scholarly journals Sonar Estimation of Methane Bubble Flux from Thawing Subsea Permafrost: A Case Study from the Laptev Sea Shelf

Geosciences ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 411
Author(s):  
Denis Chernykh ◽  
Vladimir Yusupov ◽  
Aleksandr Salomatin ◽  
Denis Kosmach ◽  
Natalia Shakhova ◽  
...  
Keyword(s):  
Laptev Sea ◽  
Sea Floor ◽  
Backscattering Cross Section ◽  
Siberian Arctic ◽  
Methane Fluxes ◽  
Methane Bubble ◽  
Acoustic Surveys ◽  
Subsea Permafrost ◽  
The Laptev Sea

Seeps found offshore in the East Siberian Arctic Shelf may mark zones of degrading subsea permafrost and related destabilization of gas hydrates. Sonar surveys provide an effective tool for mapping seabed methane fluxes and monitoring subsea Arctic permafrost seepage. The paper presents an overview of existing approaches to sonar estimation of methane bubble flux from the sea floor to the water column and a new method for quantifying CH4 ebullition. In the suggested method, the flux of methane bubbles is estimated from its response to insonification using the backscattering cross section. The method has demonstrated its efficiency in the case study of single- and multi-beam acoustic surveys of a large seep field on the Laptev Sea shelf.

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 Source apportionment of methane escaping the subsea permafrost system in the outer Eurasian Arctic Shelf

2021 ◽  
Vol 118 (10) ◽  
pp. e2019672118
Author(s):  
Julia Steinbach ◽  
Henry Holmstrand ◽  
Kseniia Shcherbakova ◽  
Denis Kosmach ◽  
Volker Brüchert ◽  
...  
Keyword(s):  
Arctic Shelf ◽  
Laptev Sea ◽  
Methane Release ◽  
Horizontal Gradients ◽  
The Past ◽  
Gas Source ◽  
Stable Isotopic ◽  
Siberian Arctic ◽  
Subsea Permafrost ◽  
The Laptev Sea

The East Siberian Arctic Shelf holds large amounts of inundated carbon and methane (CH4). Holocene warming by overlying seawater, recently fortified by anthropogenic warming, has caused thawing of the underlying subsea permafrost. Despite extensive observations of elevated seawater CH4 in the past decades, relative contributions from different subsea compartments such as early diagenesis, subsea permafrost, methane hydrates, and underlying thermogenic/ free gas to these methane releases remain elusive. Dissolved methane concentrations observed in the Laptev Sea ranged from 3 to 1,500 nM (median 151 nM; oversaturation by ∼3,800%). Methane stable isotopic composition showed strong vertical and horizontal gradients with source signatures for two seepage areas of δ13C-CH4 = (−42.6 ± 0.5)/(−55.0 ± 0.5) ‰ and δD-CH4 = (−136.8 ± 8.0)/(−158.1 ± 5.5) ‰, suggesting a thermogenic/natural gas source. Increasingly enriched δ13C-CH4 and δD-CH4 at distance from the seeps indicated methane oxidation. The Δ14C-CH4 signal was strongly depleted (i.e., old) near the seeps (−993 ± 19/−1050 ± 89‰). Hence, all three isotope systems are consistent with methane release from an old, deep, and likely thermogenic pool to the outer Laptev Sea. This knowledge of what subsea sources are contributing to the observed methane release is a prerequisite to predictions on how these emissions will increase over coming decades and centuries.

scholarly journals Ocean-Bottom Seismographs Based on Broadband MET Sensors: Architecture and Deployment Case Study in the Arctic

Sensors ◽  
2021 ◽  
Vol 21 (12) ◽  
pp. 3979
Author(s):  
Artem A. Krylov ◽  
Ivan V. Egorov ◽  
Sergey A. Kovachev ◽  
Dmitry A. Ilinskiy ◽  
Oleg Yu. Ganzha ◽  
...  
Keyword(s):  
Site Response ◽  
The Arctic ◽  
Laptev Sea ◽  
Ocean Bottom ◽  
Arctic Seas ◽  
Shirshov Institute ◽  
Study Results ◽  
Ocean Bottom Seismographs ◽  
The Laptev Sea

The Arctic seas are now of particular interest due to their prospects in terms of hydrocarbon extraction, development of marine transport routes, etc. Thus, various geohazards, including those related to seismicity, require detailed studies, especially by instrumental methods. This paper is devoted to the ocean-bottom seismographs (OBS) based on broadband molecular–electronic transfer (MET) sensors and a deployment case study in the Laptev Sea. The purpose of the study is to introduce the architecture of several modifications of OBS and to demonstrate their applicability in solving different tasks in the framework of seismic hazard assessment for the Arctic seas. To do this, we used the first results of several pilot deployments of the OBS developed by Shirshov Institute of Oceanology of the Russian Academy of Sciences (IO RAS) and IP Ilyinskiy A.D. in the Laptev Sea that took place in 2018–2020. We highlighted various seismological applications of OBS based on broadband MET sensors CME-4311 (60 s) and CME-4111 (120 s), including the analysis of ambient seismic noise, registering the signals of large remote earthquakes and weak local microearthquakes, and the instrumental approach of the site response assessment. The main characteristics of the broadband MET sensors and OBS architectures turned out to be suitable for obtaining high-quality OBS records under the Arctic conditions to solve seismological problems. In addition, the obtained case study results showed the prospects in a broader context, such as the possible influence of the seismotectonic factor on the bottom-up thawing of subsea permafrost and massive methane release, probably from decaying hydrates and deep geological sources. The described OBS will be actively used in further Arctic expeditions.

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 A multiproxy-based reconstruction of the mid- to late Holocene paleoenvironment in the Laptev Sea off the Lena River Delta (Siberian Arctic)

2020 ◽  
Vol 540 ◽  
pp. 109502
Author(s):  
Оlga Rudenko ◽  
Еkaterina Taldenkova ◽  
Yaroslav Ovsepyan ◽  
Аnna Stepanova ◽  
Henning A. Bauch
Keyword(s):  
Late Holocene ◽  
River Delta ◽  
Laptev Sea ◽  
Lena River ◽  
Siberian Arctic ◽  
Lena River Delta ◽  
The Laptev Sea

Cross-validation of polynya monitoring methods from multisensor satellite and airborne data: a case study for the Laptev Sea

2010 ◽  
Vol 36 (sup1) ◽  
pp. S196-S210 ◽  
Author(s):  
S. Willmes ◽  
T. Krumpen ◽  
S. Adams ◽  
L. Rabenstein ◽  
C. Haas ◽  
...  
Keyword(s):  
Cross Validation ◽  
Laptev Sea ◽  
Monitoring Methods ◽  
The Laptev Sea

scholarly journals Carbon mineralization in Laptev and East Siberian sea shelf and slope sediment

2018 ◽  
Vol 15 (2) ◽  
pp. 471-490 ◽  
Author(s):  
Volker Brüchert ◽  
Lisa Bröder ◽  
Joanna E. Sawicka ◽  
Tommaso Tesi ◽  
Samantha P. Joye ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Carbon Mineralization ◽  
Laptev Sea ◽  
East Siberian Sea ◽  
Degradation Rates ◽  
Siberian Arctic ◽  
Sediment Carbon ◽  
The Laptev Sea ◽  
Carbon Contribution

Abstract. The Siberian Arctic Sea shelf and slope is a key region for the degradation of terrestrial organic material transported from the organic-carbon-rich permafrost regions of Siberia. We report on sediment carbon mineralization rates based on O2 microelectrode profiling; intact sediment core incubations; 35S-sulfate tracer experiments; pore-water dissolved inorganic carbon (DIC); δ13CDIC; and iron, manganese, and ammonium concentrations from 20 shelf and slope stations. This data set provides a spatial overview of sediment carbon mineralization rates and pathways over large parts of the outer Laptev and East Siberian Arctic shelf and slope and allows us to assess degradation rates and efficiency of carbon burial in these sediments. Rates of oxygen uptake and iron and manganese reduction were comparable to temperate shelf and slope environments, but bacterial sulfate reduction rates were comparatively low. In the topmost 50 cm of sediment, aerobic carbon mineralization dominated degradation and comprised on average 84 % of the depth-integrated carbon mineralization. Oxygen uptake rates and anaerobic carbon mineralization rates were higher in the eastern East Siberian Sea shelf compared to the Laptev Sea shelf. DIC ∕ NH4+ ratios in pore waters and the stable carbon isotope composition of remineralized DIC indicated that the degraded organic matter on the Siberian shelf and slope was a mixture of marine and terrestrial organic matter. Based on dual end-member calculations, the terrestrial organic carbon contribution varied between 32 and 36 %, with a higher contribution in the Laptev Sea than in the East Siberian Sea. Extrapolation of the measured degradation rates using isotope end-member apportionment over the outer shelf of the Laptev and East Siberian seas suggests that about 16 Tg C yr−1 is respired in the outer shelf seafloor sediment. Of the organic matter buried below the oxygen penetration depth, between 0.6 and 1.3 Tg C yr−1 is degraded by anaerobic processes, with a terrestrial organic carbon contribution ranging between 0.3 and 0.5 Tg yr−1.

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