scholarly journals The origin of methane in the East Siberian Arctic Shelf unraveled with triple isotope analysis

2016 ◽  
Author(s):  
Célia J. Sapart ◽  
Natalia Shakhova ◽  
Igor Semiletov ◽  
Joachim Jansen ◽  
Sönke Szidat ◽  
...  
Keyword(s):  
Water Column ◽  
Large Scale ◽  
Age Determination ◽  
Arctic Shelf ◽  
Climate Feedback ◽  
The Arctic ◽  
Small Contribution ◽  
Isotope Data ◽  
Siberian Arctic ◽  
Subsea Permafrost

Abstract. Methane (CH4) is a strong greenhouse gas emitted by human activity and natural processes that are highly sensitive to climate change. The Arctic Ocean, especially the East Siberian Arctic Shelf (ESAS) overlays large areas of subsea permafrost that is degrading. The release of large amount of CH4 originally stored or formed there could create a strong positive climate feedback. Large scale CH4 super-saturation has been observed in the ESAS waters, pointing to leakages of CH4 through the sea floor and possibly to the atmosphere, but the origin of this gas is still debated. Here, we present CH4 concentration and triple isotope data analyzed on gas extracted from sediment and water sampled over the shallow ESAS from 2007 to 2013. We find high concentrations (up to 500 μM) of CH4 in the pore water of the partially thawed subsea permafrost of this region. For all sediment cores, both hydrogen and carbon CH4 isotope data reveal the predominant presence of CH4 that is not of thermogenic/natural gas origin as it has long been thought, but resultant from microbial CH4 formation using as primary substrate glacial water and old organic matter preserved in the subsea permafrost or below. Radiocarbon data demonstrate that the CH4 present in the ESAS sediment is of Pleistocene age or older, but a small contribution of highly 14C-enriched CH4, from unknown origin, prohibits precise age determination for one sediment core and in the water column. Our data suggest that at locations where bubble plumes have been observed, CH4 can escape anaerobic oxidation in the surface sediment. CH4 will then rapidly migrate through the very shallow water column of the ESAS to escape to the atmosphere generating a positive radiative feedback.

scholarly journals The origin of methane in the East Siberian Arctic Shelf unraveled with triple isotope analysis

2017 ◽  
Vol 14 (9) ◽  
pp. 2283-2292 ◽  
Author(s):  
Célia J. Sapart ◽  
Natalia Shakhova ◽  
Igor Semiletov ◽  
Joachim Jansen ◽  
Sönke Szidat ◽  
...  
Keyword(s):  
Isotope Composition ◽  
Sediment Cores ◽  
Isotope Analysis ◽  
Age Determination ◽  
Unknown Origin ◽  
Arctic Shelf ◽  
The Arctic ◽  
Small Contribution ◽  
Siberian Arctic ◽  
Subsea Permafrost

Abstract. The Arctic Ocean, especially the East Siberian Arctic Shelf (ESAS), has been proposed as a significant source of methane that might play an increasingly important role in the future. However, the underlying processes of formation, removal and transport associated with such emissions are to date strongly debated. CH4 concentration and triple isotope composition were analyzed on gas extracted from sediment and water sampled at numerous locations on the shallow ESAS from 2007 to 2013. We find high concentrations (up to 500 µM) of CH4 in the pore water of the partially thawed subsea permafrost of this region. For all sediment cores, both hydrogen and carbon isotope data reveal the predominant occurrence of CH4 that is not of thermogenic origin as it has long been thought, but resultant from microbial CH4 formation. At some locations, meltwater from buried meteoric ice and/or old organic matter preserved in the subsea permafrost were used as substrates. Radiocarbon data demonstrate that the CH4 present in the ESAS sediment is of Pleistocene age or older, but a small contribution of highly 14C-enriched CH4, from unknown origin, prohibits precise age determination for one sediment core and in the water column. Our sediment data suggest that at locations where bubble plumes have been observed, CH4 can escape anaerobic oxidation in the surface sediment.

First experimental estimation of the methane ebullition fraction in water column from the bottom to the surface: application for the East Siberian Arctic Shelf

2021 ◽  
Author(s):  
Denis Chernykh ◽  
Denis Kosmach ◽  
Anton Konstantinov ◽  
Aleksander Salomatin ◽  
Vladimir Yusupov ◽  
...  
Keyword(s):  
Water Column ◽  
Thermal State ◽  
Terrestrial Ecosystems ◽  
Arctic Shelf ◽  
The Arctic ◽  
Arctic Ecosystems ◽  
Russian Scientific ◽  
Siberian Arctic ◽  
Methane Ebullition ◽  
Subsea Permafrost

<p>The key area of the Arctic ocean for atmospheric venting of CH<sub>4</sub> is the East Siberian Arctic Shelf (ESAS). The ESAS covers >2 million square kilometers (equal to the areas of Germany, France, Great Britain, Italy, and Japan combined). This vast yet shallow region has recently been shown to be a significant modern source of atmospheric CH<sub>4</sub>, contributing annually no less than terrestrial Arctic ecosystems; but unlike terrestrial ecosystems, the ESAS emits CH<sub>4 </sub>year-round due to its partial openness during the winter when terrestrial ecosystems are dormant. Emissions are determined by and dependent on the current thermal state of the subsea permafrost and environmental factors controlling permafrost dynamics. Releases could potentially increase by 3-5 orders of magnitude, considering the sheer amount of CH<sub>4</sub> preserved within the shallow ESAS seabed deposits and the documented thawing rates of subsea permafrost reported recently.</p><p>The purpose of this work is to determine the methane ebullition fraction in water column: from the bottom to the surface, which is a key to evaluate quantitively methane release from the ESAS bottom through the water column into the atmosphere. A series of 351 experiments was carried out at to determine the quantity of methane (and other greenhouse gases) delivered by bubbles of various sizes through a water column into the atmosphere. It has been shown for depth up to 22 m (about 30% of the ESAS) that pure methane bubbles, depending on their diameter and water salinity, transported to the surface from 60.9% to 85.3% of gaseous methane.</p><p>This work was supported in part by grants from Russian Scientific Foundation (№ 18-77-10004 to DCh, DK, AK, № 19-77-00067 to EG), the Ministry of Science and Higher Education of the Russian Federation (grant ID: 075-15-2020-978 to IS). The work was carried out as a part of Federal[ПW1]  assignment № АААА-А17-117030110031-6 to AS.</p>

scholarly journals The East Siberian Arctic Shelf: towards further assessment of permafrost-related methane fluxes and role of sea ice

2015 ◽  
Vol 373 (2052) ◽  
pp. 20140451 ◽  
Author(s):  
Natalia Shakhova ◽  
Igor Semiletov ◽  
Valentin Sergienko ◽  
Leopold Lobkovsky ◽  
Vladimir Yusupov ◽  
...  
Keyword(s):  
Arctic Shelf ◽  
The Arctic ◽  
Permafrost Degradation ◽  
Run Off ◽  
Heating Effects ◽  
Siberian Arctic ◽  
Methane Fluxes ◽  
Near Shore ◽  
Permafrost Thawing ◽  
Subsea Permafrost

Sustained release of methane (CH 4 ) to the atmosphere from thawing Arctic permafrost may be a positive and significant feedback to climate warming. Atmospheric venting of CH 4 from the East Siberian Arctic Shelf (ESAS) was recently reported to be on par with flux from the Arctic tundra; however, the future scale of these releases remains unclear. Here, based on results of our latest observations, we show that CH 4 emissions from this shelf are likely to be determined by the state of subsea permafrost degradation. We observed CH 4 emissions from two previously understudied areas of the ESAS: the outer shelf, where subsea permafrost is predicted to be discontinuous or mostly degraded due to long submergence by seawater, and the near shore area, where deep/open taliks presumably form due to combined heating effects of seawater, river run-off, geothermal flux and pre-existing thermokarst. CH 4 emissions from these areas emerge from largely thawed sediments via strong flare-like ebullition, producing fluxes that are orders of magnitude greater than fluxes observed in background areas underlain by largely frozen sediments. We suggest that progression of subsea permafrost thawing and decrease in ice extent could result in a significant increase in CH 4 emissions from the ESAS.

scholarly journals Organic matter across subsea permafrost thaw horizons on the East Siberian Arctic Shelf

2018 ◽  
Author(s):  
Birgit Wild ◽  
Natalia Shakhova ◽  
Oleg Dudarev ◽  
Alexey Ruban ◽  
Denis Kosmach ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Luminescence Dating ◽  
Arctic Shelf ◽  
The Arctic ◽  
Organic Carbon Content ◽  
Study Region ◽  
Permafrost Thaw ◽  
Siberian Arctic ◽  
Subsea Permafrost

Abstract. Thaw of subsea permafrost across the Arctic Ocean shelves might promote the degradation of organic matter to CO2 and CH4, but also create conduits for transfer of deeper CH4 pools to the atmosphere and thereby amplify global warming. In this study, we describe sedimentary characteristics of three subsea permafrost cores of 21–56 m length drilled near the current delta of the Lena River in the Buor–Khaya Bay on the East Siberian Arctic Shelf, including content, origin and degradation state of organic matter around the current thaw front. Grain size distribution and optically stimulated luminescence dating suggest the alternating deposition of aeolian silt and fluvial sand over the past 160 000 years. Organic matter in 3 m sections across the current permafrost table was characterized by low organic carbon contents (average 0.7 ± 0.2 %) as well as enriched δ13C values and low concentrations of the terrestrial plant biomarker lignin compared to other recent and Pleistocene deposits in the study region. The lignin phenol composition further suggests contribution of both tundra and boreal forest vegetation, at least the latter likely deposited by rivers. Our findings indicate high variability in organic matter composition of subsea permafrost even within a small study area, reflecting its development in a heterogeneous and dynamic landscape. Even with this relatively low organic carbon content, the high rates of observed subsea permafrost thaw in this area yield a thaw-out of 1.6 kg OC m−2 year−1, emphasizing the need to constrain the fate of the poorly described and thawing subsea permafrost organic carbon pool.

Siberian-Arctic Subsea Permafrost and Methane: Spatial variability and isotope-based source apportionment

2020 ◽  
Author(s):  
Henry Holmstrand ◽  
Natalia Shakhova ◽  
Igor Semiletov ◽  
Julia Steinbach ◽  
Arkadiy Kurilenko ◽  
...  
Keyword(s):  
Water Column ◽  
World Ocean ◽  
The Arctic ◽  
Laptev Sea ◽  
Target Area ◽  
Mixing Ratios ◽  
Siberian Arctic ◽  
Methane Fluxes ◽  
Thawing Permafrost ◽  
Subsea Permafrost

<p>There are only a few Earth System processes that can cause a net transfer of carbon from land/ocean to the atmosphere (as CO<sub>2</sub> and CH<sub>4</sub>) on the century timescale– top candidates are thawing permafrost and collapsing CH<sub>4</sub> hydrates in the Arctic. Nevertheless, there are huge uncertainties regarding the composition, inventories and functioning of these different Cryosphere-Carbon pools.</p><p>Most investigations of Arctic CH<sub>4</sub>/CO<sub>2</sub> releases have studied inland permafrost (PF), yet there is increasing attention towards coastal and subsea permafrost and hydrates. The East Siberian Arctic Ocean (ESAO) is the target area as it is experiencing among the highest climate warming and because of its vast, yet poorly constrained stores of vulnerable carbon. The ESAO is the largest yet shallowest shelf of the World Ocean, being a seaward extension of the Siberian tundra that was flooded during the Holocene transgression 7-15 kyr ago. </p><p>Recent drilling campaigns of the Laptev Sea subsea permafrost have provided the opportunity for progress in understanding its current state, composition and functioning. The temperature profiles of the PF underneath the coastal waters were in general much higher and close to zero, compared to nearby still on-land permafrost. Several sites that were drilled 30 years ago were recently re-drilled, which revealed that the thaw horizon has been moving down by several meters in just a few decades. There is thus both a potential for degradation of the organic matter (including to methane) in this subsea PF as well as an increasing permeability for pre-formed methane to penetrate toward the surface.</p><p>Methane in the ESAS water column is over extensive scales present at concentrations much above what would be predicted from equilibrium with overlying atmospheric mixing ratios.  The spatial patterns can now start to be compared with geophysical data on the composition of the sediments.  The water column to atmosphere transfer of methane is affected both by the relative importance of diffusive exchange of dissolved methane and through ebullition.  Storm-induced ventilation of the water column is shown to be an important process.</p><p>The relative contributions of different subsea compartments to the methane fluxes is also approached through isotopes. We are exploring triple isotope fingerprinting of bottom water methane to apportion its sources (i.e. d<sup>13</sup>C/dD/D<sup>14</sup>C-CH<sub>4.</sub>).  Preliminary results from two active seep regions, one in Laptev Sea and one in the East Siberian Sea will be presented.</p>

scholarly journals Understanding the Permafrost–Hydrate System and Associated Methane Releases in the East Siberian Arctic Shelf

Geosciences ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 251 ◽  
Author(s):  
Natalia Shakhova ◽  
Igor Semiletov ◽  
Evgeny Chuvilin
Keyword(s):  
Final Section ◽  
Thermal State ◽  
Arctic Shelf ◽  
The Arctic ◽  
Current State ◽  
Siberian Arctic ◽  
History Of ◽  
The Subject ◽  
Future Work ◽  
Subsea Permafrost

This paper summarizes current understanding of the processes that determine the dynamics of the subsea permafrost–hydrate system existing in the largest, shallowest shelf in the Arctic Ocean; the East Siberian Arctic Shelf (ESAS). We review key environmental factors and mechanisms that determine formation, current dynamics, and thermal state of subsea permafrost, mechanisms of its destabilization, and rates of its thawing; a full section of this paper is devoted to this topic. Another important question regards the possible existence of permafrost-related hydrates at shallow ground depth and in the shallow shelf environment. We review the history of and earlier insights about the topic followed by an extensive review of experimental work to establish the physics of shallow Arctic hydrates. We also provide a principal (simplified) scheme explaining the normal and altered dynamics of the permafrost–hydrate system as glacial–interglacial climate epochs alternate. We also review specific features of methane releases determined by the current state of the subsea-permafrost system and possible future dynamics. This review presents methane results obtained in the ESAS during two periods: 1994–2000 and 2003–2017. A final section is devoted to discussing future work that is required to achieve an improved understanding of the subject.

scholarly journals Supplementary material to "Organic matter across subsea permafrost thaw horizons on the East Siberian Arctic Shelf"

2018 ◽  
Author(s):  
Birgit Wild ◽  
Natalia Shakhova ◽  
Oleg Dudarev ◽  
Alexey Ruban ◽  
Denis Kosmach ◽  
...  
Keyword(s):  
Organic Matter ◽  
Arctic Shelf ◽  
Permafrost Thaw ◽  
Siberian Arctic ◽  
Supplementary Material ◽  
Subsea Permafrost

scholarly journals INFLUENCE OF THE PALEOCLIMATIC RECONSTRUCTIONS UNCERTAINTY ON THE SUBMARINE PERMAFROST DYNAMICS

2019 ◽  
Vol 4 (1) ◽  
pp. 99-105
Author(s):  
Valentina Malakhova ◽  
Alexey Eliseev
Keyword(s):  
Time Series ◽  
Sea Level ◽  
Air Temperature ◽  
Climate Changes ◽  
Arctic Shelf ◽  
The Arctic ◽  
Time Intervals ◽  
Ocean Level ◽  
Subsea Permafrost ◽  
Uncertainty Coefficient

The estimates of the subsea permafrost sensitivity to the uncertainty of paleoclimatic reconstructions of air temperature and ocean level have been obtained. This was done by using the model for thermophysical processes in the subsea sediments and the scenario for climate changes at the Arctic shelf for the last 400 kyr. This model was forced by four time series of temperature at the sediment top, by using different combinations of air temperature and sea level. The uncertainty coefficient of the response of the permafrost base depth is less than 0,3, with the exception of isolated time intervals and / or the deepest areas of the shelf.

Subsea Permafrost and Methane on the Siberian-Arctic Shelf: Spatial Patterns, Flux Vectors, 3D-Isotope Source Fingerprinting

2019 ◽  
Author(s):  
Ö. Gustafsson ◽  
N. Shakhova ◽  
I.P. Semiletov ◽  
J. Steinbach ◽  
H Holmstrand ◽  
...  
Keyword(s):  
Spatial Patterns ◽  
Arctic Shelf ◽  
Siberian Arctic ◽  
Subsea Permafrost

scholarly journals Macromolecular composition of terrestrial and marine organic matter in sediments across the East Siberian Arctic Shelf

2016 ◽  
Vol 10 (5) ◽  
pp. 2485-2500 ◽  
Author(s):  
Robert B. Sparkes ◽  
Ayça Doğrul Selver ◽  
Örjan Gustafsson ◽  
Igor P. Semiletov ◽  
Negar Haghipour ◽  
...  
Keyword(s):  
Organic Matter ◽  
Coastal Erosion ◽  
Principal Component ◽  
Arctic Shelf ◽  
The Arctic ◽  
Gas Chromatography Mass Spectrometry ◽  
Terrestrial Organic Matter ◽  
Pyrolysis Gas ◽  
Siberian Arctic ◽  
Extractable Organic Matter

Abstract. Mobilisation of terrestrial organic carbon (terrOC) from permafrost environments in eastern Siberia has the potential to deliver significant amounts of carbon to the Arctic Ocean, via both fluvial and coastal erosion. Eroded terrOC can be degraded during offshore transport or deposited across the wide East Siberian Arctic Shelf (ESAS). Most studies of terrOC on the ESAS have concentrated on solvent-extractable organic matter, but this represents only a small proportion of the total terrOC load. In this study we have used pyrolysis–gas chromatography–mass spectrometry (py-GCMS) to study all major groups of macromolecular components of the terrOC; this is the first time that this technique has been applied to the ESAS. This has shown that there is a strong offshore trend from terrestrial phenols, aromatics and cyclopentenones to marine pyridines. There is good agreement between proportion phenols measured using py-GCMS and independent quantification of lignin phenol concentrations (r2 = 0.67, p < 0.01, n = 24). Furfurals, thought to represent carbohydrates, show no offshore trend and are likely found in both marine and terrestrial organic matter. We have also collected new radiocarbon data for bulk OC (14COC) which, when coupled with previous measurements, allows us to produce the most comprehensive 14COC map of the ESAS to date. Combining the 14COC and py-GCMS data suggests that the aromatics group of compounds is likely sourced from old, aged terrOC, in contrast to the phenols group, which is likely sourced from modern woody material. We propose that an index of the relative proportions of phenols and pyridines can be used as a novel terrestrial vs. marine proxy measurement for macromolecular organic matter. Principal component analysis found that various terrestrial vs. marine proxies show different patterns across the ESAS, and it shows that multiple river–ocean transects of surface sediments transition from river-dominated to coastal-erosion-dominated to marine-dominated signatures.

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