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1.
Inter-annual variations of phytoplankton abundance and community organization were observed over a two-decade period along with the ancillary parameters at the land–ocean boundary associated with the Sundarban mangrove forest (21°32′ and 22°40′ N and 88°05′ and 89° E), along the NE Coast of the Bay of Bengal. The number of definable Bacillariophyceae species exceeded Dinophyceae taxa, and the total number of bloom-forming species declined from a maximum of ten in 2000 and a minimum of two in 2007. Blooms of the diatom Coscinodiscus radiatus were common in 2000 and 2007. Tide cycles and the onset of the monsoon season played important roles in diurnal and seasonal variability of phytoplankton. Phytoplankton biovolume showed seasonality, with the highest levels during post-monsoon periods and lowest levels during the monsoon period. Phytoplankton abundance was correlated to rainfall patterns, which may be altered by long-term changes in climate.  相似文献   

2.
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3.
A case study for the ion–aerosol interactions is presented from the simultaneous measurements of mobility spectra of atmospheric ions in the mobility range of 2.29 to 2.98 × 10 − 4 cm2 V − 1 s-1^{-1}(diameter range 0.41–109 nm) and of size distribution of atmospheric aerosol particles in the size ranges of 4.4–700 nm and 500–20,000 nm diameters made at Maitri (70°45′52′ ′S, 11°44′2.7′ ′E; 130 m above mean sea level), Antarctica, on two days January 17 and February 18, 2005, with contrasting meteorological conditions. In contrast to January 17, on February 18, winds were stronger from the morning to noon and lower from the noon to evening, atmospheric pressure was lower, cloudiness was more, the land surface remained snow-covered after a blizzard on February 16 and 17 and the airmass over Maitri, descended from an altitude of ~3 km after an excursion over ocean. On these days mobility spectra showed two modes, corresponding to intermediate ions and light large ions and an indication of additional one/two maxima for small/cluster ions and heavy large ions. The small ions generated by cosmic rays, and the nucleation mode particles generated probably by photochemical reactions grew in size by condensation of volatile trace gases on them and produced the cluster and intermediate ion modes and the Aitken particle mode in ion/particle spectra. Particles in the size range of 9–26 nm have been estimated to grow at the rate of 1.9 nm h − 1 on February 18, 2005. Both, ions and aerosol particles show bimodal size distributions in the 16–107 nm size range, and comparison of the two size distributions suggests the formation of multiple charged ions. Attachment of small ions to particles in this bimodal distribution of Aitken particles together with the formation of multiple charged ions are proposed to result in the light and heavy large ion modes. Growth of the nucleation mode particles on February 18, 2005 is associated with the passage of the airmass over ocean. In contrast, though the ion size distributions were not much different, the aerosol size distributions did not show a dominant peak for the formation and growth of nucleation mode particles on January 17. More measurements are needed before the conclusion of this case study is generalized.  相似文献   

4.
Summary The El Dorado Au-Cu deposit is located in an extensive intra-caldera zone of hydrothermal alteration affecting Upper Cretaceous andesites of the Los Elquinos Formation at La Serena (≈ 29°47′S Lat., 70°43′W Long., Chile). Quartz-sulfide veins of economic potential are hosted by N25W and N20E fault structures associated with quartz-illite alteration (+supergene kaolinite). The main ore minerals in the deposit are pyrite, chalcopyrite ± fahlore (As/(As + Sb): 0.06−0.98), with electrum, sphalerite, galena, bournonite-seligmanite (As/(As + Sb): 0.21−0.31), marcasite, pyrrhotite being accessory phases. Electrum, with an Ag content between 32 and 37 at.%, occurs interstitial to pyrite aggregates or along pyrite fractures. Pyrite commonly exhibits chemical zonation with some zones up to 1.96 at.% As. Electron probe microanalyses of pyrite indicate that As-rich zones do not exhibit detectable Au values. Fluid inclusion microthermometry shows homogenization temperatures between 130 and 352 °C and salinities between 1.6 and 6.9 wt.% NaCl eq. Isotope data for quartz, ankerite and phyllosilicates and estimated temperatures show that δ18O and δD for the hydrothermal fluids were between 3 and 10‰ and between −95 and −75‰, respectively. These results suggest the mineralizing fluids were a mixture of meteoric and magmatic waters. An epithermal intermediate-sulfidation model is proposed for the formation of the El Dorado deposit. Author’s present address: J. Carrillo-Rosúa, Dpto. de Didáctica de las Ciencias Experimentales, Universidad de Granada, Campus de Cartuja, 18071, Granada, Spain  相似文献   

5.
The major chemical components of bauxite deposits of Belgaum (76° 24′E : 15° 54′N) and Yercaud (78° 14′E : 11° 48′N) areas have been determined. A chemical continuity between parent rocks (zone I) to bauxites (zone IV) via clay (zone II) and laterites (zone III) clearly indicates that bauxites have been derived byin situ weathering of the respective parent rocks.  相似文献   

6.
The composition of the zooplankton community in a macrotidal (8 m tidal range), tropical estuarine system (Darwin Harbour, Australia; 12o28′ S, 130o50′ E) was studied over a 2 year period with the goal of describing biodiversity and determining the environmental factors that have the greatest impact on community structure. Most (82–84%) of the >73 μm plankton was composed of copepod nauplii and copepodites, and plankton samples taken with larger, coarser meshed (150 and 350 μm) nets did not contain significant numbers of larger (non-copepod) organisms. In all, 32 copepod species were recorded, with small euryhaline marine copepod species such as Parvocalanus crassirostris, Bestiolina similis and Oithona aruensis dominating the zooplankton. Plankton abundances ranged between 30,000 and 110,000 m−3, and there were significant year (2003 > 2004), season (wet > dry) and site differences (inner harbour sites > outer harbour sites), but negligible diurnal differences. Multivariate analyses identified three sample groups: (1) middle and outer harbour sites, (2) inner harbour and river sites and (3) the river site during the wet seasons. Middle and outer harbour stations were characterised by a diverse mixture of coastal copepods, whereas inner harbour and river sites were dominated by P. crassirostris and O. aruensis. During the wet season, there was a distinct copepod community within the Blackmore River, dominated by Acartia sinjiensis, Oithona nishidai and Pseudodiaptomus spp. Environmental variables (nutrients and chlorophyll a) were correlated with salinity, which had the strongest influence on community structure. There was a significant drop in species richness from harbour to river sites. Small copepods of the families Paracalanidae and Oithonidae dominate tide-dominated Australian tropical estuaries, whereas copepods belonging to the family Centropagidae (such as Gladioferens spp.) appear to be characteristic of wave-dominated estuaries in southern Australia.  相似文献   

7.
 The occurrence, movement and control of groundwater, particularly in hard-rock areas, are governed by different factors such as topography, lithology, structures like fractures, faults and nature of weathering. An attempt is made in the present study to investigate the extent of the influence of structures such as fractures and thereby delineate the nature of subsurface lithology with the help of an electrical resistivity method. For this study, the Upper Gunjanaeru River basin, Cuddapah district Andhra Pradesh was chosen to determine groundwater potentials. In order to understand the significance of the fracture pattern, geological, hydrogeomorphological and lineament maps were prepared based on the field data and also from the LANDSAT TM imagery. Further, electrical resistivity surveys were conducted to determine the subsurface lithology and also to confirm the studies of LANDSAT imagery. The isoresistivity contour map has been prepared based on the 45 VES conducted to determine the resistivity variations in the study area. The isoresistivity contours obtained were found to conform to the structural trends obtained by geological studies and also confirm the relationship between the structure and secondary porosity present in the rocks. The lineaments in the area have two preferred directions. One set is a NE-SW direction (N 30°–70° E; S 30°–70° W) and another is a NW-SE direction (N 0°–30° W; S 0°–30° E and N 60°–80° W; S 60°–80° E). The water-table contour map shows that the direction of groundwater flow is south to north. Received: 3 March 1997 · Accepted: 17 June 1997  相似文献   

8.
Planktonic larvae of estuarine species often develop in the coastal ocean and return to estuaries using favorable currents. This study investigated spatial distributions of brachyuran crab post-larvae during ingress to the Newport River estuary, North Carolina, USA (34°41′ N, 76°40′ W). Nearshore plankton tows were conducted across the inlet to the estuary. Settlement on passive ‘hog’s hair’ collectors was simultaneously monitored in each of four estuarine channels. Callinectes sapidus density was highest east of the inlet, whereas relative estuarine abundance was higher in western channels. In separate sampling with collectors at coastal and estuarine locations, spatial distributions of post-larvae were consistent through time but differed for C. sapidus, Uca spp., and Pachygrapsus transversus. The diel timing of C. sapidus settlement on collectors was determined at the coast and compared to previous studies of settlement in the estuary. Behavioral responses to environmental cues may alter transport pathways from those predicted by hydrodynamic models.  相似文献   

9.
The harmonic synthesis and analysis of the elements of gravitational tensor can be done in few minutes if a suitable programming algorithm is used. Vectorization is an efficient technique for such processes, but the size of matrices will increase when the resolution of synthesis or analysis is high; say higher than 0.5° × 0.5°. Here, we present a technique to manage the computer memory and computational time by excluding one computational loop from the matrix products and we call this method semi-vectorization. Based on this technique, we synthesize the gravitational tensor using the EGM96 geopotential model and after that we analyze the tensor for recovering the geopotential coefficients. MATLAB codes are provided which are able to analyze 224 millions gradiometric data, corresponding to a global grid of 2.5′ × 2.5′ on a sphere in 1,093 s by a personal computer with 2 Gb RAM.  相似文献   

10.
The Copper Creek mining district, southeastern Arizona, contains more than 500 mineralized breccia pipes, buried porphyry-style, copper-bearing stockworks, and distal lead–silver veins. The breccia pipes are hosted by the Copper Creek Granodiorite and the Glory Hole volcanic rocks. The unexposed Mammoth breccia pipe, solely recognized by drilling, has a vertical extent of 800 m and a maximum width of 180 m. The pipe consists of angular clasts of granodiorite cemented by quartz, chalcopyrite, bornite, anhydrite, and calcite. Biotite 40Ar/39Ar dates suggest a minimum age of 61.5 ± 0.7 Ma for the host Copper Creek Granodiorite and 40Ar/39Ar dates on hydrothermal sericite indicate an age of 61.0 ± 0.5 Ma for copper mineralization. Fluid inclusion studies suggest that a supercritical fluid with a salinity of approximately 10 wt.% NaCl equiv. condensed to a dilute aqueous vapor (1–2.8 wt.% NaCl equiv.) and a hypersaline brine (33.4–35.1 wt.% NaCl equiv.). Minimum trapping temperatures are 375°C and trapping depths are estimated at 2 km. Sulfur isotope fractionation of cogenetic anhydrite and chalcopyrite yields a temperature of mineralization of 469 ± 25°C. Calculated oxygen and hydrogen isotope values for fluids in equilibrium with quartz and sericite range from 10.2‰ to 13.4‰ and −60‰ to −39‰, respectively, suggesting that the mineralizing fluid was dominantly magmatic. Evidence from the stable isotope and fluid inclusion analyses suggests that the fluids responsible for Cu mineralization within the Mammoth breccia pipe exsolved from a gray porphyry phase found at the base of the breccia pipe.  相似文献   

11.
Time-series Mark VII sediment trap was deployed at 72°58.55′E, 62°28.63°S (north of the Prydz Bay, Antarctica) during the cruise of CHINARE-15 in cooperation with University of Marine of America. Seasonal variability of deep ocean particle fluxes and biogenic components were investigated in order to reveal the fluxes and biogeochemistry of sinking particles in the deep ocean. The results show that the total mass flux of sinking particles at a water depth of 1000 m ranges from 13.00 to 334.59 mg⋅d−1⋅m−2). A marked seasonal variability exists in the fluxes of all particle components reflecting the seasonal changes in upper water productivity. Biogenic material was a significant component and biogenic silica represented more than 80% of the biogenic matter, reflecting a diatom dominated system, but a lithogenic fraction is always present. The fact that the POC dominated over particulate inorganic carbon (as CaCO3) and Cinorg/Corg was always greater than 1, indicate a net removal of CO2 from surface water by biological activity. __________ Translated from Acta Oceanologica Sinica, 2006, 5: 49–55 [译自:海洋 学报]  相似文献   

12.
 Grain boundary diffusion rates of oxygen, potassium and calcium in fine-grained feldspar aggregates were determined experimentally. The starting materials were a natural albite rock from the Tanco pegmatite and aggregates hot-pressed from fragments of Amelia albite or Ab, Or and An composition glasses. The technique employed isotopic tracers (18O, 41K, 42Ca) either evaporated onto the surface or in an aqueous solution surrounding the sample, and depth profiling using an ion microprobe (SIMS). From the depth profiles, the product of the grain boundary diffusion coefficient (D′) and effective boundary width (δ) was calculated using numerical solutions to the appropriate diffusion equation. The experimental reproducibility of D′δ is a factor of 3. A separate determination of D′ independent of δ yields an effective grain boundary width of ∼3 nm, consistent with high resolution TEM observations of a physical grain boundary width <5 nm. Oxygen (as molecular water) grain boundary diffusion rates were determined in the Ab and Or aggregates at 450°–800° C and 100 MPa (hydrothermal), potassium rates in Or aggregates at 450°–700° C both at 0.1 MPa (in air) and at 100 MPa (hydrothermal), and calcium rates in An aggregates at 700°–1100° C and 0.1 MPa (in air). Oxygen grain boundary diffusion rates are similar in all three of the Ab aggregates and in the Or aggregate. Potassium and oxygen depth profiles measured in the same samples yield different D′δ values, confirming a diffusional transport mechanism. Potassium diffusion in the Or aggregate has a greater activation energy (216 vs 78 kJ/mol) than oxygen, and the Arrhenius relations cross at ∼625° C. Potassium D′δ values in Or aggregates are about a factor of five greater in hydrothermal experiments at 100 MPa than in experiments at 0.1 MPa in air. Calcium grain boundary diffusion rates in An aggregates are 4 to 5 orders of magnitude slower than potassium in Or and have a greater (291 kJ/mol) activation energy. This suggests that differences in formal charge and/or size of diffusing species may play an important role in their relative grain boundary diffusion rates. Received: 24 December 1993 / Accepted: 16 June 1994  相似文献   

13.
Summary Augite and diopside crystals from the Oligo-Miocene high-Mg and high-Al basalts, basaltic andesites and andesites of Montresta (Sardinia, Italy) have been analysed by means of X-ray single crystal diffraction and electron microprobe. It has been found that crystallization or equilibration processes took place within the crust at pressures below 5 kbar. In particular, samples from high-Al basalts, basaltic andesites and andesites crystallised at pressures below one kbar while those from high-Mg basalts crystallised in a range from about 1.5 to 4.5 kbar. The intracrystalline temperatures range between about 550 °C for high-Mg basalts and 750 °C for andesites. The M2′ site is occupied in each of the studied crystals, which implies slow cooling rates.  相似文献   

14.
Mo-Bi mineralization occurs in subvertical and subhorizontal quartz-muscovite-± K-feldspar veins surrounded by early albitic and later K-feldspathic alteration halos in monzogranite of the Archean Preissac pluton, Abitibi region, Québec, Canada. Molybdenite is intergrown with muscovite in the veins or associated with K-feldspar in the alteration halos. Mineralized veins contain five main types of fluid inclusions: aqueous liquid and liquid-vapor inclusions, aqueous carbonic liquid-liquid-vapor inclusions, carbonic liquid and vapor inclusions, halite-bearing aqueous liquid and liquid-vapor inclusions, trapped mineral-bearing aqueous liquid and liquid-vapor inclusions. The carbonic solid in frozen carbonic and aqueous-carbonic inclusions melts in most cases at −56.7 ± 0.1 °C indicating that the carbonic fluid consists largely of CO2. All aqueous inclusion types and the aqueous phase in carbonic inclusions have low initial melting temperatures (≥70 °C), requiring the presence of salts other than NaCl. Leachate analyses show that the bulk fluid contains variable proportions of Na, K, Ca, Cl, and traces of Mg and Li. The following solids were identified in the fluid inclusions by SEM-EDS analysis: halite, calcite, muscovite, millerite (NiS), barite and antarcticite (CaCl2 · 6H2O). All are interpreted to be trapped phases except halite which is a daughter mineral, and antarcticite which formed during sample preparation (freezing). Aqueous inclusions homogenize to liquid at temperatures between 75 °C and 400 °C; the mode is 375 °C. Aqueous-carbonic inclusions homogenize to liquid or vapor between 210 °C and 400 °C. Halite-bearing aqueous inclusions homogenize by halite dissolution at approximately 170 °C. Aqueous inclusions containing trapped solids exhibit liquid-vapor homogenization at temperatures similar to those of halite-bearing aqueous inclusions. Temperatures of vein formation, based on oxygen isotopic fractionation between quartz and muscovite, range from 342 °C to 584 °C. The corresponding oxygen isotope composition of the aqueous fluid in equilibrium with these minerals ranges from 1.2 to 5.5 per mil with a mean of 3.9 per mil, suggesting that the liquid had a significant meteoric component. Isochores for aqueous fluid inclusions intersect the modal isotopic isotherm of 425 °C at pressures between 590 and 1900 bar. A model is proposed in which molybdenite was deposited owing to decreasing temperature and/or pressure from CO2-bearing, moderate to high salinity fluids of mixed magmatic-meteoric origin that were in equilibrium with K-feldspar and muscovite. These fluids resulted from the degassing of a monzogranitic magma and evolved through interaction with volcanic (komatiitic) and sedimentary country rocks. Received: 6 February 1997 / Accepted: 28 January 1998  相似文献   

15.
 In 1988, wildfire burned over 50% of the Jones Creek watershed near Yellowstone Park, Wyoming. Crow Creek, an adjacent watershed, was unburned. Water quality data collected from 1989–1993 may show the fire's effect on weathering and nutrient transport. Jones Creek had 25–75% larger concentrations of dissolved solids than Crow Creek during the sampling period. Both streams revealed molar ratios consistent with the stoichiometry of andesine and pyroxene hydrolysis in the trachyandesites that underlie the basins. During 1989, nitrate transported from the unburned Crow Creek basin peaked at 2 mmol ha–1 s–1. This was twice as much as Jones Creek, possibly indicating a source from ash fallout. By 1992 these rates diminished to 0.1 mmol ha–1 s–1 in Crow Creek and increased to 1.8 mmol ha–1 s–1 in Jones Creek, suggesting later nitrate mobilization in the burned watershed. Phosphorus transported from Jones Creek basin averaged 0.011 mmol ha–1 s–1 during summer 1989, but fell to 0.004 mg ha–1 s–1 in subsequent years. Received: 28 May 1997 · Accepted: 18 November 1997  相似文献   

16.
Disturbance is an important factor influencing plant species composition and diversity. We addressed changes in plant composition and soil characteristics in Estero de Punta Banda, Baja California, Mexico following 22 years of disturbance by tidal exclusion. Currently, sediments in the non-tidal site are dry, 26 ± 1% moisture, and hypersaline, 143 ± 12; while those at the tidal marsh are wet, 36.2 ± 1% moisture, with 40.3 ± 2.6 salinity. The non-tidal site has lost seven species including annuals, short- and long-lived perennials, ephemerals, and parasites. Current dominants are the perennials Batis maritima and Sarcocornia pacifica. Average species richness at the non-tidal site is 4.4 ± 0.32 vs.10 ± 0.18 species per square meter at the tidal site. Average species diversity index is lower at the diked area. The general biodiversity loss that results from tidal exclusion in arid estuaries, contrasts with the species-rich communities that develop in diked humid-climate estuaries.  相似文献   

17.
VHF amplitude scintillations recorded during the daytime period from January 1991 to December 1993, April 1998 to December 1999 and January 2008 to December 2008 at low latitude station Varanasi (geographic lat. = 25°15′N; long. = 82°59′E; geomagnetic lat. = 14°55′N, long. = 154°E, dip angle = 37.3°, sub-ionospheric dip = 34°) have been analyzed to study the behaviour of ionospheric E-region irregularities during the active solar and magnetic periods. The autocorrelation functions, power spectral densities, signal de-correlation times are computed to study the temporal features of ionospheric E-region irregularities linked with daytime scintillations. Derived spectral index ranges between −2 and −9. Assuming velocity of irregularities, the characteristic lengths of the E-region irregularities are estimated. We have estimated the minimum and maximum range of scale length of sporadic-E (E s ) irregularities to be observed over Varanasi. These results are in close agreement with those reported from this latitude region.  相似文献   

18.
 Petrological and chemical variations, as well as oxygen and strontium isotopic data are presented for metagabbros from the Romanche and Vema fracture zones. These rocks were affected by several types and degrees of alterations ranging from slight hydrothermal alteration to complete amphibolitization. Five major kinds of alteration processes ranging from late-magmatic deuteric alteration (stage I) to low temperature (<150 °C) alteration (stage V) were identified. Water-rock interactions between 300 and 650 °C are the most dominant interactions resulting in the most prevailing secondary mineralogical assemblages which characterize the amphibolite and/or greenschist facies (amphibole ± plagioclase ± epidote ± titanite ± chlorite ± prehnite). Hydrothermal alteration of these gabbroic rocks results in isotopic exchanges between rocks and seawater-derived fluids. These exchanges lead to decrease of gabbroic δ18O toward values as low as +3.9‰, and larger Sr isotopic variations than other oceanic gabbroic rocks (87Sr/86Sr ratios shift to 0.7029–0.7051). Calculation of a chemical budget indicates that metagabbros are hydrated and enriched in Fe and probably in Mg and Cl, while Si, Ca and Ti are released to the hydrothermal fluids. In addition to metamorphic recrystallization and geochemical transformation, hydrothermal alteration of oceanic gabbros contributes to the control of the global ocean geochemistry. Received: 8 March 1999 / Accepted: 12 July 1999  相似文献   

19.
A detailed seismicity map of the Central Indian Ridge for the period 1912–1993 is presented, and the earthquakes pertaining to four major transforms offsetting the ridge are utilized to study the moment release pattern. The scalar moment release for the period 1912–1993, and the summed moment rate tensors for both short period (1977–1993) and long period (1912–1993) bring out a unified picture of moment release pattern. The fraction of seismic slip calculated based on depths of 100°C and 400°C limiting temperatures suggests that the Marie-Celeste transform requires a slip almost to a depth of 400°C isotherm to account for the observed moment, and the Argo transform requires depth of faulting much above the 400°C isotherm. A very small fraction of slip is accounted seismically for Vema (53%) and 12° 12′S (23%) even to depths of 100°C isotherm, suggesting a very low order of moment release along these transforms. The horizontal plate velocities and the corresponding strain rates obtained from moment tensor summation of long period data (82 years) give rise to (V y y ; V y x mm. yr−1) of 6.0 and 6.1 along Marie-Celeste, 1.3 and 0.50 along Argo, 0.06 and 0.06 along 12° 12′S, 1.6 and 0.25 along Vema transforms. The corresponding strain rates (ε y y ;ε y x × 10−15 S−1) are 12.7 and 6.8 along MarieCeleste, 6.9 and 1.4 along Argo, 0.27 and 0.14 along 12° 12′S, 7.3 and 0.58 along Vema transforms. These results suggest that the strain rates were highest and almost all predicted motion is taken up seismically along the Marie-Celeste transform. The strain rates are lower along Argo transform and the observed moment release require shallower depth of faulting in order to slip to be accounted seismically. The Vema and 12° 12′S transforms are characterized by low strain rates and less than 15 per cent of motion is accommodated seismically within the seismogenic layer. It is proposed that the deficiency of moment release along the Vema and 12° 12′S multiple transform system may be due to most of the plate motion occurring aseismically.  相似文献   

20.
Field studies supplemented by petrographic analyses clearly reveal complete preservation of ophiolite suite from Port Blair (11°39′N: 92°45′E) to Chiriyatapu (11°30′24″N: 92°42′30″E) stretch of South Andaman. The ophiolite suite reveals serpentinite at the base which is overlain unconformably by cumulate ultramafic-mafic members with discernible cumulus texture and igneous layering. Basaltic dykes are found to cut across the cumulate ultramafic-mafic members. The succession is capped by well exposed pillow basalts interlayered with arkosic sediments. Olivine from the basal serpentinite unit are highly magnesian (Fo80.1–86.2). All clinopyroxene analyses from cumulate pyroxenite, cumulate gabbro and basaltic dyke are discriminated to be ‘Quad’ and are uniformly restricted to the diopside field. Composition of plagioclase in different lithomembers is systematically varying from calcic to sodic endmembers progressively from cumulate pyroxenite to pillow basalt through cumulate gabbro and basaltic dyke. Plagioclase phenocrysts from basaltic dyke are found to be distinctly zoned (An60.7-An35.3) whereas groundmass plagioclase are relatively sodic (An33-An23.5). Deduced thermobarometric data from different lithomembers clearly correspond to the observed preservation of complete ophiolite suite.  相似文献   

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