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Mobilization of permafrost material to aquatic systems and its biogeochemical fate

Wide-spread permafrost thaw is expected to amplify the release of previously frozen material from terrestrial into aquatic systems: rivers, lakes, groundwater and oceans. Current projections include changes in precipitation patterns, active layer drainage and leaching, increased thermokarst lake formation, as well as increased coastal and river bank erosion that are further enhanced by rising water temperatures, river discharge and wave action. In addition, subsea permafrost that formed under terrestrial conditions but was later inundated might be rapidly thawing on Arctic Ocean shelves. These processes are expected to substantially alter the biogeochemical cycling of carbon but also of other elements in the permafrost area.

This session invites contributions on the mobilization of terrestrial matter to aquatic systems in the permafrost domain, as well as its transport, degradation and potential interaction with autochthonous, aquatic matter. We encourage submissions focusing on organic and inorganic carbon as well as on other elements such as nitrogen, phosphorus, silica, iron, mercury and others, from all parts of the global permafrost area including mountain, inland, coastal and subsea permafrost, on all spatial scales, in the contemporary system but also in the past and future, based on field, laboratory and modelling work.

Co-organized by CR6/HS13/SSS5
Convener: Birgit WildECSECS | Co-conveners: Lisa BröderECSECS, Örjan Gustafsson
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Wed, 28 Apr, 14:15–15:00

Chairpersons: Birgit Wild, Lisa Bröder, Örjan Gustafsson

5-minute convener introduction

Sigrid Trier Kjær et al.

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.

Zoé Rehder et al.

Permafrost ponds are a steady source of methane. However, it is difficult to assess the sensitivity of pond methane emissions to ongoing warming and climate-change-induced drainage, because pond methane emissions show large temporal and spatial variability already on local scale.
We study this sensitivity on the landscape level with a new process-based model for Methane Emissions from Ponds (MeEP model), which simulates the three main pathways of methane emissions (diffusion, plant-mediated transport and ebullition) as well as the temperature profile of the water column and the surrounding soils. The model was set up for the polygonal tundra in the Lena River Delta. Due to a temporal resolution of one hour, it is capable of capturing the diurnal, day-to-day and seasonal variability in methane fluxes. MeEP also considers one of the main drivers of spatial variability - ground heterogeneity. Depending on where ponds form in the polygonal tundra, they can be classified as ice-wedge, polygonal-centre or merged-polygonal ponds. In MeEP, each of these pond types is simulated separately and the representation of these ponds was informed by dedicated measurements.
The model performance is validated against eddy-covariance measurements of methane fluxes and against in-situ measurements of the aqueous methane concentration, both obtained on Samoylov Island.  We will present results regarding the sensitivity of modeled methane emissions from ponds to warming and drainage on the landscape scale.

How to cite: Rehder, Z., Kleinen, T., Kutzbach, L., Stepanenko, V., and Brovkin, V.: Sensitivity of pond methane emissions in the Lena River Delta to climate changes in new model MeEP, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8387, https://doi.org/10.5194/egusphere-egu21-8387, 2021.

Juri Palmtag et al.

Arctic rivers deliver ≈11% of global river discharge into the Arctic Ocean, while this ocean represents only ≈1% of the global ocean volume. Ongoing climate warming across the Arctic, and specifically Siberia, has led to regional-scale changes in precipitation patterns, greater rates of permafrost thaw and active layer deepening, as well as enhanced riverbank and coastal erosion. Combined, these climatic and cryospheric perturbations have already resulted in increased freshwater discharge and changes to constituent loads (e.g. dissolved organic carbon - OC) supplied from land to the Arctic Ocean.

To date, the majority of studies examining terrestrial organic matter (OM) delivery to the Arctic Ocean have focused almost entirely on freshwater (riverine) or fully-marine environments and been conducted during late summer seasons – often due to logistical constraints. Despite this, an improved understanding of how OC is transformed, mineralised and released during transit through the highly reactive nearshore estuarine environment is critical for examining the fate and influence of terrestrial OM on the Arctic Ocean. Capturing seasonality over the open water period is also necessary to identify current OM fluxes to the ocean vs the atmosphere, and aid in constraining how future changes may modify them.

Here we focus upon carbon dioxide (CO2) and methane (CH4) measurements collected during six repeated transects of the Kolyma River and nearshore zone (covering ~120 km) from 2019. Transects spanned almost the entirety of the riverine open water season (June to September). We use these results, in parallel with gas concentrations derived from prior studies, to develop and validate a simple box-model of gas emissions from the nearshore zone.

Observations and model‐derived output data reveal that more than 50% of the cumulative gross delivery of CH4 and CO2 to the coastal ocean occurred during the freshet period with dissolved CH4 concentrations in surface water reaching 660 Nanomole per liter [nmol/l]. These results demonstrate the relevance of seasonal dynamics and its spatial variability which are needed in order to estimate greenhouse gas fluxes on an annual basis.

More accurate understanding of land-ocean carbon fluxes in the Arctic is therefore crucial to mitigate the effects of climate change and to support the decisions of policy makers.

How to cite: Palmtag, J., Manning, C., Bedington, M., Fuchs, M., Göckede, M., Grosse, G., Juhls, B., Lefebvre, P., Mollenhauer, G., Ogneva, O., Overduin, P., Polimene, L., Strauss, J., Torres, R., Zimov, N., and Mann, P.: Seasonal methane and carbon dioxide emissions from the coastal nearshore of the Kolyma river, Siberia., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9535, https://doi.org/10.5194/egusphere-egu21-9535, 2021.

Birgit Wild et al.

Subsea permafrost extends over vast areas across the East Siberian Arctic Ocean shelves and might harbor a large and vulnerable organic matter pool. Field campaigns have observed strongly elevated concentrations of CH4 in seawater above subsea permafrost that might stem from microbial degradation of thawing subsea permafrost organic matter, from release of CH4 stored within subsea permafrost, from shallow CH4 hydrates or from deeper thermogenic/petrogenic CH4 pools. We here assess the potential production of CH4, as well as CO2 and N2O by organic matter degradation in subsea permafrost after thaw. To that end, we employ a set of subsea permafrost drill cores from the Buor-Khaya Bay in the south-eastern Laptev Sea where previous studies have observed a rapid deepening of the ice-bonded permafrost table. Preliminary data from an ongoing laboratory incubation experiment suggest the production of both CH4 and CO2 by decomposition of thawed subsea permafrost organic matter, while N2O production was negligible. These data will be combined with detailed biomarker analysis to constrain the vulnerability of subsea permafrost organic matter to degradation to greenhouse gases upon thaw.

How to cite: Wild, B., Shakhova, N., Dudarev, O., Ruban, A., Kosmach, D., Tumskoy, V., Tesi, T., Joß, H., Nybom, I., Alexanderson, H., Jakobsson, M., Mazurov, A., Semiletov, I., and Gustafsson, Ö.: Potential greenhouse gas production by organic matter decomposition in thawing subsea permafrost, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5766, https://doi.org/10.5194/egusphere-egu21-5766, 2021.

Denis Chernykh et al.

The key area of the Arctic ocean for atmospheric venting of CH4 is the East Siberian Arctic Shelf (ESAS). The ESAS covers >2 million square kilometers (equal to the areas of Germany, France, Great Britain, Italy, and Japan combined). This vast yet shallow region has recently been shown to be a significant modern source of atmospheric CH4, contributing annually no less than terrestrial Arctic ecosystems; but unlike terrestrial ecosystems, the ESAS emits CH4 year-round due to its partial openness during the winter when terrestrial ecosystems are dormant. Emissions are determined by and dependent on the current thermal state of the subsea permafrost and environmental factors controlling permafrost dynamics. Releases could potentially increase by 3-5 orders of magnitude, considering the sheer amount of CH4 preserved within the shallow ESAS seabed deposits and the documented thawing rates of subsea permafrost reported recently.

The purpose of this work is to determine the methane ebullition fraction in water column: from the bottom to the surface, which is a key to evaluate quantitively methane release from the ESAS bottom through the water column into the atmosphere. A series of 351 experiments was carried out at to determine the quantity of methane (and other greenhouse gases) delivered by bubbles of various sizes through a water column into the atmosphere. It has been shown for depth up to 22 m (about 30% of the ESAS) that pure methane bubbles, depending on their diameter and water salinity, transported to the surface from 60.9% to 85.3% of gaseous methane.

This work was supported in part by grants from Russian Scientific Foundation (№ 18-77-10004 to DCh, DK, AK, № 19-77-00067 to EG), the Ministry of Science and Higher Education of the Russian Federation (grant ID: 075-15-2020-978 to IS). The work was carried out as a part of Federal[ПW1]  assignment № АААА-А17-117030110031-6 to AS.

How to cite: Chernykh, D., Kosmach, D., Konstantinov, A., Salomatin, A., Yusupov, V., Shakhova, N., Gustafsson, Ö., Gershelis, E., Dudarev, O., and Semiletov, I.: First experimental estimation of the methane ebullition fraction in water column from the bottom to the surface: application for the East Siberian Arctic Shelf, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4013, https://doi.org/10.5194/egusphere-egu21-4013, 2021.

Weichao Wu et al.

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.

Meet the authors in their breakout text chats

Wed, 28 Apr, 15:30–17:00

Chairpersons: Birgit Wild, Lisa Bröder, Örjan Gustafsson

Alienor Allain et al.

In present permafrost thawing context, dissolved organic matter (DOM) is a key component that controls organic and inorganic material transfer from soil to hydrographic systems. In terrestrial environments, vegetation is the main source of DOM, before degradation by microorganisms. DOM stoichiometry, aromaticity, composition or quantity control its fate, and referential data characterizing the initial DOM originating from plant biomass leaching are scarce.

To better understand its dynamic, this study focuses on the characterization of water extractable organic matter (“WEOM”: a proxy of DOM) of main plant species belonging to different plant functional types typical of the subarctic region (lichen, willow, birch, and Eriophorum).

Dissolved organic carbon (C) and dissolved nitrogen (N) contents of WEOM samples were measured, as well as organic C and total N contents of ground plant leaf samples (“bulk” samples). C/N ratio of bulk samples and WEOM fractions were compared to evaluate the potential extractability of C and N. The composition of both WEOM and bulk samples were characterized through solid state 13C Nuclear Magnetic Resonance (NMR) and compared. Absorbance and 3D fluorescence measurements were also performed on WEOM samples to characterize their optical properties.

WEOM is significantly more extractable in vascular plants compared to non-vascular ones. Moreover, N is more extractable than C in all lichen species and Eriophorum, whereas C is as extractable as N in Salix and Betula pubescens samples. Betula nana is the only species with C more extractable than N.

The solid state 13C NMR spectra of bulk sample are very similar to the spectra of corresponding WEOM, except for Eriophorum. For this species, carbonyl C contributes to 5% of bulk sample spectrum, compared to 14% of the WEOM spectrum.

Based on absorbance measurements, optical index were calculated: E2/E3 is significantly higher for non-vascular plants, whereas E2/E4, E3/E4 and slope ratio (SR) do not show significant difference between plant functional types. In 3D fluorescence spectra, the contribution of “Protein-like” peak is lower for vascular plants compared to lichens, and is maximum for Eriophorum.

Our results highlighted the influence of plant species on the quantity and quality of produced DOM: WEOM production process is different between vegetation species due to the quality, especially hydrophobicity and extractability of bulk OM components. The high contribution of C-N bonds in WEOM of Eriophorum might be especially important for potential complexation between DOM and trace elements like cadmium (Nigam et al., 2000). Likewise, aromatic C observed only in vascular plant WEOM samples are known to bond have a good affinity with many elements like iron, vanadium and chromium (Gangloff et al., 2014). Under climate change, vegetation cover of the Arctic region is evolving with the moving of the treeline northward and a local increase of the proportion of shrubs (Berner et al., 2013). Accordingly, significant change of DOM composition are expected with potential influence on organic and inorganic material dynamics.

Berner et al., (2013). Glob. Chang. Biol. 19:3449-3462

Gangloff et al., (2014). Geochim. Cosmochim. Ac. 130:21-41  

Nigam et al., (2000). Chem. Speciation Bioavailability 12:125-132

How to cite: Allain, A., Alexis, M. A., Agnan, Y., Humbert, G., Parlanti, E., Sourzac, M., Guittet, A., Anquetil, C., Aubry, E., Vaury, V., and Rouelle, M.: Chemical characterization of water extractable organic matter from plants: A better understanding of soil dissolved organic matter sources and path in permafrost thawing regions , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12002, https://doi.org/10.5194/egusphere-egu21-12002, 2021.

Sandra Raab et al.

As a major reservoir for organic carbon, permafrost areas play a pivotal role in global climate change. Vertical carbon fluxes as well as lateral transport from land to groundwaters and surface waters towards the ocean are highly dependent on various abiotic and biotic factors. These include for example temperature, groundwater depth, or vegetation community. During summer months, when soils thaw and lateral carbon transport within suprapermafrost groundwater bodies and surface waters occurs, flow patterns and therefore carbon redistribution may differ significantly between dry and wet conditions. Since dry soil conditions are expected to become more frequent in the future, associated shifts in carbon transport patterns play an important role in quantifying the carbon input into the water body linked to permafrost degradation.

This study focuses on hydrological and carbon transport patterns within a floodplain tundra site near Chersky, Northeast Siberia. We compared a wet control site with a site affected by a drainage ring built in 2004 to study the effect of water availability on carbon production and transport. Water table depths at both sites were continuously monitored with a distributed sensor network over the summer seasons 2016-2020. At several locations, water samples were collected in 2016 and 2017 to determine organic carbon concentrations (DOC) as well as carbon isotopes (e.g. ∆14C-DOC). Suprapermafrost groundwater and surface water from the drainage ditch and the nearby Ambolikha river were included in the analysis.

Our results focus on the physical hydrological conditions as well as on DOC and ∆14C-DOC observations. The spatio-temporal dynamics of water table depth revealed systematic differences between control and drained sites. The drained area showed a stronger decrease in water tables towards peak summer season in July and stronger reactions to precipitation events. The control area responded less pronounced to short-term changes. At the drained site, the main groundwater flow direction was stable throughout the measurement period. The control site was characterized by a shift in water flow confluence depending on increasing and decreasing water levels. DOC and ∆14C-DOC data showed that the highest concentrations of organic carbon and oldest DOC can be found in late summer. DOC concentrations were higher at the drained site compared to the wet site. We will show that the distribution of dissolved carbon can be directly related to hydrological flow patterns, and that understanding of these redistribution processes is essential for interpreting the carbon budget in disturbed permafrost.


How to cite: Raab, S., Goeckede, M., Vonk, J., Hildebrandt, A., and Heimann, M.: Links between hydrological patterns and lateral carbon fluxes: a comparison between a wet and a drained site on a Siberian permafrost floodplain tundra, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15020, https://doi.org/10.5194/egusphere-egu21-15020, 2021.

Lisa Bröder et al.

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.

Madiha Khadhraoui et al.

In natural porous environments, soil particle migration during flow plays an important role in soil stability and pollutant transport by affecting soil mechanical properties and water quality. In northern areas, permafrost degradation alters the subsurface connection pathways leading to mass movements and rearrangement of the soil. To date, few models have included the influence of temporal and spatial variations of flow velocity and porous media heterogeneity on the transport and deposition of suspended particles.

In this study, laboratory column experiments and a numerical model were used to investigate these issues. The laboratory column experiments were carried out under different flow rates and the effect of porous media heterogeneity was investigated using different grain size distributions. The soil columns were reconstituted from several samples taken in the studied site, the Tasiapik Valley, located in the discontinuous permafrost zone near Umiujaq, Nunavik, Québec. During the experiments, the spatio-temporal distribution of the porosity and the hydraulic conductivity was monitored using X-ray computed tomography imaging (CT-SCAN). Using the pore water velocity computed from the groundwater flow solution, the advection–dispersion transport equation with a first-order kinetic term for particle deposition was solved using the finite element model Heatflow/Smoker. The dependency of the attachment kinetics on the pore water velocity and on the porous media heterogeneity was included. The model was tested and validated with an analytical solution and calibrated with the experimental data. Our simulations highlight the roles of hydrodynamic conditions and soil characteristics on particle transport and deposition mechanisms and the susceptibility of the porous medium to thermo-suffosion in permafrost environments.

How to cite: Khadhraoui, M., Molson, J., and Bhiry, N.: Experimental and numerical investigation of microparticle transport and deposition in the context of permafrost thaw, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13611, https://doi.org/10.5194/egusphere-egu21-13611, 2021.

Nora Nedkvitne et al.

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.

Rachele Lodi et al.

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.

Julien Fouche et al.

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.

David Marcolino Nielsen et al.

When unprotected by sea-ice and exposed to the warm air and ocean waves, the Arctic coast erodes and releases organic carbon from permafrost to the surrounding ocean and atmosphere. This release is estimated to deliver similar amounts of organic carbon to the Arctic Ocean as all Arctic rivers combined, at the present-day climate. Depending on the degradation pathway of the eroded material, the erosion of the Arctic coast could represent a positive feedback loop in the climate system, to an extent still unknown. In addition, the organic carbon flux from Arctic coastal erosion is expected to increase in the future, mainly due to surface warming and sea-ice loss. In this work, we aim at addressing the following questions: How is Arctic coastal erosion projected to change in the future? How sensitive is Arctic coastal erosion to climate change?

To address these questions, we use a 10-member ensemble of climate change simulations performed with the Max Planck Institute Earth System Model (MPI-ESM) for the Coupled Model Intercomparison Project phase 6 (CMIP6) to make projections of coastal erosion at a pan-Arctic scale. We use a semi-empirical approach to model Arctic coastal erosion, assuming a linear contribution of its thermal and mechanical drivers. The pan-Arctic carbon release due to coastal erosion is projected to increase from 6.9 ± 5.4 TgC/year (mean estimate ± two standard deviations from the distribution of uncertainties) during the historical period (mean over 1850 -1950) to between 13.1 ± 6.7 TgC/year and 17.2 ± 8.2 TgC/year in the period 2081-2100 following an intermediate (SSP2.4-5) and a high-end (SSP5.8-5) climate change scenario, respectively. The sensitivity of the organic carbon release from Arctic coastal erosion to climate warming is estimated to range from 1.52 TgC/year/K to 2.79 TgC/year/K depending on the scenario. Our results present the first projections of Arctic coastal erosion, combining observations and Earth system model (ESM) simulations. This allows us to make first-order estimates of sensitivity and feedback magnitudes between Arctic coastal erosion and climate change, which can lay out pathways for future coupled ESM simulations.


How to cite: Nielsen, D. M., Pieper, P., Brovkin, V., Overduin, P., Ilyina, T., Baehr, J., and Dobrynin, M.: Sensitivity of organic carbon fluxes from Arctic coastal erosion to climate change, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13268, https://doi.org/10.5194/egusphere-egu21-13268, 2021.

Emily Bristol et al.

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 21st 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.

Manuel Ruben et al.

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.

Anders Dalhoff Bruhn et al.

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 (SR: 0.63 (±0.02), SUVA254: 1.65 (±0.06) respectively SR: 0.68 (±0.00), SUVA254: 1.17 (±0.06)) compared to the lacustrine deposit type (SR: 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.

Yanxi Pan and Ziyong Sun

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 SR 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.

Tina Sanders et al.

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.

Olga Ogneva et al.

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.

Bennet Juhls et al.

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.

Daria Polosukhina et al.

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.

Jannik Martens et al.

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.

Felipe Matsubara et al.

    Ongoing global warming is expected to accelerate the thaw of permafrost on land and to increase the input of terrigenous organic matter (terrOM) into the Arctic Ocean through coastal erosion and river discharge. Large remobilization of terrOM into the East Siberian Arctic Shelf (ESAS) dominates the organic matter in surface sediments over large parts of the shelf and its degradation contributes to ocean acidification. Previous studies have focused on the source apportionment of terrOM and the releases of CO2 and CH4 to the atmosphere from terrOM degradation; this study focuses on its diagenetic state during cross-shelf transport, since degradation is the link between permafrost thawing and greenhouse gases emissions. This study probes the degradation status of different terrOM components across the ESAS using various molecular and isotopic proxies and hence evaluates their differences to infer degradation.

    High-molecular weight (HMW) lipid compounds and lignin phenols are exclusively produced by terrestrial plants, providing protection, strength and rigidity to the plant structure. Owing to diagenesis, microbial degradation leads to 1) loss of functional groups, thus the ratios of HMW n-alkanoic acids, HMW n-alkanols and sterols relative to HMW n-alkanes decrease; 2) reduction of unsaturated to saturated carbons, so ratios of stanols relative to stenols increase; 3) a higher formation of carboxylic acids in the lignin polymer and hence ratios of acids to aldehydes of vanillyl (Vd and Vl) and syringyl (Sd and Sl) increase.

    The concentrations of lipid- and lignin-derived products per sediment specific surface area decreased with offshore distance of the samples. During cross-shelf transport, the biomarker degradation proxies showed an increasing degradation for Sd/Sl, Vd/Vl, the “tannin-like” compound 3,5-dihydrobenzoic acid to vanillyl (3,5-Bd/V), β-sitostanol/ β-sitostenol and Carbon Preference Index (CPI) of HMW n-alkanes. Some other proxies showed no clear trend from inner to outer shelf and such inconsistent patterns are currently being investigated to better understand both the usefulness/response of different proxies and of the lability of terrOM in the ESAS. While β-sitostanol/β-sitostenol and CPI HMW n-alkane did not show strong differences between the East Siberian Sea and the Laptev Sea, Vd/Vl and Sd/Sl ratios indicated stronger degradation on the outer Laptev Sea and 3,5-Bd/V ratios indicated stronger degradation in the outer eastern East Siberian Sea. Such differences could reflect source properties of terrOM entering the ESAS, such as differences in source vegetation or transport pathway, i.e. coastal erosion or river discharge.

How to cite: Matsubara, F., Wild, B., Martens, J., Wennström, R., Dudarev, O., Semiletov, I., and Gustafsson, Ö.: Multi-proxy evaluation of terrestrial organic matter degradation across the East Siberian Arctic Seas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12328, https://doi.org/10.5194/egusphere-egu21-12328, 2021.

Junjie Wu et al.

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.

Eduardo Queiroz Alves et al.

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.

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