BG5.1

Methane and its fate in the biosphere - origin, source and cycling

Methane is one of the most important greenhouse gasses with ever-rising atmospheric concentrations. While anthropogenic sources are comparably well understood, it is still a major scientific challenge to unravel methane dynamics in natural systems: (bio)geochemical and geological controls on methane dynamics in aquatic and terrestrial systems as well as the spatial distribution of methane in marine and aquatic sediments, soils and permafrost areas is not well constrained.
The topics of the session will include:
- methane formation (biological and geological processes)
- subsurface fluid flow and methane/hydrocarbon transport mechanisms
- ‘marine’ methane-rich systems: e.g. gas hydrates, shallow gas, cold seep-related systems
- ‘terrestrial’ methane-rich systems: e.g. wetlands (natural & artificial), lakes (from puddles to inland seas), permafrost areas and rivers
- methane-associated (bio)geochemical reactions, microbial communities and food web structures
- methane-derived carbonates and microbe-mineral interactions
- monitoring of methane emission
- methane in paleo environments
- methane and as a new alternative energy source

We aim at gathering scientists from the fields of (bio/geo)chemistry, (micro)biology and ecology as well as geology and (geo)physics, to evaluate our current knowledge of aquatic and terrestrial methane dynamics, interactions between element cycles and ecosystems, environmental controls and mechanisms.

Convener: Helge Niemann | Co-convener: Alina Stadnitskaia
vPICO presentations
| Wed, 28 Apr, 11:00–11:45 (CEST)

vPICO presentations: Wed, 28 Apr

Chairpersons: Helge Niemann, Alina Stadnitskaia
11:00–11:02
|
EGU21-11489
|
ECS
Hariharan Ramachandran, Andreia Plaza-Faverola, Hugh Daigle, and Stefan Buenz

Evidences of subsurface fluid flow-driven fractures (from seismic interpretation) are quite common at Vestnesa Ridge (around 79ºN in the Arctic Ocean), W-Svalbard margin. Ultimately, the fractured systems have led to the formation of pockmarks on the seafloor. At present day, the eastern segment of the ridge has active pockmarks with continuous methane seep observations in sonar data. The pockmarks in the western segment are considered inactive or to seep at a rate that is harder to identify. The ridge is at ~1200m water depth with the base of the gas hydrate stability zone (GHSZ) at ~200m below the seafloor. Considerable free gas zone is present below the hydrates. Besides the obvious concern of amount and rates of historic methane seeping into the ocean biosphere and its associated effects, significant gaps exist in the ability to model the processes of flow of methane through this faulted and fractured region. Our aim is to highlight the interactions between physical flow, geomechanics and geological control processes that govern the rates and timing of methane seepage.

For this purpose, we performed numerical fluid flow simulations. We integrate fundamental mass and component conservation equations with a phase equilibrium approach accounting for hydrate phase boundary effects to simulate the transport of gas from the base of the GHSZ through rock matrix and interconnected fractures until the seafloor. The relation between effective stress and fluid pressure is considered and fractures are activated once the effective stress exceeds the tensile limit. We use field data (seismic, oedometer tests on calypso cores, pore fluid pressure and temperature) to constrain the range of validity of various flow and geomechanical parameters in the simulation (such as vertical stress, porosity, permeability, saturations).

Preliminary results indicate fluid overpressure greater than 1.5 MPa is required to initiate fractures at the base of the gas hydrate stability zone for the investigated system. Focused fluid flow occurs through the narrow fracture networks and the gas reaches the seafloor within 1 day. The surrounding regions near the fracture network exhibit slower seepage towards the seafloor, but over a wider area. Advective flux through the less fractured surrounding regions, reaches the seafloor within 15 years and a diffusive flux reaches within 1200 years. These times are controlled by the permeability of the sediments and are retarded further due to considerable hydrate/carbonate formation during vertical migration. Next course of action includes constraining the methane availability at the base of the GHSZ and estimating its impact on seepage behavior.

How to cite: Ramachandran, H., Plaza-Faverola, A., Daigle, H., and Buenz, S.: Time Constraints on Seepage Through Fractured Regions on the Vestnesa Ridge off the W-Svalbard Coast, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11489, https://doi.org/10.5194/egusphere-egu21-11489, 2021.

11:02–11:04
|
EGU21-176
|
ECS
Emilia Ridolfi, Stiig Wilkenskjeld, Frederieke Miesner, Victor Brovkin, Paul Overduin, and Sandra Arndt

The Arctic shelf hosts a large, yet poorly quantified reservoir of relic permafrost. It has been suggested that global warming, which is amplified in polar regions, will accelerate the thawing of this subsea permafrost, thus potentially unlocking large stocks of comparably reactive organic matter (OM). The microbial degradation of OM in the thawing and generally anoxic permafrost layer has the potential of producing and, ultimately, releasing important fluxes of  CH4 to the atmosphere. Because CH4 is a potent greenhouse gas, such a release would further intensify global warming. However, the potential role of subsea permafrost thaw on microbial CH4 production and CH4 emissions from Arctic sediments currently remains unconstrained.
Here, we use a nested model approach to address this critical knowledge gap. We developed a pseudo-three-dimensional reaction-transport model for permafrost bearing sediments on the Arctic shelf to estimate the production, consumption, and, efflux of CH4 on the Arctic shelf in response to projected subsea permafrost thaw. The model accounts for the most pertinent biogeochemical processes affecting methane and sulfur cycling in permafrost bearing marine sediments.                                                                
It is initialized based on a published submarine permafrost map (SuPerMap, [1]) and forced by a range of projected thawing rate scenarios derived from the Max Planck Institute Earth System Model (MPI-ESM) simulation results for the period 1850-2100. Critical model parameters, such as permafrost OM content and its apparent reactivity are chosen based on a comprehensive analysis of published experimental data. Here, we present the output of this environmental scenario ensemble.                                                
Simulation results reveal that CH4 production rates are highly sensitive to changes in the apparent reactivity of permafrost OM. Although simulated CH4 production rates vary over a large range (0.001-130 PgC produced over 250 years), they generally highlight the potential for producing and, thus releasing large amounts of methane from thawing subsea permafrost on the warming Arctic Shelf.

[1] Overduin, P. P., Schneider von Deimling, T., Miesner, F., Grigoriev, M. N., Ruppel, C. D., Vasiliev, A., et al. (2019).
 Submarine permafrost map in the Arctic modeled using 1‐D transient heat flux (SuPerMAP). Journal of Geophysical Research: Oceans, 124, 3490–3507. https://doi.org/10.1029/2018JC014675

How to cite: Ridolfi, E., Wilkenskjeld, S., Miesner, F., Brovkin, V., Overduin, P., and Arndt, S.: Modeling methane production and emission from thawing sub‐sea permafrost on the warming Arctic Shelf, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-176, https://doi.org/10.5194/egusphere-egu21-176, 2020.

11:04–11:06
|
EGU21-16558
Nataliia Zadorozhnaia, Gleb Oblogov, Alexander Vasiliev, and Irina Streletskaya

Many researchers study the Earth's climate change and the impact of the greenhouse effect on this process. The large amount of methane (CH4) is preserved in permafrost. In this regard, scientists recently pay a great attention to the problem of methane emission during the permafrost degradation in the Arctic zone. Until now, the methane content in underground ice, frozen Quaternary sediments has been studied insufficiently. The methane content in the active layer is especially poorly studied.

The authors researched methane content in frozen grounds of the upper permafrost horizon (transition zone) and in thawed sediments of the active layer for different tundra landscapes near the Marre-Sale polar station on the western coast of the Yamal peninsula and for landscapes of the Pechora river estuary area (Russia).

More than 420 samples of gas from sediments in active and transient layer were collected in Marre-Sale and 36 samples in Pechora area. To determine the methane content, the samples were placed in syringes and degassed using the “head space” technique. CH4 measurements were carried out on a chromatograph with flame ionization detector (FID) Shimadzu GC-2014 (Japan) in the laboratory of Federal State Institution “VNIIOkeangeologiya” (Saint-Petersburg, Russia).

Methane content in the frozen and thawed sediments of different dominant landscapes of typical tundra on Yamal peninsula and landscapes of southern tundra on Pechora area is extremely variable. The greatest amount of methane is typical for the most wet landscapes with primarily of silt loam soils. In dry primarily sandy well-drained landscapes, the methane content is low. The highest methane content is measured within the low floodplain of river, water tracks, swampy depressions of polygonal relief, and lake basins landscapes (mean varied from 0.8 to 2.5 ml [CH4] / kg, with a maximum of 9.0 ml [CH4] / kg). For landscapes of the moist surface of typical tundra, the average values of methane content were approximately 0.4 ml [CH4] / kg (with a maximum of 3.4 ml [CH4] / kg). The lowest methane contents in soils were characteristic of the landscapes of well-drained tundra, and sand fields where the average values do not exceed 0.2 ml [CH4] / kg. Mean methane content in soils of Pechora river mouth landscapes varied from 0.05 to 4.5 ml [CH4] / kg, with a maximum of 15.8 ml [CH4] / kg.

Determined that methane contents in the frozen soils of the transition zone is 2 to 5 times higher than in the soils of the active layer. High content of methane in upper layers of permafrost should be considered as a significant source of methane, which can be involved in emission of greenhouse gases into the atmosphere during permafrost degradation.

How to cite: Zadorozhnaia, N., Oblogov, G., Vasiliev, A., and Streletskaya, I.: Methane in frozen and thawed soils of the western sector of Russian Arctic, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16558, https://doi.org/10.5194/egusphere-egu21-16558, 2021.

11:06–11:08
|
EGU21-3186
Sheel Bansal, Max Post van der Burg, Rachel Lo, and Owen McKenna

Almost half of all biogenically-produced methane is emitted from small lakes and wetlands. The Prairie Pothole Region (PPR) is the largest wetland complex in North America (10th largest in the world), and contains 5–8 million wetlands and lakes, which can potentially influence continental and global methane budgets. However, there is considerable uncertainty of past, current and future emissions of methane from PPR wetlands due to a lack of landscape-scale models based on PPR-specific data. We used a bottom-up approach to develop a spatially explicit, temporally dynamic model of wetland and lake methane emissions from the PPR. Using a dataset of >20,000 static-chamber flux measurements, we first developed a chamber model to understand functional relationships between methane fluxes and covariates, and then upscaled to the landscape using GIS and remotely sensed proxies for each covariate. Covariates in the chamber model included water-filled pore space (WFPS), hydroperiod, soil temperature, wetland size, land cover, and normalized difference vegetation index (NDVI). Proxies for upscaling included the Dynamic Surface Water Extent (for WFPS, hydroperiod, and area) and NDVI based on Landsat imagery, ClimateNA (for soil temperature), and the North American Land Change Monitoring System (for land cover). Methane emissions increased nonlinearly with increasing WFPS, soil temperature and NDVI, and was greater in wetlands surrounded by grasslands compared to cropland due to low organic carbon substrates in sediment of cropped wetlands. Methane flux had a hump-shaped relationship with area, with the highest emissions in mid-sized wetlands (1-4 ha) that had relatively long hydroperiods and high vegetation cover, whereas methane flux from water bodies >10 ha was negligible due to their relatively high sulfate concentrations. Despite the potential for high total emission from the PPR as would indicate from global models, total emissions were relatively low (~5 and 100 Gg methane) per year during historic dry (1991) and current wet years (2011), respectively, with wetland extent is the primary driver of regional emissions. Future warmer temperature scenarios (under RCP 8.5) indicate that annual methane emissions from the PPR could double.

How to cite: Bansal, S., Post van der Burg, M., Lo, R., and McKenna, O.: Spatially explicit methane emissions from the largest wetland complex in North America: Past, present and future, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3186, https://doi.org/10.5194/egusphere-egu21-3186, 2021.

11:08–11:10
|
EGU21-7791
|
ECS
Mengdi Pan and Judith Schicks

Gas hydrates are ice-like crystalline solids consisting of water and gas (predominantly methane). The methane gas bound in hydrate structures and their worldwide occurrence make them interesting not only as a potential energy source but also as a possible climate-relevant factor. Estimations predict that a certain amount of atmospheric CH4 may originate through dissociation of global gas hydrates, which may exacerbate global warming (Ruppel and Kessler, 2017). In turn, climate warming is not only directly affecting the hydrate distribution, but also perturbing the hydrate stability field, leading to the release of CH4 from hydrate-bearing sediments. Gas hydrates, particularly those associated within or below shallow permafrost, are likely to be affected by the climate processes. For instance, gas hydrates in Qilian Mountain permafrost (QMP) are found below thin permafrost layers at a shallow depth of around 133~396 m. They might be vulnerable to dissociation due to global warming resulting in a possible higher CH4 gas emission in this area. Considering the environmental effect, a proper understanding of hydrate dissociation behavior under specific conditions is important for the stability of natural gas hydrate deposits with respect to climate change.

This study focuses on the potential dissociation process of gas hydrates in QMP. Before the observation of hydrate dissociation, mixed gas hydrates are synthesized from pure water and gas mixtures containing CH4, C2H6, C3H8, CO2 at conditions close to those in QMP (3.0 MPa, 278 K) with respect to feed gas composition, pressure and temperature. Formed hydrate crystals are analyzed in x-y-z directions applying confocal in situ Raman spectroscopic measurements to identify structures and guest compositions. The dissociation process is based on the thermal conduction simulating global warming and the results are discussed under several isobaric conditions. The Raman spectra continuously record changes in the hydrate phase for each selected crystal over the whole dissociation period. Preliminary results show that the Raman peak intensities for all components start to decrease when the temperature approaches 287 K, indicating the release of gas from hydrate structures. Interestingly, the varying hydrate composition for the measured crystals suggests a heterogeneous dissociation behavior of each single crystal. The results indicate a faster release of CH4 molecules from the hydrate phase than other components. In addition, the Raman signals of CH4 gas molecules that trapped in large cages of sII hydrate disappear first during the dissociation process. After a limited time, mixed gas hydrates decompose completely without evidence of self-preservation effects. These results provide essential information for the estimation of possible methane release from this area in response to future climate warming.  

 

Ruppel, C. D., and J. D. Kessler (2017). The interaction of climate change and methane hydrates, Reviews of Geophysics, 55,126-168.

 

 

How to cite: Pan, M. and Schicks, J.: Experimental simulations of mixed gas hydrates dissociation in response to temperature changes in Qilian Mountain permafrost, China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7791, https://doi.org/10.5194/egusphere-egu21-7791, 2021.

11:10–11:15
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EGU21-3328
|
ECS
|
solicited
Cordula Gutekunst, Anna-K. Jenner, Gerald Jurasinski, Michael E. Böttcher, Franziska Koebsch, Jens Kallmeyer, Klaus-Holger Knorr, Viktoria Unger, Sizhong Yang, and Susanne Liebner

Drainage of peatlands for intensive and long-term agricultural use leads to higher mineralization rates of the organic material and thus, increased carbon dioxide (CO2) emissions. However, when degraded peatlands are rewetted, high methane (CH4) emissions are frequently observed, that may offset the reductions in CO2 emissions. The created anaerobic conditions are favorable for methanogenic microorganisms and lead to the production of CH4. The presence of sulfate in marine waters typically inhibits methanogenesis because methanogens are outcompeted by sulfate reducers. Therefore, the rewetting of coastal peatlands with marine waters is assumed to keep CH4 emissions low. Flooding of coastal wetlands as a consequence of higher sea levels could strengthen the carbon sink function of these systems if the peatlands are able to grow their surface on par with the sea level. We used the January 2019 storm surge in the southern Baltic Sea to investigate the effects of brackish water intrusion on microbial abundance and community data along with CO2 and CH4 exchange data on a rewetted minerotrophic fen. Previous studies showed that despite the proximity to the Baltic Sea, the fen’s marine sulfate pool was substantially exhausted, and the microbial community was dominated by acetotrophic methanogens and high CH4 emission characteristic for freshwater environments. We took parallel soil cores to compare the microbial methane-cycling community to the former freshwater rewetted state from four locations along a brackish water gradient. We used high-throughput sequencing and quantitative polymerase chain reaction (qPCR) on pools of DNA and cDNA targeting total and putatively active bacteria and archaea (16S rRNA gene), methanogens (mcrA), methanotrophs (pmoA) and sulfate-reducing bacteria (dsrB). Greenhouse gas (GHG) fluxes along the salinity transect were measured locally with closed-chambers and in addition on the ecosystem level using the eddy covariance approach. Chamber measurements along the transect imply lower CH4 emissions at plots with higher salinity post-intrusion. This coincides with a drop in ecosystem CH4 fluxes and with shifts from methane-cycling to sulfate-reducing microorganisms. We expect that organisms involved in anaerobic CH4 oxidation with sulfate as terminal electron acceptor will be more prominent after the saltwater intrusion.

Moreover, the effect of rewetting with saltwater on GHG fluxes and microbial communities in degraded fens will be discussed relative to the effects of freshwater inundation and seasonal droughts which were assessed in the same location before.

How to cite: Gutekunst, C., Jenner, A.-K., Jurasinski, G., Böttcher, M. E., Koebsch, F., Kallmeyer, J., Knorr, K.-H., Unger, V., Yang, S., and Liebner, S.: Effects of saltwater intrusion on the methane-cycling microbial community of a freshwater rewetted coastal fen, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3328, https://doi.org/10.5194/egusphere-egu21-3328, 2021.

11:15–11:17
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EGU21-15327
Carolina Olid, Alberto Zannella, and Danny C.P. Lau

Shallow groundwater flow from the seasonally thawed active layer is increasingly recognized as an important pathway for delivering methane (CH4) into Arctic lakes and streams, but its contribution to CH4 emissions from thaw ponds has not been evaluated. Furthermore, the potential influence of the shallow groundwater-derived CH4 on the trophic support and nutritional quality of thaw pond food chains remains unexplored. In this study, we used a radon-mass balance approach to quantify the CH4 transport from the active layer into thaw ponds in a sub-Arctic catchment. We analysed stable isotopes and fatty acids of pond macroinvertebrates to evaluate the potential effects of CH4 inputs through active layer groundwater flows on the aquatic food chains. Our results indicate that CH4 fluxes from the active layer can sustain CH4 emissions from the ponds. Consumers in ponds receiving greater CH4 inputs from the active layer had lower stable carbon isotope signatures that indicates a greater trophic reliance on methane oxidizing bacteria (MOB), and they had lower nutritional quality as indicated by their lower tissue concentrations of polyunsaturated fatty acids. Accurate predictions of CH4 release from small thaw ponds will thus require improved knowledge of the contributions from various processes including internal production, flow paths of active layer groundwater, and MOB-consumer interactions.

How to cite: Olid, C., Zannella, A., and Lau, D. C. P.: The role of methane transport from the active layer in sustaining methane emissions and food chains in subarctic ponds, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15327, https://doi.org/10.5194/egusphere-egu21-15327, 2021.

11:17–11:19
|
EGU21-10461
Massimo Lupascu, Hasan Akhtar, Aditya Bandla, Rahayu S Sukri, and Sanjay Swarup

Fires and drainage are common disturbance factors in tropical peatlands (TP) in Southeast Asia. These disturbances alter the hydrology, vegetation composition, and peat biogeochemistry; thereby affecting the microbiome where microbial communities reside. Studies from northern peatlands have well established the role of vegetation composition in regulating the labile C, in the form of plant root exudates, and microbial community composition affecting the peat decomposition; however, for tropics, it remains unexplored. Recent studies have also established how these fire-degraded TP areas become a hot spot of sedge-mediated CH4 emission. To further our understanding of control mechanisms regulating CH4 dynamics, we investigated the composition of plant root exudates (n=3 per plant species) from sedges (Scleria sumatrensis) and ferns (Blechnum indicum, Nephrolepis hirsutula), the most commonly occurring plant species at our fire-degraded tropical peatland site in Brunei, Northwest Borneo, as well as microbial community composition in plant (n=9 for S. sumatrensis, and B. indicum, and n=5 for N. hirsutula) rhizo-compartments (rhizosphere, rhizoplane, endosphere).

         Using a targeted analysis, we found that the root exudates compounds secreted from sedge (Scleria sumatrensis) and one species of fern (Blechnum indicum) were significantly different (p<0.05) and showed a similar ratio of 2:1 for sugars (glucose, fructose) and organic acids (acetate, formate, lactate, malate, oxalate, succinate, tartrate), which is in contrast to that secreted from trees in intact tropical peatlands (1:2). Further, using 16S rRNA gene amplicon sequencing, we found that the microbial community composition in rhizo-compartments of plant species showed significant differences (p<0.001). Interestingly, the sedge species harboured a relatively higher abundance of methanogens (Thermoplasmata) and lesser methanotrophs (Alphaproteobacteria, Gammaproteobacteria) across all three compartments compared to fern species, which further supports the higher sedge-mediated CH4 emissions from fire-degraded TP.

            Our results provide fresh insights into the effects of post-fire vegetation composition in regulating the labile C and microbial community composition, and hence affecting CH4 emissions from fire-degraded TP. Further, our results can form an important basis for future CH4 dynamics studies as the emissions might increase with the expansion of degraded TPs as a consequence of frequent fire episodes and flooding

How to cite: Lupascu, M., Akhtar, H., Bandla, A., Sukri, R. S., and Swarup, S.: Root exudates compounds and microbial community composition regulates CH4 dynamics in fire degraded tropical peatland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10461, https://doi.org/10.5194/egusphere-egu21-10461, 2021.

11:19–11:21
|
EGU21-12685
|
ECS
Liudmila Krivenok and Vladimir Kazantsev

Methane is one of the main greenhouse gases in the atmosphere. Lakes are the third-largest natural source of methane on a global scale [Kirschke et al., 2013]. Currently, the chamber method is quite often applied in the measurements of diffusive GHG emissions from natural ecosystems, especially in remote areas, due to low cost and mobility. In lakes, methane can be transported to the atmosphere not only by diffusion but also by bubbling, so during measurements, it is important to divide these two pathways. We have complemented customary floating chambers with plastic shields located underside not blocking diffusive transfer but preventing gas bubbles from entering into the chamber.

The study was conducted on August 19–20, 2019 in the vicinity of Vaskiny Dachi field station (68.8663° N, 70.3040° E, Central Yamal, Western Siberia, Russia). Measurements were carried out in the central part of the thermokarst lake with a depth of 1.6 m. To compare results of customary and modified chambers, samples were taken in parallel from chambers with and without shields (two chambers of each type) every two hours during the day. Sampling and flux calculations were conducted according to [Bastviken et al., 2010]. The methane concentrations in samples were determined in the laboratory by a Crystal 5000.2 gas chromatograph with a flame ionization detector.

According to the sign test for the 0.05 p-level, methane fluxes measured using chambers with and without shields differ statistically significant considering their diurnal dynamics. At the same time, within the group of fluxes measured by the same type of chambers, no statistically significant differences were found, and mean and median flux values are higher for chambers without shields. It appears that observed differences are not due to natural variability, but due to the contribution of bubble component to the fluxes measured by chambers without shields.

 

References

Bastviken D., Santoro A.L., Marotta H. et al. 2010. Methane emissions from Pantanal, South America, during the low water season: toward more comprehensive sampling. – Environmental Science & Technology, vol. 44, No. 14, pp. 5450–5455.

Kirschke S., Bousquet P., Ciais P. et al. 2013. Three decades of global methane sources and sinks. – Nature Geoscience, vol. 6, No. 10, pp. 813–823.

How to cite: Krivenok, L. and Kazantsev, V.: Features of the diffusive methane emission measurements on lakes by chamber method, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12685, https://doi.org/10.5194/egusphere-egu21-12685, 2021.

11:21–11:23
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EGU21-15054
Irina Puzich, Alexey Sobisevich, and Zalim Dudarov

The results of passive seismic studies of subsurface fluid transport systems associated with mud volcanic phenomena in Northwestern Caucasus and the Taman mud-volcanic province are presented. Comparative analysis of results of geophysical cross-sections featuring the deep subsurface structures of several mud volcanoes obtained by means of passive microseismic sounding approach with respect to previous studies has demonstrated advantages of the ambient noise seismic prospecting. It has been shown that subvertical pathways of hydrocarbon migration and so feeding systems of mud volcanoes represent nearly-ideal case of local geological heterogeneities affecting the amplitudes of low-frequency microseismic noise. The analysis of the results was performed with respect to available geological as well as geomorphological data. At the same tine, results of past active seismic experiments with controlled vibroseismic sources were reanalyzed and followed by mathematical modeling of processes of hydrodynamic outflow under various mechanisms of mud volcanic eruptions. For several mud volcanoes there were outlined three-dimensional subvertical feeding structures in sedimentary layers and deeper in the crust, responsible for fluid migration and eruptive activity. Specific features of volcanic products (gas components and mineral inclusions in breccia) were analyzed with respect to the new geophysical data obtained.

How to cite: Puzich, I., Sobisevich, A., and Dudarov, Z.: Subsurface fluid migration associated with feeding systems of mud volcanoes in Northwestern Caucasus, results of passive seismic studies, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15054, https://doi.org/10.5194/egusphere-egu21-15054, 2021.

11:23–11:25
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EGU21-6224
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ECS
Claire C. Treat, Miriam C. Jones, Laura S. Brosius, Guido Grosse, Katey Walter Anthony, and Steve Frolking

The sources of atmospheric methane (CH4) during the Holocene remain widely debated, including the role of high latitude wetland and peatland expansion and fen-to-bog transitions. We reconstructed CH4 emissions from northern peatlands from 13,000 before present (BP) to present using an empirical model based on observations of peat initiation (>3600 14C dates), peatland type (>250 peat cores), and contemporary CH4 emissions in order to explore the effects of changes in wetland type and peatland expansion on CH4 emissions over the end of the late glacial and the Holocene. We find that fen area increased steadily before 8000 BP as fens formed in major wetland complexes. After 8000 BP, new fen formation continued but widespread peatland succession (to bogs) and permafrost aggradation occurred. Reconstructed CH4 emissions from peatlands increased rapidly between 10,600 BP and 6900 BP due to fen formation and expansion. Emissions stabilized after 5000 BP at 42 ± 25 Tg CH4 y-1 as high-emitting fens transitioned to lower-emitting bogs and permafrost peatlands. Widespread permafrost formation in northern peatlands after 1000 BP led to drier and colder soils which decreased CH4 emissions by 20% to 34 ± 21 Tg y-1 by the present day.

 

How to cite: Treat, C. C., Jones, M. C., Brosius, L. S., Grosse, G., Walter Anthony, K., and Frolking, S.: Methane emissions from high-latitude peatlands during the Holocene from a synthesis of peatland records, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6224, https://doi.org/10.5194/egusphere-egu21-6224, 2021.

11:25–11:45