Subsea Permafrost Research Articles

In the Warming Arctic Seas

In the Warming Arctic Seas

Seepage in Isfjorden and its tributary fjords, West Spitsbergen

Abstract This study analyses pockmark morphology and their spatial distribution in Isfjorden relative to seabed morphology, bedrock geology, fault systems, glacial landforms and processes using multibeam bathymetric data. It provides insight into the possible mechanisms of pockmark formation, high density pockmark field evolution, and fluid migration pathways. A total of 1304 pockmarks occur in the Isfjorden at water depths of 40 to 320 m, varying from circular to elongate in plan-view. Their diameter ranges from 14 to 265 m and their depths from 1 to 11 m. Elongate pockmarks are dominant in the Isfjordbanken and outer Isfjorden where the seafloor is influenced by the West Spitsbergen Current. The West Spitsbergen fold-and-thrust belt and other fault systems sub-cropping at the Isfjorden seafloor correlate spatially with the high density pockmark zones. The pockmarks are preferentially located on the marine sediments draping the bedrock of Isfjorden fjord system. They are most abundant in the areas underlain by Jurassic–Cretaceous and the Triassic–Lower Jurassic bedrock. Pockmarks found ahead of submarine slope failures may have formed due to dewatering of soft sediments as a result of rapid increase of overpressure caused by deposition of glacigenic debris lobes. Fault conduits, potential source rock and thin postglacial sediment layers are found to be crucial for the formation of pockmarks. Modeling results of the near-shore subsea permafrost and potential gas hydrate stability zone imply thawing permafrost and gas hydrate dissociation as additional possible mechanisms for pockmark formation in Isfjorden.

Modeling the evolution of climate‐sensitive Arctic subsea permafrost in regions of extensive gas expulsion at the West Yamal shelf

AbstractThawing subsea permafrost controls methane release from the Russian Arctic shelf having a considerable impact on the climate‐sensitive Arctic environment. Expulsions of methane from shallow Russian Arctic shelf areas may continue to rise in response to intense degradation of relict subsea permafrost. Here we show modeling of the permafrost evolution from the Late Pleistocene to present time at the West Yamal shelf. Modeling results suggest a highly dynamic permafrost system that directly responds to even minor variations of lower and upper boundary conditions, e.g., geothermal heat flux from below and/or bottom water temperature changes from above permafrost. Scenarios of permafrost evolution show a potentially nearest landward modern extent of the permafrost at the West Yamal shelf limited by ~17 m isobaths, whereas its farthest seaward extent coincides with ~100 m isobaths. The model also predicts seaward tapering of relict permafrost with a maximal thickness of 275–390 m near the shoreline. Previous field observations detected extensive emissions of free gas into the water column at the transition zone between today's shallow water permafrost (<20 m) and deeper water nonpermafrost areas (>20 m). The model adapts well to corresponding heat flux and ocean temperature data, providing crucial information about the modern permafrost conditions. It shows current locations of upper and lower permafrost boundaries and evidences for possible release of methane from the seabed to the hydrosphere in a warming Arctic.

Permafrost-Associated Gas Hydrate: Is It Really Approximately 1 % of the Global System?

Permafrost-associated gas hydrates are often assumed to contain ∼1 % of the global gas-in-place in gas hydrates based on a study26 published over three decades ago. As knowledge of permafrost-associated gas hydrates has grown, it has become clear that many permafrost-associated gas hydrates are inextricably linked to an associated conventional petroleum system, and that their formation history (trapping of migrated gas in situ during Pleistocene cooling) is consistent with having been sourced at least partially in nearby thermogenic gas deposits. Using modern data sets that constrain the distribution of continuous permafrost onshore5 and subsea permafrost on circum-Arctic Ocean continental shelves offshore and that estimate undiscovered conventional gas within arctic assessment units,16 the analysis done here reveals where permafrost-associated gas hydrates are most likely to occur, concluding that Arctic Alaska and the West Siberian Basin are the best prospects. A conservative estimate is that 20 Gt C (2...

Multiple failure styles related to shallow gas and fluid venting, upper slope Canadian Beaufort Sea, northern Canada

The continental slope of the Canadian Beaufort Sea presents an exceptional opportunity to study the relationship between the fluid venting and the formation of mass-transport deposits. The continental shelf was emergent and partially ice-free during the last glaciation and is underlain by widespread permafrost. Water-column backscatter has shown the locations of more than 40 active gas vents along seaward margin of the subsea permafrost at the shelf break and upper slope. New multibeam bathymetry and subbottom profiler data show shallow potentially late Holocene failures and mass-transport deposits on the upper slope. Upslope from a prominent headscarp, undulating seabed with apparent growth faults overlies an acoustically incoherent to stratified horizon at 50 m sub-bottom interpreted as a decollement surface over which progressive creep has occurred. Similar creep is present in places on the upper slope and in places seems to have evolved into small translational slides, involving more compacted sediment buried > 25 m, or into muddy debris flows where sediments buried < 25 m have failed. Much of the slope failed during a regional retrogressive event, the Ikit slump, likely initiated on steep channel walls on the lower slope. Characteristic ridge and trough morphology resulting from retrogressive spreading or rotational slumping are preserved on gradients < 2° on the upper slope, but appear to have been completely evacuated on gradients of 3° on the mid slope, where muddy debris-flow deposits are found. Correlations between radiocarbon dated cores and sub-bottom profiles show that the retrogressive failure occurred in the last 1000 years. This study implies that Holocene shelf break and upper slope stability in the Beaufort Sea are strongly linked to the dynamics of the permafrost and the presence of weak, gas-rich sediments. It demonstrates that creep deformation evolves into either muddy debris flows or translational slides, dependent on sediment strength. • Water column backscatter shows active gas vents near the subsea permafrost limit. • Creep with growth faults occurs over a gas-charged decollement zone. • Creep evolves to translational slides where thick, debris flows were thin. • A major < 1 ka retrogressive slump is the largest failure in the area.

Permafrost and snow monitoring at Rothera Point (Adelaide Island, Maritime Antarctica): Implications for rock weathering in cryotic conditions

In February 2009 a new permafrost borehole was installed close to the British Antarctic Survey Station at Rothera Point, Adelaide Island (67.57195°S 68.12068°W). The borehole is situated at 31masl on a granodiorite knob with scattered lichen cover. The spatial variability of snow cover and of ground surface temperature (GST) is characterised through the monitoring of snow depth on 5 stakes positioned around the borehole and with thermistors placed at three different rock surfaces (A, B and C). The borehole temperature is measured by 18 thermistors placed at different depths between 0.3 and 30m. Snow persistence is very variable both spatially and temporally with snow free days per year ranging from 13 and more than 300, and maximum snow depths varying between 0.03 and 1.42m. This variability is the main cause of high variability in GST, that ranged between −3.7 and −1.5°C. The net effect of the snow cover is a cooling of the surface. Mean annual GST, mean summer GST, and the degree days of thawing and the n-factor of thawing were always much lower at sensor A where snow persistence and depth were greater than in the other sensor locations. At sensor A the potential freeze–thaw events were negligible (0–3) and the thermal stress was at least 40% less than in the other sensor locations. The zero curtain effect at the rock surface occurred only at surface A, favouring chemical weathering over mechanical action. The active layer thickness (ALT) ranged between 0.76 and 1.40m. ALT was directly proportional to the mean air temperature in summer, and inversely proportional to the maximum snow depth in autumn. ALT temporal variability was greater than reported at other sites at similar latitude in the Northern Hemisphere, or with the similar mean annual air temperature in Maritime Antarctica, because vegetation and a soil organic horizon are absent at the study site. Zero annual amplitude in temperature was observed at about 16m depth, where the mean annual temperature is −3°C. Permafrost thickness was calculated to range between 112 and 157m, depending on the heat flow values adopted. The presence of sub-sea permafrost cannot be excluded considering the depth of the shelf around Rothera Point and its glacial history.

Report from the International Permafrost Association: High level of permafrost interdisciplinary research activity

Report from the International Permafrost Association : High level of permafrost interdisciplinary research activity

Offshore permafrost decay and massive seabed methane escape in water depths &gt;20 m at the South Kara Sea shelf

Since the Last Glacial Maximum (~19 ka), coastal inundation from sea‐level rise has been thawing thick subsea permafrost across the Arctic. Although subsea permafrost has been mapped on several Arctic continental shelves, permafrost distribution in the South Kara Sea and the extent to which it is acting as an impermeable seal to seabed methane escape remains poorly understood. Here we use &gt;1300 km of high‐resolution seismic data to map hydroacoustic anomalies, interpreted to record seabed gas release, on the West Yamal shelf. Gas flares are widespread over an area of at least 7500 km2 in water depths &gt;20 m. We propose that continuous subsea permafrost extends to water depths of ~20 m offshore and creates a seal through which gas cannot migrate. This Arctic shelf region where seafloor gas release is widespread suggests that permafrost has degraded more significantly than previously thought.

Activation of old carbon by erosion of coastal and subsea permafrost in Arctic Siberia

The future trajectory of greenhouse gas concentrations depends on interactions between climate and the biogeosphere. Thawing of Arctic permafrost could release significant amounts of carbon into the atmosphere in this century. Ancient Ice Complex deposits outcropping along the ~7,000-kilometre-long coastline of the East Siberian Arctic Shelf (ESAS), and associated shallow subsea permafrost, are two large pools of permafrost carbon, yet their vulnerabilities towards thawing and decomposition are largely unknown. Recent Arctic warming is stronger than has been predicted by several degrees, and is particularly pronounced over the coastal ESAS region. There is thus a pressing need to improve our understanding of the links between permafrost carbon and climate in this relatively inaccessible region. Here we show that extensive release of carbon from these Ice Complex deposits dominates (57 ± 2 per cent) the sedimentary carbon budget of the ESAS, the world’s largest continental shelf, overwhelming the marine and topsoil terrestrial components. Inverse modelling of the dual-carbon isotope composition of organic carbon accumulating in ESAS surface sediments, using Monte Carlo simulations to account for uncertainties, suggests that 44 ± 10 teragrams of old carbon is activated annually from Ice Complex permafrost, an order of magnitude more than has been suggested by previous studies. We estimate that about two-thirds (66 ± 16 per cent) of this old carbon escapes to the atmosphere as carbon dioxide, with the remainder being re-buried in shelf sediments. Thermal collapse and erosion of these carbon-rich Pleistocene coastline and seafloor deposits may accelerate with Arctic amplification of climate warming.

Derivation and analysis of a high-resolution estimate of global permafrost zonation

Abstract. Permafrost underlies much of Earth's surface and interacts with climate, eco-systems and human systems. It is a complex phenomenon controlled by climate and (sub-) surface properties and reacts to change with variable delay. Heterogeneity and sparse data challenge the modeling of its spatial distribution. Currently, there is no data set to adequately inform global studies of permafrost. The available data set for the Northern Hemisphere is frequently used for model evaluation, but its quality and consistency are difficult to assess. Here, a global model of permafrost extent and dataset of permafrost zonation are presented and discussed, extending earlier studies by including the Southern Hemisphere, by consistent data and methods, by attention to uncertainty and scaling. Established relationships between air temperature and the occurrence of permafrost are re-formulated into a model that is parametrized using published estimates. It is run with a high-resolution (&lt;1 km) global elevation data and air temperatures based on the NCAR-NCEP reanalysis and CRU TS 2.0. The resulting data provide more spatial detail and a consistent extrapolation to remote regions, while aggregated values resemble previous studies. The estimated uncertainties affect regional patterns and aggregate number, and provide interesting insight. The permafrost area, i.e. the actual surface area underlain by permafrost, north of 60° S is estimated to be 13–18 × 106 km2 or 9–14 % of the exposed land surface. The global permafrost area including Antarctic and sub-sea permafrost is estimated to be 16–21 × 106 km2. The global permafrost region, i.e. the exposed land surface below which some permafrost can be expected, is estimated to be 22 ± 3 × 106 km2. A large proportion of this exhibits considerable topography and spatially-discontinuous permafrost, underscoring the importance of attention to scaling issues and heterogeneity in large-area models.

On carbon transport and fate in the East Siberian Arctic land–shelf–atmosphere system

This review paper summarizes current understanding of the transport of organic carbon to, and the fate of organic carbon within, the East Siberian Arctic Shelf (ESAS), and of processes determining carbon dioxide (CO2) and methane (CH4) fluxes from the ESAS to the atmosphere achieved from analyzing the data sets obtained on 20 expeditions performed from 1999 to 2011. This study of the ESAS was aimed at investigating how redistribution of old carbon from degrading terrestrial and sub-sea permafrost and from coastal erosion contributes to the carbon pool of the ESAS, how changes in the hydrological cycle of the surrounding land and alteration of terrestrial carbon cycles affect the hydrological and biogeochemical parameters of shelf water masses, and which factors control CH4 and CO2 emissions from the ESAS. This report describes selected results achieved by a developing international scientific partnership that has been crucial at every stage of the study and will be even more important in the future.

Recent changes in shelf hydrography in the Siberian Arctic: Potential for subsea permafrost instability

Summer hydrographic data (1920–2009) show a dramatic warming of the bottom water layer over the eastern Siberian shelf coastal zone (<10 m depth), since the mid-1980s, by 2.1°C. We attribute this warming to changes in the Arctic atmosphere. The enhanced summer cyclonicity results in warmer air temperatures and a reduction in ice extent, mainly through thermodynamic melting. This leads to a lengthening of the summer open-water season and to more solar heating of the water column. The permafrost modeling indicates, however, that a significant change in the permafrost depth lags behind the imposed changes in surface temperature, and after 25 years of summer seafloor warming (as observed from 1985 to 2009), the upper boundary of permafrost deepens only by ∼1 m. Thus, the observed increase in temperature does not lead to a destabilization of methane-bearing subsea permafrost or to an increase in methane emission. The CH4 supersaturation, recently reported from the eastern Siberian shelf, is believed to be the result of the degradation of subsea permafrost that is due to the long-lasting warming initiated by permafrost submergence about 8000 years ago rather than from those triggered by recent Arctic climate changes. A significant degradation of subsea permafrost is expected to be detectable at the beginning of the next millennium. Until that time, the simulated permafrost table shows a deepening down to ∼70 m below the seafloor that is considered to be important for the stability of the subsea permafrost and the permafrost-related gas hydrate stability zone.

East Siberian Sea, an Arctic region of very high biogeochemical activity

Abstract. Shelf seas are among the most active biogeochemical marine environments and the East Siberian Sea is a prime example. This sea is supplied by seawater from both the Atlantic and Pacific Oceans and has a substantial input of river runoff. All of these waters contribute chemical constituents, dissolved and particulate, but of different signatures. Sea ice formation during the winter season and melting in the summer has a major impact on physical as well as biogeochemical conditions. The internal circulation and water mass distribution is significantly influenced by the atmospheric pressure field. The western region is dominated by input of river runoff from the Laptev Sea and an extensive input of terrestrial organic matter. The microbial decay of this organic matter produces carbon dioxide (CO2) that oversaturates all waters from the surface to bottom relative to atmospheric level, even when primary production, inferred from low surface water nutrients, has occurred. The eastern surface waters were under-saturated with respect to CO2 illustrating the dominance of marine primary production. The drawdown of dissolved inorganic carbon equals a primary production of ~0.8 ± 2 mol C m−2, which when multiplied by half the area of the East Siberian Sea, ~500 000 km2, results in an annual primary production of 0.4 (± 1) × 1012 mol C or ~4 (± 10) × 1012 gC. Microbial decay occurs through much of the water column, but dominates at the sediment interface where the majority of organic matter ends up, thus more of the decay products are recycled to the bottom water. High nutrient concentrations and fugacity of CO2 and low oxygen and pH were observed in the bottom waters. Another signature of organic matter decomposition, methane (CH4), was observed in very high but variable concentrations. This is due to its seabed sources of glacial origin or modern production from ancient organic matter, becoming available due to sub-sea permafrost thaw and formation of so-called taliks. The decay of organic matter to CO2 as well as oxidation of CH4 to CO2 contribute to a natural ocean acidification making the saturation state of calcium carbonate low, resulting in under-saturation of all the bottom waters with respect to aragonite and large areas of under-saturation down to 50 % with respect to calcite. Hence, conditions for calcifying organisms are very unfavorable.

Coastal permafrost landscape development since the Late Pleistocene in the western Laptev Sea, Siberia

cal (pollen, diatoms) methods. Our interpretation of the proxies focuses on landscape history and the transition of terrestrial into subsea permafrost. Marine interglacial deposits overlain by relict terrestrial permafrost within the same offshore core were encountered in the western Laptev Sea. Moreover, the marine interglacial deposits lay unexpectedly deep at 64 m below modern sea level 12 km from the current coastline, while no marine deposits were encountered onshore. This implies that the position of the Eemian coastline presumably was similar to today’s. The landscape reconstruction suggests Eemian coastal lagoons and thermokarst lakes, followed by Early to Middle Weichselian fluvially dominated terrestrial deposition. During the Late Weichselian, this fluvial landscape was transformed into a poorly drained accumulation plain, characterized by widespread and broad ice-wedge polygons. Finally, the shelf plain was flooded by the sea during the Holocene, resulting in the inundation and degradation of terrestrial permafrost and its transformation into subsea permafrost.

Geochemical and geophysical evidence of methane release over the East Siberian Arctic Shelf

The East Siberian Arctic Shelf (ESAS), which includes the Laptev Sea, the East Siberian Sea, and the Russian part of the Chukchi Sea, has not been considered to be a methane (CH4) source to hydrosphere or atmosphere because subsea permafrost, which underlies most of the ESAS, was believed, first, not to be conducive to methanogenesis and, second, to act as an impermeable lid, preventing CH4 escape through the seabed. Here recent observational data obtained during summer (2005–2006) and winter (2007) expeditions indicate the ubiquitous presence of elevated dissolved CH4 and an elevated atmospheric CH4 mixing ratio. The CH4 data were also analyzed together with high resolution seismic (HRS) data obtained by means of a “Sonic M‐141” system consisting of a high‐resolution profiler and side‐scan sonar mounted in a towed fish during the Transdrift‐X Expedition (2004) onboard the R/V Yakov Smirnitskiy. Results show anomalously high concentrations of dissolved CH4 (up to 5 μM) and an episodically (nongradually) increasing atmospheric mixing ratio of CH4 (up to 8.2 ppm) in some areas of the ESAS. A most likely source is year‐round CH4 release through taliks (columns of thawed sediments within permafrost) from seabed CH4 reservoirs such as shallow hydrates and geological sources. Such releases occur not only within the areas underlain by fault zones but also outside of them. This points to permafrost's failure to further preserve CH4 deposits in the ESAS. The total amount of carbon preserved within the ESAS as organic matter and ready to release CH4 from seabed deposits is predicted to be ∼1400 Gt. Release of only a small fraction of this reservoir, which was sealed with impermeable permafrost for thousands of years, would significantly alter the annual CH4 budget and have global implications, because the shallowness of the ESAS allows the majority of CH4 to pass through the water column and escape to the atmosphere.

Extensive Methane Venting to the Atmosphere from Sediments of the East Siberian Arctic Shelf

Remobilization to the atmosphere of only a small fraction of the methane held in East Siberian Arctic Shelf (ESAS) sediments could trigger abrupt climate warming, yet it is believed that sub-sea permafrost acts as a lid to keep this shallow methane reservoir in place. Here, we show that more than 5000 at-sea observations of dissolved methane demonstrates that greater than 80% of ESAS bottom waters and greater than 50% of surface waters are supersaturated with methane regarding to the atmosphere. The current atmospheric venting flux, which is composed of a diffusive component and a gradual ebullition component, is on par with previous estimates of methane venting from the entire World Ocean. Leakage of methane through shallow ESAS waters needs to be considered in interactions between the biogeosphere and a warming Arctic climate.

Current state of subsea permafrost on the East Siberian Shelf: Tests of modeling results based on field observations

Current state of subsea permafrost on the East Siberian Shelf: Tests of modeling results based on field observations

East Siberian Shelf Study Alleviates Scarcity of Observations

The East Siberian Arctic Shelf (ESAS) is the world's largest continental shelf and also the most understudied part of the Arctic Ocean. Composed of the Laptev Sea, the East Siberian Sea, and the Russian section of the Chukchi Sea, the ESAS is characterized by tundra discharge through the Lena, Indigirka, and Kolyma rivers; coastal erosion; methane seeps from subsea permafrost reservoirs; and the formation of water masses that spread throughout the Arctic Ocean.

Nearshore arctic subsea permafrost in transition

Models and geophysical data indicate that large areas of the Arctic shelves, as a result of their exposure during the Last Glacial Maximum, are thought to be almost entirely underlain by subsea permafrost from the coastline down to a water depth of about 100 meters. Subsea permafrost is still poorly understood, due mainly to the lack of direct observations. However, it is known to contain gas hydrates, a solid phase composed of water and gases that formed under low‐temperature, high‐pressure conditions. Large volumes of methane in gas hydrate form can be stored within or below the subsea permafrost, and the stability of this gas hydrate zone is sustained by the existence of permafrost. Degradation of subsea permafrost and the consequent destabilization of gas hydrates could significantly if not dramatically increase the flux of methane, a potent greenhouse gas, to the atmosphere.

INDICATIONS FOR AN ACTIVE PETROLEUM SYSTEM IN THE LAPTEV SEA, NE SIBERIA

The shallow shelf of the Laptev Sea offshore NE Siberia is characterized by a number of rift basins more than 10 km deep. These basins are filled with sedimentary rocks of predominantly Cenozoic age and are likely sites for petroleum generation and accumulation. One objective of the BGR97 Arctic cruise to the Laptev Sea was to explore for near-surface indications of petroleum, and for this purpose water samples and near-surface sediments were collected for geochemical analysis. Gaseous hydrocarbons adsorbed in near-surface sediments include thermally-generated gas which has probably migrated upwards from deeper sedimentary strata. The hydrocarbons’compositions together with stable carbon isotope ratios indicate an origin from a marine source rock at a maturity of between 0.9 and 1.3% vitrinite reflectance. On reflection seismic profiles, zones of poor reflectivity were observed locally, also suggesting the presence of ascending gas. These geophysical indications for gas occur most frequently in the northern part of the Laptev Sea; here, seepages of thermogenic methane were detected in the sea water at two locations. Refraction seismic and multichannel data indicate the existence of sub-sea permafrost down to a depth of 500m, which probably prevents gas from escaping into the water column in most areas. The greater water depths at the northern edge of the shelf may have prevented the formation of the permafrost layer, allowing the upward migration of hydrocarbons to occur.