Acoustic properties of surface water masses in the tropical Atlantic and their seasonal variability

The peculiarities of the vertical hydroacoustic structure of surface water masses in the tropical Atlantic are reported. The near-surface acoustic channel in areas of strong freshening of oceanic waters by continental discharge and rainfall is studied. Quantitative characteristics of the seasonal variability of the channel's parameters are given. The mechanism responsible for the long-range acoustic conductivity in the upper layer of waters is analysed. The areas of maximum horizontal refraction in the near-surface layer are identified and the refraction angles of acoustic rays determined.Translated by V. Puchkin.     

Seasonal Variability of the Thermohaline Characteristics and Volumetric Statistical Parameters of Water Masses in the Drake Passage

On the basis of the many-year monthly average thermohaline data of the oceanographic array, we study some regularities of the seasonal cycle in the fields of temperature, salinity, and the characteristics of water masses in the Drake Passage. We obtain and analyze the amplitude and phase parameters of seasonal oscillations of the investigated quantities. By using the volumetric statistical T, S-analysis, we deduce quantitative estimates of the annual variations of the volumes of main water masses in the Drake Passage. Possible mechanisms responsible for the phenomena observed in this region are discussed.__________Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 62–73, November–December, 2004.     

Halite solubility in dead sea waters

The solubilities of halite in Dead Sea waters and in their mixtures with Mediterranean Sea waters were estimated using Pitzer's equations. The calculated halite saturation for Dead Sea waters sampled at various occasions during 1979–1983 is in good agreement with the naturally observed phenomenon of halite deposition at this time. A halite saturation curve for mixtures of Dead Sea and Mediterranean Sea waters has been obtained and permits the prediction of halite deposition in these mixtures on evaporation.     

Investigation of the Dependence of the Space Structure and Phase Characteristics of the First-Mode Internal Waves in the Atlantic Ocean on the Hydrological Conditions

By using the linear theory of internal waves in a continuously stratified ideal incompressible liquid of finite depth and hydrological data, we study the dispersion properties and space structure of the vertical velocity of the first mode of free internal waves in the Atlantic Ocean. The dependence of the characteristics of waves on the hydrological structure of waters is analyzed. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 4, pp. 3–10, July–August, 2005.     

Seasonal variability of geostrophic currents in the Atlantic Ocean according to the altimetry data

The monthly average values of the anomalies of the ocean level (according to the satellite data for 1992–2002) and the annual average dynamic heights (hydrological data) are used to compute the seasonal cycle of geostrophic currents on the surface of the Atlantic Ocean. It is shown that the west and east currents are intensified with a phase difference of several months. At the same time, their latitudinal displacements are quasisynchronous. A delay of the seasonal signal in the east-west direction of about 2–3 months (on the average) is typical of currents in the tropical zone of the Northern Hemisphere. On the contrary, in the South Atlantic, the seasonal signal propagates in the west-east direction and its phase delay can be as large as almost six months. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 3, pp. 60–71, May–June, 2006.     

Variability of the gravitational lens UM 673 in 2003–2005

Results of VRI photometry of two components of the gravitationally lensed quasar UM 673 in 2003–2005 are presented. The observational data were obtained on the 1.5-m telescope of the Maidanak observatory. During the monitoring of the system, considerable brightness variations in components A and B with amplitudes of about 0.2 ^m were recorded, demonstrating variability of the quasar. The increase in the brightness of the components was accompanied by reddening of their V-R color indices. Analysis of the brightness and color variations of the components shows no variations related to microlensing.     

Natural and anthropogenic forcing of Holocene lake ecosystem development at Lake Uddelermeer (The Netherlands)

Lake Uddelermeer (The Netherlands) is characterized by turbid conditions and annual blooms of toxic cyanobacteria, which are supposed to be the result of increased agricultural activity in the twentieth century AD. We applied a combination of classic palaeoecological proxies and novel geochemical proxies to the Holocene sediment record of Lake Uddelermeer (The Netherlands) in order to reconstruct the natural variability of the lake ecosystem and to identify the drivers of the change to the turbid conditions that currently characterize this lake. We show that the lake ecosystem was characterized by a mix of aquatic macrophytes and abundant phytoplankton between 11,500 and 6000 cal year BP. A transition to a lake ecosystem with clear-water conditions and relatively high abundances of ‘isoetids’ coincides with the first signs of human impact on the landscape around Lake Uddelermeer during the Early Neolithic (ca. 6000 cal year BP). An abrupt and dramatic ecosystem shift can be seen at ca. 1030 cal year BP when increases in the abundance of algal microfossils and concentrations of sedimentary pigments indicate a transition to a turbid phytoplankton-dominated state. Finally, a strong increase in concentrations of plant and faecal biomarkers is observed around 1950 AD. Canonical Correspondence Analysis suggests that reconstructed lake ecosystem changes are best explained by environmental drivers that show long-term gradual changes (sediment age, water depth). These combined results document the long-term anthropogenic impact on the ecosystem of Lake Uddelermeer and provide evidence for pre-Industrial Era signs of eutrophication.