Methane release from pingo‐like features across the South Kara Sea shelf, an area of thawing offshore permafrost

Abstract

The Holocene marine transgression starting at~19 ka flooded the Arctic shelves driving extensive thawing of terrestrial permafrost. It thereby promoted methanogenesis within sediments, the dissociation of gas hydrates, and the release of formerly trapped gas, with the accumulation in pressure of released methane eventually triggering blowouts through weakened zones in the overlying and thinned permafrost. Here we present a range of geophysical and chemical scenarios for the formation of pingo-like formations (PLFs) leading to potential blowouts. Specifically, we report on methane anomalies from the South Kara Sea shelf focusing on two PLFs imaged from high-resolution seismic records. A variety of geochemical methods are applied to study concentrations and types of gas, its character, and genesis. PLF 1 demonstrates ubiquitously low-methane concentrations (14.2-55.3 ppm) that are likely due to partly unfrozen sediments with an ice-saturated internal core reaching close to the seafloor. In contrast, PLF 2 reveals anomalously high-methane concentrations of >120,000 ppm where frozen sediments are completely absent. The methane in all recovered samples is of microbial and not of thermogenic origin from deep hydrocarbon sources. However, the relatively low organic matter content (0.52-1.69%) of seafloor sediments restricts extensive in situ methane production. As a consequence, we hypothesize that the high-methane concentrations at PLF 2 are due to microbial methane production and migration from a deeper source.

Gas‐emission craters of the Yamal and Gydan peninsulas: A proposed mechanism for lake genesis and development of permafrost landscapes

“…Similarly, a 2 m high and 20 m wide mound preceded the emergence of AntGEC on the Gydan peninsula . Similar mounds were previously described in the submarine environment as pingo‐like features (PLFs): in the Beaufort Sea, and Barents–Kara Sea shelves 5–9 m in height and 70–1000 m in diameter, and on the Pechora Sea shelf showing base diameters from 20 to 1000 m and heights of 5–25 m. The drilling of one of these PLFs in the Pechora Sea led to the blowout of a large amount of gas from a depth of 49.5 m and failure of the drilling equipment . The concentration of microbial methane in sediments collected from the flank of a PLF in the Kara Sea exceeded 120,000 ppm .…”

“…Similar mounds were previously described in the submarine environment as pingo‐like features (PLFs): in the Beaufort Sea, and Barents–Kara Sea shelves 5–9 m in height and 70–1000 m in diameter, and on the Pechora Sea shelf showing base diameters from 20 to 1000 m and heights of 5–25 m. The drilling of one of these PLFs in the Pechora Sea led to the blowout of a large amount of gas from a depth of 49.5 m and failure of the drilling equipment . The concentration of microbial methane in sediments collected from the flank of a PLF in the Kara Sea exceeded 120,000 ppm . The source of the gas that creates overpressure in the PLFs is either decomposition of methane hydrates, or gases accumulated within lenses of thawed sands located below the base of submarine permafrost .…”

“…This is also supported by documented gas blowouts from depths of 70–120 m during drilling of boreholes in Central Yamal, mainly from sandy coastal–marine deposits . Gas flows can create pressure in areas with the development of TGI at the clay–sand interface, which results in the development of a mound‐predecessor in the terrestrial environment (Figure b) and PLFs in the nearshore environment …”

Subsea ice‐bearing permafrost on the U.S. Beaufort Margin: 1. Minimum seaward extent defined from multichannel seismic reflection data

“…[] suggest that continuous subsea permafrost acts as a seal for gas sourced below the permafrost (e.g., from gas hydrate or deeper thermogenic sources) and with degradation gas migrates up along the seaward edge of continuous subsea permafrost. Both the Canadian Beaufort and the West Kara shelves host pingo‐like features associated with seabed fluid escape [ Paull et al ., ; Portnov et al ., ; Serov et al ., ]. Though neither pingo‐like features nor seafloor degassing have ever been observed on the U.S. Beaufort, we suggest that the vicinity of the 2000 m s −1 contour is the locus at which degassing related to IBPF degradation is most likely to occur.…”

Climate engineering by mimicking natural dust climate control: the iron salt aerosol method

“…Such and other CH 4 emissions, such as anoxic sediments outside the CH 4 hydrate stable pressure and temperature region, induce deoxygenation within the overlying water layer by CH 4 emission (Römer et al, 2014;Yamamoto et al, 2014). CH 4 emissions are induced for instance by hydrothermal springs (Suess et al, 1999), sediment movement Paull et al, 2007), seawater warming induced by climate change (Serov et al, 2015;Shakhova et al, 2005), changing ocean circulation (Berndt et al, 2014) and ocean sediment subduction (Elvert et al, 2000;Fischer et al, 2013). At lower vertical sediment to ocean surface distances, the CH 4 emissions reach the troposphere.…”