Displays

Permafrost thaw is altering northern ecosystems and the services they provide at scales ranging from local subsidence to global climate feedbacks. In organic-rich peatlands, thermokarst initiation and spread rates are increasing with rising mean annual air temperatures, changes in wildfire, and human land use. This presentation will outline empirical and modeling approaches to better understand the consequences of thermokarst in peatlands as well as other types of northern terrains on carbon cycling, wildlife, and other aspects of ecosystem services.  We are using fine scale datasets and remote sensing to map thermokarst coverage and expansion in both the Northwest Territories, Canada and interior Alaska. Using chronosequences and regional gradients, we are studying thermokarst impacts along gradients of time-since-thaw. Through a Permafrost Carbon Network synthesis, we developed conceptual and numerical models to understand how thermokarst development (formation, stabilization, re-accumulation of permafrost in some conditions) affects carbon storage and release. We are using a combination of empirical and modelled data to test hypotheses about climatic, ecological, and Quaternary controls on thermokarst rates and subsequent impacts on ecosystem services. We demonstrate that thermokarst in peat-rich landscapes are hotspots for permafrost carbon release primarily through methane emissions, have the potential to impact hunter movement and safety, and affect caribou habitat quality.

How to cite: Turetsky, M., Gibson, C., and Dieleman, C.: Impacts of thermokarst on permafrost carbon losses and ecosystem services, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22219, https://doi.org/10.5194/egusphere-egu2020-22219, 2020.

Almost 65% of Siberian forests and 23% of tundra vegetation grow in permafrost zone. According to our estimate, carbon stocks in the soils of forest and tundra ecosystems of Yakutia (Eastern Siberia, Russia) amount to 17 billion tons (125.5 million hectares of forest and 37 million hectares of tundra in total) that is about 25% of total carbon resource in the forest soils of the Russian Federation.
This presentation is compiled from the results of many years time series investigations conducted on the study of carbon cycle in permafrost-dominated forests with different productivity and typical tundra and along Great Lena river basin including Aldan and Viluy tributaries. 
Seasonal photosynthesis maximum of forest canopy vegetation in dry years falls into June, and in humid ones – into July. During the growing season the woody plants of Yakutia uptake from 1.5 to 4.0 t C ha^-1 season^-1 depending on water provision. Night respiration is higher in dry and extremely dry years (10.9 and 16.1% respectively). The productive process of tree species in Eastern Siberia is limited by endogenous (stomatal conductance) and exogenous (provision with moisture and nutrients, nitrogen specifically) factors. The increase of an atmospheric precipitation after long 2-3 annual droughts accompanied with strong surge in photosynthetic activity of forest plants is almost 2.5 times. 
The temperature of soil is a key factor influencing soil respiration in the larch forests. Average soil respiration for the growing season comes to 6.9 kg C ha^-1 day^-1, which is a characteristic of Siberian forests. Annual average soil emission is 4.5±0.6 t C ha^-1 yr^-1.
As our multi-year studies showed, there is significant interannual NEE variation in the Central Yakutia larch forest, while in the Southern Yakutia  larch forest and tundra ecosystem variation is more smooth, because the climatic conditions in these zones (close to the mountain and sea)  are less changeable than in sharply continental Central Yakutia. 
According to our long-term eddy-correlation data, the annual uptake of carbon flux (NEE) in the high productivity larch forest of South eastern Yakutia, 60N – 2.43±0.23 t C ha^-1 yr^-1, in the moderate productivity larch forest of the Central Yakutia, 62N makes 2.12±0.34 t C ha^-1 yr^-1 and in the tundra zone, 70N – 0.75±0.14 t C ha^-1 yr^-1.
Interannual variation of carbon fluxes in permafrost forests in Northeastern Russia (Yakutia) makes 1.7-2.4 t C ha^-1 yr^-1 that results in the upper limit of annual sequestering capacity of 450-617 Mt C yr^-1. In connection with climate warming there is a tendency of an increase in the volume of carbon sequestration by tundra and as opposed to decrease by forest ecosystem in the result of prolongation of the growing season and changing of plant successions.  This is also supported by changes in land use as well as by CO₂ sequestration in the form of fertilizer. 
According our biogeochemical investigation annual flux of carbon from main in Eastern Siberia Lena river hydrological basin is almost 6.2 Mt C yr^-1 including 28% at Aldan and 14% at Viluy rivers.

How to cite: Maximov, T., Dolman, H., Kotani, A., Anderson, P., Maksimov, A., and Petrov, R.: Carbon cycle of permafrost transect: main terrestrial and hydrological ecosystems of Eastern Siberia , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4322, https://doi.org/10.5194/egusphere-egu2020-4322, 2020.

Permafrost-affected river plains are highly diverse in discharge regime, floodplain morphology, channel forms, channel mobility and ecosystems. Frozen floodplains range from almost barren systems with high channel mobility, to extensive wetland areas with low channel mobility, abundant abandoned channels, back-swamps and shallow floodplain lakes. Floodplain processes are increasingly affected by climate-induced changes in river discharge and temperature regime: changes in the dates of freeze-up, break-up and spring floods, and changes in the discharge distribution throughout the year.

In permafrost floodplains, changes in flooding frequency, flood height and water temperature affect active layer thickness, subsidence and erosion processes. Data from the Northeast Siberian Berelegh river floodplain (a tributary to the Indigirka river) demonstrate that increasing spring flood height potentially causes permafrost thaw, soil subsidence and increase of the floodplain area. INSAR (interferometric synthetic aperture radar) data indicate that poorly drained areas in this region are affected by soil subsidence. Morphological evidence for subsidence of the river floodplain is abundant, and river-connected lakes show expansion features also seen in thaw lakes.

These floodplain wetland ecosystems are also affected by changes in the discharge regime and permafrost. On the one hand, floodplains are sites of active sedimentation of organic matter-rich sediments and sequestration of carbon. This carbon is derived from upstream erosion of permafrost and vegetation, and from autochthonous primary production. Nutrient supply by flood waters supports highly productive ecosystems with a comparatively large biomass.

On the other hand, these ecosystems also emit high amounts of CH₄, which may be affected by flooding regime. In the example presented here, the CH₄ emission from floodplain wetlands is about seven times higher that the emission from similar tundra wetlands outside the floodplain.

The dynamic nature of floodplains hinders carbon and greenhouse gas flux measurements. Better quantification of greenhouse gas fluxes from these floodplains, and their relation with river regime changes, is highly important to understand future emissions from thawing permafrost. Given the difficulties of surface greenhouse gas flux measurements, recent remote sensing material could play an important role here.

How to cite: van Huissteden, K., Teshebaeva, K., Cheung, Y., Noorbergen, H., and van Persie, M.: Climate change and the carbon cycle of frozen floodplains., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1445, https://doi.org/10.5194/egusphere-egu2020-1445, 2020.

Due to the climate warming, permafrost on the Qinghai-Tibet Plateau (QTP) was degradating in the past decades. Since its impacts on East Asian monsoon, and even on the global climate system, it is fundamental to reveal permafrost status, changes and its physical processes. Based on previous research results and new observation data, this paper reviews the characteristics of the status of permafrost on the QTP, including the active layer thickness (ALT), the spatial distribution of permafrost, permafrost temperature and thickness, as well as the ground ice and soil carbon storage in permafrost region.

The results showed that the permafrost and seasonally frozen ground area (excluding glaciers and lakes) is 1.06 million square kilometters and 1.45 million square kilometters on the QTP. The permafrost thickness varies greatly among topography, with the maximum value in mountainous areas, which could be deeper than 200 m, while the minimum value in the flat areas and mountain valleys, which could be less than 60 m. The mean value of active layer thickness is about 2.3 m. Soil temperature at 0~10 cm, 10~40 cm, 40~100 cm, 100~200 cm increased at a rate of 0.439, 0.449, 0.396, and 0.259°C/10a, respectively, from 1980 to 2015. The increasing rate of the soil temperature at the bottom of active layer was 0.486 oC/10a from 2004 to 2018.

The volume of ground ice contained in permafrost on QTP is estimated up to 1.27×10⁴ km³ (liquid water equivalent). The soil organic carbon staored in the upper 2 m of soils within the permafrost region is about 17 Pg. Most of the research results showed that the permafrost ecosystem is still a carbon sink at the present, but it might be shifted to a carbon source due to the loss of soil organic carbon along with permafrost degradation.

Overall, the plateau permafrost has undergone remarkable degradation during past decades, which are clearly proven by the increasing ALTs and ground temperature. Most of the permafrost on the QTP belongs to the unstable permafrost, meaning that permafrost over TPQ is very sensitive to climate warming. The permafrost interacts closely with water, soil, greenhouse gases emission and biosphere. Therefore, the permafrost degradation greatly affects the regional hydrology, ecology and even the global climate system.

How to cite: Zhao, L., Hu, G., Zou, D., Li, R., Sheng, Y., and Pang, Q.: Status, Changes and Impacts of Permafrost on Qinghai-Tibet Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6246, https://doi.org/10.5194/egusphere-egu2020-6246, 2020.

Mean annual temperatures in interior Alaska, currently -1°C, are projected to increase as much as 5°C by 2100. An increase in mean annual temperatures is expected to degrade permafrost and alter hydrogeology, soils, vegetation, and microbial communities. Ice and carbon rich “yedoma type” permafrost in the area is ecosystem protected against thaw by a cover of thick organic soils and mosses. As such, interactions between vegetation, permafrost ice content, the snow pack, and the soil thermal regime are critical in maintaining permafrost. We studied how and where vegetation and soil surface characteristics can be used to identify subsurface permafrost composition. Of particular interest were potential relationships between permafrost ice content, the soil thermal regime, and vegetation cover. We worked along 400-500 m transects at sites that represent the variety of ecotypes common in interior Alaska. Airborne LiDAR imagery was collected from May 9-11, 2014 with a spatial resolution of 0.25 m. During the winters from 2013-2019 snow pack depths have been made at roughly 1 m intervals along site transects using a snow depth datalogger coupled with a GPS. In late summer from 2013-2019 maximum seasonal thaw depths have been measured at 4 m intervals along each transect. Electrical resistivity tomography measurements were collected across the site transects. A variety of machine learning geospatial analysis approaches were also used to identify relationships between ecosystem characteristics, seasonal thaw, and permafrost soil and ice composition. Wintertime measurements show a clear relationship between vegetation cover and snow depth. Interception (and shallow snow) was evident in the birch and white spruce forests and where dense shrubs are present while the open tussock and intermittent shrub regions yield the greatest snow depths. Results from repeat seasonal thaw depth measurements also show a strong relationship with vegetation where mixed birch and spruce forest is associated with the deepest seasonal thaw. The tussock/shrub and spruce forest zones consistently exhibited the shallowest seasonal thaw. Roughly 60% of the seasonal thaw along the transects occurred by mid-July and downward movement of the thaw front had mostly ceased by late August with little additional thaw between August 20 and early October. Summer precipitation shows a relationship with seasonal thaw depth with the wettest summers associated with the deepest thaw. Results from this study identify clear relationships between ecotype, permafrost composition, and seasonal thaw dynamics that can help identify how and where permafrost degradation can be expected in a warmer future arctic.

How to cite: Douglas, T., Hiemstra, C., Anderson, J., and Zhang, C.: Identifying vegetation-geomorphology relationships in permafrost with airborne LiDAR, electrical resistivity tomography, seasonal thaw depth measurements, and machine learning, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1900, https://doi.org/10.5194/egusphere-egu2020-1900, 2020.

Inland waters (rivers, lakes and ponds) are important conduits for the emission of terrestrial carbon in Arctic permafrost landscapes. These emissions are driven by turnover of contemporary terrestrial carbon and additional “pre-aged” (Holocene and late-Pleistocene) carbon released from thawing permafrost soils, but the magnitude of these source contributions to total inland water carbon fluxes remains unknown. Here we present unique simultaneous radiocarbon age measurements of inland water CO₂, CH₄ and dissolved and particulate organic carbon in northeast Siberia during summer. We show that >80% of total inland water carbon emissions were contemporary in age, but that pre-aged carbon contributed >50% at sites strongly affected by permafrost thaw. CO₂ and CH₄ were younger than dissolved and particulate organic carbon, suggesting emissions were primarily fuelled by contemporary carbon decomposition. The study region was a net carbon sink (-876.9 ± 136.4 Mg C for 25 July to 17 August), but inland waters were a source of contemporary (16.8 Mg C) and pre-aged (3.7 Mg C) emissions that respectively offset 1.9 ± 1.2% and 0.4 ± 0.3% of CO₂ uptake by tundra (‑897 ± 115 Mg C). Our findings reveal that inland water carbon emissions from permafrost landscapes may be more sensitive to changes in contemporary carbon turnover than the release of pre-aged carbon from thawing permafrost.

How to cite: Dean, J., Meisel, O., Martyn Roscoe, M., Belelli Marchesini, L., Garnett, M., Lenderink, H., van Logtestijn, R., Borges, A., Bouillon, S., Lambert, T., Röckmann, T., Maximov, T., Petrov, R., Karsanaev, S., Aerts, R., van Huissteden, J., Vonk, J., and Dolman, H.: Siberian Arctic inland waters emit mostly contemporary carbon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17416, https://doi.org/10.5194/egusphere-egu2020-17416, 2020.

The release of vast amounts of organic carbon during thawing of high-latitude permafrost is an urgent issue of global concern, yet it is unclear what controls how much carbon will be released and how fast it will be subsequently metabolized and emitted as greenhouse gases. Binding of organic carbon by iron(III) oxyhydroxide minerals can prevent carbon mobilization and degradation. This “rusty carbon sink” has already been suggested to protect organic carbon in soils overlying intact permafrost. However, the extent to which iron-bound carbon will be mobilized during permafrost thaw is entirely unknown. We have followed the dynamic interactions between iron and carbon across a thaw gradient in Abisko (Sweden), where wetlands are expanding rapidly due to permafrost retreat. Using both bulk (selective extractions, EXAFS) and nanoscale analysis (correlative SEM and nanoSIMS), we found that up to 19.4±0.7% of total organic carbon is associated with reactive iron minerals in palsa underlain by intact permafrost. However, during permafrost collapse, the rusty carbon sink is lost due to more reduced conditions which favour microbial Fe(III) mineral dissolution. This leads to high dissolved Fe(II) (2.93±0.42 mM) and organic carbon concentrations (480.06±34.10 mg/L) in the porewater at the transition of desiccating palsa to waterlogged bog. Additionally, by combining FT-ICR-MS and greenhouse gas analysis both in the field and in laboratory microcosm experiments, we are currently determining the fate of the mobilized organic carbon directly after permafrost collapse. Our findings will improve our understanding of the processes controlling organic carbon turnover in thawing permafrost soils and help to better predict future greenhouse gas emissions.

How to cite: Patzner, M. S., Logan, M., Mueller, C. W., Joss, H., Anthony, S. E., Scholten, T., Byrne, J. M., Borch, T., Kappler, A., and Bryce, C.: Organic carbon sorbed to reactive iron minerals released during permafrost collapse , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1465, https://doi.org/10.5194/egusphere-egu2020-1465, 2020.

Current global climate changes represent a threat for the stability of the polar regions and may result in cascading broad impacts. Studies conducted on permafrost in the Arctic regions indicate that these areas may store almost twice the carbon currently present in the atmosphere. Therefore, permafrost thawing may potentially cause a significant increase of greenhouse gases concentrations in the atmosphere, exponentially rising the global warming effect. Although several studies have been carried out in the Arctic regions, there is a paucity of data available from the Southern Hemisphere. The Seneca project aims to fill this gap and to provide a first degree of evaluations of gas concentrations and emissions from permafrost and/or thawed shallow strata of the Dry Valleys in Antarctica. The Taylor and Wright Dry Valleys represent one of the few Antarctic areas that are not covered by ice and therefore represent an ideal target for permafrost investigations.

Here we present the preliminary results of a multidisciplinary field expedition conducted during the Antarctic summer in the Dry Valleys, aimed to collect and analyse soil gas and water samples, to measure CO₂ and CH₄ flux exhalation, to investigate the petrological soil properties, and to acquire geoelectrical profiles. The obtained data are used to 1) derive a first total emission estimate for methane and carbon dioxide in this part of the Southern Polar Hemisphere, 2) locate the potential presence of geological discontinuities that can act as preferential gas pathways for fluids release, and 3) investigate the mechanisms of gas migration through the shallow sediments. These results represent a benchmark for measurements in these climate sensitive regions where little or no data are today available.

How to cite: Ruggiero, L., Sciarra, A., Mazzini, A., Mazzoli, C., Romano, V., Tartarello, M. C., Florindo, F., Ascani, M., Wilson, G., Dagg, B., Hardie, R., Anderson, J., Worthington, R., Lupi, M., Bigi, S., Ciotoli, G., Graziani, S., Fischanger, F., and Sassi, R.: SourcE and impact of greeNhousE gasses in AntarctiCA: the Seneca project , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1431, https://doi.org/10.5194/egusphere-egu2020-1431, 2020.

Ice wedge (IW) polygons form through thermal contraction induced by winter cooling of ice-rich permafrost which results in the formation of cracks. Hoar frost develops in the cracks in winter and meltwater infills the cracks during spring and freezes. As the cracking and infilling occurs repeatedly, IWs grow, leading to characteristic surface morphology with depressions or troughs aligned on the axis of the IW and raised rims or ridges on either side. Surface expression of IW is either characterized as low-centered polygons or high-centered polygons, the former being associated with the first stages of IW development, and the latter with IW degradation. Because IWs represent important excess ice close to the surface, considerable local subsidence and related effects on landscape parameters, such as vegetation and moisture, are likely to occur upon degradation.

IW polygons distribution, morphometry and state were characterized in the Tombstone Territorial Park (Central Yukon, Canada) using semi-automated remote sensing techniques, field observations and laboratory analyses. The data is used to define determining landscape factors for IW polygons occurrence, to characterise the stages of the IWs development and/or degradation and to estimate the volume of buried ice in the region. Results show that elevation, slope and material are important elements defining IW polygons distribution. The relationship between landscape factors and stages of development is not as clear, and, despite climate changes being homogenous in the area, IW development and degradation is very heterogenous, as shown by the differing moisture, greenness and brightness signals across the polygonal terrain.

How to cite: Frappier, R. and Lacelle, D.: Ice-wedge polygons distribution, morphometry and state in the Tombstone Territorial Park, Central Yukon, Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12044, https://doi.org/10.5194/egusphere-egu2020-12044, 2020.

At present, the degradation of permafrost caused by climate warming raises serious concerns of scientists and the public around the world. As a result of degradation of permafrost containing a huge amount of organic material and the decomposition of this organic material, the greenhouse effect can increase significantly. Some scientists estimate that the amount of carbon in the permafrost is more than two times than there is in atmospheric carbon dioxide (Schuur E. A. G.et al., 2015).  Besides, a large amount of greenhouse gasses, mostly methane, is already contained in watery glacier bottoms, where these gasses build up through anaerobic organic decomposition (Burns R., 2018). Therefore, there are concerns that permafrost thaw and glacier retreat as the Earth warms will lead to new greenhouse gasses being released into the atmosphere, thus further accelerating the global warming process. 
Our research devoted to this problem was carried out at the archaeological Upper Paleolithic site Divnogorie 9 (50.9649° N, 39.3031° E) in the National Park “Divnogorie”. Our study area occupies the southern part of the Middle Russian Upland (the East European Plain). It has experienced several Quaternary glaciations: the Don, Dnepr, Moscow, and Valdai Glaciations. The facts of the presence of permafrost and its degradation during the late Pleistocene and Holocene are established here as well. The site is located at the right bank of the Tikhaya Sosna River, a right tributary of the Don River. The Don River basin is a world known area because of high concentration of the Upper Paleolithic archaeological sites here - Kostenki-Borshevo district (51°23'40'' N, 39º30'31''E) which contains 26 open-air mammoth remnant sites (38-18 ka BP). 
Divnogorie 9 is an unique site in Europe which is well-known for numerous findings of fossilized equestrian remains of wild horses - more than eight thousands samples. Our most detailed study of the Quaternary deposits was carried out at a 18-m thick section. Bones are concentrated in seven layers (levels). This section exposes several paleosol layers, as well. Estimates of the radiocarbon age of the fossils and paleosol layers here yielded 14-12 ka BP. We studied the organic carbon from paleo-soils of Divnogorie 9. The abundant presence of such large grazers as horses and especially mammoths during the Late Pleistocene supports the widespread existence of high productivity grasslands and organic-rich soils. 
However, the results of our analysis do not show a significant amount of organic carbon in these paleo-soils at the present. It may possibly be an indication that the originally carbon rich permafrost and subglacial deposits lost their carbon upon permafrost thaw and glacial retreat during the transition from the last glaciation to the Holocene. This ancient carbon was massively released into the atmosphere and to the aquatic systems during that time. At the same time, there were not widespread catastrophic consequences to the Earth’s environment except possibly for the extinction of mammoths and other large fauna in the arctic and subarctic. These results provide some cautious optimism about the severity in current amount of changes and consequences thereof. 

How to cite: Romanovskaya, M., Romanovsky, V., and Kuznetsova, T.: Global climate warming: permafrost degradation and expected consequences, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3859, https://doi.org/10.5194/egusphere-egu2020-3859, 2020.

Thawing of permafrost and the resulting decomposition of previously frozen organic matter constitute a positive feedback to global climate. However, contrasting mechanisms are at play. Gradual increases in thawing depth and temperature are associated with enhanced vegetation growth, most notably in shrubs (“greening”). In ice-rich permafrost, abrupt thaw (thermokarst) results in disturbance of vegetation and surface wetting, which may result in an opposing trend (“browning”).

We determined the balance of shrub decline and expansion in an ice-rich lowland tundra ecosystem in north-Eastern Siberia using vegetation classification and change analysis. We used random forest classification on 3 very high resolution commercial satellite images gathered between 2010 and 2019 (GeoEye-I and WorldView-II). To mitigate (slight) differences in sensor properties and vegetation phenology, a spatio-temporal implementation of Potts model was used to utilize both spectral properties of a pixel and its degree of correspondence with spatially and temporally neighbouring pixels. This reduced artefacts in change detection substantially and improved accuracy of classification for all three images.

We found that shrub vegetation declines in this lowland tundra ecosystem. Areas of thaw features (thermokarst ponds, thermoerosion gullies) and aquatic plant types (sedges and peat mosses) however show an increasing trend. Markov Chain analysis reveals that thaw features display a succession from open water / mud to sedges to peat moss. 

This transition from shrub dominated to wetland species dominated tundra may have important implications for this ecosystem's greenhouse gas balance and is indicative of wetter conditions. Thermokarst may be an important driver of such change, as thaw features are found to expand at the expense of shrub vegetation and show rapid colonization by aquatic species. 

How to cite: Magnússon, R., Heijmans, M. M. P. D., Limpens, J., van Huissteden, K., Kleijn, D., and Maximov, T. C.: Arctic greening, Arctic browning or Arctic drowning?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7727, https://doi.org/10.5194/egusphere-egu2020-7727, 2020.

Boreal forests are located at latitudes that are predicted to experience some of the greatest warming on the planet. Forests growing on permafrost may be particularly vulnerable, with accelerated soil warming and permafrost degradation linked to changing patterns of tree growth and longevity. Many have speculated that thawing permafrost, through its effects on soil water content and ground stability, will increase forest mortality across the boreal region. However, recent evidence indicates mixed forest responses to permafrost thaw. In some areas, the onset of thaw is followed by increased tree growth and increased forest cover area. In other sites, thaw has been linked to decreased growth and forest cover loss. It is currently poorly understood what determines these contrasting responses, and the roles that different environmental and climatic factors may play. This leads to two major issues: (1) uncertainties in predicting the effects of future permafrost thaw on carbon dynamics in northern ecosystems, and (2) poor understanding of where scientific and conservation efforts should be focused. Here, we present a review of the recent evidence of permafrost thaw effects on boreal forest dynamics and propose an explanation for the differing responses across sites. We argue that the outcome is controlled by a set of factors that influence two major pathways and the interactions between them: (1) permafrost-soil water content and (2) soil water content-plant growth. We present a series of conceptual models explaining these interactions and highlight the largest sources of uncertainties. Based on these, we propose a set of hypotheses and methodologies to guide future research in this area.

How to cite: Kulawska, A., Pugh, T. A. M., Kettridge, N., MacKenzie, R., and Ullah, S.: What governs the effects of permafrost thaw on boreal forest dynamics? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5404, https://doi.org/10.5194/egusphere-egu2020-5404, 2020.

Model projections of CO₂ and CH₄ exchange in Arctic tundra during the next century diverge widely.  In this modelling study, we used ecosys to examine how climate change will affect CO₂ and CH₄ exchange through its effects on net primary productivity (NPP), heterotrophic respiration (R_h) and thereby on net ecosystem productivity (NEP) in landform features (troughs, rims, centers) of a coastal polygonal tundra landscape at Barrow AK. The model was shown to simulate diurnal and seasonal variation in CO₂ and CH₄ fluxes associated with those in air and soil temperatures (T_a and T_s) and soil water contents (q) under current climate in 2014 and 2015. During RCP 8.5 climate change from 2015 to 2085, rising T_a, atmospheric CO₂ concentrations (C_a) and precipitation  (P) increased NPP from 50 – 150 g C m^-2 y^-1,  consistent with current biometric estimates, to 200 – 250 g C m^-2 y^-1, depending on feature elevation. Concurrent increases in R_h were slightly smaller, so that net CO₂ exchange rose from values of -25 (net emission) to +50 (net uptake) g C m^-2 y^-1 to ones of -10 to +65 g C m^-2 y^-1, again depending on feature elevation. Large increases in R_h with thawing permafrost were not modelled. Increases in net CO₂ uptake were largely offset by increases in CH₄ emissions from 0 – 6 g C m^-2 y^-1 to 1 – 20 g C m^-2 y^-1, depending on feature elevation, reducing gains in NEP. Increases in CH₄ emissions with climate change were mostly attributed to increases in T_a, but also to increases in C_a and P. These increases in net CO₂ uptake and CH₄ emissions were modelled with hydrological boundary conditions that were assumed not to change with climate.  Both these increases were smaller if boundary conditions were gradually altered to increase landscape drainage during model runs with climate change. The model was then applied to the entire permafrost zone of North America to project RCP 8.5 climate change effects on active layer depth and ecosystem productivity by 2100.  

How to cite: Grant, R.: Climate change impacts on CO2 and CH4 exchange in an Arctic polygonal tundra depend on changes in vegetation and drainage, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2027, https://doi.org/10.5194/egusphere-egu2020-2027, 2020.

The Arctic is warming at twice the rate of the rest of the world, causing precipitation to shift from snowfall to rainfall, permafrost to thaw, longer snow-free land and ice-free lakes, and increased evaporation. Thermokarst lakes across the Arctic have experienced different changes over the past decades: in some regions, lakes are expanding through thawing adjacent permafrost, while in other regions they are drying up and shrinking, or not changing at all. It is important to understand what governs lake water balance as it affects lake ecosystems that support large populations of migratory birds and fish; are important to local communities for food and recreation; and control the flux of carbon and other nutrients from thawing permafrost into lakes. For example, lake inflow, evaporation and water residence time affect the concentration of nutrients within lakes, ultimately affecting the aquatic ecosystem and greenhouse gas release. Previous research has focused on quantifying the water inputs and outputs of individual lakes, but a better understanding of the drivers and processes controlling lake water balances is required to understand how they will respond to a changing climate.

We measured lake water flux components at multiple spatial and temporal scales across the 5000 km² boreal – tundra transition zone between Inuvik and Tuktoyaktuk, Northwest Territories, Canada. Lake water flux components were measured at two adjacent thermokarst lakes with different ratios of lake area to catchment area (LACA), from 2017 – 2019. Also, water isotope samples were collected from March – September 2018 from ~100 lakes across 2000 km². From these water isotope compositions we estimated the ratio of evaporation to inflow, residence time, and the mixture of snowmelt and rainfall runoff in each lake. Catchments of all 7500 lakes in the region were delineated using a high-resolution digital elevation model in order to estimate their LACA, and evaluate connectivity between lakes.

Paired lake water balance measurements showed that the lake with a larger LACA had a residence time an order of magnitude shorter than the larger lake, and displayed larger fluctuations in water level. Also, the ratio of evaporation to inflow was significantly larger in lakes with smaller LACA. Water isotope compositions showed that only 10-50% of a lake’s water is replaced by snowmelt in spring, as the majority of snowmelt runoff flowed overtop of lake ice and through the lake outlet. Deeper lakes had significantly less snowmelt mixing, as the volume of water for the snowmelt to mix with was greater than in shallower lakes. These results show that lake water balance can be characterized using lake and catchment properties, allowing future research to more easily characterize lake hydrology and build further understanding about how lake water balance is connected to other aspects of the permafrost environment.

How to cite: Wilcox, E. J., Walker, B., Hould - Gosselin, G., Sonnentag, O., Wolfe, B. B., and Marsh, P.: Landscape Controls on the Hydrological Variability of Thermokarst Lakes between Inuvik and Tuktoyaktuk, NWT , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9279, https://doi.org/10.5194/egusphere-egu2020-9279, 2020.

    Circumpolar permafrost is degrading under anthropogenic global warming, thus the large amount of soil organic carbon in it would be vulnerable to microbial decomposition and further aggravating future warming. However, solar radiation modification (SRM), as a theoretical approach to reducing some of the impacts of anthropogenic climate change, hopefully could mitigate the permafrost degradation and slow down permafrost carbon loss. Here we use two solar geoengineering experiments came up in CMIP6/GeoMIP6 -- G6solar and G6sulfur, to explore changes in circumpolar permafrost carbon under solar radiation modification scenarios. Earth system models' simulations show that under G6 scenarios, annual mean surface air temperature in circumpolar permafrost region is about 5℃ lower relative to the high forcing scenario SSP5-8.5 by year 2100, with a growing trend but remains below 0℃ from 2015 to 2100, which is close to that in the medium forcing scenario SSP2-4.5. The lower temperature causes lower degradation rate of permafrost area. In SSP5-8.5 scenario, almost all the permafrost thaws by year 2100, but up to half of it remains frozen in SSP2-4.5 and G6 scenarios compared to year 2015. The lower temperature also results in less carbon assimilation in this area, thus the lower vegetation carbon accumulation. By 2100, a maximum soil carbon loss of 18.09 PgC under SSP5-8.5 scenario regarding to different model constructions, while in G6 the soil carbon loss could be reduce to 3.70 PgC, even less than that of 5.29 PgC in SSP2-4.5 scenario.

How to cite: Chen, Y. and Ji, D.: Solar Radiation Modification Slows Down Permafrost Carbon Loss , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1740, https://doi.org/10.5194/egusphere-egu2020-1740, 2020.

Large quantities of carbon are stored in the terrestrial permafrost of the Arctic region where the rate of climate warming is two to three times more than the global mean and the largest temperature anomalies observed in autumn and winter. The quantification of the impact of climate warming on the degradation of permafrost and the associated potential release to the atmosphere of carbon stocked in the soil in the form of greenhouse gases, thus further increasing the radiative forcing of the atmosphere, is a research priority in the field of biogeosciences. Land-atmosphere turbulent fluxes of CO₂ and CH₄ have been monitored at the tundra site of Kytalyk in north-eastern Siberia (70,82 N; 147.48 E) by means of eddy covariance since 2003 and 2008, respectively; regular measurement campaigns have been carried out since then. Here we present results of the seasonal CO₂ budget of the tundra ecosystem for the 2003-2016 period based on observations encompassing the permafrost thawing season and analyze the inter-annual differences in the seasonal patterns of CO₂ fluxes considering the separate the contribution of climatic drivers and ecosystem functional parameters relative to the processes of respiration and photosynthesis. The variability of the CO₂ budget is also discussed in view of the impact of the timing and length of the snow free period.

The Kytalyk tundra acted as an atmospheric carbon dioxide sink with relatively small inter-annual variability (-96.1±11.9 gC m^-2) during the snow free season and the seasonal CO₂ budget did not show any trend over time. The pronounced meteorological variability characterizing Arctic summers was a key factor in shaping the length of the carbon uptake period, which did not progressively increased despite its tendency to start earlier, and in determining the magnitude of CO₂ fluxes. No clear evidence of inter-annual changes in the eco-physiological response parameters of CO₂ fluxes to climatic drivers (global radiation and air temperature) was found along the course of the analysed period. Methane fluxes had a minor contribution to the carbon budget of the snow-free season representing on average an emission of 3.2 gC m^-2 (2008-2016) with apparently small inter-annual variability. Similarly, the size of the carbon exported laterally from the ecosystem in the form of dissolved organic carbon flux amounted to 3.1 gC m^-2 as determined experimentally. After including these last terms in the budget, the magnitude of the carbon sink associated with the net ecosystem productivity is reduced by 6%, while the GHG budget still denotes a sink of -60.4 ± 11.9 gC-CO₂eq (methane GWP over 100-year time horizon).

The monitored tundra was to date exerting a steady climate warming mitigation effect as far as the snow free season is concerned, however the figure of its carbon sink could be potentially sensibly lower due to overlooked emissions in the autumn freeze-up and early winter periods. Also, nonlinear accelerations in the permafrost degradation could happen once tipping points in the Arctic climate are exceeded. Both aspects underline the relevance of long term and continuous biogeochemical monitoring in permafrost tundra environments.

How to cite: Dolman, H., van Huissteden, J., Dean, J., Maximov, T., Petrov, R., and Belelli Marchesini, L.: The carbon budget of a tundra in the north-eastern Russian Arctic during the snow free season and its stability in the 2003-2016 period, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19337, https://doi.org/10.5194/egusphere-egu2020-19337, 2020.

Permafrost thaw, as a consequence of climate warming, liberates large quantities of frozen organic carbon in the Arctic regions. The response of gaseous carbon release upon permafrost thaw might play a crucial role in the future evolution of atmosphere-land fluxes of biogenic gases such as volatile organic compounds (VOCs), a group of reactive gases and the dominant modulator of tropospheric oxidation capacities. Here, we examine the response of volatile release from Finnish Lapland permafrost soils to temperature increase in a series of laboratory incubation experiments. The experiments show that when the temperature rises from 0 °C to 15 °C, various VOC species are significantly emitted from the gradually thawing soils. The VOC fluxes from thawing permafrost are on average four times as high as those from active layer. Acetic acid and acetone dominate the total volatile emissions from both permafrost and active layer, with significant amounts of aromatics and terpenes detected as well. The emission rate and the composition of volatile release from thawing soils are highly responsive to temperature variations. As temperature increases, more less volatile compounds are released, i.e., sesquiterpenes and diterpenes. Collectively, these results demonstrate the highly overlooked volatile production from thawing permafrost, which will create a stronger permafrost carbon-climate feedback.

How to cite: Li, H., Mäki, M., Kohl, L., Väliranta, M., Bäck, J., and Bianchi, F.: Overlooked volatile production from Arctic permafrost triggered by global warming, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5988, https://doi.org/10.5194/egusphere-egu2020-5988, 2020.

The Arctic permafrost soils are very diverse in regard to parent material, geobiological composition and genesis. There is sparse knowledge about nutrient availability in Arctic soil and it was found that the permafrost layer differs in nutrient availability compared to the active layer. Recently, it was shown that elements like Si, Ca and P are potentially affecting the greenhouse gas from Arctic soil. However, it is not known how those elements are distributed in Arctic soils for a larger dataset. Furthermore, it is unclear whether regional differences in the availability of those elements or a change in availability due to permafrost thaw is changing microbial decomposer community. Therefore, we analyzed 445 soil depth profiles around the Arctic regarding different element availabilities.

Furthermore, we conducted an incubation experiment to measure the effect of different Si, Ca and P availabilities on the structure of the microbial decomposer community. We found large differences in the availability of Si, Ca, Al, Fe and P in the layers of the panarctic permafrost soils from Canada, Alaska, Russia, Scandinavia, Greenland and Svalbard. There are differences in the distribution of Ca and Si pools over the panarctic permafrost soils. Especially the availability of P is directly linked to the concentration of Ca and Si and the presence of Al and Fe based minerals. With rising temperatures, the thaw depth of the upper horizon may increase and elements stored in deeper layers become potentially mobilized. These processes modify the nutrient availability for microorganisms and by this the production of greenhouse gases like CO₂ and CH₄.

The community structure of bacteria and fungi is related to the availability of Ca and Si. With modified availabilities of Si and Ca, we found direct linear correlations in the changes of the microbial structure at the phylum level for Greenlandic soils. These changes depend on the origin of the soil and the original availability of Ca and Si. We found direct links between the share of gram-positive bacteria and the Ca concentration in both soils and the production of greenhouse gases. The availabilities of these elements may be helpful for better predicting greenhouse gases fluxes in the Arctic as well as element transfer to marine systems.

How to cite: Stimmler, P.: Future Arctic soil nutrient availability and microbial community structure, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6870, https://doi.org/10.5194/egusphere-egu2020-6870, 2020.

The biological conversion of frozen carbon-rich soil (permafrost) into greenhouse gases such as carbon dioxide could cause a positive feedback to climate change. Another significant consequence of permafrost thaw is the collapse of soil structure and subsequent higher water table that can shift vegetation toward water-adapted plant communities that emit high concentrations of methane (CH₄). Plants and microbes respond rapidly to labile carbon (C) and nitrogen (N) released from permafrost thaw, however, the microbial response to phosphorus (P) is unknown.  Here we investigated how the nutrient status of permafrost and peat affect microbial activities in four minerotrophic communities in a peatland undergoing permafrost thaw. We experimentally fertilized soils in vitro with a permafrost soil slurry, inorganic P, organic N, or organic N and P. This method isolated the effect of permafrost thaw on microbial processes by removing the confounding effect of plant-soil interactions. The four peatland communities include 1. palsas (intact permafrost mounds rising above the surrounding peatlands), 2. pockets of collapsed palsas dominated by Sphagnum fuscum, 3. adjacent eutrophic Sphagnum-dominated lawns with thawing permafrost and 4. inundated, sedge-dominated minerotrophic fens with no permafrost remaining. Permafrost had high extractable inorganic N concentrations, averaging 30 µg N g-1 soil dry weight (dw), whereas extractable P concentrations were low, averaging 1.4 µg P g-1 soil dw. While N concentrations in the permafrost were over four times the concentration in adjacent peatland communities, extractable P concentrations were relatively lower. Sphagnum lawns positioned at the base of palsas, had nine times the extractable P concentrations averaging 12.6 µg P g-1 soil dw compared to the permafrost, suggesting that P availability increases as permafrost thaws. However, in the fen where no permafrost remains, extractable P concentrations were again low, 2.4 µg P g-1 soil dw, despite high total P. These fen communities are also marked by higher iron concentrations, likely resulting in P immobilization by higher concentrations of metals. The addition of inorganic P and the combination of organic N and P in these fen sites strongly enhanced CH₄ oxidation rates while organic N did not, indicating the importance of P for these energy intensive transformations. Nutrient amendments did not have a significant effect on CH₄ production rates, however, permafrost slurries significantly decreased CH₄ production in Sphagnum lawn communities, suggesting an unknown inhibitory effect of permafrost chemistry on CH₄ production. The results of our study highlight the effects of permafrost degradation on nutrient release and provide new insight into how nutrients unlocked from permafrost affects greenhouse gases. 

How to cite: Kashi, N. N., Varner, R. K., Thorp, N. R., Knorr, M. A., Wymore, A. S., Ernakovich, J. G., Hobbie, E. A., and Giesler, R.: Nutrients unlocked from permafrost thaw affect microbial methane metabolism, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12521, https://doi.org/10.5194/egusphere-egu2020-12521, 2020.

In recent years, permafrost-affected soils have been shown to be gradually subject of thawing (IPCC, 2019). Formerly frozen soil organic carbon stocks hence become increasingly susceptible to microbial decomposition and transformation into greenhouse gases (Schuur et al., 2015). An estimated 20% of Arctic permafrost areas are subject of melting of belowground ice and consequent collapse (Olefeldt et al. 2016), but these thermokarst landscapes are often difficult to assess.

In 2018, a thermokarst developed into a thermal erosion gully in close vicinity to the Zackenberg Research Station. As one of the main stations of the Greenland Ecosystem Monitoring (GEM) program, the monitoring of various ecosystem parameters at this site during the past 25 years, including hydrology, soil temperature and active layer depth, enables a spatiotemporally precise description of the thermokarst's physical progression.

In order to characterize the development of a thermokarst soil microbial community and understand its spatial distribution and taxonomic biodiversity, soil cores of 30 cm above and below an ice lens were extracted in August 2018, as well as after a dry and warm summer season in September 2019, until 90 cm depth to also sample still frozen permafrost soils. Soil characterization included loss on ignition, radiocarbon dating and microbial viability assays for both years. Bacterial 16S rDNA V3-V4 and fungal ITS1 gene region amplicons of extracted DNA were sequenced and analyzed. With the microbiome involved in biochemical processes such as nitrogen fixation, methane production and oxidation as well as CO₂ respiration, knowledge about abundance, genetic and adaptation potential of bacteria, archaea and microeukaryotes in fast changing permafrost soils affects several ecosystem carbon fluxes significantly.

This work is part of a project, describing both the taxonomic and functional composition of this thermokarst microbiome, including the use of multi-omics to reveal the carbon cycling gene potential and expression in combination with in situ and laboratory incubation gas fluxes of CO₂, N₂O and CH₄. These biological and biogeochemical insights from this event are put into perspective with long-term, maintained data supplied by the GEM. 

How to cite: Scheel, M., Christensen, T. R., Rundgren, M., Suhr Jacobsen, C., and Zervas, A.: Microbial life in collapsing permafrost in NE Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17683, https://doi.org/10.5194/egusphere-egu2020-17683, 2020.

The Arctic is warming at twice the rate of the rest of the globe. While it has been increasingly highlighted that thawing permafrost accelerates soil organic matter decomposition, research on biogeochemical N cycling is still underrepresented. Arctic nitrous oxide (N₂O) emissions have long been assumed to have a negligible climatic impact but recently increasing evidence has emerged of N₂O hotspots in the Arctic. Even in small amounts, N₂O has the potential to contribute to climate change due to it being nearly 300 times more potent at radiative forcing than CO₂. Therefore, the ‘NOCA’ project aims to establish the first circumarctic N₂O budget. Following intensive N₂O flux sampling campaigns at primary sites within Northern Russia and soil N₂O concentration measurements from secondary sites across the Arctic, we are now entering the phase of spatial extrapolation. Challenges to overcome are the small-scale heterogeneity of the landscape and incorporating small features that can function as N₂O hotspots. Therefore, as a first step in upscaling the N₂O fluxes, high resolution imagery is needed. We show here novel high-resolution 3D imagery from an unmanned aerial vehicle (UAV), which will be used to upscale N₂O fluxes from plot to landscape scale by linking ground-truth N₂O measurements to vegetation maps. This approach will first be applied to the East cliff of Kurungnakh Island in the Lena River Delta of North Siberia and is based on 2019 sampling campaign data. Kurungnakh Island is characterized by ice- and organic-rich Yedoma permafrost that is thawed by fluvial thermo-erosion forming retrogressive thaw slumps in various stages of activity. Overall, 20 sites were sampled along the cliff and inland, covering the significant topographic and vegetative characteristics of the landscape. The data from this scale will provide the basis for extrapolating, by using a stepwise upscaling approach, to the regional and finally circumarctic scale, allowing a first rough estimate of the current climate impact of N₂O emissions from permafrost affected soils. Available international circumarctic data from this and past projects will be synthesized with an Arctic N₂O database under development for use in future ecosystem and process-based climate model simulations.   

How to cite: van Delden, L., Marushchak, M., Voigt, C., Grosse, G., Faguet, A., Lashchinskiy, N., Kerttula, J., and Biasi, C.: Towards the first circumarctic N2O budget – Extrapolating to the landscape scale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14347, https://doi.org/10.5194/egusphere-egu2020-14347, 2020.