Composition and distribution of meiobenthos in amursky bay (peter the great bay, the east sea)

Qualitative and quantitative composition of meiobenthos was studied in Amursky Bay (Peter the Great Bay, the East Sea). Ten taxonomic groups were found, where nematodes were dominant. Density of meiobenthos in ground sediments of the Bay were not uniform, and the average density was measured at 126.4±62.3 ind. m^-2. 56 species of nematodes were detected, and dominant species wereSabatieria palmaris, Paracanthonchus macrodon, Sphaerolaimus limosus, S. gracilis andOncholaimium ramosum. Five taxocenes of nematodes were allocated based on the results of cluster analysis and species domination according to density. Low diversity in species composition of nematodes was noted in the northwestern part of the Bay, which is a zone of desalination, and in the eastern part, which is exposed to household drains.     

Path following control system for a tanker ship model

A two-dimensional path following control system for autonomous marine surface vessels is presented. The guidance system is obtained through a way-point guidance scheme based on line-of-sight projection algorithm and the speed controller is achieved through state feedback linearization. A new approach concerning the calculation of a dynamic line-of-sight vector norm is presented which main idea is to improve the speed of the convergence of the vehicle to the desired path. The results obtained are compared with the traditional line-of-sight scheme. It is intended that the complete system will be tested and implemented in a model of the “Esso Osaka” tanker. The results of simulations are presented here showing the effectiveness of the system aiming in to be robust enough to perform tests either in tanks or lakes.     

Time domain modelling of the transient asymmetric flooding of Ro-Ro ships

This work aims at contributing to improve knowledge on transient asymmetric flooding through theoretical and experimental research. First, a time domain theoretical model of ship motions and flooding is described. Results from experimental work are presented evidencing that transient asymmetric flooding may cause the capsizing of a Ro-Ro shaped barge. The theoretical model is used to predict the capsize of the Ro-Ro shaped barge. Reasonable agreement between experimental and theoretical results was found. Finally, a review of the European Gateway accident is given and the theoretical model is applied to the study of this type of accident. The conclusion is that this theoretical model, together with an accurate modelling of the flooding of machinery compartments, reproduces successfully the capsizing of the European Gateway due to transient asymmetric flooding. Therefore, the internal arrangement of Ro-Ro ships should be carefully studied at the design stage in order to avoid this phenomenon.     

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.     

Quantitative distribution of meiobenthos in deep-water zones of the World Ocean

An analysis of published and original data on the meiobenthos abundance in the depth interval from 100 to 9807 m (in total, 665 records, 445 of them obtained for depths exceeding 1000 m) revealed general regularities in its distribution. The influence of the sampling and data processing methods on the quantitative estimates of the meiobenthos abundance is considered to demonstrate changes in the proportions of the main meiobenthic taxa at different depths and to characterize latitudinal changes in the meiobenthos abundance. The dependence of the abundance of free-living nematodes, the most abundant group of metazoan meiobenthos, on trophic conditions is analyzed. No significant differences in the meiobenthos abundance in the samples obtained by box-and multicorers are established. It is shown that the share of nematodes in metazoan meiobenthos communities increases with the depth. In temperate latitudes, a distinct maximum in the population density confined to depths exceeding 1 km is observed. The quantitative distribution of the meiobenthos at the depths gradient is controlled by the bottom macrotopography and trophic conditions.     

Biogeochemistry of organic matter in the Laurentian Trough, II. Bulk composition of the sediments and relative reactivity of major components during early diagenesis

The organic carbon of 280–320 m deep Laurentian Trough sediments at landward and seaward sites (13–24 mgN/g) consisted of carbohydrates (15–22%), hydrolysable amino acids (7–13%), lipids (1–5%), labile proteins (0.3–1%) and a non-characterized fraction (62–74%). Amino acids, proteins and uncharacterized compounds accounted for 21–43, 0.9–4 and 51–78%, respectively, of total nitrogen (1.2–2.2 mgN/g). A clear reactivity trend (pheopigments ? lipids > proteins > amino acids ≈ nitrogen > carbon > carbohydrates) was deduced from the concentration decreases between settling particles and surficial sediments. This was confirmed by one-year inventories in the top cm, burial rates at 35 cm depth, and one-G model calculations. Lipids were a dominant substrate near the sediment-water interface whereas carbohydrates and amino acids constituted the principal energy sources deeper in the sediment. In the porewaters, DOC levels were low (2–6 mg/l) in the top 4 cm, indicating rapid removal (i.e. consumption, irrigation, diffusion), and increased with depth (8–12 mg/l), reflecting the buildup of refractory products. There were also clear compositional changes of DOC with depth. Geographical differences in water column fluxes were recorded in the sediments. The organic contents and ratios were higher at the landward site due to higher rates of sedimentation, bioturbation and terrestrial and total organic inputs. At the seaward station, the lower rates of these processes and stronger marine influence resulted in lower ratios and a more complete decay of organic matter within the top 35 cm sediments.     

Reflection of large-scale inhomogeneities in the air-sea boundary layer on the intensity of surface wave breaking in the ocean

An overview of experiments is given on the observation of the dependence of the intensity of wind wave breaking on large-scale currents' inhomogeneities and atmospheric boundary layer stratification. The data were interpreted using a model in which the variance of the wind wave breaking intensity reflects fluctuations in the influx of energy to wind waves due to various factors. Translated by V. Puchkin.     

The effects of vehicular and pedestrian traffic on dune vegetation in South Africa

The effects of varying intensities of off-road vehicle and pedestrian traffic on vegetation height and percent-cover were investigated at two sites representing pioneer and climax dune shrubland communities in South African dune systems. In all cases, a decreasing trend in vegetation height and percentage cover subsequent to application of the treatments was evident, although this was more clear in the shrub than in the pioneer community. The impact on vegetation variables increased with increasing intensity of vehicle and pedestrian treatments. Vehicles driven along a curved path resulted in greater vegetation destruction than those driven along a straight path. High intensity (single application) treatments resulted in an initial decrease in vegetation height and cover immediately after the impact, which was followed by a further decline over the next 3 months. This two-step response was attributed to the subsequent gradual death of the vegetation which was not evident immediately following the impact. Due to their faster growth rate, pioneer dune communities appear to have the capacity to recover following impacts, while dune shrub communities tend to be more vulnerable, exhibiting signs of damage for longer periods. The results of this study have value for managers of coastal dune systems, particularly those impacted by human recreational activities.     

Short-term shoreline changes due to cross-shore structures: a one-line numerical model

The proposed numerical model simulates the short-term temporal changes in shoreline position due to a structure interrupting the longshore sediment flux. The impacts of both the groin-type construction and underwater trench of arbitrary orientation relative to the shore are discussed. In order to estimate the sediment mass trapped by the structure, a submodel of the longshore sediment transport induced by a random wave field is developed. The contribution of the surface roller in momentum balance as well as in sediment suspension is included. The shoreline changes are computed from the equation deduced from the mass conservation. The perturbations in the longshore sediment discharge caused by a structure are assumed to concentrate within some boundary area of which the spatial scale is proportional to the structure's length until the latter is exceeded by the width of the sediment flux. It is shown in particular that the total effect of a long trench (channel) and a pier in its nearshore part results in general shoreline recession except for the vicinity of a pier. The model is tested against the laboratory data of Baidei et al. (1994) and applied to the Baidara Bay coast (Kara Sea) where a pipeline would be designed.