scholarly journals Atmospheric methane flux from bubbling seeps: Spatially extrapolated quantification from a Black Sea shelf area

2010 ◽  
Vol 115 (C1) ◽  
Author(s):  
Jens Greinert ◽  
Daniel F. McGinnis ◽  
Lieven Naudts ◽  
Peter Linke ◽  
Marc De Batist
Keyword(s):  
Black Sea ◽  
Methane Flux ◽  
Shelf Area ◽  
Atmospheric Methane

Intensive Internal Waves with Anomalous Heights in the Black Sea Shelf Area

2019 ◽  
Vol 55 (1) ◽  
pp. 99-109 ◽  
Author(s):  
V. G. Bondur ◽  
A. N. Serebryany ◽  
V. V. Zamshin ◽  
L. L. Tarasov ◽  
E. E. Khimchenko
Keyword(s):  
Internal Waves ◽  
Black Sea ◽  
The Black Sea ◽  
Shelf Area

Captured metagenomics reveals high spatial variability in functional potential in CH4 producing and consuming microorganisms in a temperate Swedish peatland.

2021 ◽  
Author(s):  
Joel White ◽  
Lena Ström ◽  
Dag Ahrén ◽  
Janne Rinne ◽  
Veiko Lehsten
Keyword(s):  
Microbial Communities ◽  
Root Zone ◽  
Water Concentration ◽  
Methane Flux ◽  
Functional Genes ◽  
Molecular Technique ◽  
Atmospheric Methane ◽  
Functional Potential ◽  
Methane Budget ◽  
Methane Metabolism

<p>Microbial communities of methane producing methanogens and consuming methanotrophs play an important role for the earths atmospheric methane budget. Despite their global significance, the functional potential of these communities is poorly understood. To investigate this, we applied the molecular technique, captured metagenomics, to identify the variability in functional diversity of microorganisms involved in the metabolism of methane<sub></sub>in an environmentally controlled laboratory study. Nine plant-peat mesocosms dominated by the sedge Eriophorum vaginatum, with varying coverage, were collected from a temperate natural wetland is Sweden and subjected to a simulated growing season. Samples for analysis of captured metagenomes were taken from the top, bottom and root adjacent zone at the end of the experiment. In addition, over the simulated season, measured gas fluxes of carbon dioxide (CO<sub>2</sub>) and CH<sub>4</sub>, δ<sup>13</sup>C of emitted CH<sub>4</sub> and the pore water concentration of dissolved methane and low molecular weight organic acids were recorded. The functional genes resulting from the captured metagenomes had a higher Shannon α-diversity in the root zone when compared to the bottom and top. Sequences coding for methane metabolism were significantly more diverse in the root and bottom zones when compared to the top. However, the frequency of Acetyl-CoA decarbonylase and methane monooxygenase subunit A were significantly higher in the high emitting methane flux category when compared to the medium and low emitting mesocosms. We conclude that captured metagenomic analyses of functional genes provides a good measure of the functional potential methanogenic and methanotrophic microbial communities. This technique can be used to investigate how methanogens and methanotrophs function in peatlands and thus, contribute to the concentration of atmospheric methane.</p>

Field studies of variation scales of gravitational capillary waves and near-water wind in the Black Sea shelf area

2010 ◽  
Vol 46 (2) ◽  
pp. 232-238 ◽  
Author(s):  
V. V. Bakhanov ◽  
N. A. Bogatov ◽  
A. S. Volkov ◽  
A. V. Ermoshkin ◽  
E. M. Zuykova ◽  
...  
Keyword(s):  
Black Sea ◽  
Field Studies ◽  
Capillary Waves ◽  
The Black Sea ◽  
Shelf Area

scholarly journals Enrichment in <sup>13</sup>C of atmospheric CH<sub>4</sub> during the Younger Dryas termination

2011 ◽  
Vol 7 (5) ◽  
pp. 3287-3324 ◽  
Author(s):  
J. R. Melton ◽  
H. Schaefer ◽  
M. J. Whiticar
Keyword(s):  
Mass Balance ◽  
Gas Hydrates ◽  
Stable Carbon Isotope ◽  
Younger Dryas ◽  
Analytical Techniques ◽  
Carbon Isotope Ratio ◽  
Methane Flux ◽  
Atmospheric Methane ◽  
Stable Carbon ◽  
Thermokarst Lakes

Abstract. The abrupt warming across the Younger Dryas termination (~11 600 yr before present) was marked by a large increase in the global atmospheric methane mixing ratio. The debate over sources responsible for the rise in methane centers on the roles of global wetlands, marine gas hydrates, and thermokarst lakes. We present a new, higher-precision methane stable carbon isotope ratio (δ13CH4) dataset from ice sampled at Påkitsoq, Greenland that shows distinct 13C-enrichment associated with this rise. We investigate the validity of this finding in face of known anomalous methane concentrations that occur at Påkitsoq. Comparison with previously published datasets to determine the robustness of our results indicates a similar trend in ice from both an Antarctic ice core and previously published Påktisoq data measured using four different extraction and analytical techniques. The δ13CH4 trend suggests that 13C-enriched CH4 sources played an important role in the concentration increase. In a first attempt at quantifying the various contributions from our data, we apply a methane triple mass balance of stable carbon and hydrogen isotope ratios and radiocarbon. The mass balance results suggest biomass burning (42–66% of total methane flux increase) and thermokarst lakes (27–59%) as the dominant contributing sources. Our results do not suggest as large a role for tropical wetlands, boreal peatlands or marine gas hydrates as commonly proposed.

scholarly journals A model of the methane cycle, permafrost, and hydrology of the Siberian continental margin

2014 ◽  
Vol 11 (6) ◽  
pp. 7853-7900
Author(s):  
D. Archer
Keyword(s):  
Continental Shelf ◽  
Sea Level ◽  
Continental Margin ◽  
Methane Flux ◽  
Soil Freezing ◽  
Sediment Surface ◽  
Atmospheric Methane ◽  
Pore Waters ◽  
Methane Cycle ◽  
The Impact

Abstract. A two-dimensional model of a passive continental margin was adapted to the simulation of the methane cycle on Siberian continental shelf and slope, attempting to account for the impacts of glacial/interglacial cycles in sea level, alternately exposing the continental shelf to freezing conditions with deep permafrost formation during glacial times, and immersion in the ocean in interglacial times. The model is used to gauge the impact of the glacial cycles, and potential anthropogenic warming in the deep future, on the atmospheric methane emission flux, and the sensitivities of that flux to processes such as permafrost formation and terrestrial organic carbon (Yedoma) deposition. Hydrological forcing drives a freshening and ventilation of pore waters in areas exposed to the atmosphere, which is not quickly reversed by invasion of seawater upon submergence, since there is no analogous saltwater pump. This hydrological pump changes the salinity enough to affect the stability of permafrost and methane hydrates on the shelf. Permafrost formation inhibits bubble transport through the sediment column, by construction in the model. The impact of permafrost on the methane budget is to replace the bubble flux by offshore groundwater flow containing dissolved methane, rather than accumulating methane for catastrophic release when the permafrost seal fails during warming. By far the largest impact of the glacial/interglacial cycles on the atmospheric methane flux is attenuation by dissolution of bubbles in the ocean when sea level is high. Methane emissions are highest during the regression (soil freezing) part of the cycle, rather than during transgression (thawing). The model-predicted methane flux to the atmosphere in response to a warming climate is small, relative to the global methane production rate, because of the ongoing flooding of the continental shelf. A slight increase due to warming could be completely counteracted by sea level rise on geologic time scales, decreasing the efficiency of bubble transit through the water column. The methane cycle on the shelf responds to climate change on a long time constant of thousands of years, because hydrate is excluded thermodynamically from the permafrost zone by water limitation, leaving the hydrate stability zone at least 300 m below the sediment surface.

scholarly journals An analysis of atmospheric CH<sub>4</sub> concentrations from 1984 to 2008 with a single box atmospheric chemistry model

2012 ◽  
Vol 12 (11) ◽  
pp. 30259-30282 ◽  
Author(s):  
Z. Tan ◽  
Q. Zhuang
Keyword(s):  
Growth Rate ◽  
Atmospheric Chemistry ◽  
Methane Flux ◽  
Methane Emissions ◽  
Atmospheric Methane ◽  
Significant Drop ◽  
Oxidizing Power ◽  
The Mean

Abstract. We present a single box atmospheric chemistry model involving atmospheric methane (CH4), carbon monoxide (CO) and radical hydroxyl (OH) to analyze atmospheric CH4 concentrations from 1984 to 2008. When OH is allowed to vary, the modeled CH4 is 20 ppb higher than observations from the NOAA/ESRL and AGAGE networks for the end of 2008. However, when the OH concentration is held constant at 106 molecule cm−3, the simulated CH4 shows a trend approximately equal to observations. Both simulations show a clear slowdown in the CH4 growth rate during recent decades, from about 13 ppb yr−1 in 1984 to less than 5 ppb yr−1 in 2003. Furthermore, if the constant OH assumption is credible, we think that this slowdown is mainly due to a pause in the growth of wetland methane emissions. In simulations run for the Northern and Southern Hemispheres separately, we find that the Northern Hemisphere is more sensitive to wetland emissions, whereas the southern tends to be more perturbed by CH4 transportation, dramatic OH change, and biomass burning. When measured CO values from NOAA/ESRL are used to drive the model, changes in the CH4 growth rate become more consistent with observations, but the long-term increase in CH4 is underestimated. This shows that CO is a good indicator of short-term variations in oxidizing power in the atmosphere. The simulation results also indicate the significant drop in OH concentrations in 1998 (about 5% lower than the previous year) was probably due to an abrupt increase in wetland methane emissions during an intense EI Niño event. Using a fixed-lag Kalman smoother, we estimate the mean wetland methane flux is about 128 Tg yr−1 through the period 1984–2008. This study demonstrates the effectiveness in examining the role of OH and CO in affecting CH4.

ESTIMATE OF DEPENDENCE OF THE VERTICAL TRBULENT DIFFUSION COEFFICIENT FROM BUOYANCY FREQUENCY FOR COASTAL ZONE OF THE BLACK SEA

2017 ◽  
Author(s):  
Lubov Globina ◽  
Lubov Globina
Keyword(s):  
Diffusion Coefficient ◽  
Active Layer ◽  
Black Sea ◽  
Eddy Diffusivity ◽  
The Black Sea ◽  
Small Scale ◽  
Buoyancy Frequency ◽  
Shelf Area ◽  
Turbulent Diffusion Coefficient ◽  
Horizontal Convection

The article highlights the most important studies of oceanographic processes, such as horizontal convection, winter cascading on the shelf and continental slope, the processes in the bottom of the Black Sea. The results of the study of small-scale structure of the shelf upper active layer of the Black Sea in 2014 are discussed. The new information about the distribution of the eddy diffusivity with depth in the coastal part of the Heracleian peninsula is given. The investigated dependence vertical turbulent diffusion coefficient from buoyancy frequency at the active layer is found to be has a quadratic character for the entire shelf area and doesn’t depend on the stratification.

scholarly journals Characterization of Pliocene Biogenic Gas Reservoirs from the Western Black Sea Shelf (Romanian Offshore) by Integration of Well Logs and Core Data

Energies ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6629
Author(s):  
Bogdan Mihai Niculescu ◽  
Victor Mocanu
Keyword(s):  
Black Sea ◽  
Water Saturation ◽  
Sedimentary Environment ◽  
Bound Water ◽  
Confining Pressure ◽  
Well Logs ◽  
Shelf Area ◽  
Suppression Effect ◽  
Electrical Imaging ◽  
Gas Bearing

The successful interpretation of open-hole well logging data relies on jointly using all available petrophysical and geological information. This paper presents relevant case studies related to the integration of well logs with core measurements for exploration wells drilled in the Romanian continental shelf area of the Western Black Sea basin. The analyzed wells targeted gas-bearing sands and silts complexes of Early Pliocene (Dacian) age, developed in a deltaic to shallow marine sedimentary environment in two distinct fields. The wireline logging programs included conventional formation evaluation logs, pressure surveys, nuclear magnetic resonance, and borehole electrical imaging logs. The core dataset comprised routine and special measurements (porosity, grain density, permeability, water saturation, and Archie parameters) carried out at quasi-reservoir confining pressure. The wireline logging suites were interpreted via a deterministic workflow, including core-derived interpretation parameters. Other core-derived parameters were used for constraining and validating the log interpretations. The results show that a problem related to the ambiguity of formation water resistivity can be overcome through resistivity–porosity dependencies constructed to include potential aquifer zones in the proximity of the Dacian gas-bearing reservoirs. This study also revealed and quantified uncertainties regarding the estimation of gas–water contacts from formation pressure surveys, which can be mitigated by the confirmation or correction of pressure-derived fluid contacts via the well log interpretation results. Lastly, we identified a probable resistivity logs suppression effect related both to high contents of capillary-bound water and also to the limited resolution of electrical logging tools in the presence of sand-shale thin bedding or laminations.

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