Geochemistry of high H2 and CH4 vent fluids issuing from ultramafic rocks at the Rainbow hydrothermal field (36°14′N, MAR)

The Flores diving cruise was part of the MAST III-AMORES (1995-1998) program funded by the European Union. One of the major achievements of the Flores cruise was the discovery of the Rainbow hydrothermal field hosted in ultramafic rocks south of the Amar segment on the Mid-Atlantic ridge (MAR). The Rainbow hydrothermal fluids exhibit temperatures of 365 °C, pH of 2.8, high chlorinity (750 mmol/kg), and low silica (6.9 mmol/kg). The uniformity in endmember major, minor, trace element concentrations and gas contents suggests that all Rainbow fluids originate from the same deep source. Although H₂S content is relatively low (1.20 mmol/kg), all vent fluids show extraordinary high H₂ (16 mmol/kg), CH₄ (2.5 mmol/kg) and CO (5 μmol/kg) endmember concentrations compared to fluids collected from other vent sites along the MAR. Hydrogen represents more than 40% of the total gas volume extracted from the fluids. At Rainbow, H₂ production is likely associated with alteration of olivine and orthopyroxene minerals during serpentinization. Given that exposures of ultramafic rock may be common, particularly along slow-spreading ridges, the production of H₂ may have important implications for microbial activity at and beneath the seafloor.     

Strong localized variations of the low-altitude energetic electron fluxes in the evening sector near the plasmapause

Specific type of energetic electron precipitation accompanied by a sharp increase in trapped energetic electron flux are found in the data obtained from low-altitude NOAA satellites. These strongly localized variations of the trapped and precipitated energetic electron flux have been observed in the evening sector near the plasmapause during recovery phase of magnetic storms. Statistical characteristics of these structures as well as the results of comparison with proton precipitation are described. We demonstrate the spatial coincidence of localized electron precipitation with cold plasma gradient and whistler wave intensification measured on board the DE-1 and Aureol-3 satellites. A simultaneous localized sharp increase in both trapped and precipitating electron flux could be a result of significant pitch-angle isotropization of drifting electrons due to their interaction via cyclotron instability with the region of sharp increase in background plasma density.     

Permeabilities and Chemical Properties of Water in Crystalline Rocks of the Black Forest, Germany

Investigations were carried out to determine the hydraulic and hydrochemical properties of crystalline rocks in the Black Forest of Germany and neighbouring regions. Rock permeabilities (K) were determined to a depth of 3500 m. These parameters range from K = 3.5 × 10-10 ms-1 to K = 8.7 × 10-5 ms-1; and can increase up to an order of magnitude which is typical for porous aquifers. It is shown that on an average, granites are more pervious than gneisses and only the permeabilities of gneisses decrease with depth. The geochemistry of natural waters in crystalline rocks is not constant, but varies with depth and location. The concentration increases with depth and the water-type changes from a Ca–-Na–-HCO 3-type (or Na–-Ca–-HCO3–-) at shallow depths to a Na–-Cl-type at greater depths. Thermal springs are found only in granitic rocks with on average higher permeabilities than in gneisses. Thermal waters are welling up in valleys at the bottom of steep mountains. The chemical composition of thermal spring water is identical to that of water found at greater depths. Using geothermometers it is found, that the depth of the deposits of thermal spring water in the crystalline basement rocks of the Black Forest is some 1000 m below the surface. The topographic relief in the mountains induces a deep circulation of infiltrating rain-water with an upwelling as thermal springs in the valleys.     

Modern sedimentation in the Lower Negro River, Amazonas State, Brazil

The Negro River, which flows through the north central Amazon Basin, is one of the largest tributaries of the Amazon. The name “Negro” comes from the colour of its water, which reflects the large quantity of dissolved humic acids and iron oxides that also gives the water its characteristic acid pH. The river is estimated to have the fifth largest water discharge in the world, about 30,000 m³/s. The Negro River is characterized by a high dissolved load but a low energy system. Neotectonics and water quality are the principal factors that control the modern sedimentation in the Lower Negro River. The Lower Negro River is controlled largely by a NW–SE tectonic lineament, that is a segment of a major tectonic transcurrent dextral megasystem of the Amazon Basin. Neotectonism in this area is responsible for the depth of the river and for the occurrence of steep “falésias” (cliffs), along some parts of its borders. It also seems that neotectonics have influenced the origin of the Anavilhanas Islands, which are a series of anastomosed, elongated silty clayey channel bars, with internal round or long narrow lakes. The “igapó”, which is the forested area flooded during part of the year, appears to have a neotectonic origin as well. Igapós are located on intermediate blocks between the high blocks of the “terra firme” and the low blocks of the channel. The absence of clastic sediments carried in suspension is related to the rare appearance of floodplains, which are limited to very thin layers of fine sediments, located on the abrasion shelfs carved in clastic deposits of the Alter do Chão Formation. Sand bars occur in places along the base of the cliffs and along the edges of the channel system. These sand bars are composed of quartz sand, derived from the reworking of the sand of the Alter do Chão Formation.     

WHERE THE PAVEMENT ENDS

ABSTRACT. Black Rock is one of the nation's newest national conservation areas. This significant desert‐and‐mountain region 107 miles north of Reno, Nevada, is the focus of increased global attention, in part due to the annual Burning Man festival, which has become a cause celebre of the dot‐com set and many others. This photographic essay offers a visual sampling of the lyrical sensibility of this unique environment. Geography, I argue, can be an overtly photographic textual form.     

Environmental impact on the Roman monuments of Tarragona,Spain

The extant remains of the Roman monuments of Tarragona, Spain are made of different types of Miocenic rocks from the quarries surrounding the city, which vary from calcarenite to bioclastic limestones, showing different degrees of dolomitization, depending on their diagenetic evolution. The decay of these monuments is highly dependent on the mineralogy and the fabric of the stone as well as on the environmental conditions to which the monument subjected. As a consequence, different forms of decay are observed on these monuments, namely, granular disintegration, differential erosion between sparitic and micritic areas of the rock, and development of black crust and orange patinas, some of them attributed to a sulfation process. A number of processes have been established as being responsible for the decay forms observed: sulfation on sheltered areas of the building in the urban environment; differential dilatation because of the NaCl of the marine spray that crystallizes inside the porosity; hydric and thermal expansion of the stone, both related to the amount and crystallinity of the clay minerals forming the rock matrix; and biocolonization on the stone surface. An empirical model is proposed to explain the decay forms studied in relation to these factors (rock and environment).     

Retrieval of Brown Carbon based on the aerosol complex refractive indices in the winter of Wuhan

Abstract

The impact of Brown Carbon (BrC) to aerosol light absorption has been paid more attention recently and there are a large number of studies showing that the influence of BrC on radiative forcing should not be ignored. BrC also acts as an important component of haze pollution which is occurring frequently in Wuhan, China. Therefore, it is essential to estimate their optical properties, composition, and mass concentration. Considering most haze pollution happens during the coldest time, we retrieved BrC columnar content during winter in Wuhan for the first time. Our method bases on the fact that BrC showed the strong spectral dependence on UV-light absorption. Using this method, we found that BrC makes up the small proportions of total aerosol volume (less than 10%). In the winter of 2011, we retrieved the daily-averaged columnar-integrated mass concentration of BrC on clear day is 4.353 mg/m² while that of haze day is 12.750 mg/m². According to the sensitivity study, we found that the results highly relied on the assumed aerosol refractive index. To reduce the uncertainty of this approach, we need to gain a better understanding of the temporal variability of the radiation absorbing components of these aerosols in the future.     

Regional and local geothermal conditions in the northern Black Sea

More than 100 new heat flow measurements have been collected in recent years (2002–2004) in different tectonic environments of the northern Black Sea. The northern periphery of the Black Sea is characterized by strong geodynamic and seismic activity, high sedimentation rates, diapiric structures, mud volcanism, and fluid and gas escape at the sea floor. We present new thermal data from the shelf, continental slope and deep-water basin, measured off-shore using a marine thermo-probe and on-shore in drill holes. Heat flow density ranges from 20 to more than 2,000 mW/m². For two local areas (the Dnieper gas seeps and the Dvurechenski mud volcano area), we discuss the relation between heat flow variability and the geological and physical processes in the near-bottom sediment layer. The Dnieper gas seeps area is characterized by strong small-scale heat flow variability and is controlled by fluid and gas migration. In the Dvurechenski active mud volcano, the near-bottom temperature in sediments is anomalously elevated because additional heat is carried out by mass flows of fluids and clay minerals. Away from the mud volcano heat flow quickly decreases to background values.     

Synchronous deposition of massive sulphide deposits in the Iberian Pyrite Belt: New data from Las Herrerías and La Torerera ore-bodies

Two small to medium sized massive sulphide deposits, Las Herrerías and La Torerera, located in the Iberian Pyrite Belt (IPB) are examined from a geological and palynostratigraphic perspective. The palynological assemblages are assignable to the Retispora lepidophyta–Verrucosisporites nitidus (LN) miospore Biozone (Latest Devonian: Latest Famennian/Strunian) of Western Europe. This age permits correlation with some of the main massive sulphide deposits dated so far in the region (viz., Tharsis, Aznalcóllar, Sotiel-Coronada or Neves-Corvo), and validates once again the hypothesis that a single mineralizing event was responsible for the genesis of most of the IPB’s massive sulphide deposits. The present study confirms that palynostratigraphy is an invaluable high-resolution biostratigraphic tool in the IPB, applicable to dating, correlation and ore-exploration.     

Observations of substorm fine structure

Particle and magnetic field measurements on the CRRES satellite were used, together with geosynchronous satellites and ground-based observations, to investigate the fine structure of a magnetospheric substorm on February 9, 1991. Using the variations in the electron fluxes, the substorm activity was divided into several intensifications lasting about 3–15 minutes each. The two main features of the data were: (1) the intensifications showed internal fine structure in the time scale of about 2 minutes or less. We call these shorter periods activations. Energetic electrons and protons at the closest geosynchronous spacecraft (1990 095) were found to have comparable activation structure. (2) The energetic (> 69 keV) proton injections were delayed with respect to electron injections, and actually coincided in time with the end of the intensifications and partial returns to locally more stretched field line configuration. We propose that the energetic protons could be able to control the dynamics of the system locally be quenching the ongoing intensification and possibly preparing the final large-scale poleward movement of the activity. It was also shown that these protons originated from the same intensification as the preceeding electrons. Therefore, the substorm instability responsible for the intensifications could introduce a negative feedback loop into the system, creating the observed fine structure with the intensification time scales.