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

2015 ◽  
Vol 12 (10) ◽  
pp. 2953-2974 ◽  
Author(s):  
D. Archer
Keyword(s):  
Continental Shelf ◽  
Sea Level ◽  
Methane Hydrate ◽  
Fossil Fuel ◽  
Methane Flux ◽  
Pore Fluid ◽  
Permafrost Zone ◽  
Sediment Surface ◽  
Sediment Column ◽  
Atmospheric Flux

Abstract. A two-dimensional model of a sediment column, with Darcy fluid flow, biological and thermal methane production, and permafrost and methane hydrate formation, is subjected to glacial–interglacial cycles in sea level, alternately exposing the continental shelf to the cold atmosphere during glacial times and immersing it in the ocean in interglacial times. The glacial cycles are followed by a "long-tail" 100 kyr warming due to fossil fuel combustion. The salinity of the sediment column in the interior of the shelf can be decreased by hydrological forcing to depths well below sea level when the sediment is exposed to the atmosphere. There is no analogous advective seawater-injecting mechanism upon resubmergence, only slower diffusive mechanisms. This hydrological ratchet is consistent with the existence of freshwater beneath the sea floor on continental shelves around the world, left over from the last glacial period. The salt content of the sediment column affects the relative proportions of the solid and fluid H2O-containing phases, but in the permafrost zone the salinity in the pore fluid brine is a function of temperature only, controlled by equilibrium with ice. Ice can tolerate a higher salinity in the pore fluid than methane hydrate can at low pressure and temperature, excluding methane hydrate from thermodynamic stability in the permafrost zone. The implication is that any methane hydrate existing today will be insulated from anthropogenic climate change by hundreds of meters of sediment, resulting in a response time of thousands of years. The strongest impact of the glacial–interglacial cycles on the atmospheric methane flux is due to bubbles dissolving in the ocean when sea level is high. When sea level is low and the sediment surface is exposed to the atmosphere, the atmospheric flux is sensitive to whether permafrost inhibits bubble migration in the model. If it does, the atmospheric flux is highest during the glaciating, sea level regression (soil-freezing) part of the cycle rather than during deglacial transgression (warming and thawing). The atmospheric flux response to a warming climate is small, relative to the rest of the methane sources to the atmosphere in the global budget, because of the ongoing flooding of the continental shelf. The increased methane flux due to ocean warming could be completely counteracted by a sea level rise of tens of meters on millennial timescales due to the loss of ice sheets, decreasing the efficiency of bubble transit through the water column. The model results give no indication of a mechanism by which methane emissions from the Siberian continental shelf could have a significant impact on the near-term evolution of Earth's climate, but on millennial timescales the release of carbon from hydrate and permafrost could contribute significantly to the fossil fuel carbon burden in the atmosphere–ocean–terrestrial carbon cycle.

scholarly journals Limited impact of El Niño – Southern Oscillation on the methane cycle

2018 ◽  
Author(s):  
Hinrich Schaefer ◽  
Dan Smale ◽  
Sylvia E. Nichol ◽  
Tony M. Bromley ◽  
Ross J. Martin ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Mitigation Strategies ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Atmospheric Methane ◽  
Methane Cycle ◽  
Ch4 Production ◽  
The Impact

Abstract. The El Niño – Southern Oscillation (ENSO) has been suggested as a strong forcing in the methane cycle and as a driver of recent trends in global atmospheric methane levels. Such a sensitivity of the global CH4 budget to climate events would have important repercussions for climate change mitigation strategies and the accuracy of projections for future greenhouse forcing. Here, we test the impact of ENSO on the CH4 cycle in a correlation analysis. We use local and global records of methane mixing ratio [CH4], as well as stable carbon isotopic records of atmospheric CH4 (δ13CH4), which are particularly sensitive to the combined ENSO effects on CH4 production from wetlands and biomass burning. We use a variety of nominal, smoothed and detrended time series including growth rate records. We find that at most 38 % of the variability in [CH4] and δ13CH4 is attributable to ENSO, but only for detrended records in the Southern tropics. Trend-bearing records from the Southern tropics, as well as all studied hemispheric and global records show a minor impact of ENSO, i.e.

scholarly journals EMP and SIMS studies on Mn/Ca and Fe/Ca systematics in benthic foraminifera from the Peruvian OMZ: a contribution to the identification of potential redox proxies and the impact of cleaning protocols

2012 ◽  
Vol 9 (1) ◽  
pp. 341-359 ◽  
Author(s):  
N. Glock ◽  
A. Eisenhauer ◽  
V. Liebetrau ◽  
M. Wiedenbeck ◽  
C. Hensen ◽  
...  
Keyword(s):  
Water Depth ◽  
Benthic Foraminifera ◽  
Sampling Site ◽  
Redox Conditions ◽  
Sediment Surface ◽  
Test Surface ◽  
Pore Waters ◽  
Rich Phase ◽  
Icp Ms ◽  
The Impact

Abstract. In this study we present an initial dataset of Mn/Ca and Fe/Ca ratios in tests of benthic foraminifera from the Peruvian oxygen minimum zone (OMZ) determined with SIMS. These results are a contribution to a better understanding of the proxy potential of these elemental ratios for ambient redox conditions. Foraminiferal tests are often contaminated by diagenetic coatings, like Mn rich carbonate- or Fe and Mn rich (oxyhydr)oxide coatings. Thus, it is substantial to assure that the cleaning protocols are efficient or that spots chosen for microanalyses are free of contaminants. Prior to the determination of the element/Ca ratios, the distributions of several elements (Ca, Mn, Fe, Mg, Ba, Al, Si, P and S) in tests of the shallow infaunal species Uvigerina peregrina and Bolivina spissa were mapped with an electron microprobe (EMP). To visualize the effects of cleaning protocols uncleaned and cleaned specimens were compared. The cleaning protocol included an oxidative cleaning step. An Fe rich phase was found on the inner test surface of uncleaned U. peregrina specimens. This phase was also enriched in Al, Si, P and S. A similar Fe rich phase was found at the inner test surface of B. spissa. Specimens of both species treated with oxidative cleaning show the absence of this phase. Neither in B. spissa nor in U. peregrina were any hints found for diagenetic (oxyhydr)oxide or carbonate coatings. Mn/Ca and Fe/Ca ratios of single specimens of B. spissa from different locations have been determined by secondary ion mass spectrometry (SIMS). Bulk analyses using solution ICP-MS of several samples were compared to the SIMS data. The difference between SIMS analyses and ICP-MS bulk analyses from the same sampling sites was 14.0–134.8 μmol mol−1 for the Fe/Ca and 1.68(±0.41) μmol mol−1 for the Mn/Ca ratios. This is in the same order of magnitude as the variability inside single specimens determined with SIMS at these sampling sites (1σ[Mn/Ca] = 0.35–2.07 μmol mol−1; 1σ[Fe/Ca] = 93.9–188.4 μmol mol−1). The Mn/Ca ratios in the calcite were generally relatively low (2.21–9.93 μmol mol−1) but in the same magnitude and proportional to the surrounding pore waters (1.37–6.67 μmol mol−1). However, the Fe/Ca ratios in B. spissa show a negative correlation to the concentrations in the surrounding pore waters. Lowest foraminiferal Fe/Ca ratios (87.0–101.0 μmol mol−1) were found at 465 m water depth, a location with a strong sharp Fe peak in the pore water next to the sediment surface and respectively, high Fe concentrations in the surrounding pore waters. Previous studies found no living specimens of B. spissa at this location. All these facts hint that the analysed specimens already were dead before the Fe flux started and the sampling site just recently turned anoxic due to fluctuations of the lower boundary of the OMZ near the sampling site (465 m water depth). Summarized Mn/Ca and Fe/Ca ratios are potential proxies for redox conditions, if cleaning protocols are carefully applied. The data presented here may be rated as base for the still pending detailed calibration.

scholarly journals The Impact of Methane Seepage on the Pore-Water Geochemistry across the East Siberian Arctic Shelf

Water ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 397
Author(s):  
Natalia Guseva ◽  
Yulia Moiseeva ◽  
Darya Purgina ◽  
Elena Gershelis ◽  
Evgeniy Yakushev ◽  
...  
Keyword(s):  
Pore Water ◽  
World Ocean ◽  
Arctic Shelf ◽  
Anaerobic Oxidation Of Methane ◽  
Atmospheric Methane ◽  
Pore Waters ◽  
Geochemical Environment ◽  
Methane Seepage ◽  
Siberian Arctic ◽  
The Impact

East Siberian Arctic Shelf, the widest and the shallowest shelf of the World Ocean, covering greater than two million square kilometers, has recently been shown to be a significant modern source of atmospheric methane (CH4). The CH4 emitted to the water column could result from modern methanogenesis processes and/or could originate from seabed deposits (pre-formed CH4 preserved as free gas and/or gas hydrates). This paper focuses primarily on understanding the source and transformation of geofluid in the methane seepage areas using ions/trace elements and element ratios in the sediment pore-water. Six piston cores and totally 42 pore-water samples were collected in the East Siberian Sea and the Laptev Sea at water depths ranging from 22 to 68 m. In the active zones of methane release, concentrations of vanadium, thorium, phosphorus, aluminum are increased, while concentrations of cobalt, iron, manganese, uranium, molybdenum, copper are generally low. The behavior of these elements is determined by biogeochemical processes occurring in the pore-waters at the methane seeps sites (sulfate reduction, anaerobic oxidation of methane, secondary precipitation of carbonates and sulfides). These processes affect the geochemical environment and, consequently, the species of these elements within the pore-waters and the processes of their redistribution in the corresponding water–rock system.

scholarly journals A 500 kyr record of global sea-level oscillations in the Gulf of Lion, Mediterranean Sea: new insights into MIS 3 sea-level variability

2012 ◽  
Vol 8 (3) ◽  
pp. 1067-1077 ◽  
Author(s):  
J. Frigola ◽  
M. Canals ◽  
I. Cacho ◽  
A. Moreno ◽  
F. J. Sierro ◽  
...  
Keyword(s):  
Grain Size ◽  
Sea Level ◽  
Continental Margin ◽  
Time Scale ◽  
High Sensitivity ◽  
Gulf Of Lion ◽  
Sea Level Oscillations ◽  
Millennial Time Scale ◽  
The Impact ◽  
Upper Slope

Abstract. Borehole PRGL1-4 drilled in the upper slope of the Gulf of Lion provides an exceptional record to investigate the impact of late Pleistocene orbitally-driven glacio-eustatic sea-level oscillations on the sedimentary outbuilding of a river fed continental margin. High-resolution grain-size and geochemical records supported by oxygen isotope chronostratigraphy allow reinterpreting the last 500 ka upper slope seismostratigraphy of the Gulf of Lion. Five main sequences, stacked during the sea-level lowering phases of the last five glacial-interglacial 100-kyr cycles, form the upper stratigraphic outbuilding of the continental margin. The high sensitivity of the grain-size record down the borehole to sea-level oscillations can be explained by the great width of the Gulf of Lion continental shelf. Sea level driven changes in accommodation space over the shelf cyclically modified the depositional mode of the entire margin. PRGL1-4 data also illustrate the imprint of sea-level oscillations at millennial time-scale, as shown for Marine Isotopic Stage 3, and provide unambiguous evidence of relative high sea-levels at the onset of each Dansgaard-Oeschger Greenland warm interstadial. The PRGL1-4 grain-size record represents the first evidence for a one-to-one coupling of millennial time-scale sea-level oscillations associated with each Dansgaard-Oeschger cycle.

Paleogeography and Sea Level Positions on the Southeastern U.S. Continental Margin Since the LGM

2018 ◽  
pp. 90-107
Author(s):  
M. Scott Harris
Keyword(s):  
Gulf Of Mexico ◽  
Continental Shelf ◽  
Sea Level ◽  
Continental Margin ◽  
Coastal Plain ◽  
West Coast ◽  
The West ◽  
Level Curves ◽  
And Sea Level

Southeastern U.S. sea level curves are presented, showing that at LGM there was an increase of 25% to 50% more Coastal Plain exposed than there was available for Paleoamericans. Using GIA-corrected bathymetry from 26KA to present, including shorelines from Virginia to the Gulf of Mexico, this chapter demonstrates that Clovis and Pre-Clovis populations could have lived on the edge of the continental shelf, including Bull Scarp, except for the west coast of Florida.

scholarly journals Characterization of Methanotrophic Bacterial Populations in Soils Showing Atmospheric Methane Uptake

1999 ◽  
Vol 65 (8) ◽  
pp. 3312-3318 ◽  
Author(s):  
Andrew J. Holmes ◽  
Peter Roslev ◽  
Ian R. McDonald ◽  
Niels Iversen ◽  
Kaj Henriksen ◽  
...  
Keyword(s):  
Feedback Regulation ◽  
Methane Flux ◽  
Atmospheric Methane ◽  
Methane Cycle ◽  
Bacterial Populations ◽  
Methane Oxidizing Bacteria ◽  
Monooxygenase Gene ◽  
Methane Uptake ◽  
Methane Level

ABSTRACT The global methane cycle includes both terrestrial and atmospheric processes and may contribute to feedback regulation of the climate. Most oxic soils are a net sink for methane, and these soils consume approximately 20 to 60 Tg of methane per year. The soil sink for atmospheric methane is microbially mediated and sensitive to disturbance. A decrease in the capacity of this sink may have contributed to the ∼1% · year−1 increase in the atmospheric methane level in this century. The organisms responsible for methane uptake by soils (the atmospheric methane sink) are not known, and factors that influence the activity of these organisms are poorly understood. In this study the soil methane-oxidizing population was characterized by both labelling soil microbiota with14CH4 and analyzing a total soil monooxygenase gene library. Comparative analyses of [14C]phospholipid ester-linked fatty acid profiles performed with representative methane-oxidizing bacteria revealed that the soil sink for atmospheric methane consists of an unknown group of methanotrophic bacteria that exhibit some similarity to type II methanotrophs. An analysis of monooxygenase gene libraries from the same soil samples indicated that an unknown group of bacteria belonging to the α subclass of the class Proteobacteria was present; these organisms were only distantly related to extant methane-oxidizing strains. Studies on factors that affect the activity, population dynamics, and contribution to global methane flux of “atmospheric methane oxidizers” should be greatly facilitated by use of biomarkers identified in this study.

scholarly journals Were Neoarchean atmospheric methane hazes and early Paleoproterozoic glaciations driven by the rise of oxygen in surface environments?

2020 ◽  
Author(s):  
Anshuman Swain ◽  
Alan J Kaufman ◽  
Marcin Kalinowski ◽  
William F Fagan
Keyword(s):  
Initial Conditions ◽  
Interaction Model ◽  
Methane Flux ◽  
Progressive Increase ◽  
Atmospheric Methane ◽  
Methane Cycle ◽  
Deep Time ◽  
Resource Concentration ◽  
Early Proterozoic ◽  
Environmental Controls

AbstractInsofar as methane was the predominant greenhouse gas of the Archean and early Proterozoic eons, its wax and wane in Earth’s atmosphere would have contributed to climate change and the relative flux of harmful UV radiation to surface environments. If correct, understanding the first-order environmental controls (e.g., O2 or resource concentration) of the biological methane cycle might shed light on the repetition of biological, atmospheric and climatic events preserved in the sedimentary rock record between ~2.8 and 2.0 billion years ago. Environmental controls on the dynamics of methane cycling may further explain other repetitious events in deep time, as well as the present-day increase in the methane flux to the atmosphere from wetland environments. In this study, we developed an ecological interaction model to predict the conditions in which methane is preferentially released to the atmosphere, and found that the interplay of resource and O2 availability can cause complex cyclic patterns in methane dynamics that are unrelated to the size and efficiency of any of the microbial communities, to initial conditions, or to other model constraints. Based on these model results, we propose that the cyclicity of methane haze events and glacial episodes in the late Archean and early Proterozoic may have been linked to the progressive increase in oceanic and atmospheric O2 through the interval.

A Predictive Model of the Impact of the Skidding System on Forest Soil in Severe Climatic Conditions

2020 ◽  
pp. 131-144
Author(s):  
S.E. Rudov ◽  
◽  
V.Ya. Shapiro ◽  
O.I. Grigoreva ◽  
I.V. Grigorev ◽  
...  
Keyword(s):  
Forest Soil ◽  
Warm Season ◽  
Climatic Conditions ◽  
Soil Freezing ◽  
Class Iii ◽  
Freezing And Thawing ◽  
Metal Structures ◽  
Rapid Adjustment ◽  
Soil Freezing And Thawing ◽  
The Impact

In the Russian Federation logging operations are traditionally carried out in winter. This is due to the predominance of areas with swamped and water-logged (class III and IV) soils in the forest fund, where work of forestry equipment is difficult, and sometimes impossible in the warm season. The work of logging companies in the forests of the cryolithozone, characterized by a sharply continental climate, with severe frosts in winter, is hampered by the fact that forest machines are not recommended to operate at temperatures below –40 °C due to the high probability of breaking of metal structures and hydraulic system. At the same time, in the warm season, most of the cutting areas on cryosolic soils become difficult to pass for heavy forest machines. It turns out that the convenient period for logging in the forests of the cryolithozone is quite small. This results in the need of work in the so-called off-season period, when the air temperature becomes positive, and the thawing processes of the soil top layer begin. The same applies to the logging companies not operating in the conditions of cryosolic soils, for instance, in the Leningrad, Novgorod, Pskov, Vologda regions, etc. The observed climate warming has led to a significant reduction in the sustained period of winter logging. Frequent temperature transitions around 0 °C in winter, autumn and spring necessitate to work during the off-season too, while cutting areas thaw. In bad seasonal and climatic conditions, which primarily include off-season periods in general and permafrost in particular, it is very difficult to take into account in mathematical models features of soil freezing and thawing and their effect on the destruction nature. The article shows that the development of long-term predictive models of indicators of cyclic interaction between the skidding system and forest soil in adverse climatic conditions of off-season logging operations in order to improve their reliability requires rapid adjustment of the calculated parameters based on the actual experimental data at a given step of the cycles.

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