A simplified model for the transformation of the atmospheric planetary boundary layer overlying a thermal front in the sea

This paper discusses a simplified model for the evolution of the atmospheric planetary boundary layer overlying a thermal front in the sea. The model provides local values of the friction/heat transfer geostrophic coefficients and the direction of surface wind stress, as well as the wind/temperature profiles at any point on the front. With the running over a warm front, the baroclinicity of the internal boundary layer leads to the generation of a near-surface current of air directed down the front. The model can be used to interpret radar imagery of the sea surface with the purpose of determining its mesoscale variability. Translated by Vladimir A. Puchkin.     

About the relationship between acoustic fields and hydrological fields in the area of a mesoscale eddy in the Black Sea

This paper discusses the application of acoustic sounding with the purpose of identifying vortical features in the sea. Analysis of the results of a multidisciplinary acoustic/hydrological experiment conducted in the Black Sea has revealed a stable recurrent correlation between the amplitudinal variance of echo signals, on the one hand, and the peculiarities of water temperature fields, on the other. Given these characteristics, the peripheral and the central areas of a mesoscale eddy essentially differed. This allows us to apply acoustic sounding to identify mesoscale eddies in the sea. Translated by Vladimir A. Puchkin.     

Dynamic response of the leg of a tension leg platform subjected to an axial, suddenly applied load at one end

This paper deals with the solution of the problem of the dynamic response of the leg of a tension leg platform subjected to an axial, suddenly applied load at one end, considering a highly simplified model but taking into account several complicating factors. The problem is solved by means of a non-harmonic Fourier expansion in terms of eigenfunctions obtained from a non-regular Sturm-Liouville system.     

Molecular and isotopic characteristics of gas hydrate-bound hydrocarbons in southern and central Lake Baikal

We investigated the molecular composition (methane, ethane, and propane) and stable isotope composition (methane and ethane) of hydrate-bound gas in sediments of Lake Baikal. Hydrate-bearing sediment cores were retrieved from eight gas seep sites, located in the southern and central Baikal basins. Empirical classification of the methane stable isotopes (δ¹³C and δD) for all the seep sites indicated the dominant microbial origin of methane via methyl-type fermentation; however, a mixture of thermogenic and microbial gases resulted in relatively high methane δ¹³C signatures at two sites where ethane δ¹³C indicated a typical thermogenic origin. At one of the sites in the southern Baikal basin, we found gas hydrates of enclathrated microbial ethane in which ¹³C and deuterium were both highly depleted (mean δ¹³C and δD of –61.6‰ V-PDB and –285.4‰ V-SMOW, respectively). To the best of our knowledge, this is the first report of C₂ δ¹³C–δD classification for hydrate-bound gas in either freshwater or marine environments.     

Seabed morphology and gas venting features in the continental slope region of Krishna–Godavari basin,Bay of Bengal: Implications in gas-hydrate exploration

Increased oil and gas exploration activity has led to a detailed investigation of the continental shelf and adjacent slope regions of Mahanadi, Krishna–Godavari (KG) and Cauvery basins, which are promising petroliferous basins along the eastern continental margin of India. In this paper, we analyze the high resolution sparker, subbottom profiler and multibeam data in KG offshore basin to understand the shallow structures and shallow deposits for gas hydrate exploration. We identified and mapped prominent positive topographic features in the bathymetry data. These mounds show fluid/gas migration features such as acoustic voids, acoustic chimneys, and acoustic turbid layers. It is interesting to note that drilling/coring onboard JOIDES in the vicinity of the mounds show the presence of thick accumulation of subsurface gas hydrate. Further, geological and geochemical study of long sediment cores collected onboard Marion Dufresne in the vicinity of the mounds and sedimentary ridges shows the imprints of paleo-expulsion of methane and sulfidic fluid from the seafloor.     

The volumes of volcanic seamounts as a factor determining the formation of the ocean floor’s morphostructure

The volumes of formed volcanoes are an important indicator of the formation intensity of the ocean floor volcanogenic morphostructure under different geodynamic conditions. The distribution of the volumes of volcanoes that formed within the oceanic lithosphere of different geological ages is considered to analyze the spatial and time dynamics of the scopes of the seamount formation. The greatest volumes of effused rocks concentrate in volcanoes of different heights on the different-age segments of the lithosphere. The total volumes of volcanogenic substance growing with increasing age and thickness of the lithosphere is caused by the increasing range of the heights of the formed volcanoes and the growing number of big seamounts. Despite that the volcanic seamounts formed within the mid-oceanic ridges, on the divergent boundaries of the lithospheric plates and in the transform faults most often, half of the volcanogenic material was emitted to the earth’s surface during the spreading of the intraplate volcanism. A leading part in the formation of the volcanogenic morphostructure of the ocean floor belongs to the formation of big seamounts with heights of 4–6 km and volumes from 1500 to 5100 km³, respectively, in the provinces with ages from 60 to 90 mln years.     

Simulation of the impact of thunderstorm activity on atmospheric gas composition

A chemistry-climate model of the lower and middle atmosphere has been used to estimate the sensitivity of the atmospheric gas composition to the rate of thunderstorm production of nitrogen oxides at upper tropospheric and lower stratospheric altitudes. The impact that nitrogen oxides produced by lightning have on the atmospheric gas composition is treated as a subgrid-scale process and included in the model parametrically. The natural uncertainty in the global production rate of nitrogen oxides in lightning flashes was specified within limits from 2 to 20 Tg N/year. Results of the model experiments have shown that, due to the variability of thunderstorm-produced nitrogen oxides, their concentration in the upper troposphere and lower stratosphere can vary by a factor of 2 or 3, which, given the influence of nitrogen oxides on ozone and other gases, creates the potential for a strong perturbation of the atmospheric gas composition and thermal regime. Model calculations have shown the strong sensitivity of ozone and the OH hydroxyl to the amount of lightning nitrogen oxides at different atmospheric altitudes. These calculations demonstrate the importance of nitrogen oxides of thunderstorm origin for the balance of atmospheric odd ozone and gases linked to it, such as ozone and hydroxyl radicals. Our results demonstrate that one important task is to raise the accuracy of estimates of the rate of nitrogen oxide production by lightning discharges and to use physical parametrizations that take into account the local lightning effects and feedbacks arising in this case rather than climatological data in models of the gas composition and general circulation of the atmosphere.