to the light availability, due to reduced seasonal sea ice. To understand the possible impact of these changes on the coastal ecosystem it is important to understand the present role of permafrost derived tDOM and the possible changes to the nearshore circulation.

We model the hydrodynamics of the extensive shallow shelf of the Laptev sea, into which drains the Lena river – the 13^th largest in the world by discharge. The output from the hydrodynamic model is used to drive the ecosystem model ERSEM which has been adapted to explicitly include a permafrost tDOM input. This coupled model system allows us to investigate both the role of present day tDOM in an Arctic coastal ecosystem and to hypothesise on the impact of increases in future. In particular we attempt to quantify the efficacy of the microbial carbon pump under different tDOM inputs.

How to cite: Bedington, M., Torres, R., Polimene, L., Mann, P., and Strauss, J.: Modelling the impact of changing riverine permafrost input on an Arctic coastal ecosystem, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20689, https://doi.org/10.5194/egusphere-egu2020-20689, 2020.

There are only a few Earth System processes that can cause a net transfer of carbon from land/ocean to the atmosphere (as CO₂ and CH₄) on the century timescale– top candidates are thawing permafrost and collapsing CH₄ hydrates in the Arctic. Nevertheless, there are huge uncertainties regarding the composition, inventories and functioning of these different Cryosphere-Carbon pools.

Most investigations of Arctic CH₄/CO₂ releases have studied inland permafrost (PF), yet there is increasing attention towards coastal and subsea permafrost and hydrates. The East Siberian Arctic Ocean (ESAO) is the target area as it is experiencing among the highest climate warming and because of its vast, yet poorly constrained stores of vulnerable carbon. The ESAO is the largest yet shallowest shelf of the World Ocean, being a seaward extension of the Siberian tundra that was flooded during the Holocene transgression 7-15 kyr ago. 

Recent drilling campaigns of the Laptev Sea subsea permafrost have provided the opportunity for progress in understanding its current state, composition and functioning. The temperature profiles of the PF underneath the coastal waters were in general much higher and close to zero, compared to nearby still on-land permafrost. Several sites that were drilled 30 years ago were recently re-drilled, which revealed that the thaw horizon has been moving down by several meters in just a few decades. There is thus both a potential for degradation of the organic matter (including to methane) in this subsea PF as well as an increasing permeability for pre-formed methane to penetrate toward the surface.

Methane in the ESAS water column is over extensive scales present at concentrations much above what would be predicted from equilibrium with overlying atmospheric mixing ratios.  The spatial patterns can now start to be compared with geophysical data on the composition of the sediments.  The water column to atmosphere transfer of methane is affected both by the relative importance of diffusive exchange of dissolved methane and through ebullition.  Storm-induced ventilation of the water column is shown to be an important process.

The relative contributions of different subsea compartments to the methane fluxes is also approached through isotopes. We are exploring triple isotope fingerprinting of bottom water methane to apportion its sources (i.e. d¹³C/dD/D¹⁴C-CH_4.).  Preliminary results from two active seep regions, one in Laptev Sea and one in the East Siberian Sea will be presented.

How to cite: Holmstrand, H., Shakhova, N., Semiletov, I., Steinbach, J., Kurilenko, A., Salyuk, A., Kosmach, D., Chernykh, D., Koshurnikov, A., Tumskoy, V., Lobkovsky, L., and Gustafsson, Ö.: Siberian-Arctic Subsea Permafrost and Methane: Spatial variability and isotope-based source apportionment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21660, https://doi.org/10.5194/egusphere-egu2020-21660, 2020.

Sustained release of methane (CH4) to the atmosphere from thawing Arctic permafrost may be a positive and significant feedback to climate warming. Atmospheric venting of CH4 from the East Siberian Arctic Shelf (ESAS) was recently reported to be on par with flux from the Arctic tundra; however, the future scale of these releases remains unclear. Here, based on results of our 12 years observations, we show that CH4 emissions from this shelf to be determined by the state of subsea permafrost degradation. Below we consider dramatically growing release from the area located out of known fault zones.

First time, we observed CH4 emissions from this single flare in 2007 in the ESAS mid-shelf.  During 2014-2018 we revisited this area several times aiming to investigate quantitatively changing CH4 ebullition. The data show transformation of a single CH4 flare in a significant seepage area. CH4 emissions from this area emerge from largely thawed sediments via strong flare-like ebullition, producing fluxes that are orders of magnitude greater than fluxes observed in background areas underlain by largely frozen sediments. We suggest that progression of subsea permafrost thawing is much faster not only downward, but also laterally which could result in a significant increase in CH4 emissions from the ESAS.

This work was supported in part by grants from Russian Scientific Foundation (№15-17-20032, № 18-77-10004, №19-77-00067), grant from Russian Government (Grant No. 14, Z50.31.0012/03.19.2014) and Tomsk Polytechnic University Competitiveness Enhancement Program grant, Project Number TPU CEP_SESE-299\2019.

How to cite: Chernykh, D., Shakhova, N., Kosmach, D., Ananiev, R., Salomatin, A., Yusupov, V., Sergienko, V., Gustafsson, Ö., Jakobsson, M., Mayer, L., Saluk, A., Dmitrevsky, N., Kurilenko, A., Gershelis, E., Silionov, V., Lobkovsky, L., Mazurov, A., and Semiletov, I.: First quantitative estimation of growing methane release from the East Siberian Arctic seas: from a single flare to vast seepage area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22402, https://doi.org/10.5194/egusphere-egu2020-22402, 2020.