On numerical modelling of currents over the north-west shelf of the Black Sea

Water circulation in the north-west part of the Black Sea during the summer period is calculated by means of a complete non-linear thermohydrodynamic model. We have also studied the contribution of wind forcing, the thermohaline regime, the coastline configuration, and the bottom topography to the generation and transformation of a flow field. It has been shown that the thermohaline regime and wind forcing account for 30 and 70% of the total circulation, respectively. Variation in the nature of circulation at weak winds is due to thermohaline factors. Vertical motion plays a crucial role in theT, S- andH ₂ S-field formation.Translated by V. Puchkin.     

Inter-annual variability of the hydrological-chemical characteristics in the north-western Black Sea shelf area over recent decades (1960–1990)

A number of significant hydrologicla and chemical parameters of the Black Sea shelf area have been identified and investigated: the inter-annual variability of the mean annual and seasonal (winter and summer) values of the air and seawater temperatures and salinity in the vicinity of Odessa; silicon and phosphate concentrations averaged over the north-western Black Sea shelf area (NWBS); discharges of the Danube and Dnieper rivers; mean surface and near-bottom oxygen concentrations in summer acquired through the analysis of the summarized data collected at three oceanographic stations occupied between Bolshoi Fontan and the Tendra isthmus from the early 1950s up to date. From these data, the variability of the areas subject to oxygen deficit in the near-bottom layer of the NWBS shelf during the summers of 1973–1994 has been assessed. Predominant oscillation periods and trends in the inter-annual variability of the studied parameters have been revealed and their relationship and climatic dependence has been demonstrated. Translated by Vladimir A. Puchkin.     

Recent variability in the Pacific western subarctic boundary currents and Sea of Okhotsk

The objective of this research is to describe physical processes which are the cause of the recent variability of the Pacific western subarctic waters. Rapid thermohaline changes have occurred within the Oyashio and Kamchatka Current during the last decade. This variability has included a warming of the Kamchatka Current warm intermediate layer, but a cooling and freshening of the upper layer in the Oyashio and Sea of Okhotsk. The example presented here uses data obtained during the Canada/Russia INPOC and WOCE projects, as well as the new Russian studies with high resolution station grid.The possible physical mechanism that generated the upper layer freshening during the thermohaline transition is examined. Major components of the fresh water budget of the Okhotsk Sea are considered in order to describe the dramatic changes in salinity which have recently occurred in the Pacific subarctic. Significant changes in precipitation and other fresh water inputs are demonstrated. It is suggested that upper layer of the Oyashio and Kamchatka Current became cooler and fresher because of the export of cold, fresher waters from the Bering and Okhotsk seas. These waters from the marginal seas have cooled the bottom of the halocline, reducing evaporation and acting as a feedback that has kept the upper layer of the western subarctic boundary currents fresh. It is also shown that the outflow of the cold Sea of Okhotsk water has changed its path during this recent thermohaline transition.     

Seasonal variability and the types of currents in the upper layer of the Black Sea

Spectral analysis of the climatic circulation in the upper 10 m layer of the Black Sea has been carried out. The current field was calculated from a three-dimensional baroclinic non-linear model. The mode composition of the circulation was derived. It is shown that the surface climatic circulation can be represented as the superposition of a finite number of elementary currents of two types:n- andm-modes. Only 4n-modes are shown to be energy-dominant throughout the year. A relation is established between the different sources of energy supply of currents and the modes which assimilate this energy. Problems concerning the nature of the classical Black Sea currents such as the main Black Sea current (MBSC) and the Knipovich spectacles are discussed. A scenario of the field large-scale experiment is suggested which allows the reconstruction of the amplitudes of the first 10n- and the first 10m-modes from mooring data.Translated by Mikhail M. Trufanov.     

Statistical characteristics of cyclones and anticyclones over the Black Sea in the second half of the 20th century

By using the NCEP reanalysis data for 1952–2000, we estimate the parameters of cyclones and anticyclones in the Black-Sea region and evaluate the statistical characteristics of their variability for each season. It is shown that the frequency of cyclones decreases in all seasons (except summer) as a result of the intensification of the North Atlantic Oscillation in the 1960–90s and the displacement of the predominant paths of synoptic disturbances to the north. For anticyclones, we reveal the opposite trend. The parameters of cyclones and anticyclones are characterized by quasiperiodic variations on the subdecadal scale also induced by the North Atlantic Oscillation. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 47–58, November–December, 2007.     

Seasonal variability of the hydrologic-and-acoustic parameters on the Black Sea shelf off the South Crimea coast

Usingin situ temperature and salinity observations from the Marine Hydrophysical Institute's oceanographic data set, regularities of the formation of structure and seasonal variability of the calculated sound speed field, as well as elements of the latter's vertical stratification in the South Crimea shelf area, have been studied. The ray approximation is applied to consider the influence of seasonal variations of the vertical hydrologic-and-acoustic structure on the propagation of sound in the sea. Translated by Vladimir A. Puchkin.     

Interannual variability of the zooplankton on the shelf of the northeastern Black Sea in the autumn period

The variability of the mesozooplankton stock in the shelf pelagic communities was studied in the late summer and autumn of 2006–2008. The plankton community’s structure and distribution were described for the shoreward transect (Gelendzhik city vicinity). The indirect and direct effect of the ctenophores Mnemiopsis leidyi and Beroe ovata on the mesozooplankton community was studied. The long-term changes in the meso- and macroplankton communities of the Black Sea were analyzed for the period of 2001–2008. The effects of the climatic factors, the water mass circulation, and the factors’ interplay on the mesozooplankton dynamics were assessed. Despite the wide range of the environmental conditions, the stock biomass of Mnemiopsis leidyi appeared to be quite stable within the studied period.     

Long-term tendencies in the variability of characteristics of the Black Sea pycnocline

The rise of the waters of the main pycnocline in the central part of the western cyclonic gyre at the end of the winter in the 1960s–1970s and their deepening in the eastern cyclonic gyre from the mid-1960s to the late 1980s were revealed on the basis of archival hydrologic data obtained on the standard sections of the Black Sea in 1957–1992. It is shown that, simultaneously, the waters of the pycnocline descended in the Sevastopol anticyclone and rose in the Yalta and Batumi anticyclones. These tendencies indicate that the water circulation intensified in the region of the western cyclonic gyre (off the southwestern coast of the Crimea) and weakened in the vicinity of the eastern cyclonic gyre at the end of the winter season in the 1960s–1970s and in the 1960s–1980s, respectively. It is shown on the basis of NCEP reanalysis data and archival hydrometeorological data that all major circulation factors, such as a decrease in the cyclonic vorticity in the wind field during the winter season, changes in its spatial structure, an increase in the river discharge, and a decrease in the turbulent heat fluxes at the Black Sea surface, affect the energy redistribution between the gyres. The role of each of these factors is analyzed.     

Characteristics of inertial oscillations according to the experimental measurements of currents on the Russian shelf of the Black Sea

The analysis of inertial oscillations on the Gelendzhik shelf of the Black Sea is presented. Spectral characteristics of the current fields are studied based on the measurements taken by the acoustic Doppler current profiler. Strong variability of the inertial oscillation hodographs at variations in the background shear current and diverse forms of inertial oscillations measured at a fixed point at various values of the shear current are revealed. The relation between the passage of the multidirectional jets and the trains of inertial oscillations inside the jets in the studied region are established.     

Long-term trends in the variability of deep-water thermohaline characteristics of the Black Sea

By using the archival hydrological data for 1955–1998, we analyze the trends of deep-water thermohaline characteristics of the Black Sea and their interannual and decadal variability. It was discovered that the level of salinity increased at depths greater than 1000 m in the west part of the sea from the mid-1950-s till the early 1980s and the opposite trend was observed for the next 15–20 yr. The average rate of increase in the deep-water salinity between 1960 and 1980 and its decrease after 1980 was equal to 0.05‰ per 20 yr. These facts demonstrate that the water exchange through Bosporus was intensified for the first 25 yr of the analyzed period and weakened for the next 20 yr. The interannual variability with a typical period of 6.5 yr and a quasi-20-yr periodicity are detected against the background of the parabolic trend. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 4, pp. 18–30, July–August, 2006.     

Some peculiarities of the Black Sea inertial currents

By treating observations involving long-term buoy moorings, numerical characteristics of the periods, amplitudes, phases and orbits of inertial currents in some Black Sea areas have been obtained. The inertial component's contribution to the total velocity field and turbulent exchange has been determined. As a result, the maximal heights of the internal waves generated by the inertial currents have been estimated. Translated by Vladimir A. Puchkin.     

Modelling of the Black Sea seasonal variability

The paper discusses the results of numerical experiments on response of the Black Sea to the ‘real’ (mean monthly) atmospheric forcing. A new version of the multi-layer quasi-isopycnic model is applied which does not use the rigid-lid approximation and allows for a salt flux through the sea surface. Ways of obtaining quantitative agreement between the calculated data due only to the external forcing, without invokingin situ temperature/salinity observations are suggested. Translated by Vladimir A. Puchkin.     

Observing spectral characteristics over a continental shelf and slope in the South China Sea

Using in situ measurement data from May-June, 1998, and data from the Asian seas international acoustics experiment （ASIAEX） from 2001 in the South China Sea （SCS）, the spectral density function and the dissipa- tion spectrum function are estimated. In the inffa-gravity wave （IGW） band, the power spectra of velocity （u, v, w） are universal functions with respect to characteristic frequencies, which correspond to the peak fre- quencies of the dissipation spectrum （PFDS）. This suggests that high-frequency internal waves in the IGW band have similar dynamical characteristics. In addition, the evolution of these characteristic frequencies is explored and its highest value is 8.8 cph （cycles per hour, 1 cph=2.778× 10-3 Hz）.     

Seasonal variability of acoustic characteristics in the northern Black Sea continental slope area

The peculiarities of seasonal variability of the calculated sound speed and elements of its vertical stratification in the northern Black Sea continental slope are considered. Typical acoustic structures have been identified. The impact of seasonal variability of the sound speed upon the ray characteristics of acoustic fields is studied. Translated by Vladimir A. Puchkin.     

东海西部陆架海域水团的季节特征分析

On the basis of the CTD data and the modeling results in the winter and summer of 2009, the seasonal characteristics of the water masses in the western East China Sea shelf area were analyzed using a cluster analysis method. The results show that the distributions and temperature-salinity characteristics of the water masses in the study area are of distinct seasonal difference. In the western East China Sea shelf area, there are three water masses during winter, i.e., continental coastal water（CCW）, Taiwan Warm Current surface water（TWCSW） and Yellow Sea mixing water（YSMW）, but four ones during summer, i.e., the CCW, the TWCSW, Taiwan Warm Current deep water（TWCDW） and the YSMW. Of all, the CCW, the TWCSW and the TWCDW are all dominant water masses. The CCW, primarily characterized by a low salinity, has lower temperature, higher salinity and smaller spatial extent in winter than in summer. The TWCSW is warmer, fresher and smaller in summer than in winter, and it originates mostly from the Kuroshio surface water（KSW） northeast of Taiwan, China and less from the Taiwan Strait water during winter, but it consists of the strait water and the KSW during summer. The TWCDW is characterized by a low temperature and a high salinity, and originates completely in the Kuroshio subsurface water northeast of Taiwan.     

Further evidence of abrupt Holocene drowning of the Black Sea shelf

A 1999 survey of the Black Sea continental shelf off the north central Turkish seaport of Sinop using a side-scan sonar, small remotely operated vehicles, and a series of dredge lowerings located, inspected and sampled an exposed high-energy paleoshoreline at a depth of 155 m. Radiocarbon dating of mollusk shells collected from this ancient beach revealed that the marine flooding of the Black Sea took place between 7460 and 6820 yr B.P. (all ages are reported in radiocarbon years, not calendar years, without correction for reservoir age or dendro-calibration) changing it from a lacustrine to marine environment. This relic surface remained in contact with the bottom waters of the Black Sea for a long period of time before being draped by a thin layer of sapropel mud. Wood samples recovered from this same location were very well preserved and yielded dates as old as 3580 yr B.P.     

Meiofauna of the western continental shelf of India,Arabian Sea

Meiofaunal standing stock and nematode community structure were investigated in the western continental shelf of India by collecting samples from every degree square of the shelf during two cruises of the FORV (Fishery and Oceanographic Research Vessel) Sagar Sampada, conducted in 1998 and 2001. Samples were collected from 30, 50, 100 and 200 m depths using a Smith Mc Intyre grab. Meiofaunal density ranged from 8 Ind. 10 cm⁻² to 1208 Ind. 10 cm⁻² and biomass from 0.07 mg 10 cm⁻² to 6.11 mg 10 cm⁻². Nematodes were the dominant meiofaunal group, contributing 88% of the density and 44% of the biomass. Harpacticoid copepods were the second important taxa, contributing 8% of both biomass and density. Altogether, 154 species of nematodes belonging to 28 families were recorded from the study area. Numerically, Desmodora spp., Dorylaimopsis sp., Tricoma spp., Theristus spp. and Halalaimus spp. were the dominant species. In general, there was a decrease in biomass and density of meiofauna and species diversity of nematodes with increase in depth. There was a 67% drop in species number from 51 to 100 m (106 species) to the shelf edge (35 species). Species richness and diversity indices showed consistent decrease with depth. The species dominance index was higher below 150 m depth. ANOSIM (from PRIMER) showed a significant difference between the nematodes of the near shore and shelf edge. Latitudinal variation was observed only in the number of nematode species. Biomass and abundance of nematodes were found to increase from coarse to fine sediment, while copepods showed an opposite trend. Multivariate analyses of nematode communities did not reveal any latitudinal or substratum differences. Variables such as depth, latitude, organic matter (OM) and amount of clay were the most relevant parameters influencing the biomass and density of meiofauna, while depth and temperature were the important parameters explaining the distribution of the nematode communities along the western Indian shelf.     

秋季东海内陆架悬浮体分布特征

秋季是处于夏、冬季之交的过渡季节,夏季风减弱、冬季风增强的背景下海洋水文泥沙环境有独特特征,关于该时期悬浮体分布特征的研究较少.本文基于东海内陆架2016、2017与2018年秋季悬浮体及温盐数据,分析该海域秋季悬浮体浓度的水平和垂向分布特征.结果表明:悬浮体浓度近岸高于远岸,浓度等值线大致平行于等深线,近底层悬浮体浓...     

On the large-scale and mesoscale variability of thermohaline characteristics in the north-eastern part of the Black Sea

The data collected during an 18-day station and nine hydrologic surveys have been analysed. Mesoscale and large-scale temperature and salinity oscillations were revealed. Mesoscale oscillations in the sea surface layer are induced by the diurnal course of solar radiation, and in the seasonal thermocline layer by internal waves with a predominant 6–10 h periodicity. Large-scale fluctuations are related to the passage of clockwise (cold) and anticlockwise (warm) meanders and vortices. It has been determined that the contribution of large-scale temperature and salinity oscillations to the total variability is 1·5 to 3-fold larger than that of the mesoscale ones.Translated by Vladimir A. Puchkin.