Biological processes on snow and glacier surfaces in the Arctic region play a key role causing albedo reduction called as “Bio-albedo effect” due to blooms of snow and glacier phototrophs. Because the bio-albedo effect varies temporally and spatially due to their biological properties including growth, death and migration, the biological processes need to be separated from accumulation processes of the other impurities such as aeolian mineral dust and black carbon. In addition, different processes causing the bio-albedo effect, which are known as red snow, dark ice and cryoconite holes, are observed in the Arctic snowpacks and glaciers. To understand the bio-albedo effect quantitatively, a numerical model to reproduce such biological processes as well as a physically based albedo model should be established. We recently established several numerical models: the snow algae model to simulate red snow phenomena caused by snow algal blooms (Onuma et al., 2020; 2022a), the glacier algae model to simulate dark ice phenomena caused by glacier algal blooms (Onuma et al., 2022b) and the cryoconite hole model to simulate vertical dynamics of cryoconite holes (Onuma et al., In prep.). In this study, we simulate spatio-temporal changes in algal abundance and bio-albedo effect in Greenland Ice Sheet since 2000 using regional climate or land surface models coupling with the established models. The simulated spatio-temporal changes are evaluated using a polar-orbit satellite, Global Change Observation Mission for Climate (GCOM-C) which carries an optical sensor capable of multi-channel observation at wavelengths from near-UV to thermal infrared wavelengths (380nm to 12µm). In addition, we also use GCOM-W satellite with a microwave sensor to discuss relationship between snow/ice surface melt periods and algal blooms. The detailed discussion will be presented at the meeting.

References
[1] Y. Onuma, N. Takeuchi, S. Tanaka, N. Nagatsuka, M. Niwano and T. Aoki, Physically based model of the contribution of red snow algal cells to temporal changes in albedo in northwest Greenland. The Cryosphere, 14, 2087-2101. doi:10. 5194/tc-14-2087-2020 (2020)

[2] Y. Onuma, K. Yoshimura and N. Takeuchi, Global simulation of snow algal blooming by coupling a land surface and newly developed snow algae models, Journal of Geophysical Research: Biogeosciences, 127 (2), e2021JG006339. doi:10.1029/2021JG006339 (2022a).

[3] Y. Onuma, N. Takeuchi, J. Uetake, M. Niwano, S. Tanaka, N. Nagatsuka and T. Aoki, Modeling seasonal growth of phototrophs on bare ice on the Qaanaaq Ice Cap, northwestern Greenland. Journal of Glaciology, 1-13. doi:10.1017/jog.2022.76 (2022b)

How to cite: Onuma, Y., Niwano, M., Shimada, R., and Takeuchi, N.: Numerical modeling of biological processes on snow and ice surfaces on the Greenland Ice Sheet, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3146, https://doi.org/10.5194/egusphere-egu23-3146, 2023.

Glacier-fed streams (GFSs) serve as headwaters to many of the world’s largest river networks. Although being characterized by extreme environmental conditions (i.e., low water temperatures, oligotrophy) GFSs host an underappreciated microbial biodiversity, especially within benthic biofilms which play pivotal roles in downstream biogeochemical cycles. Yet, we still lack a global overview of the GFS biofilm microbiome. In addition, little is known on how environmental conditions shape bacterial diversity, and how these relationships drive global distribution patterns. This is particularly important as mountain glaciers are currently vanishing at a rapid pace due to global warming. Here, we used 16S rRNA gene sequencing data from the Vanishing Glaciers project to conduct a first comprehensive analysis of the benthic microbiome from 148 GFSs across 11 mountain ranges. Our analyses revealed marked biogeographic patterns in the GFS microbiome, mainly driven by the replacement of phylogenetically closely related taxa. Strikingly, the GFS microbiome was characterized by pronounced level of endemism, with >58% of the Amplicon Sequence Variants (ASVs) being specific to one mountain range. Consistent with the marked dissimilarities across mountain ranges, we found a very small taxonomic core including only 200 ASVs, yet accounting for >25% of the total relative abundance of the ASVs. Finally, we found that spatial effects such as dispersal limitation, isolation and spatially autocorrelated environmental conditions overwhelmed the effect of the environment by itself on benthic biofilm beta diversity. Our findings shed light on the previously unresolved global diversity and biogeography of the GFS microbiome now at risk across the world’s major mountain ranges because of rapidly shrinking glaciers.

How to cite: Ezzat, L., Peter, H., Bourquin, M., Michoud, G., Fodelianakis, S., Kohler, T., Lamy, T., Busi, S., Daffonchio, D., Deluigi, N., De Staercke, V., Marasco, R., Pramateftaki, P., Schön, M., Styllas, M., Tolosano, M., and Battin, T.: Global biogeography of the glacier-fed stream microbiome, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2757, https://doi.org/10.5194/egusphere-egu23-2757, 2023.

In Arctic soils, wintertime usually means subzero ground temperatures and only little unfrozen water available below a snow cover. While this period has less active nutrient cycling by microbes, some activity means that winter mineralization of e.g., nitrogen (N) can release a pulse of mineral N (ammonium, nitrate) into the soil solution, which can become biological available upon spring thaw. 

In springtime, plants may compete with microbes for the N pulse, but if thaw happens during winter, the N pulse could be immobilized by active microbes, which can decrease the size of the springtime N pulse, and therefore decrease the growing season N addition to the ecosystem.

Many parts of the Arctic have with climate change seen an increase in the frequency of extreme winter warming events (WW events), which are periods of positive temperatures lasting 5-7 days and causing snow to melt and the upper soil layer to thaw. 

In a field scale experiment, we quantified the amount of mineral N released into solution upon soil thaw during a simulated WW event in Disko island, Western Greenland (69.28ᵒN, 53.48ᵒW). We used ¹⁵N tracing to determine which parts of the ecosystem that benefited from this N during the WW event. We further returned the following summer to test whether vegetation was more N limited the summer after a WW event.

Our results show that after 6 days of thaw, 50-60 % of WW-released N was found either in active microbial biomass or stored in the soil, whereas none had been assimilated by the plants. The following summer, we saw that evergreen shrubs subject to the WW event had acquired less N than if they had experienced a stable winter. This indicates that evergreen shrubs are especially sensitive to a smaller spring N pulse, which is in line with studies showing that evergreen shrubs rely more on springtime N uptake. As evergreen shrubs are an important functional plant type in the tundra, increased frequency of WW events could therefore change tundra plant community composition. Our results also indicate that N immobilization during WW events could be a mechanism linking WW events to Arctic browning and decrease in photosynthetic C uptake rates.

Our research sheds light on the little studied impact of climate change-related WW events on the nutrient cycling of Arctic soils and the plant-root competition for N in the future, and we develop methods for studying this phenomenon in the broader Arctic.

How to cite: Rasmussen, L. H., Danielsen, B. K., Elberling, B., Kurczy, M., Ranjbari, E., and Andresen, L.: Arctic extreme winter warming events lead to microbial N immobilization and evergreen shrub N limitation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2069, https://doi.org/10.5194/egusphere-egu23-2069, 2023.

Currently, 20% of the Northern Hemisphere is affected by thermokarst, with an increase expected in future. In particular, ice-rich Yedoma sediments are susceptible to abrupt thaw, which leads to the formation of retrogressive thaw slumps (RTS). These erosion processes result in loss of vegetation, expose long-term frozen permafrost sediments at the surface, and makes soil organic matter (SOM) available for mineralization. Permafrost-affected soils of RTS exhibited higher N availability, as indicated by higher δ¹⁵N content of bulk soil, higher nitrate content and higher microbial N turnover (N mineralization especially net nitrification and denitrification) associated with high abundance of functional N genes compared to undisturbed soils. This elevated N availability results in significant emission of the greenhouse gas N₂O, especially from exposed permafrost. Based on measured N₂O emissions, N₂O loss could be as high as 54.8 mg N₂O-N per year, which is 0.14% of the initial inorganic N content of exposed Yedoma. The higher N availability of eroded permafrost-affected soils might affect C mineralization because eroded soils had lower aerobic CO₂ production than undisturbed soils and CH₄ production was detectable in laboratory incubations only in the absence of N₂O production.

How to cite: Fiencke, C., Marushchak, M. E., Wegner, R., and Beer, C.: Thawing permafrost in retrogressive thaw slumps leads to higher N availability, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15903, https://doi.org/10.5194/egusphere-egu23-15903, 2023.

Glacier retreat due to the warming climate is remarkable all over the world. In addition to climate warming, the “biological albedo reduction”, which the pigmented algae reduce the albedo of the glacier, enhances ice melting. Therefore, the spatial distribution of those algae is important for the glacier's mass balance. Although the altitude result in the air temperature and the duration of snow cover is recognized as the factor to affect the spatial distribution, the distribution pattern is more heterogeneous in the same altitude area. To understand the heterogeneity of snow algae and associating microbes and their effects on the glacier albedo, both eukaryotic and prokaryotic communities were analyzed using an amplicon sequencing approach in the dense coverage of the ablation area of a single glacier (total 54 sites over Gulkana Glacier, AK, USA). Furthermore, microbial diversities were analyzed with environmental factors such as carbon contents and nutrients. As a result, we found the green algae amplicon sequence variants (ASVs) closely related to the pigmented algae, Sanguina nivaloides, and Chlainomonas sp. from the surface ice and cryoconite and will show the spatial variation of microbial community structures and diversities and the relationship between the environmental factors.

How to cite: Uetake, J., Ono, M., Usuba, S., Tsushima, A., and Takeuchi, N.: Dense spatial variation of the eukaryotic and prokaryotic communities on the Gulkana Glacier, Alaska, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11725, https://doi.org/10.5194/egusphere-egu23-11725, 2023.

Permafrost is thawing at unprecedented rates, significantly altering landscapes and ecosystem trajectories by changing subsurface conditions and vegetation characteristics. The combination of in situ and laboratory analysis is important to understand microbial heterogeneity and to simulate the effects of thaw.  Dormant microbes become active as temperatures rise and permafrost soils warm and thaw, suggesting that sub-surface ecosystem processes will be altered. The extent of microbial change throughout seasons and thaw periods remain poorly understood.  We collected permafrost-affected soils at two Alaskan sites to determine the effects of sample location and warming on the permafrost microbiome.  In situ analysis of northern Alaskan soils revealed that surface communities were highly variable throughout the growing season.  In two laboratory thaw studies, we assessed permafrost microbiome taxonomy and metabolic function during thaw.  Under frozen conditions, microbial respiration rates from different PT locations were similar, ranging from 2 to 12 mg C–CO₂ per kg soil per day and permafrost microorganisms were heterogeneously distributed in space.  Following thaw, metabolomes from different locations were highly similar.  However, the trajectory of dominant taxa and potential function in a given PT sample was more strongly influenced by sample location than by incubation temperature. This indicates a differential response of permafrost microbes based on their origin. These findings have important implications for developing accurate forecasts of microbial community assemblages during thaw in that location should be considered as a strong influencing factor.  

How to cite: Barbato, R., Doherty, S., Jones, R., Baker, C., Messan, K., Barker, A., and Douglas, T.: Effects of climate change on microbial taxonomy and metabolic processes in Alaskan permafrost-affected soils, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9119, https://doi.org/10.5194/egusphere-egu23-9119, 2023.

Glaciers are receding at an unprecedented rate with expected losses of up to half their masses by 2100. Such changes will profoundly effect the physicochemical characteristics of glacier-fed stream (GFS) water, such as the composition of organic matter, turbidity, conductivity, and patterns in discharge. Hence, direct effects are anticipated for the microbial communities and assemblages inhabiting these environments. High-elevation tropical glaciers are already responding to these enhanced changes (e.g. temperature) and thus are a proxy to study the ecology of GFSs in the future. Here, we sampled and studied the Mt Stanley glacier in Africa’s ‘Mountains of the Moon’ (Rwenzori National Park, Uganda). We showed that the benthic microbiome from this GFS is distinct at several levels from other GFSs worldwide. Specifically, several novel taxa were present, and usually, common groups such as Chrysophytes and Polaromonas exhibited lower relative abundances compared to higher-latitude GFSs, while cyanobacteria and diatoms were more abundant. The rich primary producer community in this GFS likely results from the greater environmental stability of the Afrotropics, and accordingly, heterotrophic processes dominated in the bacterial community. Metagenomics revealed that almost all prokaryotes in the Mt. Stanley GFS are capable of organic carbon oxidation, while >80% have the potential for fermentation and acetate oxidation. Our findings suggest a close coupling between photoautotrophs and other microbes in this GFS and provide a glimpse into the future for high-latitude GFSs globally where primary production is projected to increase with ongoing glacier shrinkage.

How to cite: Michoud, G., Kohler, T., Ezzat, L., Peter, H., Nattabi, J., Nalwang, R., Bourquin, M., Busi, S., and Battin, T.: The dark side of the moon: A glimpse into the future of the microbiome structure and function of glacier-fed streams, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12296, https://doi.org/10.5194/egusphere-egu23-12296, 2023.

World temperature has been steadily increasing over the past century, resulting in alterations of most ecosystems. Particularly, high latitudes regions are expected to undergo severe climate changes. Soil microbes are key actors of the terrestrial system, fulfilling major functions such as nutrient cycling and therefore considerable efforts are made to understand their response to warming. Besides, they can be in tight interaction with roots, and the effect of such interactions are well documented, however, whether soil microbial community response to warming is mediated by plants through roots remains unclear.

Here, we took advantage of a geothermal temperature gradient (reaching a warming intensity of up to +6°C) located in two Subarctic grasslands to study the effect of middle (12 years) and long term (>60 years) warming on the root associated soil microbes. For this, we installed two differently mesh sized cores along the thermal gradient of both grasslands allowing us to compare portions of local soil either containing (1 mm mesh size) or excluding roots (30 µm mesh size).

We investigated the response of fungal and bacterial communities to warming under both root inclusion and exclusion over the seasons using a metabarcoding approach targeting the 16S rRNA gene and the ITS1 fungal region. We found that warming shifted both bacterial and fungal communities, and that this response was depending on the warming duration. However, root exclusion did not alter the overall microbial community. Surprisingly, we did not find an effect of season on the fungal community while it had a slight effect on bacteria. In addition, we found that Carbon and Nitrogen content were altered differently by warming when roots were excluded.

Overall, this study shows that, despite modifying soil conditions, root exclusion had low effect on the general soil fungal and bacterial communities response to warming.

How to cite: Le Noir de Carlan, C., de Tender, C., Metze, D., Bhattarai, B., Pesqueda, A., Sigurdsson, B., Penuelas, J., Richter, A., Janssens, I., and Verbruggen, E.: Effect of root exclusion on the soil microbial community response to warming, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13495, https://doi.org/10.5194/egusphere-egu23-13495, 2023.

Arctic permafrost degradation and carbon decomposition do not occur homogeneously across Arctic ecosystems due to the rich landscape diversity and the high amount of small-scale heterogeneities. Traditionally, Earth system models (ESM) are deployed to investigate future climate change in the northern permafrost areas. The typical heterogeneous landscape characteristics of the Arctic are however in scale well below the usual ESM resolutions of several hundred kilometers. To take in-depth account of small-scale heterogeneous landscapes, a higher land surface model resolution is advantageous.

To investigate whether and why resolution matters in simulating the interactions of soil physics, hydrology, and vegetation in the Arctic, we develop a high-resolution version of the land surface model (LSM) JSBACH3 on the scale of 5 km for a case study in the Chersky region in eastern Siberia. We then compare the results with the output of the same model in a low ESM resolution of about 200 km. The LSM simulations are performed in standalone mode (without feedbacks to climate) using the same climate forcing for both, high- and low- resolution setups. Our analysis shows that small-scale soil characteristics are more relevant regarding resolution than vegetation properties. We found that the formulation of supercooled water processes in the soil has a major impact on the differences between low and fine resolutions, as well as soil organic matter fractions. Other soil parameters such as hydraulic conductivity, soil porosity or heat conductivity have relatively minor effects on differences between model resolutions.

We show the relevance of model resolution in the simulation of Arctic land physical and biogeochemical interactions and thus argue that the development of a high-resolution pan-Arctic LSM would be a major advancement in modelling future Arctic permafrost and carbon projections.

How to cite: Schickhoff, M., de Vrese, P., and Brovkin, V.: Analysis of resolution-induced differences in soil - hydrology - vegetation interactions in the Arctic using state-of-the-art land surface model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5276, https://doi.org/10.5194/egusphere-egu23-5276, 2023.

Climate warming is expected to occur stronger and faster in high-latitude terrestrial ecosystems compared to other regions of the world. It has been suggested that high-latitude systems are characterized by large soil C stocks which are highly vulnerable to warming. Warmer conditions can stimulate soil microbes to decompose more soil organic matter and increase the activity of plant roots, therefore, increasing soil CO₂ emissions. However, our current understanding of soil warming effects on soil CO₂ efflux is largely restricted to short-term warming observations which could over- or under-estimate warming effects. Additionally, the warming effects could vary seasonally, and it is important to consider this variation to better predict how natural ecosystems will respond to prolonged warming.

In this study, we aim to assess the seasonal dynamics of soil CO₂ efflux in a subarctic grassland under medium-term warming (>10 years) and examine how soil warming modifies the temperature sensitivity of soil CO₂ efflux. We take advantage of a geothermally heated grassland in Iceland for 13 years that is part of the ForHot and FutureArctic Research Network. We measured soil CO₂ efflux in ambient and warmed plots (from +1°C to +10°C above ambient soil temperature) between mid-2020 and early 2022 and during various field campaigns, we analysed the isotopic composition (δ¹³C) of soil CO₂ efflux for partitioning between biogenic and geogenic soil CO₂ and disentangle the soil respiration (a biological process) response to medium-term warming. We found strong seasonality in soil CO₂ efflux, with particularly higher fluxes during the growing season. After accounting for the geogenic soil CO₂ efflux, we found that long-term warming increases soil respiration during winter, spring, and fall. That means that warmer conditions keep microbes more active during the colder months. However, during summer the response was the opposite and soil respiration was unexpectedly lower in warmed plots. This can be related to decreasing soil C stocks in the topsoil during the first years of warming and lower root biomass and soil microbial biomass, limiting soil CO₂ efflux under warming during the growing season. Additionally, we found that the apparent temperature sensitivity of soil CO₂ efflux (Q₁₀) decreases with warming in a non-linear way, inducing thresholds at different soil warming levels. From these results, we conclude that medium-term warming effects on soil CO₂ efflux vary seasonally and warming decreases the temperature sensitivity of soil respiration.

How to cite: Protti Sanchez, F., Janssens, I., Sigurdsson, B. D., Sigurdsson, P., and Bahn, M.: Seasonal dynamics and temperature sensitivity of soil CO2 efflux in a medium-term warmed subarctic grassland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14861, https://doi.org/10.5194/egusphere-egu23-14861, 2023.

Climate change is causing rapid changes in sub-Arctic and Arctic terrestrial ecosystems compared to the other biomes. As these ecosystems are so sensitive to climate change, more research on how the rising of temperature affects these ecosystems is essential.

This study is implemented in the ForHot research site located in Iceland encompassing geothermally heated natural grasslands. This research site contains two areas, one that has been warmed geothermally for over 60 years (long-term warming; LTW) and the other since 2008 (medium-term warming; MTW). The LTW area contains 24 plots and the MTW contains 30 plots, with the mean annual soil temperature ranging between 5 to 21 °C for LTW and 6 to 46 °C for MTW in 2022. 

The main goal of this study was to understand how the warming level and the duration of warming (MTW vs. LTW) have affected the average seasonal Normalized Difference Vegetation Index (NDVI) during 2022.

For this study, we repeatedly collected high-resolution multispectral data using Micasense dual camera system and DJI Matrice 600 drone each month from April 2022 to October 2022 as well as soil temperature data of each plot, and some other parameters such as precipitation, air temperature, wind speed, and soil water content.

Here we present the results on how the warming level and the duration of warming affected the monthly and seasonal average NDVI in the MTW and LTW grassland ecosystems.

How to cite: Hamedpour, A., D. Sigurdsson, B., Peñuelas, J., Filella, I., Einarsson, H., Latré, S., and Stefánsson, T.: Analyzing the effect of the duration of soil warming on subarctic grasslands using high-resolution multispectral images, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4408, https://doi.org/10.5194/egusphere-egu23-4408, 2023.

Climate change affects ecosystems considerably worldwide, but as warming is happening at an accelerated pace at higher latitudes, it is essential to study how warming affects ecosystem structure and function in Arctic and sub-Arctic ecosystems.

In this research, we looked at changes in the aboveground biomass (AGB) of two Icelandic sub-Arctic grasslands located at the ForHot site. The ForHot site is an exceptional studying site where the soils are naturally warmed. Thus, making it an important natural laboratory to assess and learn more about the long-term effect of global warming. At the research site, one grassland ecosystem has soils that have been warmed for over 60 years (long-term warming; LTW) and the other since 2008 (medium-term warming; MTW), when an earthquake disrupted geothermal channels in the underlying bedrock. Fifty permanent survey plots were established in the autumn of 2012 along the two grassland soil temperature gradients (ranging from 0 to +18°C).

We assessed how vegetation structure (non-vascular; AGB_non-vasc and vascular plants; AGB_vasc) and the ecosystem's maximum aboveground total biomass(AGB_tot) were affected by different levels of soil warming over multiple studied years (i.e. 2013, 2016, 2018, 2020, 2021 and 2022).

Our preliminary results showed unexpectedly relatively small changes in AGB_tot with warming. We hypothesise that changes in AGB_vasc would typically induce opposite changes in AGB_non-vasc, probably because of light competition. When looking separately at the vegetation structures, for AGB_vasc, the duration of soil warming induced contrasted responses between MTW and LTW grasslands. That is, in the MTW grassland, there were no changes for most years (p > .05) and strong negative responses (p < .05) with warming in seasonally maximum AGB_vasc for other years. Whereas in the LTW grassland, warming generally increased AGB for most years (p < .05), and also a strong negative response as observed in the MTW for the respective years despite statistically not significant. This strong negative response could be because of untypically high AGB production in control (unwarmed) plots during those years and less positive reactions with different levels of soil warming. We will show some potential drivers (environmental variables) for those unexpected temporal variations in the warming response. AGB_non-vasc, such as lichens and mosses, have an unclear pattern across the soil warming gradient in both grassland ecosystems.

How to cite: Tchana Wandji, R. P., Leblans, N., Verbrigghe, N., Filella, I., Lootens, P., Merand, A., Janssens, I., and D. Sigurdsson, B.: Long and medium-term interannual assessment of sub-Arctic grassland aboveground biomass at different soil warming levels, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3806, https://doi.org/10.5194/egusphere-egu23-3806, 2023.

Mosses and lichens may play an important role for the future release of carbon from permafrost soils in high-latitude ecosystems. They significantly increase ecosystem carbon sequestration through productivity, and they also reduce soil temperature through insulation, thereby preventing permafrost carbon from being emitted as CO2. However, quantitative, large-scale estimates of the contribution of mosses and lichens to the future state of soil carbon at high latitudes are rare so far. Here, we use a processed-based model of mosses and lichens, which is integrated into a global land surface model, to predict the overall effect of these organisms on the soil carbon balance. We find that mosses and lichens double the increase in total soil carbon by the year 2100 compared to a simulation without the organisms, which can be explained by two factors: First, the cooling effect of mosses and lichens on soil temperature increases by around 1 degree C from today to 2100. Secondly, increased productivity of mosses and lichens due to CO2-fertilisation results in a larger carbon flux into the soil. Hence, we predict that mosses and lichens will contribute substantially to the future carbon balance of northern ecosystems and should not be neglected in simulations of the future carbon cycle.

How to cite: Porada, P. and Beer, C.: Impact of mosses and lichens on future carbon emissions from permafrost soils, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14182, https://doi.org/10.5194/egusphere-egu23-14182, 2023.

Climate warming is occurring faster in high latitudes and that trend is predicted to continue. How vegetation responds to past warming or to manipulation experiments has proven to be quite site-specific. To better understand the underlying reasons for contrasting responses it is important to study both the direct and the indirect responses to warming that are often mediated through the underlying soil processes.

The ForHot site in Iceland offers possibilities to look at the indirect warming effects that are mediated through soil processes. There, a natural soil warming experiment was created in May 2008 by a major earthquake that shifted geothermal bedrock channels to previously cold areas. In this study we use an experimental site with 50-year-old Sitka spruce (Picea sitchensis) and soil warming gradient ranging from 0 to +6 °C between 2008 to 2018. The main objective is to get deeper insights into how rising soil temperatures will affect aboveground growth dynamics in sub-Arctic forest ecosystems.

For this paper we used tree-ring analysis of dominant trees from 1988 to 2018, measurements of their height increment from 2000 to 2018, as well as forest stand measurements on permanent inventory plots and litter trap data from 2013 to 2018 and foliar chemical analysis done in 2016.

Here we present results on the radial- and height growth before and after the warming was initiated and the consequent changes in tree mortality, stand volume and aboveground primary productivity (ANPP) under different soil warming levels.

How to cite: Sigurdsson, B. D., Sigurðsson, P., Lindau, A., and Eggertsson, Ó. E.: Aboveground growth responses of mature Picea sitchensis forest stand at different levels of soil warming, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2809, https://doi.org/10.5194/egusphere-egu23-2809, 2023.

The present distribution pattern of Siberian boreal forests that are dominated by larches is to an unknown extent influenced by the glacial history. Here, we investigated whether we can observe patterns in the genetic variability of Siberian larches (Larix spp.) that can help us to unravel biogeographic migration routes since the Last Glacial Maximum (LGM). We revealed the spatial distribution of 14,003 Single Nucleotide Polymorphisms (SNPs) derived by Genotyping by Sequencing (GBS) in a subset of 148 larch individuals with a cluster analysis. To shed light on Larix’ postglacial migration routes, we applied an Approximate Bayesian Computation (using the software DIYABC). The results of the cluster analysis revealed the presence of three to four statistically verified clusters from Western to Eastern Eurasia that match well to the already expected distinction into the main larch species Larix sibirica, L. gmelinii and L. cajanderi. It can be discussed that under the light of ecological aspects and the spatial assignment to geographic regions, six clusters are plausible instead of the statistically derived most probable optimum of three to four main clusters. The tested hypotheses in DIYABC show that all present existing populations seem to be initiated far before the LGM. We presume that the different populations originate from larch populations that survived the glacial periods. Having the complex terrain in mind, we deduce that those individuals rather survived in refugia in the North, than migrated through complete recolonization from the South. The northernmost expansion during the Holocene seems to have benefitted from refugial populations ahead of the treeline, which explains the existence of Larix in the Far North although the treeline migration rates were slow. From our results, we expect that the present migration is probably slow at first, as there are currently no refugial populations far north, as there were probably in Holocene. But in the future, isolated trees in the tundra could become a starting point for rapid dispersal of boreal forests in the course of current climate warming.

How to cite: Haupt, S., Meucci, S., Herzschuh, U., Harpke, D., Bernhardt, N., Killing, S., Pestryakova, L. A., Zakharov, E. S., and Kruse, S.: Biogeography of Larches in North-East Siberia - using Single Nucleotide Polymorphisms derived by Genotyping by Sequencing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15735, https://doi.org/10.5194/egusphere-egu23-15735, 2023.

Permafrost soils located in high latitudes contain about 1500 petagrams of carbon. The strong and rapid warming of the Arctic climate threatens this important carbon stock. Permafrost thaw exposes previously frozen organic matter to decomposition by microorganisms, resulting in CO2 and CH4 emissions into the atmosphere that contribute to strengthening the initial warming. On the other hand, rising atmospheric CO2 concentration increases vegetation primary productivity in a feedback known as fertilization effect. In addition, the melting of permafrost may also likely provide more nitrogen in the soil that could stimulate plant growth. The balance between these competing processes is thought to be the primary driver of future permafrost carbon stocks. However, both the amplitude and timing of future net carbon emissions of permafrost areas remain highly uncertain. Reducing the uncertainty on net carbon balance in high latitudes would help improve the accuracy of carbon budget, and thus would impact political and social decisions towards the net zero target.

Up to then, the impact of different future climate scenarios (RCP, SSP or similar) on permafrost have been largely explored with offline Land Surface Model simulations but feedbacks with the atmosphere and ocean cannot be represented in such configurations. Using the IPSL Earth System Model that couples the atmosphere, the ocean and continental surfaces (i.e., ORCHIDEE model), the future evolution of climate-carbon feedbacks in permafrost regions is assessed. In particular, the feedback between climate change and the carbon cycle and the fertilization effect are analyzed with the C4MIP formalism (γ and β parameters). A particular focus is put on the role of the nitrogen cycle through its interactions with the carbon cycle. In addition, the impact of soil insulation by soil organic carbon and surface mosses on thermal transfers is also analyzed in the context of coupled land - atmosphere simulations. The importance of surface insulation i) to maintain realistic surface air temperature, especially during spring time, avoiding large surface - atmosphere feedbacks with unrealistic cooling in the arctic and ii) to sustain large permafrost extent (close to observations) is highlighted.

How to cite: Gaillard, R., Guenet, B., Peylin, P., Cadule, P., Chéruy, F., Ghattas, J., and Vuichard, N.: Estimating future permafrost carbon-climate feedbacks using a coupled Earth System Model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14644, https://doi.org/10.5194/egusphere-egu23-14644, 2023.