L. I. Lobkovskii

The degradation of submarine permafrost and the destruction of hydrates on the shelf of east arctic seas as a potential cause of the “Methane Catastrophe”: some results of integrated studies in 2011

On the basis of the analysis of published data and in the course of the authors’ long-term geochemical and acoustic surveys performed in 1995–2011 on the East Siberian shelf (ESS) and aimed to research the role of the Arctic shelf in the processes of massive methane outbursts into the Earth’s atmosphere, some crucially new results were obtained. A number of hypotheses were proposed concerning the qualitative and quantitative characterization of the scale of this phenomenon. The ESS is a powerful supplier of methane to the atmosphere owing to the continued degradation of the submarine permafrost, which causes the destruction of gas hydrates. The emission of methane in several areas of the ESS is massive to the extent that growth in the methane concentrations in the atmosphere to values capable of causing a considerable and even catastrophic warning on the Earth is possible. The seismic data were compared to those of the drilling from ice performed first by the authors in 2011 in the southeastern part of the Laptev Sea to a depth of 65 m from the ice surface. This made it possible to reveal some new factors explaining the observed massive methane bursts out of the bottom sediments.

Mechanisms responsible for degradation of submarine permafrost on the eastern arctic shelf of Russia

In 2011, a marine interdisciplinary expedition on the R/V Akademik M.A. Lavrentyev was carried out in the eastern Arctic seas. The expedition was conducted within the framework of the project of targeted basic investigations under the aegis of the Russian Founda� tion for Basic Research. These investigations regis� tered intense methane blowouts related to degradation of submarine permafrost (SMPF) in these basins. The mechanisms responsible for their degradation are determined by paleogeographic factors and recent sedimentation, as well as by structural features of the Arctic region. Under continuing degradation of sub� marine permafrost, methane emission should inten� sify. This process results in the formation of significant values of both gas and water, which migrate upward through the sedimentary section of the shelf and along the bedding surfaces from coastal heated areas to colder deeper parts of the basins forming subhorizon� tal convective cells, thus, stimulating permafrost deg� radation even under negative bottom temperatures. Submarine permafrost rocks are widespread mostly on the shelf in the eastern sector of the Russian Arctic region. This is explained by the peculiar paleogeo� graphic development of the region: due to the absence of the ice shield during the Quaternary glacial epochs, the shelf was dominated by subaerial settings with low temperatures. Alternation of subaerial and marine environments on the shelf resulted in the formation of a stratified sedimentary sequence. The regressive cycles (cooling epochs) were accompanied by intense frosting of the primary surface and formation of com� pact dehydrated members (for example, during the last Late Quaternary regression). On the contrary, the transgressive cycles (warming epochs) were marked by accumulation of unconsolidated sediments. In these periods, stable negative temperatures of the bottom water favored conservation of the stratified structure in the sedimentary section [1, 2].

The Submeridional Strike Slip Zone in the Structure of the Chukchi Sea Continental Margin and the Mechanism of Opening of the Canada Oceanic Basin

The Chukchi segment of the Eurasian Arctic pas� sive continental margin that commenced forming in response to initiation and opening of the Canada oce� anic basin in the Jurassic–Cretaceous is of importance for reconstructing the initial stage in the geodynamic evolution of the formation of the ocean in the Arctic region. The available paleogeodynamic reconstructions of the Arctic region evolution [4, 7] show that the eastern Arctic margin of Eurasia was characterized by devel� opment of collision–convergence belts with shear and compressive strains subconformable with simulta� neously forming sublatitudinal sedimentary basins of several generations. Moreover, it cannot be ruled out that these processes were accompanied by develop� ment of major fault zones orthogonal to these struc� tures [2, 3, 6, 13, 14] and related deformations deter� mined by differently oriented strains in the lithosphere at the stage of differentiated motion of blocks and microplates that are now involved in the Chukotka– North Alaska continental margin. In this communication, we discuss different geo� logical–geophysical data indicating the existence of one such submeridional transverse strike slip zone in the region under consideration. It extends from the Canada Basin along the eastern escarp of the North� wind Rise and across the shelf continental margin in the Chukchi Sea toward the Bering Strait (Fig. 1). The role of this zone in the geodynamic evolution of the Canada oceanic basin and the adjacent continental margin of the Chukchi Sea is also a subject of this research.

Genesis of the Alpha-Mendeleev and Lomonosov ridges (Amerasian Basin)

In order to specify the origin and evolution of the Alpha-Mendeleev and Lomonosov ridges, profiles of the bottom relief and crustal basement were made. Additionally, the coefficients characterizing the rate of subsidence of the crustal basement in different parts of the ridges for the last 25 Ma were calculated and the depth of the crustal basement prior to the beginning of subsidence in the Early Miocene was estimated. The calculation results were compared with the model of thermal subsidence of the Greenland-Iceland and Iceland-Faroe thresholds, which were also formed by plume-tectonic processes. A large dome rise of the basement was found in the central parts of the Alpha-Mendeleev and Lomonosov ridges. It was also found that the coefficients of thermal subsidence of the crustal basement in the central parts of the Alpha-Mendeleev and Lomonosov ridges are close to those for the Greenland-Iceland and Iceland-Faroe thresholds. It was shown that the depth of the crustal basement prior to the beginning of subsidence in the Early Miocene grew going outwards from the central parts of the ridges, analogous to the present-day pattern. All the information given above indicates the thermal origin of subsidence for the Alpha-Mendeleev and Lomonosov ridges starting from the Early Miocene and the substantial influence of the Arctic Plume on the genesis and evolution of these ridges.

Late Cretaceous-Paleogene transform zone between the Eurasian and North American lithospheric plates

Within the limits of the Chukchi Sea and the Amerasian Basin of the Arctic Ocean, study have been carried out to calculate D function anomalies. The result was the discovery of elongated faults that cut, according to the positions of the upper and lower extents of the disturbing masses, both the upper crust and the upper mantle. It is shown that these faults are right-lateral strike-slips continuing the Late Cretaceous-Paleogene structures of the same type in the Bering Sea. This suggests that the en echelon strike-slip system of the Bering Sea, Chukchi Sea, and Amerasian Basin is a relic of the Late Cretaceous-Paleogene transform fault zone between the Eurasian and North American lithospheric plates.

Landslides on the Eastern Slope of Sakhalin Island as Possible Tsunami Sources

An underwater landslide located in the central partof the eastern slope of Sakhalin Island was found andmapped during investigations under the auspices ofthe Korean–Russian Project Sakhalin Slope GasHydrates (SSGH) [1, 2]. The study region was confined to a depression oriented in the northeasterlydirection (Fig. 1a). The research in this region [1–4]demonstrated that closed depressions with round andslightly elongated forms in the northeasterly directionare characteristic peculiarities of the morphology ofthis depression (Fig. 1b). The slope angles of theirwalls are 7–10°, while the sizes are in the rangebetween 600 m and 10 km. They are located at depthsfrom 20 to 150 m. One of the largest depressions has anotable morphology. Its northern edge is quite flat(~7°), while the southern edge is steep (25–30°). Itconsists of one or a few cliffs with a total height up to100 m (Fig. 2).Two types of the sedimentary sections were foundwithin the study region. The first one is common. It ischaracterized by numerous reflecting levels that provide evidence about the layered structure of the sedimentary column. The second type of seismic section isobserved only in the southernmost depression crossedby seismic profile LV5603 (Fig. 2). Here, we distinguish a sedimentary body whose cover has a hillystructure, while the foot corresponding to a highamplitude reflecting level cuts off the underlyingreflectors. The body is acoustically transparentbecause there are no reflecting layers. Slope boundaries and diffracted reflections are seen on the highresolution section of seismic profiler SES2000DS,which is caused by the chaotic internal structure of thissedimentary body.The abovementioned peculiarities of the sedimentary cover structure together with the morphology ofthe depression give grounds to think that this sedimentary formation is a landslide. A section made usingseismic profiler SES2000DS with a resolution on theorder of 10 cm [4] does not demonstrate that the roofof the landslide is covered with horizontally locatedsediments. Taking into account that the rate of sediment deposition in this region during the Holocenewas 33 cm over 1000 years [2], the age of the landslideis less than 300 years. The breakoff wall of the landslide is very steep (25–30°). In some regions it consistsof two cliffs. Its form is undulating, and its length is22 km (Fig. 1b). The area occupied by the landslide is42 km@2, and its volume is approximately 4 km

Methane anomaly in the waters of the Anapa shelf and its possible relation to oil-and-gas bearing structures

The results of gas geochemical and seismoacoustic measurements obtained in the course of the expedition for the studies of gas seepages at the Anapa shelf of the Black Sea are presented. According to the data of the gas survey in the surface waters of the Anapa shelf, a large methane anomaly was discovered and mapped. The correlation of the anomaly with the bottom sources located over the Pionerskaya structure is proved. The geological structure of the area studied is analyzed. The data set allowed us to positively characterize the prospects of the oil-and-gas content of the Anapa shelf interiors and of the Pionerskaya structure proper.

Slump structures in quaternary slope sediments of the northern Derbent Basin (Caspian Sea)

During Cruise 20–3 of the R/V Rift (April, 2006), the area that includes the shelf and slope of the Derbent Basin in the northern Middle Caspian was studied using the continuous seismoacoustic profiling method. In accordance with the previous standpoint, two Pleistocene deltaic complexes formed in the Enotaevian and Mangyshlakian time are defined in this area. The seismoacoustic records obtained for the northern slope of the Derbent Basin demonstrate the development of specific rootless exogenic-gravitational fold structures in the upper (∼150–200 m) Quaternary part of the sedimentary sequence. The Quaternary section encloses angular unconformities indicating the pulsating mode of gravitational processes in the northern slope of the basin. South-dipping gravitational normal faults (and/or normal fault-related flexures) displacing the bottom surface and uppermost sedimentary layers (with vertical amplitudes up to 5–6 m) were defined in the southern part of the study area. Several impulses of the submarine slump structures predated and accompanied the deposition of the upper deltaic sequence (Mangyshlakian), although their most intense formation took place later during the Novocaspian (Holocene) time. Thus, the structural analysis of the seismoacoustic data revealed intense development of different-origin and different-age gravitational structures within the Quaternary sediments in the northern slope of the Derbent Basin. These results should be taken into consideration when designing, building, and operating submarine constructions in order to prevent potential natural hazards and reduce their consequences.

The Origin and Age of the Alpha-Mendeleev and Lomonosov Ridges in the Amerasia Basin

The results of the bathymetry simulation indicate the emplacement of the Mesozoic Arctic plume into the lithosphere of the Alpha-Mendeleev and Lomonosov ridges. The study also presents a model of the thermal subsidence to the asthenosphere. The calculated coefficients are compared with those obtained for the Greenland-Iceland and Iceland-Faeroe ridges, which were formed in response to hotspot activity. It was shown that the coefficients of the thermal subsidence in the central part of the Alpha-Mendeleev and Lomonosov Ridges are similar to those calculated for the Greenland-Iceland and Iceland-Faeroe ridges. This indicates the thermal regime of the subsidence of the Alpha-Mendeleev and Lomonosov ridges since the Early Miocene and the increased influence of the Arctic plume on the ridge genesis. The ridges are interpreted to have formed over a broad geological timeframe, from the late Cretaceous to the Cenozoic. A geothermal method, which is highly informative in terms of the age of the lithosphere, provides better constraints on the timing of ridge formation. The age estimates for the Alpha-Mendeleev (97–79 Ma) and Lomonosov ridges (69–57 Ma) derived from the geothermal data allowed us to draw a convincing conclusion about the genesis of these ridges.

Estimation of parameters of the flows forming sediment waves on the western slope of the middle caspian sea

By means of mathematical modeling, the parameters of flows forming sedimentary waves on the western slope of the Derbent basin were estimated. The height of these flows depends on the slope steepness and varies from 25 to 170 m to reach its maximum values at gentler slope areas. However, the flow rate is independent of the slope steepness and depends only on the concentration of sediment matter supplied by the flow. At the upper part of the slope (the flow starting), the rate amounts to 0.4–1.4 m/s, being almost halved at the depths where the sedimentary waves are damped. The present rates of near-bottom currents show pronounced seasonal differences, and their values are close to flow rates obtained by numerical modeling.