Permafrost distribution offshore of West Yamal : extended abstract

The results of seismic studies in the near-shore, shallow waters of the south-western Kara Sea - at the Shpindler, Kharsavey and Mare-Sale sites - showed the presence of a seismic interface which can be interpreted as a submarine permafrost table. The proposed permafiost exhibits a continuous distribution and a strongly dissected top surface overlain by unfrozen sediments. The permafrost table is located at a depth of 4-6 m and 5-10 m below the sea floor at the Shpindler and Mare-Sale sites, respectively. Three dimensional modeling of the permafrost table suggests the presence of relict buried thermodenudational depressions (up to 2 km across) at a minimum sea depth of 40-45 m at the Shpindler and Mare-Sale sites. The depressions may be considered as paragenetic to thermocirques found in cliffs at the Shpindler site. At the Kharasavey site, the permafrost table has an elongated depression parallel to the modern shoreline. The maximum depression depth is 20 m below the seafloor. At present, the relict therrnocirques (Shpindler and Mare-Sale) and the elongated depression (Kharasavey) are completely filled in with sediment and are not evident in modern bottom topography

Submarine permafrost in the nearshore zone of the southwestern Kara Sea

The results of seismic studies in the shallow waters of the southwestern Kara Sea show the presence of a seismic unit that can be interpreted as relict submarine permafrost. The permafrost table has a strongly dissected upper surface and is located at a water depth of 5–10 m. A 3D modeling of the permafrost table suggests the presence of relict buried thermodenudational depressions (up to 2 km across) at a water depth of 5–10 m. The depressions may be considered to be paragenetic to thermocirques found at the Shpindler site. Relict thermocirques are completely filled with sediment and not exposed at the sediment surface

Role of subsea permafrost and gas hydrate in postglacial Arctic methane releases

The papers of this thesis are not available in Munin.<br>Paper I: 'Offshore permafrost decay and massive seabed methane escape in water depths > 20 m at the South Kara Sea shelf.' Alexey Portnov, Andrew J. Smith, Jürgen Mienert, Georgy Cherkashov, Pavel Rekant, Peter Semenov, Pavel Serov, Boris Vanshtein. Available in <a href=http://dx.doi.org/10.1002/grl.50735> Geophysical Research Letters, vol. 40, 1–6</a><br>Paper II: 'Modeling the evolution of climate-sensitive Arctic subsea permafrost in regions of extensive gas expulsion at the West Yamal shelf.' Alexey Portnov, Jurgen Mienert, Pavel Serov. Available in <a href=http://dx.doi.org/10.1002/2014JG002685> Journal of Geophysical Research: Biogeosciences, vol. 119, issue 11, 2014</a> <br>Paper III: 'Methane release from pingo-like features across the South Kara Sea shelf, an area of thawing offshore permafrost'. Pavel Serov, Alexey Portnov, Jurgen Mienert, Peter Semenov, Polina Ilatovskaya. (Manuscript). Published version available in <a href=http://dx.doi.org/10.1002/2015JF003467> Journal of Geophysical Research: Earth Surface, vol. 120, issue 8, 2015</a> <br>Paper IV: 'Ice-sheet driven methane storage and release in the Arctic.' Alexey Portnov, Sunil Vadakkepulyambatta, Jurgen Mienert, Alun Hubbard. (Manuscript)Greenhouse gas methane is contained as gas hydrate, an icy structure, under the seabed in enormous amounts of Arctic regions. West Svalbard continental margin, which we investigated here, is one of these regions. Also, in the Russian Kara Sea the subsea permafrost is acting as a cap for the gas to be released in the future. But continuous expulsions of methane have been already observed in both places. This study shows how the subsea permafrost in the Kara Sea, and gas hydrate systems offshore West Svalbard, have evolved from the last ice age to the present day. The conclusions are based on integrated field geophysical and gas-geochemical studies as well as modeling of permafrost, gas hydrate reservoirs and Barents Sea ice sheet dynamics. It shows that continuous permafrost of the Kara Sea is more fragile than previously thought. It is likely to be limited to the shallow water depths of 20 meters on this Arctic shelf region, allowing expulsions of methane from an area of 7500 sq km. Offshore Svalbard almost 2000 active and inactive gas expulsion sites are associated with melting of gas hydrate and thawing of shallow permafrost from past to present. Our research approach shows that natural climate drivers such as methane release can change and that they are connected to the ice sheet retreat since the last ice age. These processes triggered widespread seafloor gas discharge, observed in Arctic shelf and upper continental margins to this day

First discovers of Pleistocene authigenous carbonate crusts (ACC) at the Mendeleev Rise, Arctic Ocean

The Mendeleev Rise (or Mendeleev Ridge) is a part of Central Arctic Uplifts domain that extends from the Eastern Siberian Shelfto the central areas of the ocean, where it is adjacent to the Alpha Ridge bisecting the Amerasian Basin. The crust of Mendeleev Rise belongs to the continental type (Poselov et al. 2007). New geological, geophysical and tectonic data were obtained within Alpha-Mendeleev Rise after few expeditions to Arctic Ocean in year 2000, 2005 and 2012. Thousands of rock fragments were dredged: 50–65% – carbonate rocks (mainly dolomite and limestone); 20–25% – sandstones, siltstones, mudstones; 5–20% – igneous rocks (mainly granites, gabbro-dolerite and few types of basalt); ~ 10% – metamorphic rocks (mainly greenschist facies). Light dolomites with little flora and fauna represent about two-thirds of the total amount of carbonate rocks, the rest are limestones, often containing well-preserved faunal remains. Paleontological study of limestones show abundance of D-P 1 fauna remnants that give us an evidence of structural connection of Mendeleev Rise and Wrangel Island (Morozov et al. 2013). Carbonate crusts were dredged from steep slopes (25–29°) with neotectonic faults on two sites at water depth more than 2 km during expedition “Arktika-2012”. Primary study showed that crusts compose of strong matrix with rounded and angular debris of local (edaphogenic) material: dolomites, dolerites, granites, metasomatic and terrigenous rocks of different size (0.5 mm to 5 cm) (Morozov et al. 2013, Kremenetskii et al. 2015). Three samples of matrix and two of soft clay-carbonate crust’s cover were selected for detailed analysis. Petrographic features were studied using optical microscope, microprobe and X-ray analysis. Chemical elements analysis was performed with XRF and ICP-MS. All analyses were carried out in A.P. Karpinsky Russian Geological Research Institute (VSEGEI) in Saint-Petersburg. AAC’s Matrix studied with microprobe in details and consists offine-grained calcite with angular quartz grains from 1 μm to 300 μm. X-ray analysis shows calcite predominance in the matrix (>70%), rest content is presented with clasts of quartz, illite and albite – about 10%, dolomite, chlorite, montmorillonite, chamosite – 1–2%. Clasts of local debris are presented by two association: 1) large, mainly angular clasts with size from 0.5 mm to 5 cm; 2) small, mainly rounded clasts with size from 200 μm to 0.5 mm. Surface of matrix and debris is covered with soft rose clay-carbonate mass. Mineral content of clay-carbonate mass is: quartz and illite – 25–30%, calcite and albite 15–20%, chlorite, orthoclase, halite, dolomite, montmorillonite – 1–5%. Chemical composition (in percents) of matrix is close to clay-carbonate terrigenous rocks: SiO 2 – 18, Al 2 O 3 – 3.62, TiO 2 – 0.2, Fe 2 O 3 t – 1.4, MnO – 0.05 MgO – 2.35, CaO – 39.2, Na 2 O – 0.18, K 2 O – 0.47, P 2 O 5 – 0.12, L.O.I. – 34.3. Rose mass differs from matrix with silica – 46, CaO – 19, higher alkalis (Na and K) – 1.15 and 1.3. Difference in content of silica (18% vs 46%), CaO (39.2% vs 19%) says that AAC matrix and rose mass have various sources. In contrast to Paleozoic remnants in carbonates, the AAC contain planktonic and benthic foraminifera of Pleistocene age. In Arctic seas, these species are distributed in modern conditions mainly in places where the Gulf Stream arrives (Herman 1974). These data indicates local origin of ACC, main evidences includes distribution, good preservation of samples, local debris in matrix, paleontological age. However, carbonates are very limited in the Arctic Ocean (Emelyanov 2005, Chierici & Fransson 2009). In view of these parameters, AAC can’t form by itself so it may be due only to external factors. Bottom water doesn’t provide such factors. Neither necessary conditions nor material occur in these waters. So in our opinion AAC were formed with help of neotectonic fault which are supposed to be a possible path for hot fluids, which created the conditions for crusts forming and Paleozoic carbonate rocks was a source of CaCO 3

Pleistocene sediment sequence of the southern Lomonosov Ridge, Arctic Ocean : preliminary stratigraphic subdivision based on iceberg-rafted debris and benthic foraminiferal records

Two sediment cores retrieved from the southern Lomonosov Ridge (LR) in 2007 (core ALR07-26C from the top of the ridge, water depth 1359 m, and core ALR07-15C from the base of Geophysicists’ Spur, water depth 2500 m) were investigated for lithology (wt % > 63 μm, terrigenous lithic grains >500 μm) and microfossils. Prominent peaks of coarse-grained material in ALR07-26C represented largely by quartz and clastic rocks are regarded as inputs of ice and, especially, iceberg-rafted debris (IRD) of Eurasian origin. In accordance with previously obtained evidence from age-constrained cores from the central LR, the highest peak 4 is correlated with the MIS 6–5 boundary and the disintegration of the Saalian ice sheet. The three younger IRD peaks are provisionally correlated with the MIS 5–4, MIS 4–3, and MIS 2–1 boundaries, respectively. Small peaks of coarse-grained material in ALR07-15C dominated by various rocks in contrast represent local material transported by downslope slides mixed with some IRD. No calcareous microfossils occur in the cores, but only agglutinated benthic foraminifers are found. In ALR07-26C, they correlate with IRD-rich layers, which correspond to glacial terminations with more open-sea ice conditions and, probably, higher productivity in the sea-ice marginal zone. The Cyclammina-dominated assemblage in ALR07-26C below IRD peak 4 supports the proposed age estimate for this peak (MIS 6–5), as similar foraminiferal assemblages in other LR cores are recorded in sediments of MIS 7–9 and older. Younger assemblages show a transition from a Recurvoides-dominated assemblage in the early Late Pleistocene to a more “oligotrophic” recent assemblage with a predominance of Reophax and Rhabdammina

Offshore permafrost decay and massive seabed methane escape in water depths >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 >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 >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

Morphology of seamounts at the Mendeleev Rise, Arctic Ocean

Geological and geophysical studies undertaken during the Russian Arktika-2012 Expedition of 2012 produced evidence of basement outcrops on the steep slopes of the Mendeleev Rise seamounts. Observations of the outcrops from research submarines showed that part of the steep slopes interpreted as basement outcrops based on seismic data were overlain by a light sediment cover. The actual areas of the basement outcrops are therefore much less than indicated by the seismic data alone. The outcrops found are of 5–10 to 100–200 m and are often stretched along some hypsometric level or arranged obliquely, crossing a slope at an angle to the horizon. The rocks are massive and layered, often strongly weathered, cavernous, with visible fissures and extended by dislocations

Morphology of seamounts at the Mendeleev Rise, Arctic Ocean

Geological and geophysical studies undertaken during the Russian Arktika-2012 Expedition of 2012 produced evidence of basement outcrops on the steep slopes of the Mendeleev Rise seamounts. Observations of the outcrops from research submarines showed that part of the steep slopes interpreted as basement outcrops based on seismic data were overlain by a light sediment cover. The actual areas of the basement outcrops are therefore much less than indicated by the seismic data alone. The outcrops found are of 5–10 to 100–200 m and are often stretched along some hypsometric level or arranged obliquely, crossing a slope at an angle to the horizon. The rocks are massive and layered, often strongly weathered, cavernous, with visible fissures and extended by dislocations