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

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.

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

10.5194/bg-2016-367 ◽

2016 ◽

Cited By ~ 3

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.

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

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2014.0451 ◽

2015 ◽

Vol 373 (2052) ◽

pp. 20140451 ◽

Cited By ~ 65

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.

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

10.5194/egusphere-egu21-4013 ◽

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

The key area of the Arctic ocean for atmospheric venting of CH4 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 CH4, contributing annually no less than terrestrial Arctic ecosystems; but unlike terrestrial ecosystems, the ESAS emits CH4 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 CH4 preserved within the shallow ESAS seabed deposits and the documented thawing rates of subsea permafrost reported recently.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.This work was supported in part by grants from Russian Scientific Foundation (&#8470; 18-77-10004 to DCh, DK, AK, &#8470; 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[&#1055;W1]&#160; assignment &#8470; &#1040;&#1040;&#1040;&#1040;-&#1040;17-117030110031-6 to AS.

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

10.5194/tc-2018-229 ◽

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.

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

Geosciences ◽

10.3390/geosciences9060251 ◽

2019 ◽

Vol 9 (6) ◽

pp. 251 ◽

Cited By ~ 17

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.

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Comment on “The origin of methane in the East Siberian Arctic Shelf unraveled with triple isotope analysis” by Sapart et al. (2017)

Biogeosciences ◽

10.5194/bg-15-4777-2018 ◽

2018 ◽

Vol 15 (15) ◽

pp. 4777-4779

Author(s):

Katy J. Sparrow ◽

John D. Kessler

Keyword(s):

Natural Environment ◽

Isotope Analysis ◽

Critical Evaluation ◽

Arctic Shelf ◽

Anthropogenic Contamination ◽

Sample Collection ◽

Quality Of Data ◽

Siberian Arctic ◽

Systematic Methodology

Abstract. In this comment, we outline two major concerns regarding some of the key data presented in this paper. Both of these concerns are associated with the natural abundance radiocarbon-methane (14C-CH4) data. First, no systematic methodology is presented, nor previous peer-reviewed publication referenced, for how these samples were collected, prepared, and ultimately analyzed for 14C-CH4. Not only are these procedural details missing, but the critical evaluation of them using gaseous and aqueous blanks and standards was omitted although these details are essential for any reader to evaluate the quality of data and subsequent interpretations. Second, due to the lack of methodological details, the source of the sporadic anthropogenic contamination cannot be determined and thus it is premature for the authors to suggest it was in the natural environment prior to sample collection. As the natural 14C-CH4 data are necessary for the authors' stated scientific objectives of understanding the origin of methane in the East Siberian Arctic Shelf, our comment serves to highlight that the study's objectives have not been met.

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

10.5194/tc-2018-229-supplement ◽

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

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INFLUENCE OF THE PALEOCLIMATIC RECONSTRUCTIONS UNCERTAINTY ON THE SUBMARINE PERMAFROST DYNAMICS

Interexpo GEO-Siberia ◽

10.33764/2618-981x-2019-4-1-99-105 ◽

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.

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Supplementary material to "The origin of methane in the East Siberian Arctic Shelf unraveled with triple isotope analysis"

10.5194/bg-2016-367-supplement ◽

2016 ◽

Author(s):

Célia J. Sapart ◽

Natalia Shakhova ◽

Igor Semiletov ◽

Joachim Jansen ◽

Sönke Szidat ◽

...

Keyword(s):

Isotope Analysis ◽

Arctic Shelf ◽

Siberian Arctic ◽

Supplementary Material

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Testing the synchronicity of Pleistocene biostratigraphic events in the central Arctic – Do we have a consistent biostratigraphic framework?

10.5194/egusphere-egu21-8345 ◽

2021 ◽

Author(s):

Flor Vermassen ◽

Helen K. Coxall ◽

Gabriel West ◽

Matt O'Regan

Keyword(s):

Arctic Ocean ◽

Sediment Cores ◽

Age Determination ◽

The Arctic ◽

Calcareous Nannofossils ◽

Central Arctic Ocean ◽

Eurasian Basin ◽

Future Work ◽

Amerasian Basin

Harsh environmental and taphonomic conditions in the central Arctic Ocean make age-modelling for Quaternary palaeoclimate reconstructions challenging. Pleistocene age models in the Arctic have relied heavily on cyclostratigraphy using lithologic variability tied to relatively poorly calibrated foraminifera biostratigraphic events. Recently, the identification of Pseudoemiliania lacunosa in a sediment core from the Lomonosov Ridge, a coccolithophore that went extinct during marine isotope stage (MIS) 12 (478-424 ka), has been used to delineate glacial-interglacial units back to MIS 14 (~500 ka BP). Here we present a comparative study on how this nannofossil biostratigraphy fits with existing foraminifer biohorizons that are recognised in central Arctic Ocean sediments. A new core from the Alpha Ridge is presented, together with its lithologic variability and down-core compositional changes in planktonic and benthic foraminifera. The core exhibits an interval dominated by Turborotalita egelida, a planktonic foraminifer that is increasingly being adopted as a marker for MIS11 in sediment cores from the Amerasian Basin of the Arctic Ocean. We show that the new age-constraints provided by calcareous nannofossils are difficult to reconcile with the proposed MIS 11 age for the T. egelida horizon. Instead, the emerging litho- and coccolith biostratigraphy implies that Amerasian Basin sediments predating MIS5 are older than the egelida-based age models suggest, i.e. that the T. egelida Zone is older than MIS11. These results expose uncertainties regarding the age determination of glacial-interglacial cycles in the Amerasian basin and point out that future work is required to reconcile the micro- and nannofossil biostratigraphy of the Amerasian and Eurasian basin.

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