[1] 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 >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 km 2 in water depths >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.Citation: Portnov, A., A. J. Smith, J. Mienert, G. Cherkashov, P. Rekant, P. Semenov, P. Serov, and B. Vanshtein (2013), Offshore permafrost decay and massive seabed methane escape in water depths >20 m at

Microsporidia are obligatory intracellular parasites, most species of which live in the host cell cytosol. They synthesize and then transport secretory proteins from the endoplasmic reticulum to the plasma membrane for formation of the spore wall and the polar tube for cell invasion. However, microsporidia do not have a typical Golgi complex. Here, using quick-freezing cryosubstitution and chemical fixation, we demonstrate that the Golgi analogs of the microsporidia Paranosema (Antonospora) grylli and Paranosema locustae appear as 300-nm networks of thin (25- to 40-nm diameter), branching or varicose tubules that display histochemical features of a Golgi, but that do not have vesicles. Vesicles are not formed even if membrane fusion is inhibited. These tubular networks are connected to the endoplasmic reticulum, the plasma membrane and the forming polar tube, and are positive for Sec13, γCOP and analogs of giantin and GM130. The spore-wall and polar-tube proteins are transported from the endoplasmic reticulum to the target membranes through these tubular networks, within which they undergo concentration and glycosylation. We suggest that the intracellular transport of secreted proteins in microsporidia occurs by a progression mechanism that does not involve the participation of vesicles generated by coat proteins I and II.

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.

This paper describes two gas‐emission craters (GECs) in permafrost regions of the Yamal and Gydan peninsulas. We show that in three consecutive years after GEC formation (2014–2017), both morphometry and hydrochemistry of the inner crater lakes can become indistinguishable from other lakes. Craters GEC‐1 and AntGEC, with initial depths of 50–70 and 15–19 m respectively, have transformed into lakes 3–5 m deep. Crater‐like depressions were mapped in the bottom of 13 out of 22 Yamal lakes. However, we found no evidence that these depressions could have been formed as a result of gas emission. Dissolved methane (dCH4) concentration measured in the water collected from these depressions was at a background level (45 ppm on average). Yet, the concentration of dCH4 from the near‐bottom layer of lake GEC‐1 was significantly higher (824–968 ppm) during initial stages. We established that hydrochemical parameters (dissolved organic carbon, major ions, isotopes) measured in GEC lakes approached values measured in other lakes over time. Therefore, these parameters could not be used to search for Western Siberian lakes that potentially resulted from gas emission. Temperature profiles measured in GEC lakes show that the water column temperatures in GEC‐1 are lower than in Yamal lakes and in AntGEC – close to values of Gydan lakes. Given the initial GEC depth > 50 m, we suggest that at least in GEC‐1 possible re‐freezing of sediments from below might take place. However, with the present data we cannot establish the modern thickness of the closed talik under newly formed GEC lakes.

No abstract