On diapycnal mixing induced by internal tidal waves in the Arctic Ocean

In order to reproduce the diapycnal mixing induced by internal tidal waves (ITWs) in the Arctic Ocean, we use a modified version of the three-dimensional finite-element hydrothermodynamic model QUODDY-4. We found that the average (over the tidal cycle) and integral (by depth) baroclinic tidal energy dissipation rate in individual areas of the Siberian continental shelf and in the straits between the Canadian Arctic archipelago are much higher than in the open ocean and its values on ridges and troughs are qualitatively similar to one another. Moreover, in the area of open-ocean ridges, the baroclinic tidal energy dissipation rate increases as it approaches the bottom, but only in the bottom boundary layer; on the Mid-Atlantic and Hawaii ridges, such an increase is observed within a few hundreds of meters away from the bottom. The average (in area and depth of the open ocean) coefficient of diapycnal mixing defined by the baroclinic tidal energy dissipation rate is higher than the coefficient of molecular kinematic viscosity and only a few times lower than the canonical value of the coefficient of vertical turbulent viscosity, which is used in models of global oceanic circulation. Coupled with the reasoning on the localization of baroclinic tidal energy dissipation, this fact leads to the conclusion that disregarding the contribution that ITW-induced diapycnal mixing makes to the ocean-climate formation is hardly justified.     

On features of structure of bottom gravity current frontal zone

The results of qualitative laboratory and numerical experiments on two-dimensional non-linear model are described, aiming at an investigation of the structure of the front of bottom gravity current. Non-coincidence of frontal interfaces in density and velocity fields within the bottom gravity current leading (frontal) part is stated on the base of comparative analysis of numerical and laboratory experiments. This fact is experimentally confirmed by field example of marine water inflow into a brackish lagoon. The density gradient along the stream line is shown to be an additional effective criterion for the localization of the frontal zone.     

Thermodynamic characteristics of water in natural water bodies with a high mineralization

To adequately describe the hydrophysical processes in water bodies with a high mineralization, it is necessary to take into account the dependence that the thermodynamic characteristics of water have on the amount of salts contained in it. This work investigates some widely known formulas for calculating a number of thermodynamic parameters of mineralized water. The density, freezing temperature, specific heat of evaporation, and relative pressure of saturated vapor over the surface are considered. The possibilities of using these formulas when modeling hydrophysical processes in water bodies with salinity in the range of 0–250 pro mille are analyzed. It is shown that the formulas under consideration should be used when the salinity does not exceed 100 pro mille. If the mineralization is higher, it is necessary to elaborate more suitable formulas on the basis of an approximation of in situ data or data from handbooks.     

Optical characteristics of coastal waters and atmosphere near the south coast of the crimea at the end of summer 2008

We present the results of measurements of optical characteristics of waters (the beam attenuation coefficient, volume scattering function, sea water reflectance, and Secchi depth) and optical characteristics of the atmosphere (aerosol optical thickness, content of vapors, and the ?ngstr?m exponent) carried out in September 2008 on the oceanographic platform near Katsiveli. We carried out the comparative analysis of hydrooptical characteristics measured in various years. The optical type of sea waters in the period of observations is determined.     

Circulation in the southwestern part of the Kara Sea in September 2007

During cruise 54 of the R/V Akademik Mstislav Keldysh to the southwestern Kara Sea (September 6 to October 7, 2007), a large amount of hydrophysical data with unique spatial resolution was obtained on the basis of measurements using different instruments. The analysis of the data gave us the possibility to study the dynamics and hydrological structure of the southwestern Kara Sea basin. The main elements of the general circulation are the following: the Yamal Current, the Eastern Novaya Zemlya Current, and the St. Anna Trough Current. All these currents are topographically controlled; they flow over the bottom slopes along the isobaths. The Yamal Current begins at the Kara Gates Strait and turns to the east as part of the cyclonic circulation. Then, it turns to the north and propagates along the Yamal coast over the 100-m isobath. The Eastern Novaya Zemlya Current (its core is located over the eastern slope of the Novaya Zemlya Trough) flows to the northeast. Near the northern edge of Novaya Zemlya, it encounters the St. Anna Trough Current, separates from the coast, and flows practically to the east merging with the continuation of the Yamal Current. A strong frontal zone is formed in the region where the two currents merge above the threshold that separates the St. Anna Trough from the Novaya Zemlya Trough and divides the warm and saline Arctic waters from the cooler and fresher waters of the southwestern part of the Kara Sea. This threshold, whose depth does not exceed 100–150 m, is a barrier that prevents the spreading of the Barents Sea and Arctic waters to the southwestern part of the Kara Sea basin through the St. Anna Trough.     

Deterministic non-linear wave prediction using probe data

The accurate prediction of non-linear sea states represents a great challenge, with a number of applications in oceanography, marine engineering, security of people and marine transportation, etc. In this paper, we report on the development of two efficient deterministic prediction models for 2D irregular wave-fields. These models are based on the exploitation of wave elevation time series given by one or more probes and on the use of two different numerical models for the wave-fields simulation. Two effective data assimilation processes are developed to improve the wave-field estimates obtained from the study of one or several probe signals, so that we obtain proper initial conditions for the forecast. The assimilation schemes have been validated on the reconstruction of model-generated observations and accurate predictions of the corresponding synthetic wave-fields evolution have been obtained.     

Geochemical and microbiological characteristics of sediments near the Malenky mud volcano (Lake Baikal, Russia), with evidence of Archaea intermediate between the marine anaerobic methanotrophs ANME-2 and ANME-3

Detailed lithological, biogeochemical and molecular biological analyses of core sediments collected in 2002–2006 from the vicinity of the Malenky mud volcano, Lake Baikal, reveal considerable spatial variations in pore water chemical composition, with total concentrations of dissolved salts varying from 0.1 to 1.8‰. Values of methane δ¹³С in the sediments suggest a biogenic origin (δ¹³С_min. ?61.3‰, δ¹³С_max. ?72.9‰). Rates of sulphate reduction varied from 0.001 to 0.7 nmol cm^?3 day^?1, of autotrophic methanogenesis from 0.01 to 2.98 nmol CH₄ cm^?3 day^?1, and of anaerobic oxidation of methane from 0 to 12.3 nmol cm^?3 day^?1. These results indicate that methanogenic processes dominate in gas hydrate-bearing sediments of Lake Baikal. Based on clone libraries of 16S rRNA genes amplified with Bacteria- and Archaea-specific primers, investigation of microbial diversity in gas hydrate-bearing sediments revealed bacterial 16S rRNA clones classified as Deltaproteobacteria, Gammaproteobacteria, Chloroflexi and OP11. Archaeal clone sequences are related to the Crenarchaeota and Euryarchaeota. Baikal sequences of Archaea form a distinct cluster occupying an intermediate position between the marine groups ANME-2 and ANME-3 of anaerobic methanotrophs.     

Petroleum prospectivity of the Canada Basin, Arctic Ocean

Reconnaissance seismic reflection data indicate that Canada Basin is a >700,000 sq. km. remnant of the Amerasia Basin of the Arctic Ocean that lies south of the Alpha-Mendeleev Large Igneous Province, which was constructed across the northern part of the Amerasia Basin between about 127 and 89-83.5 Ma. Canada Basin was filled by Early Jurassic to Holocene detritus from the Beaufort-Mackenzie Deltaic System, which drains the northern third of interior North America, with sizable contributions from Alaska and Northwest Canada. The basin contains roughly 5 or 6 million cubic km of sediment. Three fourths or more of this volume generates low amplitude seismic reflections, interpreted to represent hemipelagic deposits, which contain lenses to extensive interbeds of moderate amplitude reflections interpreted to represent unconfined turbidite and amalgamated channel deposits.Extrapolation from Arctic Alaska and Northwest Canada suggests that three fourths of the section in Canada Basin is correlative with stratigraphic sequences in these areas that contain intervals of hydrocarbon source rocks. In addition, worldwide heat flow averages suggest that about two thirds of Canada Basin lies in the oil or gas windows. Structural, stratigraphic and combined structural and stratigraphic features of local to regional occurrence offer exploration targets in Canada Basin, and at least one of these contains bright spots. However, deep water (to almost 4000 m), remoteness from harbors and markets, and thick accumulations of seasonal to permanent sea ice (until its possible removal by global warming later this century) will require the discovery of very large deposits for commercial success in most parts of Canada Basin.     

Spectral contributions of the components of seawater to the beam attenuation coefficient in surface waters of the Mediterranean Sea

We compute model spectra of the beam attenuation coefficient in surface waters of the Mediterranean Sea. These spectra are used to determine the contribution of the components of seawater (suspended matter, yellow substance, pigments of phytoplankton, and pure water) to the beam attenuation coefficient in different types of seawater. For the surface waters, we establish the relationship between the light scattering coefficient and the attenuation coefficient at a wavelength of 547 nm and determine the background (limiting minimum) value of the coefficient of absorption by the yellow substance in waters of the Mediterranean Sea. It is compared with the values of the same parameter for some other basins (Black Sea, Lake Baikal, Baltic Sea, and oceanic waters).     

Spatial variability of the chlorophyll <Emphasis Type="Italic">a</Emphasis> and the specific structure of the phytoplankton in the northwestern part of the Sea of Japan during the winter period

To evaluate the structure and photosynthetic activity of the phytoplankton of the northwestern part of the Sea of Japan, the results of the surveys conducted from February 26 to March 9, 2003, during the 30th cruise of the R/V Akademik Lavrentyev were used. The species composition was considered taking into account the influences of the hydrological conditions. In particular, the studied water area was divided into four zones with various sizes of the mixed layer depth (MLD). An inverse relationship between the MLD and the content of chlorophyll a (Chl a) in various zones was established. The diatom algae were the basic dominants of the composite structure of the phytoplankton everywhere. It is revealed that, at a MLD increase, smaller forms of microalgae receive development. The intrapopulation relations are caused by the adaptation of various species of phytoplankton to the influence of external factors, among which the size of MLD is fundamental.