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The concentration distribution was studied for dissolved oxygen, phosphorus forms, and particulate matter in Curonian Bay of the Baltic Sea in poorly known consolidated ice cover conditions during the winter seasons of 2010, 2011, and 2013. The surface and near-bottom waters were sampled at 51 stations. The ice cover exerts no significant effect on the typical seasonal variation of all considered parameters in the basin. The concentrations of mineral and organic phosphorus in the bay appeared to be lower by factors of 2-4 compared to summer values. A two- to threefold decrease in the concentrations of organic phosphorus since 2010 to 2011 and then to 2013 was recorded in the bay, which resulted from a decrease in phosphorus production by phytoplankton. Despite water being isolated from air by ice, the absence of wave mixing, and the decrease in oxygen production owing to the seasonal winter decrease in the intensity photosynthetic processes, no oxygen deficiency was found in the basin. This is because oxygen supplied to the bay by river runoff and production by photosynthesis in the bay exceed the utilization for oxidation of organic matter resulting from low bioproductivity of the waters during winter. The winter decrease in the fraction of biogenic particulate matter is seen as a four- to sevenfold drop in its total concentration in the waters compared to summer seasons. The absence of wave roiling of bottom sediments also caused a decrease in the secondary supply of biogenic particulate matter from sediments into near-bottom waters. No negative trends of geoecological conditions in the bay were revealed by the studied parameters under consolidated ice cover conditions. [ABSTRACT FROM AUTHOR]

Numerical simulation based on the Princeton Ocean Model (POM) was performed for a region of the Southeast Baltic in order to compare data on the spatial distribution of velocity and bottom sediments. Special attention was focused on the influence of western and northeastern winds, which generate intense quasi-geostrophic currents can may cause very high velocities in the near bottom layer, which results in the elution of bottom sediments and transport of their fine fractions. An abrupt change in wind velocity intensifies the effect of elution due to generation of inertial internal waves that penetrate into the bottom layer. The spatial distributions of the velocity in the surface and near bottom layers are compared with data on bottom sediments. It turned out that areas with the highest velocities that formed under the effect of western and northeastern winds in most cases coincide with areas where bottom sediments are represented by coarse-grain fractions of gravel and sands. [ABSTRACT FROM AUTHOR]

Monitoring studies in the area of Kravtsovskoe oil field in the southeastern Baltic Sea have been carried out since 2003. Terrigenous bottom sediments (0-5 cm layer) in the area (23 stations) are represented by all grain size types. Down to the depth of 30-50 m, these are mostly quartz sands; at depths of 60-110 m, these are terrigenous mud with C content of 1-3%. The concentration and distribution of toxic elements (Cu, Co, Cd, Pb, Ba, and Hg) over sediment types and bed area are the same as in the Baltic Sea as a whole: Cu, Co, Cd, Pb, and, partially, Hg are distributed in accordance with the 'fraction rules' (with minimums in sands and coarse aleurites and maximums in mud); Ba distribution is independent of the sediment type. The concentrations of toxic elements tend to increase with time: the concentrations of such elements in samples (at the same stations) somewhat increase compared with their concentrations before the construction of D-6 oil platform, during its construction, and during oil production. This trend in the concentrations of toxic elements in sediments can be due to the steelwork of D-6 platform. The increase in Ba concentration is likely due to drill mud spills during exploration drilling. None of the elements shows sediment pollution in excess of MAC anywhere in the area. [ABSTRACT FROM AUTHOR]

In depressions of the Baltic Sea, where the bottom is periodically marked by stagnation, silt contains as much as 5% Mn (up to 17% in some layers) and 9-10% C. Silt in such depressions is laminated. The marine sediment sequence is stratified due to the influx of oceanic water into sea: the upper layers are oxic, while the lower (near-bottom) layers are hydrosulfuric. Boundary between them is represented by the transitional O-HS layer. This zone (redox barrier) is marked by drastic variation in Eh. Zone below this barrier is characterized by the accumulation of huge amounts of the dissolved manganese (Mn) and iron (Fe), which diffuse from the hydrosulfuric layer into the oxic layer under the influence of gradient and precipitated as suspeusion with as much as 15% Fe and 45% Mn. When fresh oxygenated saline water is transported to depressions, the hydrosulfuric setting gives way to oxic one and the dissolved elements are transformed into the particulate phases as hydroxides and geologically instantly precipitated at the bottom. After 5-10 yr, the setting changes; hydrogen sulfide is again delivered to water column from the bottom. This is accompanied by supply of the dissolved Mn and Fe previously accumulated as gel-type sediment at the bottom. Thus, the cycle of elements is repeated. The latter, however, is not completely dissolved. Some portion remains at the bottom as black rhodochrosite microlayers (laminas) that contain as much as 29% Mn. The black laminas accumulated during aeration include remains of bottom foraminifers. In addition, the bottom comprises pale diatom laminas and brownish gray varieties composed of clayey and organic substances. Bulk samples of the laminated silt contain as much as 12.9% Mn or 26.9% MnCO. Depressions in the Baltic Sea represent a unique site of the Earth marked by accumulation of the carbonate-manganiferous sediments at present. We believe that Oligocene manganese carbonate-oxide ores described by N.M. Strakhov and coauthors were accumulated in the same manner. Compositions of manganiferous sediments in the Baltic region and some ancient ores in Europe are compared. The author studied five stages of Mn accumulation and sediment transformation into ores. [ABSTRACT FROM AUTHOR]