Turbulence structure in the upper ocean: a comparative study of observations and modeling

Observations of turbulent dissipation rates measured by two independent instruments are compared with numerical model runs to investigate the injection of turbulence generated by sea surface gravity waves. The near-surface observations are made by a moored autonomous instrument, fixed at approximately 8 m below the sea surface. The instrument is equipped with shear probes, a high-resolution pressure sensor, and an inertial motion package to measure time series of dissipation rate and nondirectional surface wave energy spectrum. A free-falling profiler is used additionally to collect vertical microstructure profiles in the upper ocean. For the model simulations, we use a one-dimensional mixed layer model based on a k–ε type second moment turbulence closure, which is modified to include the effects of wave breaking and Langmuir cells. The dissipation rates obtained using the modified k–ε model are elevated near the sea surface and in the upper water column, consistent with the measurements, mainly as a result of wave breaking at the surface, and energy drawn from wave field to the mean flow by Stokes drift. The agreement between observed and simulated turbulent quantities is fairly good, especially when the Stokes production is taken into account.     

Evaluation of Negative Economic-Environmental Externalities of Overextraction of Groundwater

In recent decades, increased extraction of groundwater for human and agriculture consumption has led to a substantial drop in groundwater level in large areas of across the world. Declining groundwater levels is a serious problem in itself and has multiple economic, social, cultural, political, security-related, and environmental externalities. The negative economic-environmental externalities of overextraction of groundwater in the Orzouiyeh plain in the Kerman Province, Iran, were evaluated using methods such as replacement cost, production function, market prices, shadow price, and the value of the input marginal product. After evaluating externalities, the Positive Mathematical Programming method was used to evaluate different water policies to reduce the consumption of groundwater. The total economic losses due to the externalities were calculated to equal 2.8 U.S. million dollars. The damages caused by environmental externalities were calculated to equal 436.1 U.S. million dollars. The results related to the positive planning model show that the best policy among different options, such as deficit irrigation policy or combined policies, involves implementation of pressurized irrigation systems.     

Indoor activity size distribution of the short-lived radon progeny

Activity size distribution of the short-lived radon progeny in indoor air was measured continuously over several weeks. Two different measurement techniques were used: a direct measurement with a low-pressure Berner cascade impactor for attached fraction of ²¹⁴Pb and ²¹⁴Bi (≥100 nm) and an indirect determination based on measurement with a wire screen diffusion battery (unattached fraction 0.5–5 nm, ²¹⁸Po, ²¹⁴Pb). In parallel, the meteorological parameters like temperature, humidity were registered. Measured activity size distribution of radon progeny can be approximated by a sum of three log-normal distributions modes (nucleation, accumulation and coarse). The greatest activity fraction was adsorbed on aerosol particles in the accumulation size range (100–1000 nm) with activity median aerodynamic diameters (AMAD_a) and geometric standard deviations (GSD _a ) values of 250–500 nm, and 1.5–3.5, respectively. The influence of the weather conditions on the activity of the accumulation particles was not significant. In contrast to the results of measurements a small but significant fraction of the radon progeny (average value 5 %) was attached to coarse particles (>1000 nm). This fraction varied between 0 and 10 %. On the other hand, although the amount of unattached activities not more 10 % of the total activity, but is considered to yield about 50 % of the total radiation dose. The mean thermodynamic equivalent diameters of ²¹⁸Po and ²¹⁴Pb were determined to be 1.28 and 1.30 nm with relative mean geometric standard deviations of 1.30 and 1.24, respectively. Based on the obtained results of radon progeny size distributions (attached and unattached), the total deposition fractions of the human lung were evaluated by using a lung deposition model.     

Unique desert caves as a valuable geological resource: first detailed geological heritage assessment of the Sannur Cave,Egypt

Arabian Journal of Geosciences - Surface albedo is a key parameter in earth energy budget and global climate change studies. In this aspect, variation in vegetation covers is one of the most...     

Performance evaluation of WAVEWATCH III model in the Persian Gulf using different wind resources

The third-generation wave model, WAVEWATCH III, was employed to simulate bulk wave parameters in the Persian Gulf using three different wind sources: ERA-Interim, CCMP, and GFS-Analysis. Different formulations for whitecapping term and the energy transfer from wind to wave were used, namely the Tolman and Chalikov (J Phys Oceanogr 26:497–518, 1996), WAM cycle 4 (BJA and WAM4), and Ardhuin et al. (J Phys Oceanogr 40(9):1917–1941, 2010) (TEST405 and TEST451 parameterizations) source term packages. The obtained results from numerical simulations were compared to altimeter-derived significant wave heights and measured wave parameters at two stations in the northern part of the Persian Gulf through statistical indicators and the Taylor diagram. Comparison of the bulk wave parameters with measured values showed underestimation of wave height using all wind sources. However, the performance of the model was best when GFS-Analysis wind data were used. In general, when wind veering from southeast to northwest occurred, and wind speed was high during the rotation, the model underestimation of wave height was severe. Except for the Tolman and Chalikov (J Phys Oceanogr 26:497–518, 1996) source term package, which severely underestimated the bulk wave parameters during stormy condition, the performances of other formulations were practically similar. However, in terms of statistics, the Ardhuin et al. (J Phys Oceanogr 40(9):1917–1941, 2010) source terms with TEST405 parameterization were the most successful formulation in the Persian Gulf when compared to in situ and altimeter-derived observations.     

High-resolution seismic imaging of crooked two-dimensional profiles in greenstone belts of the Canadian shield: results from the Swayze area,Ontario, Canada

In 2017, the Metal Earth multi-disciplinary exploration project acquired a total of 921 km of regional deep seismic reflection profiles and 184 km of high-resolution seismic reflection profiles in the Abitibi and Wabigoon greenstone belts of the Superior province of Canada. The Abitibi belt hosts several world-class mineral deposits, whereas the Wabigoon has sparse economic mineral deposits. Two high-resolution surveys in the Swayze area, a poorly endowed part of the western Abitibi greenstone belt, served as pioneer surveys with which to better understand subsurface geology and design a strategy to process other surveys in the near future. Swayze seismic data were acquired with crooked survey geometries along roads. Designing an effective seismic processing flow to address these geometries and complex geology required straight common midpoint lines along which both two-dimensional prestack dip-moveout correction and poststack migration processing were applied. The resulting seismic sections revealed steeply dipping and subhorizontal reflections; some correlate with folded surface rocks. An interpreted fault/deformation zone imaged in Swayze north would be a target for metal endowment if it extends the Porcupine–Destor structure. Because of the crooked line geometry of the surveys, two-dimensional /three-dimensional prestack time migration and swath three-dimensional processing were tested. The prestack time migration algorithm confirmed reflections at the interpreted base of the Abitibi greenstone belt. The swath three-dimensional images provided additional spatial details about the geometries of some reflections, but also had less resolution and did not detect many reflectors observed in two dimensions. Geological contacts between felsic, mafic and ultramafic greenstone rock layers are thought the main cause of reflectivity in the Swayze area.     

Multistage mineralization in the Haoyaoerhudong gold deposit,Central Asian Orogenic Belt:Constraints from the sedimentary-diagenetic and hydrothermal sulfides and gold

The Central Asian Orogenic Belt,as one of world-class gold economic belts,preserves a number of giant,large black shale-hosted gold deposits,while it is still debated for origin of sulfides and gold mainly due to lack of identification for multiple stages of sulfides.The Haoyaoerhudong gold deposit is hosted in a sequence of Mesoproterozoic carbonaceous and pyritic slate,phyllite,and schist that form a tight syncline along the north margin of the North China Craton.Detailed petrography of the host rocks and mineralization have defined five stages of pyrites.The earliest form of pyrite(Py₁)occurs as fine-grained dispersed pyrite in black carbonaceous slate and medium-to coarse-grained disseminated pyrite in pyrite-rich layers,contains relative low gold and high arsenic content,indicating a syn-sedimentary or diagenetic in origin.Stage Ⅱ pyrite(Py₂)occurs with garnet and quartz inclusions and Py₃ occurs as pyrite veins,contains higher gold and lower As content,and are interpreted to have formed from the dissolution-reprecipitation of Py₁ during the peak metamorphism or post-peak metamorphism.Stage Ⅳ pyrite(Py₄)from the pyrite-quartz veins crosscut the metamorphic garnet,contains the highest gold concentrations and other trace elements,and is considered to have formed post-peak metamorphism.Abundant native gold,electrum,and maldonite occur as inclusions within Py₄ and monazite and in fractures that crosscut garnet.While,Py₅ with typical remobilized feature is thought to be a product of melting of former pyrites(Py₁ to Py₄)triggered by the large-scale Hercynian magmatism.The sedimentary/diagenetic Py₁ have δ³⁴S values that range from +12.4‰to +16.2‰.Later generations of sulfides,including Py₂ to Py₅,and Ccp₂ to Ccp₃,have δ³⁴S values from +9.5‰to +12.7‰.Monazite with maldonite inclusions from quartz-pyrite veins yielded an intercept age of 341.3±6.6 Ma,while coarse grained monazite associated biotite along fractures in the reefs yielded an intercept age of 254.6±8.2 Ma.The paragenetic,textural,chemical,and isotopic data suggest three distinct gold producing episodes at Haoyaoerhudong gold deposit.Gold and arsenic were clearly initially concentrated in organic muds,and enriched along the structures of diagenetic arsenic-rich pyrite.Subsequently,accompanying metamorphism and deformation,gold was liberated from the dissolution of diagenetic pyrites to form the pyrite veins.Finally,accompanying transformation of pyrite into pyrrhotite,gold was released into the metamorphic fluids to become concentrated as native gold,electrum,and maldonite in pyrite-quart veins.Monazite with age of 341 Ma from quartz-pyrite veins suggests that the third major gold mineralizing event in Haoyaoerhudong occurred before the Hercynian magmatism,suggesting that the Haoyaoerhudong deposit is a typical orogenic gold deposit rather than intrusion-related deposit.     

Plio-Quaternary reactivation of the Neogene margin off NW Algiers, Algeria: The Khayr al Din bank

The Algiers region, northern Algeria, is known to be seismically active, with recurrent large (M>6) earthquakes. Because of the lack of high-resolution bathymetry, the offshore structures remained for a long time poorly known. Thanks to a new marine data base (MARADJA 2003 cruise), the offshore part of the margin is accurately mapped, and new active and recent structures are described. West of the bay of Algiers, the margin enlarges, forming the Khayr al Din bank, interpreted as a tilted block of the passive margin born during the opening of the Algero-Provençal basin. At the slope break, a 80 km-long fault-tip Quaternary fold, namely the Khayr al Din fault, extends at the foot of the margin off NW Algiers and represents the largest active structure of the coastal area, together with the Sahel anticline. We also map for the first time a set of overlapping, en echelon active folds in the upper part of the Khayr al Din bank, located off previously known active structures on land. Most of these faults represent actually a threat for the Algiers region in terms of seismic hazard but also geological hazards, such as tsunamis, as most of them depicts significant dimensions and slip rates. The highest long-term horizontal shortening rate is found on the Khayr al Din fault and is estimated at 0.5 ± 0.1 mm/yr, with a maximal magnitude of 7.3, which provides one of the highest seismogenic potential in the region.A new tectonic framework for the Algiers region is proposed, in which the main south-dipping offshore structure, of opposite vergence relative to most thrusts on land, appears to be nowadays the main driving fault system, as also found further east in the Boumerdès (M 6.8) 2003 rupture zone. The overall apparent pop-up structure of the recent and active faults may result from a progressive migration of the plate limit from the Late Miocene, north-dipping suture zone on land, to the Quaternary, south-dipping main Khayr al Din fault at sea, suggesting a process of subduction inception.     

Combining visual and geochemical analyses to source chert on Southern Baffin Island,Arctic Canada

A combined methodological approach using visual and geochemical methods is introduced and preliminary results of a study illustrating its effectiveness to determine chert source provenance are presented. This study focuses on lithic debitage and raw chert samples collected from the interior of southern Baffin Island, Arctic Canada. Chert is abundant throughout this region yet it occurs as small, scattered surface nodules that are highly variable in color. Prior to this study, little was known about the provenance of this local toolstone and whether it derived from local outcrops, glacial till sheets, or both. Given the pronounced variability exhibited by this chert, we use individual attribute analysis and petrography to impose some kind of analytical order upon an otherwise random aggregation of rocks. Thereafter, inductively coupled plasma mass spectrometry and secondary ion mass spectrometry are used to test the validity of these color categories to determine from how many geochemically distinct sources they derive. Using a standard that measures Al to a ratio of Ga/Zr, our results indicate that all of the raw chert samples derive from a single local source, while the debitage derives from four different sources, including the one that is local. We are confident that this combined methodological approach can be applied in other regions where chert variability is pronounced and source provenance is unknown. © 2009 Wiley Periodicals, Inc.