Phosphogenesis on selected low atolls in the near-equatorial part of the Western Indian Ocean

The compositions, structures, and microstructures of different types of phosphorites and poorly phosphatized rocks from low atolls in the near-equatorial part of the Western Indian Ocean are described. The rocks were examined under optical and scanning microscopes using microprobing techniques and etching of selected samples with weak solvents as well as with the help of chemical analyses. It is proved that phosphorites have been formed owing to the uneven phosphatization of the primary carbonate rocks; the degree of their phosphatization ranges from traces to 40% P₂O₅. In the phosphorites, numerous organic remains were encountered; they included fragments of plankton, debris of tortoise shells, and coccoidal and filamentous bacteria-like formations. It is suggested that the phosphorites were formed due to the high local biological productivity over the outer edges of coral reefs and are not related to guano accumulation or to endoupwelling.     

Quaternary phosphatized limestones with initial Fe-Mn mineralization from the Kammu Seamount (Milwaukee Seamounts, northern Pacific)

Phosphatized biogenic limestones and phosphorites with initial Fe-Mn mineralization dredged from the summit surface of the Kammu Seamount (Milwaukee Seamounts, northwestern Pacific) are studied. The rocks are largely composed of nannofossils and planktonic foraminifers with an admixture of benthic foraminifers, bryozoans, and other organic remains, presumably including bacterial ones. The nannofosssil and foraminiferal assemblages indicate the Quaternary age of the sediments, and their phosphatization is consistent with the phosphatization age determined previously based on nonequilibrium uranium (within the limits of 1 My). The age of phosphatization and the Fe-Mn mineralization in the sediments from Pacific seamounts that young implies the dependence of these ore-forming processes on oceanic environments favorable for ore accumulation rather than on their age.     

Changes in the shoreline caused by coastal structures

A model is described that was designed to predict the shoreline changes due to the most widely distributed types of coastal structures such as groins, jetties, breakwaters, and access channels, which disturb the alongshore sediment fluxes. The key assumptions based on empirical data are related to the extension of the areas with the sediment excess and deficit. It is shown that the most important factors are, on the one hand, the size of the structure and the depth of its location and, on the other hand, the width of the alongshore sediment flux and the depth at its outer edge. The relations between these parameters determine the spatial scales of the morphology perturbations at a given coast. The temporal scale of the shoreline changes considered is restricted to the period a few years after the structure was built. The input data and the typical output results are illustrated by an example of calculations.     

Generation of normal atmospheric modes by stratospheric vacillations

A number of numerical experiments were performed with the use of the middle and upper atmosphere model (MUAM). In these experiments, the atmospheric response to an external excitation in the troposphere was calculated and internal stratospheric vacillations caused by the interaction of stationary planetary waves (SPWs) with the zonal mean flow were modeled. The MUAM is shown to well reproduce the known high-frequency global resonance responses of the atmosphere to an external excitation. The results of modeling show that the stratospheric vacillations caused by the interaction of SPWs and the mean flow are responsible for the generation of low-frequency normal modes in the lower and middle atmosphere. The activity of normal atmospheric modes in the troposphere and stratosphere is noted to increase simultaneously with the development of sudden stratospheric warmings. However, in order to understand which process is primary, an additional analysis of the results of numerical experiments and stratospheric data is necessary. It is inferred that, for an adequate modeling of stratospheric vacillation cycles, atmospheric general circulation models must be capable of reproducing global resonance properties of the atmosphere.     

Analysis of the magnetic anomaly field of the volcanic district of the Bay of Naples, Italy

We here present and discuss the results of the analysis and qualitative interpretation of two magnetic surveys performed in the Bay of Naples in 1998 and 2000. A map of the Bay of Naples based on the data acquired during these surveys has already been published by the Italian CNR-IAMC Research Institute. We re-processed the same data to produce maps of the pole reduced, analytic signal and horizontal derivative data and correlated them with the bathymetry and the gravimetric data of the area. The analysis shows strong anomalies in the NW and NE volcanic areas of the Bay of Naples, while the central area seems magnetically quiet. In the Phlegrean area the maps clearly show the southern rim of the Phlegrean caldera and demonstrate that while the Magnaghi Canyon is correlated to gravimetric highs and magnetic structures, and can therefore be interpreted as an active lineament, most of Dohrn Canyon is not characterized by volcanic activity and does not correlate to any gravimetric or magnetic structures. An important round-shaped magnetic anomaly is for the first time identified in the central slope of the gulf between the two canyons, probably correlated to a large buried volcanic edifice. In the Vesuvian area some intense circular anomalies, aligned in the NNW–SSE direction, are localized in the Torre del Greco and Torre Annunziata offshore, related to the submerged part of Vesuvius and possibly connected to buried vents.     

On the behavior of stratospheric ozone in the western Arctic during the 2003–2004 winter and spring

We present the results of simultaneous measurements of variations in the ozone layer in the north-western Arctic conducted with the help of different instruments. It is shown that, in the winter of 2003–2004, when the stratosphere was relatively warm and the wave activity was high, spatial inhomogeneities in the field of ozone distribution were observed. For April 2004, we detect a decrease in the ozone content in the range of heights between 25 and 40 km. This decrease was recorded simultaneously by the HALOE, SAGE, and POAM satellite instruments.     

Statistical relations of the run-up height of Tsunami waves to the distance and energy of the source

A statistical analysis of the relation between the run-up height of historical tsunami events and the distance and magnitude of the source was performed on the basis of the known Historical Tsunami Data Base [5]. The sample from the database used for the analysis comprises 5638 run-ups caused by 628 seismic events. This analysis, together with the dimensionality theory, shows that the statistical average of the run-up height is inversely proportional to the distance from the source to a power close to 1/2 (that is characteristic of the cylindrically symmetrical case) and directly proportional to the 3/8 power of the earthquake energy.     

Wind-induced motion of water in shallow-water closed basins

The motion of water induced by tangential wind stresses in a circular basin of finite depth is studied by the finite-element method. The dependences of vertical displacements of the surface of the basin and the field of horizontal wave currents on the topography of the bottom and the direction of the wind are analyzed. The transformations of wind-induced disturbances observed after termination of the wind action are investigated.Translated from Morskoi Gidrofizicheskii Zhurnal, No. 5, pp. 35–44, September–October, 2004.This revised version was published online in May 2005 with corrections to cover date.     

On the possible mechanism of the intensification of the vertical exchange in the ocean during earthquakes

In recent years, some papers reported events of the lowering of the temperature of the sea surface subsequent to earthquakes. This paper is devoted to a discussion of the possible mechanism of the intensification of the mixing of seawater under earthquakes. The possible role of the intensive turbidity flows that are sometimes generated in the near-bottom layer over a sloping bottom subsequent to earthquakes is discussed. The estimates made on the basis of a semiempirical theory of turbulence show that the shear currents caused by these flows can lead to a fast turbulization and mixing of rather thick water layers.     

Field measurements of the vertical shears for a drift current

We describe the procedure of field experiments aimed at measuring the vertical profiles of the vectors of a drift current with the help of quasi-Lagrangian drifters. We present the data on the vertical shears of the current at depths of 0.5–5 m obtained under the conditions of neutral stratification in the upper 5-m layer of the sea in the presence of weak and moderate winds. The correspondence of the obtained data to the concept according to which the subsurface layer of the sea is regarded as a near-wall turbulent layer with Ekman current located below is analyzed. A conclusion is made that the results of measurements correspond, on the average, to the classical concepts demonstrating both the region of logarithmic sublayer and its transition into the Ekman spiral. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 1, pp. 32–44, January–February, 2007.