Seasonal variability of the equatorial undercurrent termination and associated salinity maximum in the Gulf of Guinea

The termination of the Equatorial Undercurrent (EUC) in the eastern equatorial Atlantic during boreal summer and fall, and the fate of the associated saline water masses, are analyzed from in situ hydrological and currents data collected during 19 hydrographic cruises between 2000 and 2007, complemented by observations from Argo profiling floats and PIRATA moorings, and from a numerical simulation of the Tropical Atlantic Ocean for the period 1993–2007. An intense variability of the circulation and hydrological properties is evidenced from observations in the upper thermocline (24.5–26.2 isopycnal layer) between June and November. During early boreal summer, saline water masses are transported eastward in the upper thermocline to the African coast within the EUC, and recirculate westward on both sides of the EUC. In mid-boreal summer, the EUC weakens in the upper thermocline and the equatorial salinity maximum disappears due to intense mixing with the surface waters during the upwelling season. The extra-equatorial salinity maxima are also partially eroded during the boreal summer, with a slight poleward migration of the southern hemisphere maximum until late boreal summer. The upper EUC reappears in September, feeding again the eastern equatorial Atlantic with saline waters until boreal spring. During December–January, numerical results suggest a second seasonal weakening of the EUC in the Gulf of Guinea, with a partial erosion of the associated equatorial salinity maximum.     

Ocean swell variability along the northern coast of the Gulf of Guinea

This study analyses a 4.5 year (September 2009–March 2014) time-series of remotely-sensed data of altimeter significant wave heights to describe the temporal and spatial variability of ocean swells along the northern coast of the Gulf of Guinea. The NOAA WAVEWATCH III (NWW3) wave model data were used with altimeter data to determine the origin of the swells that occur along the coast of Côte d'Ivoire in West Africa. We show that the ocean swells along the northern coast of the Gulf of Guinea are generated in the Southern Ocean and then propagate from south to north in the South Atlantic Ocean, before turning south-west to north-east close to the coast. This finding corroborates previous studies in this area. The remotely-sensed and NWW3 significant wave height data captured the strong swells observed along the coast of Côte d'Ivoire from the period 28 August–3 September 2011, which were responsible for an extreme erosion event of more than 12?m along that country's coastline. This extreme event was triggered by a strong storm in the region between 40° and 60° S that occurred eight days previously in the South Atlantic. The waves propagated as swells at a speed of about 875?km day–¹ before reaching the northern African coast.     

Tungsten accessory minerals in lithium-fluoric granites of the Russian Far East

By means of the technique of local analysis, the presence of a wide variety of tungsten and tungsten-containing accessories was first revealed in the composition of lithium-fluoric granites of the Far East, which represents a substantial similarity and regional peculiarity of these rocks. It was concluded that the tungsten accessory mineralization might be considered as an indication of the genetic relationship of the mineralization of the East Asian tin-tungsten zone to the Pacific rare-metal granites.     

Gahnite in Rare-Metal Metasomatic Rocks of the Verkhneurmiysky Ore Cluster,Amur River Region

A new finding of Zn-spinel (gahnite) in biotite metasomatic rock of the Verkhneurmiysky copper–tungsten–tin ore cluster is described in this paper, including the chemical composition of gahnite, its paragenesis, and place in the regional evolution history of hydrothermal processes. Gahnite is commonly localized in biotite–microcline metasomatic rocks at the lower subore stage of the greisen metasomatic column in proximity to the exocontact of the rare-metal granite massif. Gahnite from rare-metal ore occurrences belongs to the hercynite–gahnite–franklinite isomorphic series and contains significant isomorphic admixtures of iron (24.3%) and manganese (0.65%). Based on our results and earlier published data, it is suggested that gahnite can be a mineral-indicator of rare-metal metasomatism.     

Hydrogen and Carbon Groups in the Structures of Rock-Forming Minerals of Rocks of the Lithospheric Mantle: FTIR and STA + QMS Data

Using IR–Fourier spectrometry (FTIR) and simultaneous thermal analysis combined with quadrupole mass spectrometry of thermal decomposition products (STA + QMS), olivines and clinopyroxene from xenolites of spinel and garnet lherzolites contained in kimberlites and alkaline basalts were studied to confirm the occurrence of hydrogen and carbon within the structure of the minerals, as well as to specify the forms of H and C. The presence of hydroxyl ions (OH–) and molecules of crystal hydrate water (H₂Ocryst) along with CO₂, CH, CH₂, and CH₃ groups was detected, which remained within the structures of mantle minerals up to 1300°C (by the data of both techniques). The total water (OH–and H2Ocryst) was the prevailing component of the C–O–H system.