Numerical modelling of radiant energy extinction by water medium containing bubbles and particles of various natures

In the framework of the Mie theory, we developed a numerical model of weakly absorbing medium, containing particles having an arbitrary chemical composition. This model can be applied to the study of the extinction characteristics of the optical radiation by a water layer with gas bubbles or volume-shape particles. The results of the numerical experiment illustrate changes in optical properties of the water due to the presence of bubbles or solid particles. The work displays some calculations of the extinction efficiency factor, the extinction coefficient, and transmission function at visible wavelengths. The influences of concentration and sizes of gas bubbles on the extinction characteristics of optical radiation are illustrated. Features of the extinction of radiant energy are discussed as dependent on a size parameter and a complex index of refraction of scatterers

Mud volcanism and gas seeps in Lake Baikal: causes and consequences

After the discovery in 1999 of a series of mud volcanoes on the deep basin floors of Lake Baikal and of the presence of an anomalous thermally-mixed water layer attributed to methane venting, the lake floor was investigated in more detail in order to identify all possible sources of methane and to understand the processes leading to mud volcanism and methane release at the Baikal lake floor. New data show the presence of at least 4 mud volcano provinces, each consisting of several individual mud volcano structures, and of several areas of gas venting. All mud volcanoes occur in water depths of > 1000 m, within the GHSZ and in areas of abnormally shallow BSR, and are closely associated to large, active faults. They are attributed to hydrate destabilisation at the base of the GHSZ under the influence of a geothermal fluid pulse along the nearby fault. Methane release is not continuous (probably tectonically controlled; most mud volcanous are not active at present) and the source of methane is destabilising gas hydrates at 200-300 m subbottom depth. In addition, a whole series of methane vents (i.e. without distinct morphological expression) occur in shallower-water areas. These venting sites occur mostly in deltaic environments, but some are also associated with faults, and are always outside the GHSZ. Methane release appears to be more continuous (many are now active) and the source of the methane is probably shallow subsurface methane formed by the decomposition of organic matter, although deeper sources can not be excluded.Consequences of methane venting for the waters of Lake Baikal are the presence of a thermally-mixed water layer, wich could (if persisting and increasing in thickness) lead to a permanent stratification of the water column. This could influence the water mixing process and have major influences on the oxygenation of the lake and the benthic biota. In addition, increasing evidence is becoming available that some of these seeps may influence the water column (directly, or via associated temperature-driven circulation effects) up to the surface, causing localised melting or non-freezing of the winter-ice cover and even massive fish deaths. Measurements of surface-water and near-surface air methane concentrations are currently underway. The influence of the methane seeps (up to a few years not even suspected in the largest lake on Earth) on the entire lake system may thus be extremely important

Mud volcanoes and gas vents in the Okhotsk Sea area

Gas emissions from mud volcanoes on Sakhalin Island and water-column gas flares arising from cold seeps in the Okhotsk Sea appear to be related. They are likely activated by tectonic movements along the transform plate boundary separating the Okhotsk Sea Plate from the Eurasian and Amur plates. Gas vents (flares) and methane anomalies occur in the waters offshore Sakhalin Island, along with NE-SW-trending mounds and fluid escape structures on the seafloor. The intersection of the NE-striking transverse faults on land with the Central Sakhalin and Hokkaido-Sakhalin shear zones apparently determines the sites of mud volcanoes, a pattern that continues offshore where the intersection with the East Sakhalin and West Derugin shear zones determines the sites of the submarine gas vents

Heavy mineral composition of bottom sediments from the South China Sea

This paper presents results of investigations of unusual carbonate formations found in bottom sediments of the South China Sea shelf. These sediments were sampled from a deep fracture found by geophysical methods. According to gas-geochemical data there are high concentrations of methane, hydrogen and carbon dioxide in bottom waters of this area. The carbonate formations were defined as calcium siderite or siderodot by roentgenostructural, microprobe, atomic absorption, and thermal analyses, asawellas infrared spectroscopy. Formation of this mineral results from carbon dioxide and methane flows through bottom sediments