Erratum to: Methane Emission from Arctic Shelf Sediments upon Violation of Hydrate Stability Conditions

The thickness and spatial distribution of a methane hydrate stability zone (MHSZ) associated with submarine permafrost is estimated based on numerical simulation. Using CMIP6 ensemble model calculations with a scenario of high anthropogenic greenhouse gas emissions (SSP5-8.5), a weak dependence of MHSZ shrinkage on ongoing warming is found, and mainly on the side of its base. This process is, first of all, a consequence of the Holocene marine transgression and depends on geothermal flux intensity. The spatial distribution of methane fluxes from bottom sediments caused by degradation of gas hydrates under the violation of their existence conditions is derived. The intensity of methane emission from seafloor to water is estimated at 15 Tg/yr in the modern period and 16–17 Tg/yr to 2300 (similar estimates of the intensity of methane emission from water to the atmosphere are not made in this work). Significant changes in the intensity of methane emissions from seafloor to water are hardly probable for at least several thousand years. The resulting fields of methane fluxes from bottom sediments can be used in numerical ocean models for assessing methane emissions to the atmosphere.

Destabilization of intrapermafrost gas hydrates is one of the possible mechanisms responsible for methane emission in the Arctic shelf. Intrapermafrost gas hydrates may be coeval to permafrost: they originated during regression and subsequent cooling and freezing of sediments, which created favorable conditions for hydrate stability. Local pressure increase in freezing gas-saturated sediments maintained gas hydrate stability from depths of 200–250 m or shallower. The gas hydrates that formed within shallow permafrost have survived till present in the metastable (relict) state. The metastable gas hydrates located above the present stability zone may dissociate in the case of permafrost degradation as it becomes warmer and more saline. The effect of temperature increase on frozen sand and silt containing metastable pore methane hydrate is studied experimentally to reconstruct the conditions for intrapermafrost gas hydrate dissociation. The experiments show that the dissociation process in hydrate-bearing frozen sediments exposed to warming begins and ends before the onset of pore ice melting. The critical temperature sufficient for gas hydrate dissociation varies from −3.0 °C to −0.3 °C and depends on lithology (particle size) and salinity of the host frozen sediments. Taking into account an almost gradientless temperature distribution during degradation of subsea permafrost, even minor temperature increases can be expected to trigger large-scale dissociation of intrapermafrost hydrates. The ensuing active methane emission from the Arctic shelf sediments poses risks of geohazard and negative environmental impacts.

Methane hydrate close to the hydrate stability limit in seafloor sediment could represent an important source of methane to the oceans and atmosphere as the oceans warm. We investigate the extent to which patterns of past and future ocean‐temperature fluctuations influence hydrate stability in a region offshore West Svalbard where active gas venting has been observed. We model the transient behavior of the gas hydrate stability zone at 400–500 m water depth (mwd) in response to past temperature changes inferred from historical measurements and proxy data and we model future changes predicted by seven climate models and two climate‐forcing scenarios (Representative Concentration Pathways RCPs 2.6 and 8.5). We show that over the past 2000 year, a combination of annual and decadal temperature fluctuations could have triggered multiple hydrate‐sourced methane emissions from seabed shallower than 400 mwd during episodes when the multidecadal average temperature was similar to that over the last century (∼2.6°C). These temperature fluctuations can explain current methane emissions at 400 mwd, but decades to centuries of ocean warming are required to generate emissions in water deeper than 420 m. In the venting area, future methane emissions are relatively insensitive to the choice of climate model and RCP scenario until 2050 year, but are more sensitive to the RCP scenario after 2050 year. By 2100 CE, we estimate an ocean uptake of 97–1050 TgC from marine Arctic hydrate‐sourced methane emissions, which is 0.06–0.67% of the ocean uptake from anthropogenic CO2 emissions for the period 1750–2011.

Based on the regional ocean-ice model SibCIOM, calculations have been made for modeling the Arctic Ocean water masses conditions and dissolved methane transfer for the period from 1970 to 2019. We have performed the model analysis of methane emissions from the Arctic seas caused by gas release at the "ocean-bottom" interface. It is shown that the East Siberian shelf seas provide significant contributions to the total methane emission in the region. The spatial variability of the methane emissions into the atmosphere is primarily due to the region's peculiarities and ice conditions circulation. The estimated methane flux from the Arctic shelf seas has amounted to 2 Tg per year.

<p>The East Siberian Sea is known for its high methane emissions, and the extent of massive methane emissions in remote areas from the coast is considered an important factor in estimating total methane emissions in the Arctic Ocean. In 2021, a multidisciplinary survey was conducted on the continental shelf of the East Siberian Sea aboard the Korean icebreaker <em>Araon.</em> The area is in international waters and is located more than 500 km from the coast. We conducted high-resolution sparker seismic survey and sub-bottom profiling to find detailed geological structure for gas expulsion and high-frequency echo sounding using EK80 to detect gas bubbles in water column EK80. We also measured underway CH4 concentration and sampled water and sediment with CTD and a multi corer. A high methane-concentration zone was found on the very shallow continental shelf at depths of 50–70 m by the underway CH4 measurements. It is developed in a northwest-southeast direction and has a width of several kilometers in the northwest and about 50 kilometers in the southeast. Because thick sea ice remained in the southeast zone, we have to surveye in the northwest zone. During the survey, many gas flares in the echograms and gas bubbles on the sea surface were found. In the gas flare field, we conducted extensive experiments with CTDs and sediment sampling using a multi-corer. A single channel sparker seismic survey was conducted crossing the high concentration zone with a source of 3000–5000 J. The acquired data were processed to get migration section and seismic profiles show well-stratified sedimentary layers clearly. On the gas expulsion sites, the seismic profiles show many vertical faults in the shallow sedimentary layers and vertical reflections in the water column caused by the methane emission from the seafloor. Acoustic features related to gas expulsion and gas charged sediments were also observed in the SBP data. Narrow and vertical reflections are also observed in the water column above the seafloor and the location of these reflections corresponds with the edge of the high amplitude, undulated subsurface reflector at shallow depths (~5 m) below the seafloor.</p>

Based on a regional ice-ocean model, we simulated the state of the water masses of the Arctic Ocean to analyze the transport of dissolved methane on the Arctic shelves. From 1970 to 2019, we obtained estimates of methane emissions at the Arctic seas due to the degradation of submarine permafrost and gas release at the ocean–bottom interface. The calculated annual methane flux from the Arctic shelf seas into the atmosphere did not exceed 2 Tg CH4 year−1. We have shown that the East Siberian shelf seas make the main contribution to the total methane emissions of the region. The spatial variability of the methane fluxes into the atmosphere is primarily due to the peculiarities of the water circulation and ice conditions. Only 7% of the dissolved methane originating from sediment enters the atmosphere within the study area. Most of it appears to be transported below the surface and oxidized by microbial activity. We found that increasing periods and areas of ice-free water and decreasing ice concentration have contributed to a steady increase in methane emissions since the middle of the first decade of the current century.

Satellite data on tropospheric methane and dynamical permafrost model simulations were used to analyze the methane emission in the subaquatic permafrost on the East Siberian Arctic shelf. The hypothesis of potential methane release from the dissociation of submarine gas hydrates was studied. It was demonstrated that the methane emission on the Arctic shelf is governed mainly by geological factors and is not related to contemporary climate change. Numerical experiments with the INM-CM48 Earth system model showed that there is no feedback between the methane emission on the shelf and global air temperature. A conceptual model of methane emission on the East Siberian Arctic shelf was developed.

Trigger mechanisms are proposed for gas hydrate decomposition, methane emissions, and glacier collapse in polar regions. These mechanisms are due to tectonic deformation waves in the lithosphere–asthenosphere system, caused by large earthquakes in subduction zones, located near the polar regions: the Aleutian arc, closest to the Arctic, and the Antarctica–Chilean and Tonga–Kermadec–Macquarie subduction zones. Disturbances of the lithosphere are transmitted over long distances (of the order of 2000–3000 km and more) at a speed of about 100 km/year. Additional stresses associated with them come to the Arctic and Antarctica several decades after the occurrence of seismic events. On the Arctic shelf, additional stresses destroy the microstructure of metastable gas hydrates located in frozen rocks at shallow depths, releasing the methane trapped in them and leading to filtration and emissions. In West Antarctica, these wave stresses lead to decreases in the adhesions of the covered glaciers with underlying bedrock, sharp accelerations of their sliding into the sea, and fault occurrences, reducing pressure on the underlying rocks containing gas hydrates, which leads to their decomposition and methane emissions.

The Arctic is rapidly transitioning toward a seasonal sea ice‐free state, perhaps one of the most apparent examples of climate change in the world. This dramatic change has numerous consequences, including a large increase in air temperatures, which in turn may affect terrestrial methane emissions. Nonetheless, terrestrial and marine environments are seldom jointly analyzed. By comparing satellite observations of Arctic sea ice concentrations to methane emissions simulated by three process‐based biogeochemical models, this study shows that rising wetland methane emissions are associated with sea ice retreat. Our analyses indicate that simulated high‐latitude emissions for 2005–2010 were, on average, 1.7 Tg CH4 yr−1 higher compared to 1981–1990 due to a sea ice‐induced, autumn‐focused, warming. Since these results suggest a continued rise in methane emissions with future sea ice decline, observation programs need to include measurements during the autumn to further investigate the impact of this spatial connection on terrestrial methane emissions.

Recent and expected changes in Arctic sea ice cover, snow cover, and methane emissions from permafrost thaw are likely to result in large positive feedbacks to climate warming. There is little recognition of the significant loss in economic value that the disappearance of Arctic sea ice, snow, and permafrost will impose on humans. Here, we examine how sea ice and snow cover, as well as methane emissions due to changes in permafrost, may potentially change in the future, to year 2100, and how these changes may feed back to influence the climate. Between 2010 and 2100, the annual costs from the extra warming due to a decline in albedo related to losses of sea ice and snow, plus each year's methane emissions, cumulate to a present value cost to society ranging from US$7.5 trillion to US$91.3 trillion. The estimated range reflects uncertainty associated with (1) the extent of warming-driven positive climate feedbacks from the thawing cryosphere and (2) the expected economic damages per metric ton of CO2 equivalents that will be imposed by added warming, which depend, especially, on the choice of discount rate. The economic uncertainty is much larger than the uncertainty in possible future feedback effects. Nonetheless, the frozen Arctic provides immense services to all nations by cooling the earth's temperature: the cryosphere is an air conditioner for the planet. As the Arctic thaws, this critical, climate-stabilizing ecosystem service is being lost. This paper provides a first attempt to monetize the cost of some of those lost services.

Submarine fluid flow system can transport methane into ocean. However, its evolution is not fully understood, particularly methane migration through the gas hydrate stability zone (GHSZ) in deep‐water settings. Here, we used 3D seismic and well‐logging data to show the currently active fluid flow system in the northern South China Sea. It was interpreted to have two parts and they together feed intermittent methane emission. Three gas clouds have been seismically imaged beneath the base of gas hydrate stability zone (BGHSZ) and a set of new faults can be identified within them. Twenty‐eight seismic pipes were found to penetrate three vertically stacked mass transport deposits (MTDs) above the gas clouds. Log‐seismic correlation shows that the seismic reflections in the pipe represent MTD sediment, bulk carbonate and gas hydrate‐ or free gas‐bearing sediments. We interpreted faults and pipes as the main migration conduits below and above the BGHSZ respectively. The MTD within the GHSZ could seal the underlying free gas transported by faults and thus overpressure built up at the base prior to the occurrences of the pipes and the fracturing through the overlying sedimentary succession. Subsequently, focused fluid flow entered the GHSZ, with the methane probably bypassing the GHSZ before pore clogging of gas hydrates occurred. Additionally, mapping of high‐amplitude reflections surrounding the upper portion of gas clouds reveals the relict free gas associated with three paleo‐GHSZ bases. Episodic emplacements of new MTDs repeatedly caused the upward shifts of the BGHSZ and the resultant gas hydrate dissociation, contributing to methane emission. We proposed that the occurrences of MTDs may facilitate methane emission by intermittently trapping methane and inducing gas hydrate dissociation in deep‐water settings.

To study the impact of future climate change on the methane emissions to the atmosphere as a result of the Arctic submarine permafrost degradation, scenario experiments were carried up to 2100 out using the SibCIOM ocean and sea ice model. For the atmospheric forcing, we used the results of six climate model simulations from the RCP8.5 scenario of the Coupled Model Inter-comparison Project Phase 5 archive. Based on the numerical results, it is found that the total annual methane fluxes will increase by a factor of 2–4 depending on the atmospheric forcing by 2100 compared to current levels. The flux intensity calculated in the numerical experiments does not exceed 8 Tg/yr. High future methane emissions are mainly due to reduced ice extent and increased ice-free periods. This resulted in a shift in the timing of maximal methane emissions from summer to fall and winter.

Существует значительная неопределенность в отношении масштабов эмиссии метана из морей арктического шельфа. Потоки метана в этом регионе могут быть недооценены и играть значимую роль из-за большого объема газа, который содержится в донных отложениях в слое многолетнемерзлых пород и газовых гидратов. Проведен анализ чувствительности модели эмиссии метана к параметризации процессов газообмена на поверхности моря на основе результатов численного моделирования переноса растворенного метана в морях Арктики. Модель переноса растворенного метана включена в базовую модель океана и морского льда SibCIOM, разработанную в ИВМиМГ СО РАН. Оценки эмиссии метана в атмосферу выполнены на основе различных соотношений для параметризации процесса газообмена в системе «вода – атмосфера» и «вода – лед – атмосфера» с использованием данных реанализа NCEP/NCAR. Неопределенность оценки годовой эмиссии метана составила 6–12% с учетом различных зависимостей коэффициента газообмена от ветра. Более выраженное влияние при расчете потока оказывает схема учета ледового покрова – неопределенность увеличилась до 50–130%. Параметризация взаимосвязи между ледовым покровом и газообменом может оказывать большое влияние на расчетные потоки метана и приводить к недооценке его эмиссии из морей арктического шельфа. There is considerable uncertainty about the methane emission from the Arctic shelf seas. Methane fluxes in this region can be underestimated and play a significant role due to the large volume of gas contained in bottom sediments in the permafrost and gas hydrates. We have analyzed the model sensitivity to the parametrization of gas exchange processes on the sea surface. The study is based on the numerical modeling results of the transport of dissolved methane in the seas of the Arctic. The dissolved methane transport model is included in the basic model of the ocean and sea ice developed at the Institute of Computational Mathematics and Mathematics, Siberian Branch, Russian Academy of Sciences. Estimates of methane emissions into the atmosphere were made with various parametrization of the gas exchange process in the "water – atmosphere" and "water – ice – atmosphere" systems using NCEP/NCAR reanalysis data. The uncertainty of the estimate of annual methane emission amounted to 6–12% when considering different dependencies of gas exchange on wind. The scheme accounting the ice cover has a more pronounced influence on the flux: the uncertainty increased to 50–130%. Parameterization of the relationship between ice cover and gas exchange can have a great influence on the calculated methane fluxes and lead to underestimation of its emission from the seas of the Arctic shelf.

Although the Arctic methane reservoir is large, the emission of methane from the Arctic Ocean into the atmosphere remains poorly constrained. Continuous ship-borne measurements of atmospheric methane near the surface ocean were carried out during two cruises to investigate methane emission from the Arctic Ocean up to the latitude of 87oN. Three-day air mass back trajectories along the cruise tracks indicated that the surface Arctic Ocean could be a potentially important source of methane to the atmosphere. Rapid bursts in methane concentration occurred mainly along the ocean frontal area, suggesting that frontal upwelling in the upper layer of the Arctic Ocean might contribute to methane emissions into the atmosphere.

The phase transition problem of methane hydrate in porous sediments is solved. Based on the obtained solution, the impact of faulting on the stability conditions of gas hydrates is investigated by the numerical modeling of the filtration and thermal regimes in the sedimentary cover of the Central Basin of Lake Baikal within the segment of the anomalous behavior of the bottom simulating reflector (BSR). It is assumed that such behavior is caused by the tectonic action. The calculations testify to the plausibility of the proposed model of formation of the anomalous area with total decomposition of the contained hydrates. It is shown that dissociation of gas hydrates in sediments due to faulting and the subsequent uplift of the products of these transformations along the incipient channel toward the bottom of the lake can result in the extensive accumulation of gas hydrates on this surface. It is also shown that if the total amount of the free gas, which left the hydrate dissociation zone, reached the level of the lake surface at normal pressure and temperature, its volume could be equivalent to the resources of a medium-size gas field. The results of numerical modeling the violation of the gas-hydrate stability conditions in Lake Baikal sediments can also be valid for the other regions with hydrate-bearing sediments if the case specific conditions and regional tectonic activity are taken into account.