But…, understanding methane dynamics in the aquatic realm is still a major scientific challenge because it is governed by a vast diversity of geological, oceanographic/limnological, biological factors and anthropogenic causes.
In this session we will discuss controls on methane dynamics in marine and freshwater systems at present, in the geological past, and in future scenarios. Within this overarching theme we welcome contributions related to the following topics:
- methane formation: from water-rock interactions to petroleum systems and microbial methanogenesis
- methane transport: from subsurface fluid flow to bubble and diffusive transport mechanisms and fluxes.
- methane seepage and mud volcanoes
- anthropogenic factors: from hydrocarbon exploitation to energy infrastructure and hydraulic structures
- methane sinks: from microbes, biogeochemical pathways and kinetics to physicochemical processes and gas hydrate formation
- timescales: variations on diel, seasonal, and geological time scales
- methane-derived carbonates, microbe-mineral interactions, and molecular/micro/macro fossils
- methane releases in the geological past, consequences and climate change
Orals: Thu, 1 May | Room 2.95
The Upper Paleozoic Carboniferous Taiyuan-Shanxi Formation acts as the main hydrocarbon supply layer for tight sandstone gas in the Ordos Basin. The hydrocarbon generation and expulsion characteristics as well as the hydrocarbon generation potential of coal, carbonaceous mudstone, and dark mudstone are crucial matters in the exploration and development of tight sandstone gas in the southern part of the basin. Considering that the maturity in the southern Ordos Basin is generally above 2.0%, to restore the original hydrocarbon generation potential, in this study, low-mature samples of three types of coal-measure source rocks from the Carboniferous Taiyuan Formation in the Chengning Uplift of the Huanghua Depression in the Bohai Bay Basin were collected from the same strata. Different simulation temperatures ranging from 350 to 700 °C with a gradient of 50 °C were set. Hydrocarbon generation and expulsion simulation experiments in a closed system were conducted, and the residual and expelled hydrocarbons of the source rock simulation samples under different maturity gradients were obtained. The maturity of each simulated temperature point was calibrated by coal samples. Additionally, the source rock samples before and after the simulation were subjected to mass weighing, total organic carbon (TOC) analysis, rock pyrolysis (Rock-Eval), and quantitative analysis of hydrocarbon expulsion. The results indicate that as the simulation temperature increases, the oil generation process mainly occurs before 400 °C (Ro = 1.13%). Meanwhile, gas generation continuously increases from 300 °C (Ro = 0.83%) to 700 °C (Ro = 4.35%) without reaching a peak. The percentage of methane gradually rises and reaches over 95%. Combined with basin modeling, it is determined that the Late Jurassic to Early Cretaceous is the main gas generation period. At an experimental temperature of 700 °C in the closed system, the organic carbon conversion rate of dark mudstone is 77.1%. In contrast, coal has an organic carbon conversion rate of less than 20%, and carbonaceous mudstone has a rate of less than 30%. This shows that coal and carbonaceous mudstone still have significant hydrocarbon generation potential under high-temperature conditions.
How to cite: Zhang, Y.: Study on gas generation process of high-over mature coal-measure source rocks in southern Ordos Basin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3166, https://doi.org/10.5194/egusphere-egu25-3166, 2025.
The studies of deep-sea gas venting associated with occurrences of gas hydrates in the Amazon Cone has increased the interest of the world scientific community in understanding the role of the Amazon region in the Earth's climate system. Gas plumes have been observed to align along the edge of the regional gas hydrate stability zone in several areas, suggesting the climate-driven dissociation of gas hydrates, and along faults related to the gravitational collapse of the fan. The gas that migrates toward the seabed is stored in gas hydrates and/or authigenic carbonates or released to the oceans by seafloor venting.
Here, we present data from gas hydrates that were sampled during the AMAGAS campaign offshore Brazil in May-June 2023. Five samples of methane hydrates were sampled and their dD and d13C measured. In addition, the abundance of doubly substituted isotopologues of methane (13CH3D and 12CH2D2) were measured for one sample. It is very important to mention that if the compounds have reached equilibrium with respect to their distributions of isotopes among all possible isotopologues, the proportions of 13CH3D and 12CH2D2 will be a function of temperature.
Results of the methane stable isotopes (δ13C and δD) of hydrate-bound for the Amazon fan indicated the dominant microbial origin of methane via carbon dioxide reduction, in which 13C and deuterium isotopes were depleted (δ13C and δD of -90% to -70% V-PDB and -250 to -150% V-SMOW, respectively). Regarding clumped isotopes, Δ13CH3D and Δ12CH2D2 values from +5.5 ‰ and +16.6 ‰, respectively. The hydrate samples are located around the thermodynamic equilibrium line in the Δ13CH3D vs. Δ12CH2D2 space, and their isotopic compositions correspond to apparent temperatures of °C and °C for Δ13CH3D and for Δ12CH2D2, respectively.
Given the geothermal gradient in the area, this temperature corresponds to a depth of about 1000 meters suggesting methane is migrating upwards with deeper fluids. These observations concur with seismic evidence of signal wipe-outs consistent with the rise of gas-bearing fluids along the faults.
How to cite: Rodrigues, L. F., Gilbert, A., Nakagawa, M., Ketzer, J. M., Sivan, M., Röckmann, T., Augustin, A. H., Miller, D., Cupertino, J. A., and Junior, F. C.: Clumped isotope constraints on the origin of methane hydrate from the Amazon Cone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21093, https://doi.org/10.5194/egusphere-egu25-21093, 2025.
Active venting of methane from organic matter buried below the seafloor supports a unique diversity of life in the overlying sediment and on the seafloor. The consumption of this methane by microbial consortia sustains animal symbionts and reduces the amount of methane reaching the atmosphere, representing a key methane sink in the marine carbon cycle. Microbially mediated sulfate-dependent anaerobic methane oxidation also precipitates authigenic carbonate rocks. Under anoxic conditions, these carbonates can form large outcropping rock features on the seafloor that provide hard substrate for seep-associated endemic symbiotic macro and micro fauna, affecting deep ocean biodiversity. In the presence of oxygen, however, microbial and animal activity promotes the dissolution of seep carbonates, returning carbon to the water and short-term carbon cycle. To examine how seep chemical and biologic activity affects carbonate formation and dissolution, we determined the age, composition, and growth structure of seep carbonates from a range of water depths, ambient oxygen concentrations, and methane flux environments. Carbonates were collected from Southern California Borderland (800 and 1020 m) and Aleutian Trench (2020 m) seeps and subsampled to allow comparisons across both km- and µm- scales. U/Th dating revealed carbonate ages ranging from 201±100 to 10,138±63 years. Micro-scale rock fabric texture, microbe-mineral paragenesis, and elemental composition were determined from Scanning Electron Microscope backscatter images and energy-dispersive x-ray detector spectrum maps along with thin-section Electron Probe Micro-Analyzer images. Micro-scale results are used to examine the microbial-mineral interactions visible through fossil and crystal inclusions and discontinuities. We contextualize the macro-scale growth histories of the dated carbonates by relating them to variations in glacial-interglacial associated sea level and methane hydrate stability; overlying water column productivity and circulation related oxygen availability; and tectonic or tidal associated methane flux. These preliminary results improve our understanding of long-term biological and chemical processes associated with seep carbonate formation and dissolution, and their implications for global carbon cycling.
How to cite: Homola, K., Norbert, F., Schroeder-Ritzrau, A., Smrzka, D., Himmler, T., and Treude, T.: Reconstructing Microbial & Animal Associated Formation and Dissolution of Methane Seep Carbonates using U/Th Dates and Electron Microscope Imagery, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15270, https://doi.org/10.5194/egusphere-egu25-15270, 2025.
Microbial iron and manganese respiration processes have been observed in deep methanic sediments of lacustrine and marine environments, sometimes accompanied by deep methane sink. These findings challenge the “classical” model of microbial respiration in aquatic systems. Nonetheless, assessments of the type and relative role of these respiration processes in the methanic zone are lacking. Here, we quantify both the thermodynamic and the kinetic controls of potential iron and manganese respiration processes in the methanic sediments of lacustrine and marine sites – Lake Kinneret (LK) and the Southeastern Mediterranean Sea (MedS). Using theoretical bioenergetic methods, we develop a model to calculate catabolic rates, considering both kinetic and thermodynamic factors. Then, we estimate the biomass growth rates and microbial community sizes of expected iron and manganese reducers. Additionally, we perform a Monte Carlo simulation to account for variations in uncertain parameter values, along with a sensitivity analysis. Together, these calculations enable estimation of the expected total reaction rates of the various metabolic processes.
Our results indicate that the type of consumed oxide, which determines its thermodynamic and kinetic properties, is more significant in influencing bioreaction rates than its concentration. Thus, bioreactions with amorphous manganese oxides are more favorable than those with highly reactive iron oxides. Among the iron oxides, the reduction of amorphous iron oxyhydroxide and ferrihydrite are the only reactions capable of generating biomass in the methanic sediments at both sites. In both environments, manganese oxide reduction by ammonium and methane oxidation are expected to be significant, while manganese oxide reduction by hydrogen and acetate oxidation are expected to be considerable only in LK. The most probable iron oxide reduction process in LK is hydrogen oxidation, followed by methane oxidation. In the MedS iron oxide reduction is most probably coupled to the oxidation of ammonium (Feammox) to molecular nitrogen, and in a few cases may be coupled to methane oxidation. The Monte Carlo simulation agrees with the nominal model results for manganese reduction, and additionally predicts that iron reduction may be possible with some combinations of parameter values. These findings improve our understanding of the thermodynamic and kinetic controls on the composition of microbial communities and their effect on the geochemistry of methanic sediments.
How to cite: Neumann Wallheimer, R., Halevy, I., and Sivan, O.: Modeling the Controls on Microbial Iron and Manganese Reduction in Methanic Sediments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19544, https://doi.org/10.5194/egusphere-egu25-19544, 2025.
The anaerobic oxidation of methane (AOM) coupled to sulfate reduction (SR) is a key microbial process in the sulfate-methane transition zones (SMTZ) of cold seeps. In this process, anaerobic methanotrophic archaea (ANME) oxidize methane to inorganic carbon and transfer gained electrons to their sulfate-reducing partner bacteria (SRB), which, in turn, reduce sulfate to sulfide. While electron transfer is a well-established interaction mechanism, interactions on the molecular level, involving, for example, low-molecular-weight organics, have not been investigated.
Here, we examined the presence of such molecules in cold seep sediments from Astoria Canyon. We found unusually high concentrations of the disaccharide’s trehalose and sucrose in both the pore water and the solid phase of the sediments. Elevated levels of these sugars in the SMTZ, along with negative δ¹³C values between -55 and -80‰, indicate the production by the AOM core community. The presence of ANME-2 and SRB lipids with similar δ¹³C values supports this interpretation. A stable isotope probing experiment on sediments from the same cold seep system confirms the AOM-dependent production of these disaccharides. There, trehalose and sucrose showed strong 13C-incorporation upon addition of ¹³C-labeled inorganic carbon, alongside the lipids of the autotrophic AOM community.
While the precise role of trehalose and sucrose production during AOM remains unclear, our findings suggest that they may serve as intermediates in ANME/SRB interactions and possibly in the production or conservation of the extracellular polymeric substance (EPS) that encases them. To further elucidate their biochemical significance and functional role, we aim to quantify trehalose and sucrose in both pore water and sediment. Understanding the role of these disaccharides in AOM consortia will provide deeper insights into microbial interaction and adaptations in methane-dominated and other extreme environments.
How to cite: Stock, L., Wegener, G., Torset, S., Lipp, J., Dirksen, L., Liebeke, M., Lapham, L. L., Hildebrand, A., Pohlman, J., Lalk, E., and Elvert, M.: Production of the disaccharide’s trehalose and sucrose by ANME‑2/SRB consortia in a cold seep at the Astoria Canyon , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5580, https://doi.org/10.5194/egusphere-egu25-5580, 2025.
Cold seeps are chemosynthetic ecosystems on the seafloor that harbor diverse benthic communities by the supply of methane-rich fluids from subsurface reservoirs. Despite the global significance in biogeochemical cycling of cold seeps, the relative importance of methane-related microbial processes and the impact of methane leakage on the upper ocean remains not fully understood. We integrated a suite of biogeochemical approaches to elucidate microbial activity of methane oxidation in cold seeps sediment and overlying waters of South China Sea, and further estimate the role of methane oxidation in the regulation of methane emissions. Stable carbon isotope of methane suggested a biological origin and δ13C values of DIC indicated the dominance of methane oxidation. Radiotracer labelling showed that methanogenesis, anaerobic oxidation of methane and sulfate reduction concurrently occurred in seep sediments. In the overlying waters, methane concentrations in the vicinity of the seeps (up to ~71 µM) were well above background levels (~1−2 nM) and methane oxidation rates reached up to 8658 nmol L−1 day−1, among the highest rates documented in pelagic ocean. Using a machine learning model, we complied a database of methane emission and oxidation from global seeps. We estimated a global methane emission rate of 57.8 Tg yr−1 from seeps to the overlying water columns and 31%−63% of this methane could be oxidized aerobically around seeping waters, suggesting that aerobic methanotrophy significantly reduces the emissions of methane released from submarine seeps. Our results also indicated that methane leakage from seeps could impact metabolic activity and carbon cycling in the deep ocean.
How to cite: Zhuang, G. and Mao, S.: Methane oxidation and emissions in cold seeps: from South China Sea to global scale, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4957, https://doi.org/10.5194/egusphere-egu25-4957, 2025.
Continental margins harbor substantial reservoirs of methane, generated by microbial activity or thermogenic processes. In the North Sea, commercial extraction of subsurface methane is common, and wellheads of depleted gas field are typically sealed with concrete. Despite these measures, abandoned wells may still leak methane to the water column and potentially to the atmosphere contributing to atmospheric methane levels. With several thousand of such wells scattered across the North Sea, the scale of these emissions and the processes leading the fate of the released methane—whether through microbial oxidation or direct escape into the atmosphere—are still not well understood. We investigated methane dynamics at 3 different locations in the Dutch sector of the North Sea (A15-03 and B17-05 abandoned wells, B17-04 likely natural seepage), combining various methods, including autonomous tools. For a time period of 3 days, we continuously measured in situ bottom water methane concentrations and near-bed hydrodynamics using a laser spectrometer and ADCP mounted on a mini-lander. We recorded several episodic events characterized by increasing methane concentrations peaking at 550nM at A15-03 and 800nM at B17-05. In contrast, maximum concentrations remained comparably low at B17-04 with values of up to 80nM. To further resolve vertical methane distribution, we conducted repeated hydro casts that also showed events of rising water column methane concentrations. Discrete water samples were additionally taken to quantify microbially mediated methane oxidation rates, revealing the presence of methanotrophs that could act as a filter for methane escaping to the atmosphere. In this presentation, we will discuss our data in relation to environmental drivers, including tides, currents and biological factors such as methanotrophic community dynamics.
How to cite: Delre, A., de Bruin, G., Velzeboer, I., de Haas, H., Mienis, F., de Stigter, H., Riekenberg, J., van Dijk, R., Huybens, R., Engelmann, J., Reichart, G.-J., and Niemann, H.: In situ monitoring reveals episodic water column methane anomalies at abandoned wells in the Dutch North Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12579, https://doi.org/10.5194/egusphere-egu25-12579, 2025.
Methane, traditionally thought to be produced only under anoxic conditions, is widely observed in oxic surface layers of freshwater lakes-a phenomenon known as "methane paradox". The methane paradox results from a complex interaction of biotic and abiotic processes which could vary substantially across different lacustrine systems. The variability in biological and geochemical characteristics of lakes can influence methane production and transport, limiting our understanding of the main drivers sustaining elevated methane concentrations in oxic surface waters.
In this study, we investigated the methane paradox in three Austrian peri-alpine lakes differing in size and trophic state, and compared the factors controlling oxic methane production in these lakes during different seasons. Two of the studied lakes, Mondsee (14.2 km²) and Attersee (49.5 km²), are located within the same catchment area. Lake Mondsee is mesotrophic and lake Attersee ultra-oligotrophic. Lake Lunzsee is oligotrophic, and the smallest lake studied (0.7 km²). Elevated methane concentrations were observed in all three lakes during both summer and autumn seasons indicating year-round occurrence of the methane paradox in the lakes. Subsurface methane concentrations ranged from 100 to 400 nM which was substantially higher than the atmospheric equilibrium (~3 nM), indicating oxic methane production as a potential, yet unaccounted, source of methane to the atmosphere. Positive correlations of methane concentrations with chlorophyll-a and ammonium concentrations suggested a link with biological activity. Additionally, high phytoplankton abundances coincided with the methane maximum, further indicating that primary productivity was one of the main drivers associated with oxic methane production. Methane concentrations were the highest in mesotrophic lake Mondsee, which was dominated by cyanobacterial phytoplankton. In contrast, the phytoplankton composition in lake Attersee and Lunzsee was mainly composed of eukaryotic species.
Our findings indicate that the magnitude of subsurface methane concentrations in peri-Alpine lakes is influenced by nutrient availability, which is one of the key factors determining phytoplankton taxonomic composition. Our results demand a further investigation of oxic methane production pathways associated with different phytoplankton taxa to better understand how future eutrophication events might affect methane dynamics in peri-Alpine lakes.
How to cite: Sharma, N., Felsberger, M., and Bayer, B.: Potential drivers and seasonal comparison of the methane paradox in three Austrian peri-Alpine lakes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16134, https://doi.org/10.5194/egusphere-egu25-16134, 2025.
Eutrophic shallow freshwater ecosystems often develop floating filamentous microalgae on their surface during spring and summer. In recent years, this phenomenon has become more pronounced due to rising temperatures and drier conditions, with floating algae sometimes even covering the entire surface of water bodies. These floating mats, known as Floating Algal Beds (FLAB), are primarily composed of phytoplankton from the group Chlorophyte. New evidence suggests that phytoplankton can produce methane (CH₄), raising the possibility that these floating beds may represent overlooked sources of CH₄ emissions to the atmosphere. However, FLAB may also reduce CH4 emissions by decreasing the CH₄ diffusion at the air-water interface and/or trapping CH₄ bubbles. Consequently, the net impact of FLAB on CH₄ emissions in freshwater ecosystems remains unclear. To address this knowledge gap, this study aims to investigate how FLAB influence CH₄ dynamics by examining both biological processes (such as CH₄ production pathways and CH₄ oxidation) and physical factors (as CH4 bubble retention). To achieve this, we conducted field mesocosm experiments in a eutrophic ditch in the Netherlands during the summer of 2024. Eight mesocosms were deployed, with four containing FLAB on their surface and four controls without FLAB. The mesocosms were closed at the sides to prevent lateral transport and open at the surface and bottom allowing for the inclusion of CH₄ sediment production, CH₄ oxidation, CH₄ bubble dissolution, CH₄ diffusive flux at the air-water interface, and potential CH₄ production in the water column (including contributions from FLAB). Over a five-day period, we monitored all these CH₄ pathways alongside several other limnological parameters in both the treatment and control mesocosms. Additionally, we also incubated sediment, water and FLAB separately, to test for CH4 production and oxidation in each one of these compartments. Preliminary results indicate that mesocosms with FLAB exhibited CH₄ diffusive emissions on average ten times higher compared to the control mesocosms. Further analysis is needed to determine whether these elevated emissions originate from CH₄ production by FLAB, increased sediment and/or water column CH₄ production, or reduced CH₄ oxidation in the presence of FLAB; but these preliminary findings already suggest that FLAB significantly influences CH₄ dynamics in eutrophic systems. This points to a potential increase in the climate-ecosystem feedback loop, were climate change drives higher temperatures and periods of drought, leading to more stagnant waters. This, in turn, promotes the growth of FLAB, which enhances CH4 emissions.
How to cite: Baliña, S., Paranaiba, J. R., Colina, M., Weideveld, S. T. J., Fomenko, H., Seitz, D., Groenboss, R. E., Sooniste, S. A., Qu, Q., and Kosten, S.: Floating algal beds and aquatic methane emissions:a potential positive ecosystem-climate feedback loop, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6858, https://doi.org/10.5194/egusphere-egu25-6858, 2025.
Methane (CH4) emissions from lakes were considered entirely natural by the Intergovernmental Panel on Climate Change (IPCC) and the Global Methane Budget (Saunois et al., 2020). However, eutrophication, via enhanced inputs of nutrients (mostly total dissolved phosphorus, TDP) from the surrounding catchments has been shown to be a substantial control factor of both diffusive and ebullitive lake CH4 fluxes, suggesting that a fraction of these emissions are in fact attributable to human factors. Here, we adopted a newly developed physically-resolved process-based model of the coupled carbon-oxygen-methane cycles, FLaMe (Fluxes of Lake Methane), to simulate decadal trends (1901-2070) in CH4 emissions and decompose them into natural and anthropogenic components. By configurating global lakes from the HydroLAKES database (with an area of 2.47 million km2), we estimated that global lake CH4 emissions already increased by about 20 % over the last century (from 28±1 to 34±1 Tg CH4 yr-1). Furthermore, we adopted a factorial experiment approach to conduct the attribution analysis, and found that over this time period, eutrophication and climate contributed to 70% and 30% of the cumulative growth in global lake CH4 emissions, respectively. Moreover, we identified a progressive shift from eutrophication to climate control on global lake CH4 emissions from the early part till the end of the last century. In the future, we project that global lake CH4 emissions will further increase to reach 39±2, 44±4 and 45±5 Tg CH4 yr-1 by year 2070 under climate scenarios SSP1-2.6, SSP3-7.0 and SSP5-8.5, respectively. Our analysis implies that the future risks stemming from lake CH4 emissions could be reduced by efficient nutrient removal from urban and agricultural sources.
How to cite: Feng, M., Maisonnier, M., Bastviken, D., Lauerwald, R., Peng, S., Ciais, P., Arndt, S., and Regnier, P.: Attribution of increasing global lake methane emissions to climate and eutrophication using the FLaMe model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10399, https://doi.org/10.5194/egusphere-egu25-10399, 2025.
Posters on site: Wed, 30 Apr, 08:30–10:15 | Hall X1
Global warming induced alterations in ocean temperature regimes, and precipitation patterns are increasingly impacting coastal ecosystems, leading to shifts in water column properties. These changes may have profound implications for microbial communities such as methane-oxidizing bacteria (MOBs), which play a critical role in regulating methane fluxes and ecosystem dynamics. In this study, we investigate the resilience and adaptability of aerobic MOBs in response to changing environmental conditions. Through microcosm incubation experiments with waters from the North Sea and the Wadden Sea collected during different seasons, we explore how variations in methane availability, temperature, and salinity influence the MOB community structure and functional capacity. Our results reveal an increase in the relative abundance of MOBs to up to 57% in experiments with elevated methane concentrations, highlighting the primary role of methane availability for MOB community development. Temperature and salinity variations, on the other hand, exerted lesser effects on MOB composition and relative abundance. A strong effect on MOB community development was furthermore caused by the origin of the inoculum (location and season). Our results thus suggest a functional redundancy in the variable pools of microbial inocula enabling multiple MOB clades to cope with drastic changes in environmental parameters. The adaptability of MOB communities is key to understand their role in mitigating methane emissions from coastal regions in a future ocean with potentially elevated methane, temperature and variable salinity levels.
How to cite: Niemann, H., de Groot, T., Engelmann, J. C., Ramond, P., Diorgio, J., and van Bleijswijk, J.: Adaptation of methane-oxidizing bacteria to environmental changes: implications for coastal methane dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4139, https://doi.org/10.5194/egusphere-egu25-4139, 2025.
With a contribution of about one third, methane is the second most important greenhouse gas in the climate system. In addition to a biogenic formation, e.g. in wetlands, methane also is emitted during anthropogenic industrial activities. BGR is investigating abandoned onshore oil and gas wells in Germany, which are generally plugged and buried, for their relevance as sources of methane. Initial results from studied wells examined so far (about 75 wells) indicated no or very low methane emissions at very few sites. A controlling process for low methane emissions for the wells could be microbial methane oxidation, which is an important process in organic-rich soils overlying wells in Northern Germany (Jordan et al., accepted).
We present here data from soil above a plugged oil well, drilled in the early 1920s and located at Nienhagen near Hannover (Germany). At the well ~40 mg CH4 h-1 were emitted (average range for plugged US oil wells ~50 to 170 mg h-1 per well; Williams et al. 2021). Gas geochemical analyses of the soil gas confirm the presence of natural gas (up to 8 % methane and 600 ppm ethane) and the δ13C of the methane supports that the majority is thermogenic (-47.1 ‰). In addition to natural gas, we also found petroleum in the soil, which reached up to 80 % soil total organic carbon. Our data suggest a complex mosaic of hydrocarbon-altering effects dominated by products from the microbial degradation of well-derived oil and natural gas (e.g., propane oxidation). It is likely that O2 availability controls the degradation of petroleum in the soil under investigation, because the strongest degree of degradation was found in the upper soil horizons. The properties of the formerly produced oil exclude biodegradation in the reservoir, so the degraded oil must have been formed during the ascent or in the topsoil. The gas geochemical composition of the soil gases indicates also deeper, anaerobic processes, such as methanogenesis, probably with petroleum as the carbon source. Soil microcosms from different depths showed, indeed, a rapid onset of microbial degradation of added oil both under aerobic and anaerobic conditions in the lab. Although processes in a deeper biosphere appear to play a role here, it is likely that mostly the microbial processes in the soil surrounding the well regulate the composition and quantity of oil and gas. In conclusion, the (i) high degree of degradation in the natural gas components in the soil and petroleum, as well as the overall (ii) only low methane emissions, indicate that the Nienhagen well is only leaking relatively little and that a “microbial hydrocarbon filter” is established and active.
References
Jordan, S.F.A., Schloemer, S., Krüger, M., Heffner, T., Horn, M.A., Blumenberg, M., (accepted) Preprint. Interferences caused by the microbial methane cycle during the assessment of abandoned oil and gas wells. EGUsphere. doi:10.5194/egusphere-2024-1461
Williams J. P., Regehr A. and Kang M. (2021) Methane Emissions from Abandoned Oil and Gas Wells in Canada and the United States. Environmental Science & Technology 55, 563–570.
How to cite: Blumenberg, M., Scheeder, G., Jordan, S. F. A., Krüger, M., and Schlömer, S.: Microbial turnover of hydrocarbons at a leaking abandoned oil well in Germany, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4230, https://doi.org/10.5194/egusphere-egu25-4230, 2025.
The study of organic matter in sediments is crucial for advancing energy resource exploration and understanding geological and biogeochemical processes. This study focuses on the Amazon Cone (Brazil), a region of significant interest following the last decade's discovery of gas hydrates in Brazilian waters. Methane, the main gas released by dissociating hydrates, is a potent greenhouse gas with biogenic or thermogenic origins. Therefore, understanding its pathways in sedimentary environments is fundamental for energy exploration and climate sciences. Building on data from the 2023 Amaryllis-Amagas Oceanographic Mission aboard the Marion Dufresne research vessel, this work investigates gas hydrate systems on Brazil’s equatorial margin through biomarker analysis. A total of 89 samples from seven piston cores were analyzed by Rock-Eval Pyrolysis, and 20 samples were selected based on Total Organic Carbon (TOC) values and core positions (top, middle, and bottom). Soxhlet extraction with dichloromethane/methanol (8:2) was followed by liquid chromatography to separate saturated hydrocarbons, aromatic hydrocarbons, and polar fractions, and GC/MS (Gas Chromatography-Mass Spectroscopy) was used for compound identification. N-alkanes ranging from n-C18 to n-C35 were identified with a predominance of long-chain n-alkanes (n-C25 to n-C35) with a marked odd-over-even carbon number preference (e.g., the greater abundance of nC27, nC29, nC31, and nC33), which indicate an input of terrestrial plant-derived organic matter. Furthermore, pristane and phytane are present in very low abundance. Terpanes distribution points to anoxic depositional conditions, and the domination of ββ-C30, ββ-C31, and ββ-C32 compounds corresponds to a low level of thermal maturity. The steranes analysis also observed low maturity, showing a predominance of biological isomers, while the diasteranes DIA27S > DIA27R ratio emphasizes clay-catalyzed processes in a clastic, clay-rich sedimentary environment, characteristic of the Amazon Cone. The terrestrial input coupled with evidence of bacterial activity highlights the role of microbial processes in shaping the organic matter composition. Also, the low thermal maturity of the organic matter aligns with favorable conditions for biogenic methane production. Likewise, the clay-rich environment of the Amazon Cone facilitates the trapping and preservation of gas hydrates by providing structural stability to the sediments. Combined with the anoxic conditions inferred from the biomarkers, these findings are consistent with the microbial pathways critical for methane production and gas hydrate stability. Therefore, the Amazon Cone appears to be a region where microbial and geological processes converge to create and maintain methane hydrate deposits. This underscores the potential of the area not only as a site of scientific interest but also as a candidate for future energy exploration, with the added significance of understanding methane’s role in global carbon cycling and greenhouse gas emissions.
How to cite: Rizzi, M. A. M., da Silva, T. F., Cagliari, J., Girelli, T. J., Augustin, A. H., Rodrigues, L. F., Miller, D. J., Cupertino, J. A., and Chemale Jr., F.: Exploring biomarker signatures of methane hydrates in the Amazon Cone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4511, https://doi.org/10.5194/egusphere-egu25-4511, 2025.
The late-stage gas charging diversifies the material composition and chemical characteristics of the early reservoir, while the differences in the range and intensity of gas invasion lead to the formation of complex distribution pattern of oil and gas, which restricts a detailed understanding of the mechanisms of oil and gas accumulation. The research focuses on the Tahedong area of the Tarim Basin, utilizing geological background and integrating techniques such as crude oil geochemical analysis, fluid inclusion observation, scanning electron microscopy, and methane carbon isotope analysis to quantitatively characterize the intensity of gas invasion. The results indicate that: (1) The loss of n-alkanes in the research area is significant, with a loss rate ranging from 60.11% to 80.58%, while aromatics are relatively enriched, and the reservoir rocks develop gas inclusions with the presence of gas pores in the asphalt. (2) The gas charging ratio in condensate oil reservoirs and natural gas reservoirs ranges from 48% to 92%, with a high degree of gas invasion; in light oil reservoirs, the ratio ranges from 25% to 34%, with a moderate degree of gas invasion; in normal oil reservoirs, gas invasion is not significant. (3) The gas generation range of the source rocks in the Himalayan period matches the range of gas charging ratio greater than 35%, and the drying coefficient of natural gas decreases gradually from southeast to northwest, and the relative density increases, reflecting the decrease of natural gas charging ratio.It is therefore believed that the study area has developed varying intensities of gas invasion, with the southeastern region experiencing the strongest gas invasion, resulting in the formation of condensate oil and natural gas reservoirs. As the distance increases towards the northwest, the gas invasion weakens and overlaps with earlier oil reservoirs, transitioning in phase to light oil and medium oil. This understanding is of significant guiding importance for the exploration of late high-maturity oil and gas in the Tahedong area.
How to cite: Wang, J., Liu, H., and Su, Y.: Quantitative characterization of gas invasion intensity in oil and gas reservoirs using methane carbon isotopes: Example from Tahedong Area in the Tarim Basin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5293, https://doi.org/10.5194/egusphere-egu25-5293, 2025.
Blue Carbon Ecosystems (BCEs) play a crucial role in carbon sequestration and climate change mitigation. However, their carbon cycle dynamics, particularly under changing environmental conditions, remain insufficiently understood. This study investigates the Qigu lagoon ecosystem, a representative BCE along Taiwan's southwestern coast. Adjacent to mangrove forests, the lagoon harbors rich biodiversity and holds substantial carbon storage potential but faces increasing threats from global climate change and intensified human activities. To address these challenges, we conducted integrated field sampling and laboratory analyses to examine the biogeochemical processes governing carbon cycling in the Qigu lagoon. Sediment cores were collected from multiple locations across the lagoon and analyzed for dissolved methane concentrations, total alkalinity, dissolved ions, and nutrient levels. These measurements aim to quantify sedimentary carbon burial rates, assess greenhouse gas emissions, and evaluate nutrient cycling within the ecosystem. Preliminary results indicate that, while the lagoon effectively sequesters organic matter in its sediments, it simultaneously emits significant amounts of methane (CH₄), a potent greenhouse gas. This discovery raises important questions about whether methane emissions from wetlands—traditionally regarded as natural carbon sinks—may substantially offset the carbon burial and absorption capacity of marine blue carbon systems. Understanding the balance between carbon sequestration and greenhouse gas emissions is critical for accurately evaluating the climate mitigation potential of BCEs. Findings from this study will provide valuable insights for the conservation and sustainable management of coastal ecosystems, contributing to global efforts in combating climate change.
How to cite: Chuang, P.-C., Tseng, Y.-K., Lee, H.-F., and Hsu, C.-W.: Exploring Carbon Dynamics in Taiwan's Qigu Lagoon: The Balance Between Carbon Burial and Methane Emissions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7624, https://doi.org/10.5194/egusphere-egu25-7624, 2025.
Cold-water corals in the Hola area off the coast of Vesterålen (N. Norway), thrive on a substrate made of methane-derived carbonate and are closely associated with microbial mats. High resolution seafloor imagery and sediment samples collected during the EMAN7 expedition in June 2022 allowed us to reconstruct the spatial relationships between methane seepage and seafloor habitats and gain insights into subsurface biogeochemical processes directly influencing benthic ecosystems. Here, we present the fine-scale orthomosaics and habitat maps covering 1680 m2 of seafloor in proximity to the coral mounds and the geochemistry (sedimentary carbon and nitrogen, pore waters) of a pushcore and blade core collected from a microbial mat and a reference area, respectively. The push core revealed the presence of a macroscopic microbial biofilm at 9 cm depth within the sediment, which is associated with a sharp drop in downcore δ13C of sedimentary organic matter and dissolved inorganic carbon and in C/N ratios. Results from 16S rRNA gene analyses conducted on the uppermost 10 cm of sediment in the pushcore showed a drop in alpha diversity and a compositional change from high abundance of ASVs representing Protebacteria to those representing Halobacterota that we ascribe to the occurrence of methanotrophic consortia performing anaerobic oxidation of methane
Acknowledgments: this research was funded by EMAN7 project (Research Council of Norway grant No. 320100) and supported by AKMA project (Research Council of Norway grant No. 287869) and EXTREMES (UArctic UA 06/2024)
How to cite: Ferré, B., Argentino, C., Fallati, L., Panieri, G., Petters, S., Bernstein, H. C., Barrenechea, I. A., and Savini, A.: Methane-related seafloor habitats and sediment microbiome at a cold-water corals site off the Vesterålen coast, northern Norway, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9501, https://doi.org/10.5194/egusphere-egu25-9501, 2025.
The Tatarsky Trough lies near the eastern coast of the Far Eastern Russia, extending into the northern parts of the East Sea of Korea (also known as the Sea of Japan). This region is renowned for its tectonic activity and active gas seeps, making it an ideal natural laboratory for studying the biogeochemical dynamics of gas-rich sediments. In this study, we investigated two sediment cores, LV67-07HC (358 cm core length) and LV67-19HC (398 cm core length), recovered from active fault zones on the eastern slope (water depths of 300–700 m) during the SSGH expedition aboard the R/V Akademik M. A. Lavrentyev in 2014. Using a combination of lipid and nucleic acid analyses alongside other parameters (i.e., gas and porewater composition), we aim to assess the potential environmental roles of archaeal communities inhabiting these seepages. Both cores exhibited high abundances of lighter hydrocarbon gases, primarily methane and carbon dioxide. The sulfate-methane transition zone (SMTZ) was clearly delimited, with its depth varying based on the extent of deep fluid ascent within coal-gas areas. Notably, significant concentrations of 13C-depleted archaeal lipids - glycerol dialkyl diethers (DGDs) and glycerol dialkyl glycerol tetraethers (GDGTs) - were observed near dense carbonate concretions in core LV67-07HC (91–185 cm depth). This finding suggests sustained methanotrophic activity associated with gas seepage events in the Tatarsky Trough. In these settings, archaeal sequences predominantly revealed the presence of ANME-1 clades, which are known to thrive under intense seepage conditions within coal-gas zones. Considering that gas hydrate destabilization in the Tatarsky Trough could trigger slope failures, a notable geological hazard, our results offer valuable insights into the transport and removal processes of hydrocarbon gases, aiding in the evaluation of their impact on regional carbon cycling.
How to cite: Lee, D.-H., Kim, J.-H., Stadnitskaia, A., Lee, Y. M., Jin, Y.-K., Huguet, C., Jeong, E.-J., and Shin, K.-H.: Biogeochemical signatures for archaeal communities involved in active gas seeping on Tatarsky Trough, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15926, https://doi.org/10.5194/egusphere-egu25-15926, 2025.
Gas hydrates are relevant to global carbon cycling, climate change and ocean acidification. In particular, hydrates play an important role in sub-seafloor fluid migration because they reduce the porosity and permeability of sediments. Gas hydrates, and their associated underlying free gas zones, have also been linked to sediment failure and submarine mass transports. The active Hikurangi Margin hosts New Zealand’s largest gas hydrate province, with concentrated accumulations generally focused below accretionary thrust ridges.
Recently acquired high-resolution Ocean-Bottom-Seismometer (OBS) data at the southern Hikurangi Margin images highly reflective layers beneath the accretionary Honeycomb Ridge. This ridge is of particular interest as it is thought to host a concentrated gas hydrate system. Unlike previous surveys, we have the advantage of being able to record converted shear waves that help us identify the nature of the highly reflective layers in the gas hydrate stability zone. In March 2023, we deployed 20 OBS from R/V Tangaroa with a USBL-wired system to position each OBS with 100 m spacing along an existing 2D seismic profile. A 150 in3 GI-gun was fired at a shot rate of 7 s, to ensure for excellent lateral and vertical resolution. This setup allows us to present an updated high-resolution seismic velocity model and inversion of Honeycomb Ridge, and partially Glendhu Ridge.
OBS data were processed in Seismic Unix and Vista 2023. In Vista 2023, the data were flattened, filtered with Ormsby bandpass, FK-filter and a threshold median noise attenuation and reduction (THOR) filter. Reflection and refraction phases were picked with PASTEUP and used for forward modeling with MODELING (RAYINVR). The detailed P-wave forward model served as input for the 2D tomography inversion (TOMO2D). The tomography for 8 iterations results in a χ2 of 2.1 and RMS-fit of 30 ms.
The P-wave tomography confirms a low velocity zone below the BSR in both ridges. Higher velocities are resolved in the landward limbs of the ridges compared to seaward limbs in agreement with previous findings. The areas of higher velocities correspond to high-reflectivity layers in the seismic data. We suggest that the anomalously high-reflectivity layers above the BSR in the ridge represent concentrated gas hydrate accumulations, fed by underlying free gas via stratigraphic pathways that enable fluid migration into the system. We also aim to test whether positive and negative polarity reflections within the regional gas hydrate stability zone are due to simultaneous presence of gas hydrates and free gas, respectively. Supplementary analysis of S-waves will allow us to test our hypothesis that free gas is injected into the hydrate stability zone and remains, at least partially, in the gaseous phase. Our detailed study contributes to a better understanding of how gas hydrate systems and fluid migration pathways evolve at active margins.
How to cite: Sokolkova, E., Bialas, J., Dannowski, A., Crutchley, G., Berndt, C., Papenberg, C., Pecher, I., Hilbert, H.-S., Timm, H., Pandolpho, B. T., and Kroeger, K.: High-resolution OBS modeling beneath Honeycomb and Glendhu ridges on the southern Hikurangi subduction margin reveals concentrated gas hydrate accumulations in unprecedented detail, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19068, https://doi.org/10.5194/egusphere-egu25-19068, 2025.
Seagrass meadows are essential coastal ecosystems that play a crucial role in carbon sequestration and greenhouse gas regulation. However, our understanding of methane (CH4) production and emission from these important carbon sinks remains limited. This study investigates CH4 dynamics in a temperate seagrass meadow in Swan Lake (Shandong, China), with a focus on the production and emission of CH₄. The addition of 13C-labelled substrates revealed that CH₄ production rate constant in sediments ranged from 0.072 to 2.2 day⁻¹, with methylotrophic methanogenesis predominating, accounting for over 96% of the total CH₄ production, while hydrogenotrophic methanogenesis contributed less than 4%. These rate constants were significantly lower (up to 20 times) compared to those observed in tropical seagrass meadows, likely due to the lower temperatures in temperate ecosystems. Additionally, anaerobic oxidation of CH₄ was not detected based on the 13CH4 incubation experiments. Time-series observations of 222Rn, CH4 and various hydrological parameters indicated that the CH₄ emission fluxes from sediment-water interface were 1065±176 μmol m-2 day-1 in the summer and 1415±233 μmol m-2 day-1 in the winter, exceeding the range of CH₄ fluxes previously reported from other seagrass meadows. The CH₄ outgassing fluxes were 184±55 μmol m-2 day-1 in the summer and 216±65 μmol m-2 day-1 in the winter. Notably, over 80% of the CH4 was oxidized in the water column before reaching the atmosphere. The higher CH₄ emissions observed in winter were attributed to the seasonal presence of swans in Swan Lake. Swan excreta and the food provided to them significantly increased the availability of dissolved organic carbon (DOC), which, in turn, supplied ample substrates for CH₄ production, consistent with the higher DOC concentrations observed in the winter. Our study provides valuable insights into CH₄ production and emission dynamics, highlighting the seagrass meadow as a source of atmospheric CH₄.
How to cite: Dai, G., Chen, X., Zhuang, G., Zhu, P. Z., Sun, Y., Wang, Q., and Li, L.: Methane dynamics in a temperate seagrass meadow, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19271, https://doi.org/10.5194/egusphere-egu25-19271, 2025.
Methane dynamics in groundwater flow systems are critical to understanding underground microbial methane systems. The migration of methane in aqueous solution is understudied, although it can only concentrate in large quantities along longer horizontal groundwater flow paths. This is a necessary condition for the formation of commercial accumulations (as hydrocarbon resources) but also increases the potential amount of gas released to the atmosphere in the discharge areas of groundwater flows.
This study focuses on understanding the fundamental elements of an underground microbial methane system, highlighting the microbial gas generation depth range and key groundwater flow system parameters such as volume discharge, Darcy velocity, pressure, temperature, and salinity. To achieve this, by innovatively integrating hydrogeological and petroleum geological knowledge and methodologies, a Python-based computational model was developed. In addition, extensive methane and carbon dioxide solubility databases containing over 200,000 data points were created considering temperature, pressure and salinity conditions. To address gaps related to methane and carbon dioxide solubility reverse data engineering was applied using Python language.
The model comprises two principal domains: (1) a midline zone where semi-horizontal groundwater flow maintains roughly constant pressure, temperature, and salinity conditions, facilitating microbial gas dissolution, and (2) a discharge zone where upward groundwater flow triggers decrease of these parameters, leading to oversaturation and gas exsolution. Present-day microbial gas generation depth was established based on generation kinetics, while the theoretical regional groundwater flow system was characterized by the basin-scale evaluation of measured hydraulic data. Model input parameters, such as pressure, temperature, salinity, and flow velocity were sourced from existing publications. As a result, the model defines (a) the minimum horizontal migration length necessary for groundwater saturation with methane, (b) the volume of methane transported in solution, (c) the quantity of methane gas released in underground discharge zones that can be trapped, and (d) the quantity of methane gas released to the surface.
When applied to the Central Pannonian Basin, including the largest microbial gas accumulation in Hungary (Hajdúszoboszló field), the model can explain the formation of this accumulation at the end of a horizontal flow converging zone where flow direction turns upward due to the regional flow conditions and a major fault zone. From the gas amount which arrives at the discharge area during 1 million years from a 300 km2 charge area, about 226 million m3 released under the surface that could be trapped and about 700 million m3 released to the surface. The latter means 700 m3 gas emission per year which only comes from groundwater discharge. Sensitivity analyses provided further insights into the controlling factors of microbial gas migration and their relationships highlighting the complexity of the system.
Ongoing work is testing the model around another significant microbial gas accumulation in Hungary (Kunmadaras field), where hydrogeological conditions are different, further refining our understanding of methane dynamics in groundwater flow systems.
The research was supported by the Papp Simon Foundation, Hungary.
How to cite: Adonya, R. A.: Microbial methane dynamics in groundwater flow systems and their potential contribution to atmospheric emissions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5268, https://doi.org/10.5194/egusphere-egu25-5268, 2025.
Due to its permanent vertical stratification, the Black Sea is the world’s largest aquatic methane reservoir, holding an estimated 96 Tg of methane1. Understanding the biogeochemical processes at work in this unique system is crucial for evaluating the vulnerability of the methane reservoir to environmental perturbations. Additionally, such knowledge is essential for assessing the potential of deep Black Sea waters as a viable option for carbon storage, contributing to strategies aimed at mitigating greenhouse gas emissions.
Below approximately 150 m of water depth, the anoxic waters are enriched with reduced compounds such as dissolved CH₄ and H₂S, and dissolved organic matter. These unique chemical conditions sustain a specialized ecosystem dominated by anaerobic chemotrophic microbes, which rely on these compounds for energy production and play a critical role in the biogeochemical cycling of carbon and sulfur. Specifically, the anaerobic oxidation of methane (AOM) is a critical methane sink regulating the content of methane in the water column. The methanotrophic archaea comprise 3-4% of microbial cells in the water column2 and are believed to drive pelagic AOM. While this process typically involves a symbiosis between anaerobic and sulfate-reducing bacteria in marine sediments, AOM mechanisms in the Black Sea water column remain poorly understood.
To better understand the Black Sea’s methane dynamics, a new biogeochemical model of the water column has been developed. This model explores microbial metabolism coupling both thermodynamic and microbiology approaches, shedding light on the processes governing methane oxidation and transfer across water layers. The study also aims to address uncertainties in methane production, oxidation, and storage. By providing updated methane stock estimates and insights into flux dynamics, this research will inform future environmental impact assessments.
1 Reeburgh, William S., Bess B. Ward, Stephen C. Whalen, Kenneth A. Sandbeck, Katherine A. Kilpatrickt, et Lee J. Kerkhof. 1991. « Black Sea methane geochemistry ». Deep Sea Research Part A. Oceanographic Research Papers, Black Sea Oceanography: Results from the 1988 Black Sea Expedition, 38.
2 Durisch-Kaiser E, Klauser L, Wehrli B, et Schubert C. 2005. « Evidence of Intense Archaeal and Bacterial Methanotrophic Activity in the Black Sea Water Column. » Applied and Environmental Microbiology.
How to cite: Perhirin, A., Crémière, A., Fandino, O., and Toffin, L.: Thermodynamic constraints on the biogeochemical cycle of methane in the Black Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21777, https://doi.org/10.5194/egusphere-egu25-21777, 2025.
Since their introduction to European waters in the 1970s, the invasive red swamp crayfish Procambarus clarkii has rapidly expanded due to traits such as rapid reproduction, high environmental tolerance, and opportunistic feeding. P. clarkii can significantly transform freshwater ecosystems, causing extensive reduction in plant coverage, predation on amphibians and other macroinvertebrates, and a decline in native crayfish species populations. In many systems, the expansion of P. clarkii has lead to a dramatic reduction in plant coverage at specific sites. While numerous studies have explored how climate change influences the spread of invasive species, little is known about the reverse relationship: how invasive species contribute to climate change.
As a country with an extensive network of freshwater ecosystems, the Netherlands provides an excellent opportunity to study the effect of invasive species on aquatic GHG emissions. More than half of the Dutch territory has already been invaded by crayfish, with detrimental effects on submerged plants. Additionally, ditches serve as significant hotspots for GHG emissions, with estimates suggesting they are responsible for approximately 10–16% of the Dutch national annual CH4 emissions. These estimates are largely based on measurements in ditches dominated by submerged plants, which have been shown to mitigate CH₄ emissions through mechanisms such as CH4 oxidation and reduction of CH4 formationLoss of submerged plants can therefore lead to a considerable increase in CH4 emissions, further exacerbating the impact of ditches on the national GHG budget.
By combining data on ditch CH4 emissions, the area invaded by P. clarkii, and results from a controlled mesocosm experiment focusing on the cascading effects of crayfish on submerged plants and GHG emissions (particularly CH4), we found that high crayfish densities (2 individuals/m2) increase CH4 emissions by 2.4 times compared to systems without crayfish. This effect seems primarily driven by plant clipping and bioturbation
These findings highlight the ecological and climatic consequences of P. clarkii invasions. By enhancing CH4 emissions, this invasive species not only disturbs local aquatic ecosystems but also contributes to global climate change. Understanding the effects of crayfish bioturbation is essential for developing targeted management strategies to mitigate their environmental impact.
How to cite: Cabrera-Lamanna, L., Roessink, I., Edwin THM, P., and Kosten, S.: Crayfish and Climate: how invasive species amplify aquatic GHG emissions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6790, https://doi.org/10.5194/egusphere-egu25-6790, 2025.
The methane flux from coastal water areas such as fjords and the underlying control mechanisms have been little studied to date. Fjords are characterized by a complex hydrography that is shaped by marine and limnic interactions and leads to a pronounced stratification of the water column. The resulting low ventilation of the deep water together with high primary production rates in the surface water and the subsequent transport of the organic material to the seabed often lead to high methane releases from the seabed. In our study, we analyzed a fjord system in the Chilean part of Patagonia, the Golfo Almirante Montt. The investigation is based on studies of water column methane concentration and stable carbon isotopes, the distribution and activity of methane-oxidizing bacteria, and oceanographic and geological observations. Our results indicate that methane is of biogenic origin is released from gas-rich sediments at the entrance of the main fjord basin, which is characterized by pockmarks and gas flares. Tidal currents and turbulent mixing at the sill cause a methane plume near the surface to spread into the main fjord basin and mix with the methane- and oxygen-depleted deep water. The wind-induced mixing at the sea surface controls the methane flux from the methane plume into the atmosphere. The methane plume is consumed mainly by methanotrophic bacteria. An enrichment of the signature gene particulate methane monooxygenase (pmoA) in the methane-poor deep water, and a conspicuously high δ13C-CH4 signature of the methane suggest that methane-rich intrusions are periodically introduced into the deep water, which are subsequently converted microbially. Additionally, a δ13C-CH4 anomaly in deep water that correlates with a zooplankton accumulation in this depth during daytime is considered to be a product of zooplankton-associated methane production. Our interdisciplinary study offers a comprehensive insight into the complex physical and biological processes that modulate methane dynamics in fjords and thus help to better assess how methane emissions from these systems will change under anthropogenic influence.
How to cite: Schmale, O., Mohrholz, V., Papenmeier, S., Jürgens, K., Blumenberg, M., Feldens, P., Jordan, S., Ruiz-Fernández, P., Meeske, C., Fabian, J., Iwe, S., and Umlauf, L.: The control of physical and biological drivers on pelagic methane fluxes in a Patagonian fjord (Golfo Almirante Montt, Chile), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3813, https://doi.org/10.5194/egusphere-egu25-3813, 2025.
From October 3 to November 9, 2024, a manned deep-sea dive expedition in the Okinawa Trough was successfully conducted by the expedition team from the Chinese Academy of Sciences and Ministry of Natural Resources of China. Utilizing the exploration vessel "TAN-SUO-ER-HAO" and the manned submersible "SHEN-HAI-YONG-SHI," the expedition aimed to investigate the geological, environmental, and biological phenomena associated with the submarine fluid systems on the seafloor in the Middle Okinawa Trough. The expedition uncovered large-scale active cold seeps developing at the back-arc spreading center axis, covering an area of approximately several dozen square kilometers. Geological activities related to the release of high-temperature supercritical carbon dioxide fluids were also observed, with multiple venting sites identified that generate a carbon dioxide-rich hydrothermal plume. These discoveries provide an exceptional natural laboratory for observational research on critical issues such as deep-seated carbon release at back-arc spreading centers, localized deep-sea water acidification, and the life adaptation strategies in extreme environments.
How to cite: Li, J., Sun, Z., and Wang, D.: The investiagtion of methane seeps and hydrothermal vents in the Middle Okinawa Trough, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5340, https://doi.org/10.5194/egusphere-egu25-5340, 2025.
Eutrophication and anoxic and hypoxic conditions can drive substantial CH4 production in sediment and potentially in the water column. However, the extent of CH4 oxidation in the water column of marginal seas remains poorly quantified, leading to a possible overestimation of CH4 fluxes to the atmosphere. Here, we investigate the fate of CH4 in the deep-water column analysing its concentration and stable isotope (δ13C-CH4) along a 5000-km cruise track in the Baltic Sea. CH4 concentrations increased with water column depth, more so under low oxygen conditions. The median CH4 concentration in the bottom layer in different basins ranging from 4 to 1300 nM. δ13C-CH4 values ranging from -82 to -46‰ with respect to VPDB indicates benthic CH4 production. Methane oxidation causes isotopic fractionation, resulting in a more 13C-enriched CH4. Here oxidation in the water column removed 1% to 90% of benthic-produced CH4 before it reaches the surface. Large differences in CH4 concentrations and δ13C-CH4 were observed between basins related to oxygen concentrations, reflecting distinct biogeochemical dynamics. For instance, benthic CH4 concentrations in the anoxic, deep Baltic Proper were 2 to 295 times higher than those in the oxygenated, shallower Gulf of Bothnia. Our results underline the importance of CH4 oxidation in the water column, mitigating CH4 emissions to the atmosphere. Accurate regional CH4 budgets should consider oxidation processes and the unique characteristics of different basins.
How to cite: Henriksson, L., Yau, Y. Y. Y., Cheung, H. L. S., Majtényi-Hill, C., Ljungberg, W., Singh Tomer, A., Bonaglia, S., MacKenzie, T., and Santos, I.: Methane oxidation along oxygen gradients in the Baltic Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11163, https://doi.org/10.5194/egusphere-egu25-11163, 2025.
Microbial methane production represents an important source of methane on Earth. In oil and gas reservoirs, microbial methane can be formed from secondary methanogenesis, i.e., from C2+ hydrocarbons biodegradation, either directly [1] or indirectly from the biodegradation products [2]. Despite its global significance [2], secondary methanogenesis is arguably challenging to detect, mainly because methane isotopic signature overlaps with that of the existing thermogenic methane in the reservoir, and is thus inferred only from indirect proxies such as high 13C content of propane and CO2.
Here, we combine methane clumped isotopes with propane position-specific isotope analysis (PSIA) of 19 samples from mud volcanoes and gas seepages located in Tokamachi area (Niigata, Japan). Previous studies have shown that both propane and CO2 in Tokamachi natural gas samples are 13C-enriched, consistent with biodegradation-associated methanogenesis [3]. Propane 13C-PSIA shows a clear biodegradation trend where δ13C of the central position of propane is specifically enriched as the relative amount of propane decreases [4]. Interestingly, the extent of propane biodegradation, as indicated by the difference between the two positions of propane (∆Central = δCentral - δTerminal), correlates with ∆13CH3D and ∆CH2D2 of methane, both of which tending towards equilibrium values at high biodegradation rates. A simple models shows that ca. 20% of methane present in the subusrface is produced directly or indirectly from hydrocarbons anaerobic biodegradation. This study emphasizes the importance of using multiple indicators to tackle hydrocarbons cycling in the subsurface, in particular methanogenesis associated with hydrocarbons biodegradation.
References:
[1] Zhou et al. 2022 Nature v. 601, 257
[2] Milkov 2011 Org. Geochem. v. 42, 184
[3] Etiope et al. 2011 Appl. Geochem., v. 26, 348
[4] Gilbert et al. 2019 Proc. Natl. Acad. Sci., v. 116, 6653
How to cite: Gilbert, A., Jajalla, M., Nakagawa, M., Taguchi, K., and Zhang, N.: Quantification of secondary methanogenesis from multiple isotopologue proxies: a case study in Tokamachi mud volcano, Japan, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17015, https://doi.org/10.5194/egusphere-egu25-17015, 2025.
To assess the role of gas hydrates in global resources and the carbon cycle, it is crucial to estimate the volume of natural gas hydrate resources. Most hydrate resource estimates typically focus on methane hydrates. However, hydrate drilling at many sites in the South China Sea (SCS) has found Structure II hydrates containing heavier hydrocarbons, suggesting that methane hydrates may lead to an underestimation of the total hydrate resources. This study, based on the biogenic and thermogenic gases in the SCS, analyses three different gas compositions including 100% methane, 96% methane+4% ethane, and 86.1% methane+13.9% ethane (Gumusut-Kakap gas). The thickness and distribution of the gas hydrate stability zone (GHSZ) for Structure II hydrates were calculated using statistical thermodynamic methods. The results indicate that the thickness of the GHSZ in the SCS varies from 0 to 800 m. In the continental slope area, most of the thickness of the GHSZ are less than 500 m. In contrast, in localized areas such as the Manila Trench, the southwestern Nansha Trough, the South Palawan Basin, and the Luzon Strait, the thickness of the GHSZ exceeds 500 m. The new estimates of the GHSZ thickness for methane hydrates, 96% methane plus 4% ethane, and Gumusut-Kakap gas are 203 m, 219 m, and 254 m, respectively. Based on the volumetric method, the corresponding resource volumes are 82.65 Gt (115.43×1012 m³), 93.11 Gt (130.04×1012 m³), and 111.29 Gt (155.43×1012 m³) using the gas expansions of 155, 162 and 160, respectively. On this basis we calculated the incremental hydrate resource using the GHSZ thickness difference. The incremental resource volumes for the two Structure II hydrates are 10.46 Gt (14.61×1012 m³) for the 96% methane+4% ethane composition, representing an increase of approximately 13%, and 18.18 Gt (25.39×1012 m³) for the Gumusut - Kakap gas composition, representing an increase of approximately 22%. This study recalculates the natural gas hydrate resources in the South China Sea and can be used to assess global Structure II hydrate resources.
How to cite: Liu, Z. and Qian, J.: Gas hydrate potential of heavier order hydrocarbons in the South China Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17215, https://doi.org/10.5194/egusphere-egu25-17215, 2025.
This seep area, estimated to extend over 17 km2 at depths of 400 m, is located in the west-central Baltic Proper at the Landsort Deep, the deepest part of the Baltic Sea. The Landsort Deep is a deep and narrow trough fault (Fromm, 1943) filled with around 100 m of late glacial and post-glacial sediments at its axis. The ebullition field is associated with a local drift deposit extending along the fault axis with higher than average sedimentation rates (1 cm/year; Jofesson, 2022). High current-associated sedimentation rates with relatively slow terrigenous deposition result in notable organic matter accumulation (TOC average of 11.4 weight %; Ketzer et al., 2024). The inflow of salty water from the North Sea and the freshwater runoff from the catchment area gives rise to a permanent halocline in the Baltic Proper at a depth of around 80 m. The euxinic waters below the halocline, resulting from limited vertical water exchange and eutrophication, combined with sapropel deposition, promote anomalous high biogenic methane production within the sediments.
Methane oversaturation in the sediment porewater leads to bubble formation, which escapes the seafloor intermittently and sporadically within the ebullition field. Mid-water acoustic data acquired at the study site reveal that many bubbles rise more than 300 m from the seafloor, with some reaching all the way to the sea surface (>400 m). Data analysis identified two groups of bubbles based on rise velocities, indicating two separate bubble size ranges. When comparing the observations with a bubble dissolution model, the results suggest that only extraordinarily large bubbles can explain the large rise heights.
Further methane flux estimations derived from acoustic data in combination with dissolution modelling will provide insights into the efficiency of the vertical methane flux from the ebullition field and help determine whether methane discharge from Landsort Deep sediments, at 400 m below the sea surface, can actually end up in atmosphere.
Fromm, E., 1943. Havsbottnens Morfologi Utanför Stockholms Södra Skärgård. Geografiska Annaler 25:3-4, 137-169. https://doi.org/10.1080/20014422.1943.11880722
Josefsson, S., 2022. Contaminants in Swedish offshore sediments 2003–2021. 103 pages. Geological Survey of Sweden.
Ketzer, M., Stranne, C., Rahmati-Abkenar, M., Shahabi-Ghahfarokhi, S., Jaeger, L., Pivel, M.A.G., Josefsson, S., Zillén, L., 2024. Near seafloor methane flux in the world's largest human-induced dead zone is regulated by sediment accumulation rate. Marine Geology 468, 107220. https://doi.org/10.1016/j.margeo.2024.107220
How to cite: Doñate Felip, V., Ketzer, M., Ladroit, Y., Jakobsson, M., O'Regan, M., Humborg, C., and Stranne, C.: One of Europe’s largest methane ebullition field lies at 400 m below sea level in the Baltic Sea., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19885, https://doi.org/10.5194/egusphere-egu25-19885, 2025.
In the western Black Sea, gas hydrates are found at water depths greater than 660 m and are often associated with areas of active gas seepages. Their occurrence has been inferred from both geophysical data (1) and coring operations (2). During the GHASS-2 cruise (2021) offshore Romania, gravity cores containing hydrate were recovered from a ridge site and from a newly mapped mud volcano site. This work integrates data from field observations coupled with physico-chemical and geochemical analyses of gas hydrate, pore fluids and sediments in order to explore the local dynamics of gas hydrate and their interplays with geochemical processes. Gas hydrates are mainly composed of methane (99.6%), and are formed by filling subparallel fractures, as networks of interconnected veins, or as agglomerated nodules, resulting from the combined effect of sediment properties and the fault/fractures system. The combination of chloride porewater anomalies and in situ pore pressure and temperature measurements argues in favor of a recent and/or fast hydrate formation at the ridge area. In addition, microstructural analysis by Raman spectroscopy shows local enrichment of H2S in hydrate cages at the mud volcano site. This H2S, trapped in gas hydrates, is interpreted to stem from the anaerobic oxidation of methane coupled with sulfate reduction (AOM-SR) taking place just above the hydrate occurrence zone. Taken together, these results provide new insights onto processes occuring at hydrate areas in the Romanian sector of the Black Sea.
Acknowledgements
The authors thank the different projects and programs for their financial supports: DOORS by the EU Project number 101000518, and BLAME by the ANR (ANR18-CE01-0007).
References
1. Popescu I, Lericolais G, Panin N, De Batist M, Gillet H. Seismic expression of gas and gas hydrates across the western Black Sea. Geo-Marine Letters. 2007;27(2):173-83.
2. Ker S, Thomas Y, Riboulot V, Sultan N, Bernard C, Scalabrin C, et al. Anomalously Deep BSR Related to a Transient State of the Gas Hydrate System in the Western Black Sea. Geochemistry, Geophysics, Geosystems. 2019;20(1):442-59.
How to cite: Agnissan, C. A.-C., Fandino, O., Haidar, R., Giunta, T., Crémière, A., Guimpier, C., Chazallon, B., Desmedt, A., Pirim, C., Brandily, C., Donval, J.-P., Chéron, S., Philippon, X., Riboulot, V., and Ruffine, L.: Physical and geochemical dynamics of shallow hydrates-bearing sediments at two active seepages sites in the western Black Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21766, https://doi.org/10.5194/egusphere-egu25-21766, 2025.
Additional speaker
- Tina Treude, University of California, Los Angeles, United States of America