Methane fluxes on the water–atmosphere boundary in the Sea of Okhotsk

Doklady Earth Sciences - High variability in methane fluxes at the water–atmosphere boundary was found for the first time for the period 1990–2016 using expeditionary data. Variability...     

Deep Structure and Geodynamics of the Black Sea–Caspian Region

Geotectonics - New data on the crust structure of the Black Sea?Caspian region, including the Scythian and Anatolian plate margins, the Caucasus, Black Sea and Southern Caspian structures are...     

Glacial–interglacial records of the reflectance of sediments from the Norwegian–Greenland–Iceland Sea (Nordic seas)

 The reflectance of sediments (gray level) were measured on 11 sediment cores from the Norwegian–Greenland–Iceland Sea (Nordic seas). The analyzed time interval covers the past five glacial–interglacial cycles. Although the results demonstrate that the gray-level method has a potential for stratigraphic purposes, it is indicated that gray-level changes in the Nordic seas are not necessarily driven by variations in the content of biogenic calcite. A detailed comparison of gray-level values with contents of total CaCO₃ (carbonate) and total organic carbon (TOC) reveals no overall causal link between these proxies. However, specific glacial core sections with layers containing organic-rich sediment clasts as a consequence of iceberg-rafting seem to correlate well with law gray-level values. Of those cores which show relatively high and comparable carbonate values in the last three main interglacial intervals (stages 11, 5.5, and 1), stage 11 is always marked by the highest gray-level values. A close inspection of the surface structure of the foraminiferal tests as well as the conduction of reflectance measurements on these tests leads to the conclusion that enhanced carbonate corrosion occurred during stage 11. The test corrosion not only affected the reflectance of the tests by making them appear whiter, it also seems responsible for the comparatively high gray-level values of the total sediment in stage 11. In contrast, the relatively low gray-level values found in stages 5.5, and 1 are not associated with enhanced test corrosion. This observation implies that variable degrees of carbonate corrosion can have a profound effect on total sediment reflectance. Received: 6 September 1998 / Accepted: 4 April 1999     

Structural Evidence of Recent Activity of the Khatanga–Lomonosov Fault Zone in the Laptev Sea

Doklady Earth Sciences - New structural data obtained by a geophysical survey during Cruise 69 of the R/V Akademik Mstislav Keldysh in 2017 indicate that the Khatanga−Lomonosov fault zone is...     

Anomalously deep convection in the Irminger Sea during the winter of 2014–2015

The anomalous thermohaline properties of the core of the Labrador Sea water (LSW), a product of winter convection resulted from the ocean–winter interaction, which were recorded in the Irminger Sea in 2014 and 2015, are discussed. It is found that, in the summer of 2015, the LSW filled the entire deepwater basin in the south of the sea down to a depth of 1300 m over the periphery of the Irminger gyral, and down to a depth of 1800 m, in the anticyclone eddy formed in early June of 2015. The maximum density of the LSW core here was 27.75 σ_θ. Such deep and intense winter convection in the Irminger Sea was last recorded 20 years ago. As a result, the temperature of the LSW dropped to values observed in the years 2002 and 2007, but its average salinity remained high. The LSW that have been formed in recent years are reported to have great amplitude and nonmonotonic variability of the properties.     

Structure and Composition of the Holocene–Pleistocene Sediments in the Northern Barents Sea

Lithology and Mineral Resources - Signs of extensive migration of gas-bearing fluids from the sedimentary cover into the water column were identified in the northern Barents Sea during Cruises 25...     

Formation of the Japan Sea basin: Reassessment from Ar–Ar ages and Nd–Sr isotopic data of basement basalts of the Japan Sea and adjacent regions

Many studies have examined the Japan Sea basalts recovered during Ocean Drilling Program (ODP) Leg127/128. Of these, the ⁴⁰Ar–³⁹Ar dating undertaken is important in constraining the timing of the formation of the Japan Sea; however, the implications of their results do not appear to be fully appreciated by the geological community. In this paper, I reassess the ⁴⁰Ar–³⁹Ar age data of the basalts with reference to Nd–Sr isotopic data. The ⁴⁰Ar–³⁹Ar dating was performed on basalts somewhat enriched in large-ion lithophile elements and recovered from ODP Sites 794, 795 and the lower part of 797, yielding the plateau ages of 21.2–17.7 Ma. These basalts show the Nd–Sr isotopic signature of a moderately depleted mantle source (ε_Nd: 0.6–6.9). In contrast, the basalts from the upper part of Site 797 have yet to be dated due to their low K content, although their Nd isotopic compositions are similar to that of MORB (ε_Nd: 8.4–10.4). By analogy to the secular Nd–Sr isotopic trends reported for Sikhote-Alin and northeast Japan, the age of the upper basalts at Site 797 may be inferred to be younger than the lower basalts, probably around 16 Ma. The Nd–Sr isotopic compositions of the Japan Sea basalts have been interpreted in terms of eastward asthenospheric flow, as have the lavas of the Sikhote-Alin and northeastern Japan. The timing of volcanic activity in the Japan Sea region (i.e., from 21.2 to 14.86 Ma) is consistent with the timing of rotational crustal movements inferred from paleomagnetic studies of the Japanese Islands (i.e., 14.8–4.2 Ma for southwest Japan and 16.5–14.4 Ma for northeast Japan).     

Onshore–offshore structure and hydrocarbon potential of the South Yellow Sea

Recent high-resolution airborne gravity data taken over the South Yellow Sea and its western onshore–offshore transition zone, combined with ground gravity data taken over the onshore area (Subei Basin), China, show that the South Basin of the South Yellow Sea and the Subei Basin correspond to the same gravity low anomaly. Magnetic data also support our interpretations. Both areas have similar strata, structures and hydrocarbon potential, and form a large Cenozoic terrestrial sedimentary basin controlled by the Tanlu Fault. Cenozoic terrestrial strata are well developed in the South Basin of the South Yellow Sea, and thick Meso–Paleozoic marine strata are preserved in the Central uplift area. Future hydrocarbon exploration in the South Yellow Sea should focus on the Cenozoic continental sequence, especially the Paleogene in the South Basin, as well as the Meso–Paleozoic marine rocks in the Central uplift area. The western part of the middle depression and middle and western parts of the north depression in the South Basin of the South Yellow Sea have the greatest potential for hydrocarbon accumulation.     

Polycyclic aromatic hydrocarbons in Holocene–Pleistocene sediments of the Laptev Sea

The distribution and genesis of polycyclic aromatic hydrocarbons (PAHs) were studied in a 40-m core from a lagoon of the Laptev Sea that appeared during the Holocene resulting from the flooding of seawater into a freshwater lake in the area of the Buor-Khaya Gulf. The bulk of the core is constituted of permafrost rocks, thawed partially in their upper layers and covered with recent sediments (mainly by the products of intense thermoabrasion). The ratio of petrogenic and pyrogenic PAHs was evaluated.     

Monitoring the Spatiotemporal Evolution of Sea Ice in the Bohai Sea in the 2009–2010 Winter Combining MODIS and Meteorological Data

The spatiotemporal evolution of sea ice of Bohai Sea in the 2009–2010 winter was studied by time-series remote sensing data, and real-time meteorological data in combination with cumulative freezing degree days (CFDD). Sea ice acreage was determined using a ratio-threshold segmentation together with visual interpretation of daily MODIS 250 m imagery. We found the sea ice acreage soared to 31,849 km² on January 23, covering 40.8% of the Bohai Sea. But on February 12, it reached 26,700 km² in Liaodong Bay only, covering almost 90.0% of Liaodong Bay. The rapid formation and expansion of sea ice was caused by continuous cold snaps superimposed on a background of anomalously cold weather. CFDD calculated from surrounding cities highly correlated with sea ice acreage in Liaodong Bay (R ² = 0.72) suggesting CFDD is one of the significant controlling factors. Sea ice expansion showed 7 days lag with respect to the lowest temperature from surrounding coastal cities, and it mainly occurred close to land, along the coastline, and gradually expanded from the shore outwards.     

The Nature of the “Voice of the Sea”

Strong vibrations of the Earth’s crust in the frequency range of 7–9 Hz, referred to as the “voice of the sea,” have been recorded in the course of processing synchronous experimental data obtained during recording of variations in the deformation of the Earth’s crust using a shore laser strainmeter, atmosphere pressure variations using a laser nanobarograph, and hydrosphere pressure variations using a laser meter for hydrospheric pressure and wind velocity variations. The nature of these vibrations and their transformation to adjacent geospheres have been discussed.     

Mesozoic–Cenozoic Structure of the Black Sea–Caucasus–Caspian Region and Its Relationships with the Upper Mantle Structure

Geotectonics - Abstract—Mesozoic‒Cenozoic tectonic zoning and its evolution are characterized by analysis of geological data on the Black Sea–Caucasus–Caspian region. The...     

Lower–Middle Jurassic foraminiferal and ostracode biostratigraphy of the Barents Sea shelf

The Barents Sea shelf is an attractive target as a prospective large petroleum province. Further development of geological and geophysical exploration in the area requires high-resolution biostratigraphic constraints and update stratigraphic charts. The zonal succession of Lower and Middle Jurassic assemblages of foraminifers and ostracodes of the Barents Sea fits well the division for northern Siberia based on correlated independent Jurassic and Cretaceous zonal scales on all main microfossil groups, of which some scales were suggested as the Boreal Zonal Standard. The stratigraphic range of the Barents Sea microfossil assemblages has been updated through correlation with their counterparts from northern Siberia constrained by ammonite and bivalve data. Joint analysis of foraminiferal and ostracode biostratigraphy and lithostratigraphy of the sections allowed a revision to the stratigraphic position and extent of lithological and seismic units. The discovered similarity in the Lower and Middle Jurassic lithostratigraphy in the sections of the Barents Sea shelf and northern Siberia, along with their almost identical microfossil taxonomy, prompts similarity in the Early and Middle Jurassic deposition and geological histories of the two areas.     

Ecology of the bottom fauna and bioaccumulation of trace metals along the Lena River–Laptev Sea transect

The first data on ecology and trace metal (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb) bioaccumulation by macrozoobenthic organisms in area along the 130°E meridional transect from shallow water near the Lena River’s delta till the 78°N are presented. At the newly discovered methane seeps in the shallow Laptev Sea areas (72 m depth), a higher total abundance and biomass compared with background stations were recorded. In carbonate shells and soft tissues of Bivalvia Portlandia arctica and Astarte borealis, the high concentrations of Mn, Fe, Pb, Ni and Co were detected that varied in dependence from sampling site. In the dominating taxa of brittle stars (Ophiuroidea), there were found no significant differences between majority of trace metal content in organisms inhabiting the seeps area and background ones. An elevated content of some metals was detected in the Asteroidea bodies that may be attributed to its trophic behavior (deposit feeder).     

Lithology,Biostratigraphy, and Geochronology of the Late Pleistocene–Holocene Sediments on the Coast of Onega Bay of the White Sea

Doklady Earth Sciences - This paper reports on the lithological, micropaleontological, and chronometric data (radiocarbon dating) for one of the areas of the White Sea coast. The sedimentary...     

Particle size composition of Holocene–Pleistocene deposits of the Laptev Sea (Buor-Khaya Bay)

New data on the particle size composition of the Laptev Sea shelf deposits were obtained on the basis of results of low-angle laser light-scattering of core samples from the columns studied. It was revealed that the sand fraction dominates. The results of comparative analysis of the particle size composition of deposits show that the Laptev Sea shelf zone was characterized by highly variable spatial–temporal conditions and settings of sedimentation in the Quaternary, a polygenic character of deposits, and a pulsating influence of fluvial and slope processes on the conditions of sedimentation. A tendency of coarsening in the vertical sequence that contributes to thawing of the permafrost was revealed in the Ivashkina lagoon.     

Natural background of hydrocarbon gases (C1–C5) in the waters of the Kara Sea

The distributions of methane and hydrocarbons (HC) C2+ throughout the vertical section of the water mass and sediments of the Kara Sea and the estuaries of the Ob and Yenisei rivers were examine during expeditions aboard the R/V “Akademik Boris Petrov” in 1997–2002. Data obtained during the expeditions and extensive information provided by the complex study of the carbon cycle in the aquatic area were used to analyze the genesis of hydrocarbon gases in marine water. The example of particulate matter was used to demonstrate that hydrocarbon gases of the composition C2–C5 contained in seawater are genetically related to aquatic organic matter (OM), regardless of seawater salinity. The hydrocarbon complex is dominated (80%) by higher C4–C5 homologues. The concentration of C4–C5 hydrocarbons in the estuarine fresh waters is comparable with the high methane concentration (2–3 μl/l), drastically decreases in the zone of water mixing, and then rapidly increases to values several times higher than the methane concentration in seawater outside the outer boundary of the sedimentation depocenter of riverine particulate matter. A direct correlation was established for the concentration of the C4 + C5 homologues with the OM of the water mass, and the leading role was demonstrated to be played by labile OM of the autochthonous biomass (marine phytoplankton) in the genesis of higher hydrocarbon gases (alkenes, alkanes, and isoalkanes) during the early diagenetic stage of OM transformations in water. Along with the biomass of phytoplankton, a significant role in the genesis of C2–C3 hydrocarbons is played by destruction products of terrigenous OM. The destruction of OM and generation of gaseous hydrocarbons, including methane, are restricted to the pycnocline and the water-sediment interface. The absolute predominance of the sum of the C4 + C5 homologues in the hydrocarbon C2+ gases and the presence of unsaturated C2–C4 hydrocarbons are typical of the natural background of hydrocarbons of the Kara Sea water mass.     

A Long-Lived Center of Gas–Fluid Emanations on the Western Slope of the Kuril Basin (Sea of Okhotsk)

Lithology and Mineral Resources - The paper presents the results of multidisciplinary studies in the carbonate–barite mineralization area revealed on the western slope of the Kuril deep-water...     

Finding the Location of Generation Zones of “Voice of the Sea” Microseisms

Doklady Earth Sciences - The generation zones of “voice of the sea” microseisms of three typhoons were determined from the field data using a two-coordinate laser strainmeter. From...