Study of long-term variations in the Black Sea fields using an interdisciplinary physical and biogeochemical model

Using an interdisciplinary three-dimensional physical and biogeochemical model developed for the Black Sea, the long-term evolution of marine dynamics and ecosystem is investigated. The hydrophysical fields were calculated from a model of Black Sea circulation with assimilation of hydrographic survey and satellite measurement data from 1971 to 2001. The circulation model reproduces well processes of various scales in both space and time (particularly the seasonal course and interannual variability of main hydrophysical fields). The resulting flow fields are then used to calculate the long-term evolution of the components of the lower level of the food chain in the Black Sea ecosystem. The biogeochemical model used in the calculations is based on the nitrogen cycle and includes a parameterization of the main biological and chemical interactions and processes in the upper layer of the Black Sea. The numerical experiments indicated that the biogeochemical component of the model rather successfully reproduces the main features and evolution trends in the Black Sea ecosystem for the period under consideration: the growth in the phytoplankton biomass during eutrophication and changes in seasonal cycles of the main ecosystem components. Also, the hydrophysical processes were shown to be important for a reliable reproduction of long-term changes in the ecosystem.     

Data-computing technologies: A new stage in the development of operational oceanography

An analysis is given of the methods of operational oceanography based on measurements derived from satellite data, observations acquired by drifters and passing vessels, and modern simulations of marine and oceanic circulations. In addition, a historical review is conducted of the previous and current research in this field carried out in the Soviet Union, Ukraine, and Russia. A discussion is given of the principles underlying the design of an effective data-computing system (DCS) for solving the problems of operational oceanography and the implementation of the prototype system for the Black Sea within the joint research project of the Russian Academy of Sciences (RAS) and the National Academy of Sciences of Ukraine (NASU) “The Black Sea as an Ocean Simulation Model.” The effectiveness of applying the multicomponent splitting method in the construction of sea circulation models and specialized DCSs with integrated algorithms of variational assimilation of observational data is estimated. The concept of using the Black Sea as a testing site for innovations is developed. The underlying idea of the concept is the similarity of the Black Sea dynamics with processes in the oceans. The numerical Black Sea circulation models used in the project are described, their development areas are discussed, and the requirements to a Black Sea observing system are defined.     

Study of the possibility of the use of the magnetotelluric sounding method in the Arctic ocean with quantitative modeling

The task of the magnetotelluric (MT) sounding of the heterogeneous deep section of the Arctic ocean floor on the idealized model of gorst and graben lying on the typical oceanic, or continental Earth’s, crust is solved with the use of 3D quantitative modeling. In both cases, the sequence is covered by a layer of seawater with a thickness of 4 km. In this work, the difference in the MT sounding with the use of ocean-floor and surface equipment is considered. As a result, the conclusion was made that the floor equipment has a higher resolution than the surface equipment, in spite of the fact that the observations from the ice cover’s surface can be done more easily.     

Seasonal variability of climatic currents in the Caspian Sea reconstructed by assimilation of climatic temperature and salinity into the model of water circulation

We present the results of an analysis of the seasonal variability of current fields in the Caspian Sea, reconstructed by assimilation of climatic temperature and salinity into the primitive-equation model of water circulation on the basis of an algorithm for adaptive statistics of prediction errors. The sources in heat and salt transfer-diffusion equations depend on the spatial and temporal variability of the variances of prediction errors and one-dimensional (in the vertical coordinate) variances of measurement errors for temperature and salinity. The variances of prediction errors are adjusted at the moments of data assimilation in accordance with a simplified Kalman filter. The climatic circulation of waters in the Caspian Sea is shown to be highly varying. The maximum of its intensity over the entire depth is reached in February. The minimum of kinetic energy is observed in April. The currents in deep-sea areas are determined by the balance between wind and baroclinic factors of the formation of circulation with wind currents prevalent.     

The holocene history of the river deltasalong the arctic coast of Siberia

The evolution of estuarial geomorphological and sedimentary systems in the Late Holocene is considered using the river deltas along the Arctic coast of Siberia as an example. Presented are the stadial development patterns of the main morphogenetic types of estuarial systems for the period of stabilization of postglacial transgression of the World Ocean.     

Study of formation process of cold intermediate layer based on reanalysis of Black Sea hydrophysical fields for 1971–1993

A reanalysis of hydrophysical fields for 1971–1993 is used to study the formation mechanisms of the cold intermediate layer (CIL): the advective mechanism (associated with the advection of cold waters formed in the northwestern shelf (NWS)) and the convective mechanism (caused by wintertime convection inside cyclonic gyres in the central part of the sea). We consider the periods of alternating atmospheric conditions: the mild winter of 1980–1981, normal winter of 1987–1988, and cold winter of 1992–1993. Interannual features of replenishment and renewal of “old” CIL waters caused by these mechanisms are identified. In particular, cooled shelf waters sink along the continental slope and merge with “old” CIL waters during the mild winter of 1980–1981 more than 1 month later than during the cold winter 1992–1993 and more than 3 weeks later than during the normal winter of 1987–1988. The Sevastopol anticyclonic gyre and the northwest branch of the Black Sea Rim Current markedly influence the transformation of entrained cold NWS waters transported to the southwest and the central part of the water area. The local formation process of cold intermediate waters is found to be caused by the wintertime penetrating convection over domelike isosurfaces of temperature and salinity arising due to rising constant halocline (pycnocline) at the centers of cyclonic gyres because of the intensification of the wintertime circulation. Anomalously cold surface water, characterized by increased density, gradually sinks. An analysis of TS indices indicates that the transformed cold water spreads out over isopycnic surfaces with time, being entrained in cyclonic circulation and spreading throughout the sea, thus renewing “old” CIL waters.     

Relationship between variations in the electric field’s vertical component in Lake Baikal and solar activity

Based on the data of deepwater measurements of the electric field’s vertical component in Lake Baikal, the relationship between electric field variations and those in background X-ray solar radiation has been revealed. A high correlation between these variations within periods of more than three months has been discovered.     

Black Sea Intrapycnocline Lenses according to the Results of a Numerical Simulation of Basin Circulation

Izvestiya, Atmospheric and Oceanic Physics - The exact scenario of the propagation of highly saline Marmora Sea waters in the Black Sea basin is not clear. Together with river runoff, they form the...     

Morphostructures and Sedimentary Cover Structure of the Inner Shelf of Western Crimea

Oceanology - The article presents the results of geophysical and geomorphological works on the western shelf of the Crimean Peninsula (Yevpatoriya–Balaklava). The sedimentary sequence...     

Prospects of magnetotelluric sounding in some large structures in the Arctic ocean

In the work, the results of modeling of electric resistivity distribution at the Gakkel and Alpha-Mendeleev underwater ridges are given. Based on the seismostratigraphic models, the apparent resistivity curves at a few points of the profile at the crossing of the ridge were constructed. The advantages and disad-vantages of the MT sounding method are presented. The results obtained can be used for future experiments.