Vertical structure of seasonal climatic fields of the sea water temperature and salinity in front of the Bulgarian Black Sea coast

Refined results from climatic seasonal averaging of data from multi-years in-situ measurements of fields of the water temperature T and salinity S are presented. The historical data set used consists of more than 21000 hydrological stations and is built on the base of information from SeaDataNet infrastructure. The vertical hydrological structure of the coastal, open shelf, continental slope, and deep-sea water in front of the Bulgarian coast stretching 32ËšE is described. As distinct from both the most complete of the present-day hydrological arrays prepared by V. Tuzhilkin and V. Belokopitov on a regular horizontally mesh for the entire Black sea basin, in this study the water area is divided into several regions according to their hydrodynamical and oceanographical characteristics. The layer`s centers between next horizons: 0, 10, 20, 30, 50, 80, 120, 180, 250, 350, 500, 800, 1000, 1250, 1500, 2250 m are used describing the vertical peculiarities of T and S from the seasurface to the bottom. Principal features of the seasonal climatic variability of the thermohaline fields in the study water area are shown. The results obtained give possibility for assessments in wide range of fields relevant to external effects both from natural and anthropogenic character upon the marine environment

The Black Sea general circulation and climatic temperature and salinity fields

The Black Sea is a nearly enclosed ocean basin, exhibiting many features common with larger ocean basins. Lacking an open boundary and having a limited exchange with sources of fresh and salt water, this basin is an ideal laboratory for developing and evaluating numerical circulation models. The present report describes one numerical model of the Black Sea, developed by Bulgarian and Russian scientists. The new approach has the advantages of both diagnostic models (incorporation of experimental data) and prognostic models (producing hydrodynamical adjustment and filtered fields). Successive application of diagnostic and prognostic models is used. The temperature and salinity fields obtained from observations, and currents obtained from diagnostic models, are used as the initial approximation to the prognostic model. Judicious selection of an integration time prevents over-smoothing of the results while preserving the stability of the solution. Using this model, caculations have been made at 25 levels over a grid interval of 0.25° (latitude) by 0.5°. Input data consist of nearly 50,000 observations taken over nearly 100 years, averaged over 0.5° by 0.5° cells. Seasonal fields of temperature, salinity, and velocity form the output of these experiments. The results provide the basis for various hypotheses that must be tested using future field observations and more sophisticated models

Modelling sub-surface dynamics in the Black Sea

Dependency of major hydrophysical/chemical features of highly stratified basins on density surfaces in the vertical makes isopycnic models an attractive tool for simulating the dynamics of marginal marine environments such as the Black Sea because of the ability of these models to restrict vertical transport to some desirable degree. In the present work the seasonal variations of the subsurface dynamics of the Black Sea are investigated using an isopycnic model. Particular attention is given to the interfaces of the Cold inter-mediate layer and Suboxic layer and finally, the deep layer circulation in the basin is studied. It appears that although the depth range of the base of the Cold intermediate layer and the lower Soboxic layer interface do not change seasonally, their horizontal distribution is defined by the upper layer dynamics of the basin. Cyclonic surface circulation diminishes with increasing depth and the deep layer circulation is characterised by an anti-cyclonic rim current driven by density gradients created from river runoff and the influx of Mediterranean water. (C) 2002 Ifremer/CNRS/IRD/Editions scientifiques et medicales Elsevier SAS. All rights reserved.La liaison entre les facteurs hydrologiques et chimiques et les densités de surface dans les mers stratifiées rend attractive lˈutilisation de modèles isopycnaux pour simuler la dynamique de mers comme la mer Noire. Ce modèle réduit en effet le transport vertical à un niveau acceptable. Les variations saisonnières de la dynamique de sub-surface de la Mer Noire ont été simulées en se servant dˈun modèle isopycne. Une attention particulière a été portée aux interfaces entre la couche intermédiaire froide et la couche faiblement oxygénée. Finalement, la circulation profonde du bassin est étudiée. Alors que le niveau dˈimmersion de la base intermédiaire et de lˈinterface inférieure de la couche sous- oxygénée ne présentent pas de fluctuations saisonnières, leur répartition horizontale dépend de la dynamique de la couche de surface. La circulation cyclonique superficielle diminue quand la profondeur augmente et la circulation profonde est caractérisée par un courant annulaire anticyclonique entraîné par le gradient de densité crée par lˈapport dˈeau douce et lˈentrée d’eau méditerranéenne