Understanding how physical-biological coupling influences harmful algal blooms,low oxygen and fish kills in the Sea of Oman and the Western Arabian Sea     

Paul J. Harrison  Sergey Piontkovski  Khalid Al-Hashmi 《Marine pollution bulletin》2017,114(1):25-34

In the last decade, green Noctiluca scintillans with its symbiont and other dinoflagellates such as Cochlodinium polykrikoides, Prorocentrum micans and Scrippsiella trochoidea have become the dominant HABs, partially replacing the previously dominant diatoms and red Noctiluca scintillans, especially during the northeast monsoon. Fish kills in the Sea of Oman are linked to a slow seasonal decline in oxygen concentration from January to November, probably due to the decomposition of a series of algal blooms and the deep, low oxygen waters periodically impinging the Omani shelf. In the western Arabian Sea, cyclonic eddies upwell low oxygen, nutrient-rich water and the subsequent algal bloom decays and lowers the oxygen further and leads to fish kills. Warming of the surface waters by 1.2 °C over the last 5 decades has increased stratification and resulted in a shoaling of the oxycline. This has increased the probability and frequency of upwelling low oxygen water and subsequent fish kills.  相似文献   

Interpretation of Magnetic Data Through Particle Swarm Optimization: Mineral Exploration Cases Studies     

Essa  Khalid S.  Elhussein  Mahmoud 《Natural Resources Research》2020,29(1):521-537

Natural Resources Research - This paper emphasizes the use of the particle swarm optimization to infer second moving average residual magnetic anomalies. This approach was used to remove the impact...  相似文献   

Mineralogy and Geochemistry of Uraniferous Sandstones in Fault Zone,Wadi El Sahu Area,Southwestern Sinai,Egypt: Implications for Provenance,Weathering and Tectonic Setting     

Osama R. SALLAM  Hamed I. MIRA  Amira M. El TOHAMY  Abd Elhadi A. ABBAS 《《地质学报》英文版》2021,95(3):830-845

Paleozoic rocks in the Wadi El Sahu area are affected by many major faults in different directions. A reverse fault trending NE-SW is exposed for about 300 m of its length as it cuts through the Abu Hamata and Adedia formations on the south side of Wadi El Sahu. A secondary ascending hydrothermal solution carrying heavy metals and radioactive minerals passed through the fault plain and the surrounding fractures, forming mineralized and radioactive zone. The mineralized zone thickness ranges from 60 cm to 200 cm along the fault plain. These rocks were analyzed radiometrically using a portable gamma-ray spectrometer, chemically by employing ICP-ES and ICP-MS, as well as mineralogically by both binocular and Environmental Scanning Electron microscope. Gold content was also determined by fire assay. REE and U contents reached up to 2682 and 1216 ppm, respectively. Mineralogical investigations indicated the presence of uraninite, torbernite, autunite, sklodowskite, kasolite as uranium minerals, thorite as a thorium mineral, monazite, allanite and xenotime as REE-bearing minerals, zircon and columbite as accessory minerals, gold and nickel as precious and base metals, in addition to cassiterite, chalcopyrite, chalcocite and chrysocolla. High REE and U contents are attributed to the circulation of epigenetic U and REE-bearing hydrothermal solutions along the fault plain and its surrounding fractures. Hydrothermal alteration processes could then be confirmed by the presence of the M-type tetrad effect in the REE-patterns of the ferruginous sandstone. The non-chondritic ratio of Nb/Ta, Zr/Hf and Y/Ho in the studied sandstone may be attributed to the tetrad effect. The Ce and Eu anomaly with unusual REE-patterns was represented by the presence of conjugated M-W tetrad effects, indicating either the dual effect of hydrothermal solutions or groundwater with seawater. The results clarify that the tetrad-effects could be used as evidence for the environment of deposition and as an indication for gold mineralization.  相似文献   

From paleostresses to paleoburial in fold-thrust belts: Preliminary results from calcite twin analysis in the Outer Albanides     

Olivier Lacombe  Julien Malandain  Khalid Amrouch  François Roure 《Tectonophysics》2009,475(1):128-141

This paper presents a new approach to constrain paleoburial and subsequent uplift by folding in fold-thrust belts, combining differential stress estimates from mechanically-induced calcite twins with the assumption that stress in the upper crust is in frictional equilibrium. Calcite twin data were collected from pre-folding veins in late Cretaceous limestones from the Ionian zone in Albania in order to (1) determine Paleogene-Neogene stresses associated with the development of the major vein sets in the frontal anticlines of the Outer Albanides and (2) estimate paleoburial of the Cretaceous reservoir rocks during pre-folding flexural subsidence of the foreland. The first vein set (set I) trends N140 (± 20) and the second set (set II) is oriented N060 (± 20). Calcite twinning analysis from set I veins reveals a pre-folding N030° extension likely related to foreland flexure; a later pre-folding, NE-directed compression (LPS) is identified either from one or from both vein sets in the samples from the Saranda anticline; this NE compression is instead recorded by twinning in set II veins from the Kremenara anticline during late stage fold tightening. This NE compression well agrees with independent microtectonic data, regional transport direction and contemporary stress. The differential stress values related to this NE compression are combined with the hypothesis of crustal frictional stress equilibrium to derive first-order estimates of paleoburial of the Cretaceous limestones just before they were uplifted by folding. The ~ 4 km paleoburial of these limestones estimated in the Saranda anticline is consistent with independent paleoburial estimates from stratigraphy, maturity rank of organic matter, paleotemperature/paleogeothermal gradients from fluid inclusions and predictions of kinematic modelling of the Albanian foreland. Our results therefore place reliable constraints on the amount and rate of vertical uplift of these Cretaceous limestones and yield a promising methodology for better constraining paleoburial and therefore erosion and uplift in fold-thrust belts.  相似文献   

Phosphorus and nitrogen losses associated with runoff and erosion on an Aridisol in northern Iraq     

MOHAMMAD H. HUSSEIN  ABBAS J. HUSSEIN  MUHSEN M. AWAD 《水文科学杂志》2013,58(5):657-664

Abstract

Runoff and soil erosion are known to cause a degradation in soil and water quality. Six natural runoff plots (three 10 m long and three 30 m long) were established on 6% uniform slope area for the study of P and N losses associated with runoff and soil erosion in northern Iraq. The soil at the site belongs to the Calciorthid suborder which dominates in the low rainfall zone of northern Iraq. Runoff, erosion, and associated P and N losses, were recorded from these plots for three rainfall seasons. Results illustrated that eroded sediment is always rich in available P and inorganic N compared to the original soil. Concentrations of soluble P and soluble N in runoff illustrated significant variability both between storms and between seasons. Both sediment-bound P and soluble P were significantly correlated with the ratio of runoff to rainfall.  相似文献   

Recent glacier changes in the Kashmir Alpine Himalayas,India     

Khalid Omar Murtaza 《国际地球制图》2017,32(2):188-205

Using Landsat data at decadal interval (1980–2013), the glacier fluctuations (glacier area, equilibrium line altitude and specific mass balance) of nine benchmark glaciers in Kashmir Himalaya were estimated. The observed changes were related to topographic and climatic variables in order to understand their influence. From the data analysis, it was observed that the glaciers have shrunk by 17%, ELA has shifted upwards (80–300 m) and SMB shows variation in glacier mass loss from ?0.77 to ?0.16 m.w.e. Annual air temperature showed a significant increasing trend, and a slight but insignificant decrease in precipitation was observed during the period. It is evident that in the same climatic regime, varying topography plays a key role in determining the glacier changes. It is believed that the observed changes in the glacier geometry and dynamics, if continued, shall have adverse effect on the streamflows, water supplies and other dependent sectors in the region.  相似文献   

Experimental investigation of slip‐stick behaviour in granular materials     

Khalid A. Alshibli  Lynne E. Roussel 《国际地质力学数值与分析法杂志》2006,30(14):1391-1407

This paper presents the results of an experimental programme to study load oscillation in granular materials. Spherical glass beads were used in the investigation. Cylindrical specimens were compressed under axisymmetric triaxial loading condition at 25,100,250 and 400 kPa confining pressures. The test parameters included: (i) particle size; (ii) gradation (uniform versus non‐uniform specimens); (iii) confining pressure; (iv) loading rate; and (v) specimen density. In general, a slight post‐peak principal stress softening was observed as well as a continuous volume increase (dilation) even at relatively high strains. This appears to be caused by the uniform shape and smooth surface of the spherical particles. Load oscillations were observed in the very small, small, and well‐graded beads at each confining pressure. For the medium beads, the oscillations appeared at high confining pressure (250 and 400 kPa), and they did not appear in the large beads. The influences of the confining pressure, loading rate, particle size, gradation and specimen density on load oscillation are presented and discussed. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Comprehensive framework for gradient-based optimization in closed-loop reservoir management     

Vladislav Bukshtynov  Oleg Volkov  Louis J. Durlofsky  Khalid Aziz 《Computational Geosciences》2015,19(4):877-897

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Characteristics of moisture flux convergence in Central Southwest Asia     

Khalid M. Malik  Peter A. Taylor  Kit Szeto 《Theoretical and Applied Climatology》2015,120(3-4):643-659

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TM reflection from an insulating layer within a lossy half-space     

Khalid A. Nabulsi  James R. Wait 《Journal of Applied Geophysics》1996,34(4):271-276

In this paper the possibility of detecting a semi-insulating layer in a homogeneous half-space model of the earth is examined using VHF electromagnetic waves (30–300 MHz). The scheme is to employ an obliquely incident TM (transverse magnetic) plane wave. The corresponding TM reflection coefficient in the vicinity of the Brewster angle null is then considered for possible clues. It is shown that when the host medium is not excessively lossy, the TM reflection coefficient shows significant deviation from the homogeneous half-space case. The measurement and interpretation have possible relevance to the detection of liquid hazardous waste layers at depth.  相似文献