Diamonds from placers in western and central Africa: A problem of primary sources

This paper discusses diamonds and their accessory minerals from the Koidu kimberlites, placers on the Bafit River in Sierra Leone, and Chikapa placers in the Democratic Republic of Congo. Minerals from the placers are characterized by fine preservation and bear no evidence of long-term transportation. In placers, garnet, ilmenite and zircon have been found, but the specific features of their chemical composition do not coincide with those of minerals from kimberlites. Diamonds from the placers are of a mantle origin, but they have no direct analogs in the known kimberlite and lamproite pipes.     

Organic matter of the North Atlantic

The areas that we studied in the North Atlantic (53 and 60°N) and in the Labrador Sea in the summer were characterized by a wide variability of the concentrations of dissolved and particulate organic matter and its elemental composition both in the surface and in the deep waters. The concentrations of dissolved and particulate C_org varied within 69–360 μM and 0.7–25.6 μM, respectively; the N_org and P_org contents varied within 1.4–22.2 μM and 0.02–0.86 μM, respectively. The maximal concentrations were registered in the photic layer and in the zones of mixing between the waters of different genesis. The particulate matter contribution to the total organic matter (OM) content varied from 0.5 to 15.4%. The waters of the photic layer contained more particulate C_org than those of the near-bottom layer. The values of the C/N molar ratios from the surface to the bottom over the entire aquatic area surveyed varied 5-to 6-fold; at that, the values of the C/P molar ratios varied more than tenfold. In the most productive waters, the values of the C/N ratios were close to the Redfield ratios (6–10). The values of the C/P molar ratios varied from 160 in the photic layer to 4831 in the deep waters. The pronounced non-uniformity in the spatial distribution of the OM and its elemental composition is caused not only by the penetration of the waters of different origins but also by the changes in the microplankton metabolism under mixing of these waters.     

Instability of the thermal bar formed in a gravity current

The results of experiments concerning fresh water at the temperature more than 4°C released along a free surface into water with a temperature less than 4°C are presented. As a result of Relay-Taylor instability caused by the nonmonotonic dependence of water density on the temperature, the denser water initially sank to the inclined bottom. At the same time, a vertical front separating water masses less and greater than 4°C formed. In limnology such an effect is called the “thermal bar.” Under certain conditions along with the Relay-Taylor instability, the Kelvin-Helmholtz instability tending to destroy the vertical front was also observed. Corresponding illustrations are presented.     

Interaction of the Atmosphere and Lithosphere in the Minute Range of Periods

Doklady Earth Sciences - The interaction between the atmosphere and the lithosphere in the minute range of periods is considered. The technique of assessment of the influence of atmospheric...     

A New Approach to ID-TIMS U–Pb Dating of Cassiterite by the Example of the Pitkäranta Tin Deposit

Doklady Earth Sciences - A new technique for the complete dissolution of cassiterite, which makes it possible to determine the age of this mineral by U–Pb isotope dilution (ID-TIMS), has been...     

A cost–benefit appraisal of coastal managed realignment policy

European coasts are coming under increasing threat as a result of climate change from erosion and flooding. While coastal defences such as sea walls have been constructed since Roman times to protect human settlements from the sea, it is now increasingly recognised that these defences are unsustainable. The security provided by ‘hard’ engineered defences has encouraged development on the coast, and the defences themselves have led to the loss of intertidal habitat and the natural protection it provides.An alternative to maintaining ‘hard’ defences (hold-the-line) to protect land from increasing sea levels is managed realignment, where the engineered defences are deliberately breached. By allowing the coastline to recede to a new line of defence further inland, intertidal habitat is created providing natural protection from flooding and erosion.The study evaluates the economic efficiency—using cost–benefit analysis—of various managed realignment scenarios compared to a strategy of holding-the-line within the Humber estuary in North-east England. The results of this analysis show that managed realignment can be more economically efficient than holding-the-line over a sufficiently long time period—generally greater than 25 years. Sensitivity analysis demonstrates that results are more sensitive to the amount and value of intertidal habitat generated than they are to the amount and value of carbon stored by this habitat. Cost–benefit analysis is viewed as one component of a wider policy appraisal process within integrated coastal management.     

Naming undersea features of the Sea of Japan: History and modern problems

This communication is dedicated to the investigation history and naming of the undersea morphostructures of the Sea of Japan for the last 50 years. Many of them were first described and studied during long-term geological-geophysical investigations in this basin carried out by Russian scientists. The analysis of 60 names of its undersea feature names revealed that only approximately half of them are cited in the GEBCO Gazetteer some of the undersea morphostructures are known under two or more names, the origin of their names is unknown, or their names were chosen voluntarily. For maintaining the priority of Russian investigations, the nomenclature and names of the undersea features should be adjusted in accordance with the national and international principles and regulations.     

Structure,Matter Composition,and Deep Structure of the Oceanic Slope of the Central Kuril Islands: New Evidence

The results of reinterpretation of the geophysical data obtained during the study of the central sector of the Kuril Island Arc (2005–2010) are reported. The new boundaries of the shallow bedding of the basement and its block uplifts of varied composition are defined within the previously discovered zone of tectonic stretching and destruction of the Vityaz submarine ridge and interarc trough. Interblock depressions filled with sedimentary and volcanogenic-sedimentary rocks are distinguished. Areas represented by volcanoplutonic complexes including basic and sialic series (up to granite) are distinguished within the unbroken basement of the Vityaz Ridge. Intrusions and volcanic edifices composed of basic rocks are registered on the whole area studied. The relationship between the formation of the destruction zone and the geodynamic processes in the mantle is illustrated by the map of the Moho relief and structural-density model of the Earth’s crust.     

Observations of the Ushant tidal front in September 2007

The Ushant tidal front is the dominant feature of the summer season hydrological structure of the Iroise Sea. It separates tidally mixed coastal waters from thermally stratified open Celtic Sea waters. This article reports on observations made in September 2007 during two short cruises that took place aboard R/V “Côtes de la Manche”, and gives a general account of the physical structure of the front along one cross-frontal transect. The data set comprises data from a 4 month ADCP mooring, short CTD/fluorescence/nutrients transects, Lagrangian drifter trajectories, and HF radar surface current measurements. One finding is that the surface and bottom fronts, being affected by different dynamical influences, are not necessarily coincident in the vertical. This entails that the opposite density gradients located above and below the thermocline depth do not necessarily compensate, and can each be associated with a significant surface geostrophic expression. A second finding is that mixing effects bear a very strong influence on the thermal structure of the warm-water intrusions associated with frontal cyclonic eddies of the kind described by Pingree [1978. Cyclonic eddies and cross-frontal mixing. Journal of the Marine Biological Association of the United Kingdom 58 (4), 955–963].