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.     

Out of Africa: detrital zircon provenance of central Madagascar and Neoproterozoic terrane transfer across the Mozambique Ocean

The Neoproterozoic East African Orogen reflects closure of the Mozambique Ocean and collision of the Congo and Dharwar cratons. This palaeogeographical change and its environmental consequences are poorly understood, but new detrital zircon ages from Madagascar and published data from elsewhere provide evidence for multiple ocean basins and two-stage collision. We propose that central Madagascar rifted from the Congo Craton and crossed a Palaeomozambique Ocean to collide with the Dharwar Craton at c. 700 Ma, opening a Neomozambique Ocean in its wake. Closure of the Neomozambique Ocean at c. 600 Ma juxtaposed the Congo and Dharwar cratons and resulted in prolonged collisional orogenesis concluding at c. 500 Ma.     

Photo—gravitational effects in the two—body problem

The effect of the radiation-pressure in the problem of the two bodies is analysed. It is found that such an effect is the same as that of reducing the stellar mass, m, by the factor p (0 ≤ p ≤ 1). The case p < 0 leads to stellar instability and, consequently, it is not considered here. The problem of the mass determination from spectroscopic observations is reviewed and an iterative method is recommended.     

The Crust–Mantle Carbon Cycle and Origin of Abiogenic Hydrocarbons

Oceanology - Abstract—The paper studies carbon transformation and transfer processes in the crust and mantle. Sediments dragged into subduction zones are dewatered, broken down, and altered...     

A Method for Obtaining the Nuclear Component in Active Galaxies

We present a new method for the obtention of the nuclear component of active galatic nuclei, that relies on the convolution of a two-dimensional model of the host galaxy, based on seeing-free morphological parameters, with the seeing PSF. The procedure overcomes some limitations of the methods currently in use and does not assume that the nucleus is unresolved. This revised version was published online in July 2006 with corrections to the Cover Date.     

Response of single benthic metrics and multi-metric methods to anthropogenic pressure gradients, in five distinct European coastal and transitional ecosystems

In recent times many benthic indices have been proposed to assess the ecological quality of marine waters worldwide. In this study we compared single metrics and multi-metric methods to assess coastal and transitional benthic status along human pressure gradients in five distinct environments across Europe: Varna bay and lake (Bulgaria), Lesina lagoon (Italy), Mondego estuary (Portugal), Basque coast (Spain) and Oslofjord (Norway). Hence, 13 single metrics (abundance, number of taxa, and several diversity and sensitivity indices) and eight of the most common indices used within the European Water Framework Directive (WFD) for benthic assessment were selected: index of size spectra (ISS), Benthic assessment tool (BAT), Norwegian quality index (NQI), Multivariate AMBI (M-AMBI), Benthic quality index (BQI), (Benthic ecosystem quality index (BEQI), Benthic index based on taxonomic sufficiency (BITS), and infaunal quality index (IQI). Within each system, sampling sites were ordered in an increasing pressure gradient according to a preliminary classification based on professional judgement. The different indices are largely consistent in their response to pressure gradient, except in some particular cases (i.e. BITS, in all cases, or ISS when a low number of individuals is present). Inconsistencies between indicator responses were most pronounced in transitional waters (i.e. IQI, BEQI), highlighting the difficulties of the generic application of indicators to all marine, estuarine and lagoonal environments. However, some of the single (i.e. ecological groups approach, diversity, richness) and multi-metric methods (i.e. BAT, M-AMBI, NQI) were able to detect such gradients both in transitional and coastal environments, being these multi-metric methods more consistent in the detection than single indices. This study highlights the importance of survey design and good reference conditions for some indicators. The agreement observed between different methodologies and their ability to detect quality trends across distinct environments constitutes a promising result for the implementation of the WFD’s monitoring plans. Moreover, these results have management implications, regarding the dangers of misclassification, uncertainty in the assessment, use of conflicting indices, and testing and validation of indices.     

Acute Toxicity of Sodium Nitrite on Channa punctatus (BLOCH) and Mystus (Mystus) vittatus (BLOCH)

This paper deals with the toxicity of sodium nitrite to freshwater fishes, Channa punctatus (BL.) and Mystus (M). vittatus (Bl.) as to determine the acute toxicity. The LC 50 values were obtained by using a static bioassay method for a period of 24, 48, 72 and 96 hour intervals. The LC 50 values of sodium nitrite for C. punctatus were 375, 325, 250 and 200 ppm and for M. (M). vittatus 164, 140, 90 and 64 ppm, respectively. A profuse mucus secretion was evident at higher concentrations as compared to lower ones. The probable causes of mortality of the fishes are also discussed.     

An Aerosol Model of the Marine and Coastal Atmospheric Surface Layer

We present a microphysical model for the surface layer marine and coastal atmospheric aerosols that is based on long-term observations of size distributions for 0.01–100 µm particles. The fundamental feature of the model is a parameterization of amplitudes and widths for aerosol modes of the aerosol size distribution function (ASDF) as functions of fetch and wind speed. The shape of ASDF and its dependence on meteorological parameters, height above sea level (H), fetch (X), wind speed (U) and relative humidity (RH), are investigated. At present, the model covers the ranges H = 0–25 m, U?=?3–18 km s^?1, X?≤?120 km and RH?=?40–98%.

The latest version of the Marine Aerosol Extinction Profiles model (MaexPro) is described and applied to the computation and analysis of the spectral profiles of aerosol extinction coefficients α(λ) in the wavelength band λ?=?0.2–12 µm. MaexPro is based on the aforementioned aerosol model assuming spherically shaped aerosol particles and the well-known Mie theory.

The spectral profiles of α(λ) calculated by MaexPro are in good agreement with observational data and the numerical results obtained from the Navy Aerosol Model (NAM) and the Advanced Navy Aerosol Model (ANAM). Moreover, MaexPro was found to be an accurate and reliable tool for investigating the optical properties of atmospheric aerosols.     

Objective method for classifying air masses: an application to the analysis of Buenos Aires’ (Argentina) urban heat island intensity

Summary ?During recent years, numerous studies have examined the Buenos Aires urban climate, but the relationship between large-scale weather conditions and the Buenos Aires urban heat island (UHI) intensity has not been studied. The goal of this paper is to apply an objective synoptic climatological method to identify homogeneous air masses or weather types affecting Buenos Aires during winter, and to relate the results to the UHI intensity. A K-means clustering method was used to define six different air masses considering the 03:00, 09:00, 15:00 and 21:00 LT surface observations of dry bulb temperature, dew point, cloud cover, atmospheric pressure and wind direction and velocity at Ezeiza, the most rural meteorological station of the Buenos Aires metropolitan area (Fig. 1). Results show that the mean UHI intensity is at its maximum (2.8 °C) a few hours before sunrise when conditions are dominated by cold air masses associated with cold-core anticyclones, weak winds and low cloud cover. Inverse heat islands are found during the afternoon for all air masses indicating that surface processes are not dominant at that time. The relatively infrequent and warmest air mass is the only one that presents a mean negative urban-rural temperature difference (−0.1 °C) during the afternoon with the smallest diurnal cycle of the UHI intensity probably due to the prevailing high humidity and cloudy sky conditions. The paper provides an insight into the Buenos Aires urban–rural temperature difference under a variety of winter weather types and results could be useful to improve local daily temperature forecasts for the metropolitan area of Buenos Aires on the basis of the routine forecasts of weather types. Received October 24, 2001; revised June 12, 2002; accepted October 10, 2002