In response to warming climate, methane can be released to Arctic Ocean sediment and waters from thawing subsea permafrost and decomposing methane hydrates. However, it is unknown whether methane derived from this sediment storehouse of frozen ancient carbon reaches the atmosphere. We quantified the fraction of methane derived from ancient sources in shelf waters of the U.S. Beaufort Sea, a region that has both permafrost and methane hydrates and is experiencing significant warming. Although the radiocarbon-methane analyses indicate that ancient carbon is being mobilized and emitted as methane into shelf bottom waters, surprisingly, we find that methane in surface waters is principally derived from modern-aged carbon. We report that at and beyond approximately the 30-m isobath, ancient sources that dominate in deep waters contribute, at most, 10 ± 3% of the surface water methane. These results suggest that even if there is a heightened liberation of ancient carbon–sourced methane as climate change proceeds, oceanic oxidation and dispersion processes can strongly limit its emission to the atmosphere
Methane seepage from the upper continental slopes of Western Svalbard has previously been attributed to gas hydrate dissociation induced by anthropogenic warming of ambient bottom waters. Here we show that sediment cores drilled off Prins Karls Foreland contain freshwater from dissociating hydrates. However, our modeling indicates that the observed pore water freshening began around 8 ka BP when the rate of isostatic uplift outpaced eustatic sea-level rise. The resultant local shallowing and lowering of hydrostatic pressure forced gas hydrate dissociation and dissolved chloride depletions consistent with our geochemical analysis. Hence, we propose that hydrate dissociation was triggered by postglacial isostatic rebound rather than anthropogenic warming. Furthermore, we show that methane fluxes from dissociating hydrates were considerably smaller than present methane seepage rates implying that gas hydrates were not a major source of methane to the oceans, but rather acted as a dynamic seal, regulating methane release from deep geological reservoirs.
One source of these emissions "may be highly potential and extremely mobile shallow methane hydrates, whose stability zone is seabed permafrost-related and could be disturbed upon permafrost development, degradation, and thawing." Even if the methane hydrates are deep, fissures, taliks and other soft spots createheat pathways from the seabed which warms quickly due to shallow depths. Various mechanisms for such processes have been elaborated in detai
As the ESAS is shallow at only 50 metres, most of the methane being released is escaping into the atmosphere rather than being absorbed into water.
we consider release of up to 50 Gt of predicted amount of hydrate storage as highly possible for abrupt release at any time. That may cause ∼12-times increase of modern atmospheric methane burden with consequent catastrophic greenhouse warming."
So, to summarize you have dissassociated methane lingering about in shallow waters being barred from escape into the atmosphere ONLY by a layer of permafrost that because of the shallow waters is vulnerable to rapid warming. The other quotes speak for themselves and contradict Rockdoc's link. And of course we have an extensive body of science that implicates global warming and specifically methane as prime culprits and contributors in Mass Extinction Events in the past.
Gas hydrate, a frozen, naturally-occurring, and highly-concentrated form of methane, sequesters significant carbon in the global system and is stable only over a range of low-temperature and moderate-pressure conditions. Gas hydrate is widespread in the sediments of marine continental margins and permafrost areas, locations where ocean and atmospheric warming may perturb the hydrate stability field and lead to release of the sequestered methane into the overlying sediments and soils. Methane and methane-derived carbon that escape from sediments and soils and reach the atmosphere could exacerbate greenhouse warming. The synergy between warming climate and gas hydrate dissociation feeds a popular perception that global warming could drive catastrophic methane releases from the contemporary gas hydrate reservoir. Appropriate evaluation of the two sides of the climate-methane hydrate synergy requires assessing direct and indirect observational data related to gas hydrate dissociation phenomena and numerical models that track the interaction of gas hydrates/methane with the ocean and/or atmosphere. Methane hydrate is likely undergoing dissociation now on global upper continental slopes and on continental shelves that ring the Arctic Ocean. Many factors—the depth of the gas hydrates in sediments, strong sediment and water column sinks, and the inability of bubbles emitted at the seafloor to deliver methane to the sea-air interface in most cases—mitigate the impact of gas hydrate dissociation on atmospheric greenhouse gas concentrations though. There is no conclusive proof that hydrate-derived methane is reaching the atmosphere now, but more observational data and improved numerical models will better characterize the climate-hydrate synergy in the future.
And of course we have an extensive body of science that implicates global warming and specifically methane as prime culprits and contributors in Mass Extinction Events in the past
and you counter with some journalist's view on things from 5 years ago?
They are referencing the scientists Semiletov and Shakhova and their publication.. You know like the scientists doing the actual fieldwork and focused specifically on the ESAS.
As for 5 years ago, well that only means the author and the scientists have only more reason to be alarmed given the rapidly rising methane levels from 2014-6 as linked earlier in this thread.
Sparrow told IFLScience that her team “make no attempt to upscale our findings to other areas of the Arctic,” and similar studies are needed elsewhere. Their site also has no known methane seeps, unlike those causing alarm in other parts of the Arctic. Nevertheless, the fact the Bay is quite shallow and yet the ancient methane Sparrow found near the seafloor is not reaching surface waters presents an encouraging sign for the deeper locations.
Deep vs Shallow
Hydrates vs Free gas reservoirs
Isostatic rebound around Svalbard vs Coastal plain inundation of the ESAS
dissociation vs permafrost cap degredation
His dissembling is his trademark. He knows exactly what he is doing.
Many factors—the depth of the gas hydrates in sediments, strong sediment and water column sinks, and the inability of bubbles emitted at the seafloor to deliver methane to the sea-air interface in most cases—mitigate the impact of gas hydrate dissociation on atmospheric greenhouse gas concentrations though. There is no conclusive proof that hydrate-derived methane is reaching the atmosphere now, but more observational data and improved numerical models will better characterize the climate-hydrate synergy in the future.
...."no conclusive proof that hydrate-derived methane is reaching the atmosphere ...".
The amount of CH4 sequestered in and spatially associated with gas hydrates remains uncertain, and better constraints on these values and on the distribution of hydrates and associated free gas in different physiographic settings will advance understanding of the exogenic carbon cycle and long-term synergies between the hydrate reservoir and the climate system. Special attention should be focused on mapping the contemporary distribution and inferring the saturation of methane hydrates in settings that are most susceptible to climate-driven dissociation. For example, data that can delineate the baseline state of upper continental slope gas hydrates will prove useful in future decades as warming intermediate waters continue to drive dissociation. On Arctic Ocean margins, field expeditions that constrain the current distribution of subsea permafrost can identify where PAGH may remain in association with intact permafrost and in thawed zones beyond the edge of that permafrost. With rapid thawing of subsea permafrost expected to continue throughout the 21st century [Rachold et al., 2007], baseline data sets on Arctic Ocean shelves will have particular significance for tracking the impact of climate change.
Anomalously shallow gas hydrates have been postulated for the Yamal Peninsula [Chuvilin et al., 2002] and invoked to explain some observations on the East Siberian Arctic Shelf [Shakhova et al., 2010a], as discussed above. Neither area was glaciated at the LGM, and the shallow gas releases on which the anomalous hydrate interpretation is based [Chuvilin et al., 2002] are common in permafrost areas during drilling and thought to be unrelated to gas hydrate dynamics. Even if proof for anomalous gas hydrates is eventually found, it remains uncertain how the pressure and temperature conditions at shallow depths (e.g., less than 100 m) could have been within the gas hydrate stability field absent recent glacial loading or a highly unusual mixture of hydrocarbons.
... Rupple 2017 ....
Are you trying to tell us all here that somehow Eastern Siberia was never affected by continental glaciation and somehow avoided isostatic rebound?
The shallow Bering Strait connection to the Pacific and the huge Siberian shelves were subaerially exposed and covered by a periglacial tundra steppe [Hopkins, 1982; Sher, 1995; Elias et al., 1996]. Model simulations of the LGM climate show that the expansion of ice sheets over North America and NW Eurasia caused severe changes in atmospheric temperatures, pressure gradients, and geostrophic wind patterns [Kutzbach and Guetter, 1986; Ganopolski et al., 1998; Kageyama et al., 2001], which must also have influenced the Arctic Ocean environment. Paleobotanical data [Tarasov et al., 1999] support model outputs, which indicate a much drier and colder climate in the ice sheet-free areas of northern Eurasia than today, resulting in a decreased freshwater supply from Siberian rivers.
Methane in situ production occurs frequently in the oxygenated upper ocean. A principal pathway by which methane can be formed is methylotrophic methanogenesis, while an important methylated substrate is DMSP (dimethylsulfoniopropionate) produced by marine phytoplankton. Here we report on an in situ methane production/consumption cycle during a summer phytoplankton bloom and a potential link to DMSP concentration in Storfjorden (Svalbard Archipelago) – a polar shelf region.
We propose that methane in situ production occurs during the summer phytoplankton bloom. The concentration of methane increases up to a certain threshold value, above which methane consumption begins. A methane production-removal cycle is established, which is reflected in the varying methane concentrations and δ13CCH4 values. DMSP and methane are inversely correlated suggesting that DMSP could be a potential substrate for the methylotrophic methanogenesis.
Actually, there are numerous observations and documentation of methane bubbles reaching the surface of the ocean, including some that are clearly derived from methane hydrates.
There is no conclusive proof that hydrate-derived methane is reaching the atmosphere now,
So Ms. Rupple is claiming throughout her paper that no CH4 emissions have been measured coming from the ocean, and in another place she is acknowledging that CH4 emissions HAVE been measured coming from the ocean,
The inclusion of hydrate dissociation as a possible source of atmospheric CH4 in the IPCC reports is a rightful acknowledgement of the fact that the amount of CH4 sequestered in this reservoir dwarfs that in some other parts of the Earth system. On the other hand, the IPCC reports cite no direct sources that constrain emissions of CH4 to the atmosphere as a result of gas hydrate dissociation. Indeed, while gas hydrate deposits are likely dissociating and releasing CH4 to sedimentary sections and the ocean on contemporary Earth, there remains no evidence that this hydrate-derived CH4 reaches the atmosphere or that the amounts that could potentially reach the atmosphere are significant enough to affect the overall CH4 budget. In the following sections, we discuss some of the difficulties in discerning methane released from gas hydrates from other populations of methane in the ocean and atmosphere and also underscore the powerful role of sinks in mitigating the transfer to the atmosphere of methane released by dissociating gas hydrates.
To date, numerous direct measurements have been made to quantify bulk CH4 emissions from tundra, high-latitude wetlands, and thermokarst lakes [e.g., Christensen, 1993; Walter et al., 2006; Whalen and Reeburgh, 1988; Wille et al., 2008; Zona et al., 2016], but attributing a fraction of this CH4 stream to gas hydrate dissociation is not currently possible. Furthermore, the observed increase in atmospheric CH4 concentrations since about 2007 [Dlugokencky et al., 2009] cannot be attributed to arctic emissions, which are expected to continue rising as global warming leads to enhanced methane production and/or release from several sources [World Meteorological Organization, 2013]. Even under a possible future scenario of rising arctic CH4 emissions, which are expected to lag warming, discerning the component related to gas hydrate dissociation may always remain more challenging at high northern latitudes due to the number of methane sources in these settings and their overlapping depths of origin (Figure 10).
On the contemporary Earth, gas hydrate is dissociating in specific terrains in response to post-LGM climate change and probably also due to warming since the onset of the Industrial Age. Nevertheless, there is no conclusive proof that the released methane is entering the atmosphere at a level that is detectable against the background of ~555 Tg yr−1 CH4 emissions. The IPCC estimates are not based on direct measurements of methane fluxes from dissociating gas hydrates, and many numerical models adopt simplifications that do not fully account for sinks, the actual distribution of gas hydrates, or other factors, resulting in probable overestimation of emissions to the ocean-atmosphere system.
Ruppel has been at the forefront of the methane hydrate disinformation campaign, attacking any papers suggesting methane hydrates are unsafe to extract, or may pose a danger to the environment.
Our data show that at a shallow water depth, approximately 67–72% of CH4 remains in the bubbles when the bubbles reach the sea surface.
Dissolved CH4 in the outer ESAS requires 300–1000 days to be oxidized in the water column because CH4 oxidation rates are very low (mean±1 s.d.: 0.0988±0.1343 nM d−1, p=0.95, n=328). During this time, some of the aqueous CH4 inventory is likely to be released to the atmosphere during storms [10]. The remaining dissolved CH4, captured beneath the sea ice in winter, can spread further from the ESAS via currents (figure 4), and some can escape to the atmosphere through leads and breaks in the ice [34].
Sea ice serves as a natural physical barrier that restricts CH4 emissions from the ESAS during the ice-covered period. Because the temperature in the Arctic has increased at twice the rate as in the rest of the globe, and the region is expected to increase an additional 8°C (14°F) in the twenty-first century [3], longer periods of open water and shorter ice-covered periods [35,36] are occurring. Increasing periods of open water implies an increasing number of storm events, when wind speed increases to 15 m s−1 or more and the boundary between sea surface and air increases many times due to deep water mixing. Such events have the potential to rapidly ventilate bubble-transported and dissolved CH4 from the water column, producing high emission rates to the atmosphere. Because more than 75% of the total ESAS area is less than 50 m in depth, the water column provides bubbles with a very short conduit to the atmosphere. Storms enable more CH4 release because they destroy shallow water stratification and increase the boundary between sea surface and air, thus increasing gas exchange across phase boundaries. As a result, bubble-mediated, storm-induced CH4 ‘pulses’ force a greater fraction of CH4 to bypass aqueous microbial filters and reach the atmosphere [10].
In addition, about 10% of the ESAS remains open water in winter due to formation of flaw polynyas. It was shown that flaw polynyas provide pathways for CH4 escape to the atmosphere during the arctic winter [37]. Areas of flaw polynyas in the ESAS increased dramatically (by up to five times) during the last decades, and now exceed the total area of the Siberian wetlands (electronic supplementary material, figure S5). This implies that the ESAS remains an active source of CH4 to the atmosphere year-round.
Exactly.
The shallow Bering Strait connection to the Pacific and the huge Siberian shelves were subaerially exposed and covered by a periglacial tundra steppe [Hopkins, 1982; Sher, 1995; Elias et al., 1996]. Model simulations of the LGM climate show that the expansion of ice sheets over North America and NW Eurasia caused severe changes in atmospheric temperatures, pressure gradients, and geostrophic wind patterns [Kutzbach and Guetter, 1986; Ganopolski et al., 1998; Kageyama et al., 2001], which must also have influenced the Arctic Ocean environment. Paleobotanical data [Tarasov et al., 1999] support model outputs, which indicate a much drier and colder climate in the ice sheet-free areas of northern Eurasia than today, resulting in a decreased freshwater supply from Siberian rivers.
The Laptev Sea and East Siberian Sea are extended shallow shelf seas which were largely land fallen during glacial periods when the global mean sea level was more than 100 m below its present value. To understand the environmental history, and, in particular, the evolution of the large offshore permafrost complexes in this region, a reconstruction of the sea-level variation and shoreline migration was undertaken. Sufficient geological information by sea-level indicators is missing and, in recent studies, the eustatic sea-level curve is commonly applied, neglecting any isostatic adjustment processes. In this study, we discuss the influence of glacial isostatic adjustment (GIA), which describes the deformational response of the solid earth and the resulting sea-level variations due to the water mass redistribution between ice sheets and ocean during a glacial cycle. Motivated as a sensitivity study, we consider GIA-induced sea-level variations from the last glacial maximum (LGM) to present and apply an earth model ensemble which covers the range of reasonable rheological parametrisations for a passive continental margin. The geodynamically consistent sea-level reconstructions are applied to predict the shoreline retreat in the Laptev and East Siberian seas. We confirm with this study that the application of the eustatic sea-level curve is a valid first-order approximation for reconstructing the shoreline position from LGM to present, whereas the sea-level heights away from the shoreline inferred from the eustatic sea-level curve differ markedly from GIA predictions.
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