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1.
G. S. Meena 《Journal of Earth System Science》2010,119(3):249-257
The zenith sky scattered light spectra were carried out using zenith sky UV-visible spectrometer in clear and cloudy sky conditions
during May-November 2000 over the tropical station Pune (18°32′N, 73°51′E). These scattered spectra are obtained in the spectral
range 462–498 nm between 75° and 92° solar zenith angles (SZAs). The slant column densities (SCDs) as well as total column
densities (TCDs) of NO2, O3, H2O and O4 are derived with different SZAs in clear and cloudy sky conditions. The large enhancements and reductions in TCDs of the
above gases are observed in thick cumulonimbus (Cb) clouds and thin high cirrus (Ci) clouds, respectively, compared to clear
sky conditions. The enhancements in TCDs of O3 appear to be due to photon diffusion, multiple Mie-scattering and multiple reflections between layered clouds or isolated
patches of optically thick clouds. The reductions in TCDs due to optically thin clouds are noticed during the above period.
The variations in TCDs of O3 measured under cloudy sky are discussed with total cloud cover (octas) of different types of clouds such as low clouds (C
L
), medium clouds (C
M
) and high clouds (C
H
) during May-November 2000. The variations in TCDs of O3 measured in cloudy sky conditions are found to be well matched with cloud sensitive parameter colour index (CI) and found
to be in good correlation. The TCDcloudy are derived using airmass factors (AMFs) computed without considering cloud cover and CI in radiative transfer (RT) model,
whereas TCDmodel are derived using AMFs computed with considering cloud cover, cloud height and CI in RT model. The TCDmodel is the column density of illuminated cloudy effect. A good agreement is observed between TCDmodel, TCDDob and TCDGOME. 相似文献
2.
Nandita D. Ganguly 《Journal of Earth System Science》2008,117(1):79-82
The Indian reserve of coking coal is mainly located in the Jharia coal field in Jharkhand. Although air pollution due to oxides
and dioxides of carbon, nitrogen and sulphur is reported to have increased in this area due to large-scale opencast mining
and coal fires, no significant study on the possible impact of coal fires on the stratospheric ozone concentration has been
reported so far. The possible impact of coal fires, which have been burning for more than 90 years on the current stratospheric
ozone concentration has been investigated using satellite based data obtained from Upper Atmospheric Research Satellite (UARS
MLS), Earth Observing System Microwave Limb Sounder (EOS MLS) and Ozone Monitoring Instrument (OMI) in this paper. The stratospheric
ozone values for the years 1992–2007, in the 28–36 km altitude range near Jharia and places to its north are found to be consistently
lower than those of places lying to its south (up to a radius of 1000 km around Jharia) by 4.0–20%. This low stratospheric
ozone level around Jharia is being observed and reported for the first time. However, due to lack of systematic ground-based
measurements of tropospheric ozone and vertical ozone profiles at Jharia and other far off places in different directions,
it is difficult to conclude strongly on the existence of a relationship between pollution from coal fires and stratospheric
ozone depletion. 相似文献
3.
Concentration profiles of O2, NH4 +, NO3 −, and PO4 3− were measured at high spatial resolution in a 12-cm thick benthic mat of the filamentous macroalga Chaetomorpha linum. Oxygen and nutrient concentration profiles varied depending on algal activity and water turbulence. High surface irradiance stimulated O2 production in the surface layers and introduced O2 to deeper parts of the mat while the bottom layers of the mat and the underlying sediment were anoxic. Nutrient concentrations were highest in the bottom layers of the mat directly above the sediment nutrient source and decreased towards the surface layers due to algal assimilation and enhanced mixing with the overlying water column. Increased turbulence during windy periods resulted in more homogeneous oxygen and nutrient concentration profiles and shifted the oxic-anoxic interface downward. Denitrification within the mat, as measured by the isotope pairing technique on addition of 15NO3 −, was found to take place directly below the oxic-anoxic interface. Denitrification activity was always due to coupled nitrification-denitrification, whereby nitrifiers in the mat utilize NH4 + diffusing from below and O2 diffusing from above. The denitrification rate in the mat ranged from 22 μmol m−2 h−1 to 28 μmol m−2 h−1, approximately equivalent to that measured in the surrounding nonvegetated sediment. Although sediment denitrification is suppressed when the sediment surface is covered by a dense macroalgal mat, the denitrification zone may migrate up into the mat. In eutrophic estuaries with a large area of macroalgal cover, the physical structure and growth stage of algal mats may thus play an important role in the regulation of nitrogen removal by denitrification. 相似文献
4.
G. S. Bhat 《Journal of Earth System Science》2003,112(2):131-146
This paper describes the near surface characteristics and vertical variations based on the observations made at 17.5‡N and
89‡E from ORV Sagar Kanya in the north Bay of Bengal during the Bay of Bengal Monsoon Experiment (BOBMEX) carried out in July–August
1999. BOBMEX captured both the active and weak phases of convection. SST remained above the convection threshold throughout
the BOBMEX. While the response of the SST to atmospheric forcing was clearly observed, the response of the atmosphere to SST
changes was not clear. SST decreased during periods of large scale precipitation, and increased during a weak phase of convection.
It is shown that the latent heat flux at comparable wind speeds was about 25–50% lower over the Bay during BOBMEX compared
to that over the Indian Ocean during other seasons and tropical west Pacific. On the other hand, the largest variations in
the surface daily net heat flux are observed over the Bay during BOBMEX. SST predicted using observed surface fluxes showed
that 1-D heat balance model works sometime but not always, and horizontal advection is important. The high resolution Vaisala
radiosondes launched during BOBMEX could clearly bring out the changes in the vertical structure of the atmosphere between
active and weak phases of convection. Convective Available Potential Energy of the surface air decreased by 2–3 kJ kg-1 following convection, and recovered in a time period of one or two days. The mid tropospheric relative humidity and water
vapor content, and wind direction show the major changes between the active and weak phases of convection. 相似文献
5.
A. N. Gruzdev E. P. Kropotkina S. V. Solomonov A. S. Elokhov 《Doklady Earth Sciences》2016,468(2):602-606
Measurements of the stratospheric contents of O3 and NO2 in the Moscow region were used to analyze the anomalies of these species related to the sudden stratospheric warming in the winter and the following deformation of the stratospheric circumpolar vortex in early February 2010 and the latitudinal displacement of the vortex towards the European sector in late March 2011 before the final warming in the spring. In the first case, an increase in the O3 and NO2 contents up to 85% and by two times, respectively, was recorded. In the second case, the O3 content decreased by one-fourth and the NO2 content dropped by two times as compared to the average values for the periods that preceded the beginning of the anomalies. 相似文献
6.
This paper addresses temporal variability in bottom hypoxia in broad shallow areas of Mobile Bay, Alabama. Time-series data
collected in the summer of 2004 from one station (mean depth of 4 m) exhibit bottom dissolved oxygen (DO) variations associated
with various time scales of hours to days. Despite a large velocity shear, stratification was strong enough to suppress vertical
mixing most of the time. Bottom DO was closely related to the vertical salinity gradient (ΔS). Hypoxia seldom occurred when
ΔS (over 2.5 m) was <2 psu and occurred almost all the time when ΔS was >8 psu in the absence of extreme events like hurricanes.
Oxygen balance between vertical mixing and total oxygen demand was considered for bottom water from which oxygen demand and
diffusive oxygen flux were estimated. The estimated decay rates at 20°C ranging between 0.175–0.322 d−1 and the corresponding oxygen consumption as large as 7.4 g O2 m−2 d−1 fall at the upper limit of previously reported ranges. The diffusive oxygen flux and the corresponding vertical diffusivity
estimated for well mixed conditions range between 8.6–9.5 g O2 m−2 d−1 and 2.6–2.9 m2 d−1, respectively. Mobile Bay hypoxia is likely to be associated with a large oxygen demand, supported by both water column and
sediment oxygen demands, so that oxygen supply from surface water during destratification events would be quickly exhausted
to return to hypoxic conditions within a few hours to days after destratification events are terminated. 相似文献
7.
Molly M. Miller Scott W. Phipps Clinton S. Major Kelly M. Major 《Estuaries and Coasts》2011,34(6):1182-1193
This study was designed to investigate non-point source nutrient pollution and its influences on submerged aquatic plant community
structure and biological invasion in the Weeks Bay National Estuarine Research Reserve (WBNERR). A monthly vegetation survey
was conducted to document plant abundance and changes in community structure; physicochemical data and water samples were
collected on a bi-monthly basis to monitor environmental conditions (i.e., pH, salinity, dissolved oxygen, light intensity,
and attenuation) and water column nutrient (NO2−/NO3− and NH4+) and chlorophyll a concentrations. A total of seven submerged aquatic species were identified at the WBNERR with the occurrence of only one
non-native species (Hydrilla verticillata). Statistical analyses suggest that water column nitrogen concentrations along with variations in dissolved oxygen (0.6–11.5 mg L−1), light attenuation, pH (5.6–8.6), and temperature (11–33°C) play key roles in determining the aquatic plant abundance and
distribution in the WBNERR. 相似文献
8.
Carbon Cycling and the Coupling Between Proton and Electron Transfer Reactions in Aquatic Sediments in Lake Champlain 总被引:1,自引:0,他引:1
Wei-Jun Cai George W. LutherIII Jeffrey C. Cornwell Anne E. Giblin 《Aquatic Geochemistry》2010,16(3):421-446
We used fine-scale porewater profiles and rate measurements together with a multiple component transport–reaction model to
investigate carbon degradation pathways and the coupling between electron and proton transfer reactions in Lake Champlain
sediments. We measured porewater profiles of O2, Mn2+, Fe2+, HS−, pH and pCO2 at mm resolution by microelectrodes, and profiles of NO3
−, SO4
2−, NH4
+, total inorganic carbon (DIC) and total alkalinity (TA) at cm resolution using standard wet chemical techniques. In addition,
sediment–water fluxes of oxygen, DIC, nitrate, ammonium and N2 were measured. Rates of gross and net sulfate reduction were also measured in the sediments. It is shown that organic matter
(OM) decomposes via six pathways: oxic respiration (35.2%), denitrification (10.4%), MnO2 reduction (3.6%), FeOOH reduction (9.6%), sulfate reduction (14.9%), and methanogenesis (26.4%). In the lake sediments, about
half of the benthic O2 flux is used for aerobic respiration, and the rest is used for the regeneration of other electron acceptors produced during
the above diagenetic reactions. There is a strong coupling between O2 usage and Mn2+ oxidation. MnO2 is also an important player in Fe and S cycles and in pH and TA balance. Although nitrate concentrations in the overlying
water were low, denitrification becomes a quantitatively important pathway for OM decomposition due to the oxidation of NH4
+ to NO3
−. Finally, despite its low concentration in freshwater, sulfate is an important electron acceptor due to its high efficiency
of internal cycling. This paper also discusses quantitatively the relationship between redox reactions and the porewater pH
values. It is demonstrated here that pH and pCO2 are sensitive variables that reflect various oxidation and precipitation reactions in porewater, while DIC and TA profiles
provide effective constraints on the rates of various diagenetic reactions. 相似文献
9.
Interstitial water and hydrochemistry of a mangrove forest and adjoining water system, south west coast of India 总被引:1,自引:0,他引:1
Eh, pH, salinity, total alkalinity, dissolved O2, NO2
–, PO4
–3, SiO2 and NH4
+ of waters from a mangrove forest, an estuary and a creek connecting the mangrove forest and the estuary have been measured.
Further, the chemistry of interstitial waters of surficial and core sediments from the mangrove forest have been analyzed
for the above parameters, except dissolved oxygen. To understand the flux of nutrients from the mangrove forest to the adjoining
estuary, creek waters were monitored during tidal phases. PO4
–3, SiO2 and NH4
+ were found to be at elevated levels in mangrove waters whereas NO2
– shows no variation compared to the estuary. Dissolved O2 is low in mangrove waters. PO4
–3, NH4
+ and SiO2 are several times higher in interstitial waters than in overlying waters. Several fold enrichment of PO4
–3, NH4
+ and, to some extent, SiO2 were measured in creek waters during ebbing relative to flooding, indicating that mangroves act as a perennial source for
the above nutrients.
Received: 26 May 1998 · Accepted: 21 July 1998 相似文献
10.
Groundwater nitrate contamination and risk assessment in an agricultural area,South Korea 总被引:2,自引:1,他引:1
Jae-Yeol Cheong Se-Yeong Hamm Jeong-Hwan Lee Kwang-Sik Lee Nam-Chil Woo 《Environmental Earth Sciences》2012,66(4):1127-1136
The nitrate of groundwater in the Gimpo agricultural area, South Korea, was characterized by means of nitrate concentration,
nitrogen-isotope analysis, and the risk assessment of nitrogen. The groundwaters belonging to Ca–(Cl + NO3) and Na–(Cl + NO3) types displayed a higher average NO3
− concentration (79.4 mg/L), exceeding the Korean drinking water standard (<44.3 mg/L NO3
−). The relationship between δ18O–NO3
− values and δ15N–NO3
− values revealed that nearly all groundwater samples with δ15N–NO3
− of +7.57 to +13.5‰ were affected by nitrate from manure/sewage as well as microbial nitrification and negligible denitrification.
The risk assessment of nitrate for groundwater in the study area was carried out using the risk-based corrective action model
since it was recognized that there is a necessity of a quantitative assessment of health hazard, as well as a simple estimation
of nitrate concentration. All the groundwaters of higher nitrate concentration than the Korean drinking water standard (<44.3 mg/L NO3
−) belonged to the domain of the hazard index <1, indicating no health hazard by nitrate in groundwater in the study area.
Further, the human exposure to the nitrate-contaminated soil was below the critical limit of non-carcinogenic risk. 相似文献
11.
Thermodynamic structure of the marine atmosphere in the region between 80 and 87‡E along 13‡N over the Bay of Bengal was studied
using 13 high resolution radiosonde profiles from surface-400 hPa collected onboard ORV Sagar Kanya during the period 27th–30th
August, during BOBMEX-99. Saturation point concept, mixing line analysis and conserved variable diagrams have been used to
identify boundary layer characteristics such as air mass movement and stability of the atmosphere. The results showed relatively
dry air near the ocean surface between 1000 and 950 hPa. This feature is confirmed by the conserved tetav structure in this layer. Further, tetav seldom showed any inversions in this region. The tetae and tetaes profiles showed persistent low cloud layers between 900 and 700 hPa. The conserved variable diagrams (tetae-q) showed the existence of double mixing line structures approximately at 950 and 700 hPa levels. 相似文献
12.
Summary ?Hydrothermal experiments to synthesize pumpellyite group minerals of the pumpellyite–okhotskite series and to investigate
their stability have been carried out at 200, 300 and 400 MPa P
fluid and 250–500 °C by using cold-seal pressure vessels and solid buffers of MnO2–Mn2O3, Cu2O–CuO and Cu2O–Cu buffer assemblages. Okhotskite and pumpellyite rich in the okhotskite component crystallized from an oxide mixture starting
material of Ca4MgMn3+
3Al2Si6O24.5-oxide+excess H2O at P
fluid of 200, 300 and 400 MPa and temperatures of 300 and 400 °C. However, a single phase of okhotskite was not produced, and associated
piemontite, hausmannite, wollastonite, clinopyroxene, corundum, braunite–neltnerite solid solution and alleghanyite also formed.
Mn-pumpellyite of the okhotskite–pumpellyite join occurs as aggregates of needle crystals, rounded grains or flaky crystals.
Chemical compositions are variable and range from pumpellyite-(Mn2+) to okhotskite: 31–36 SiO2, 13–21 Al2O3, 12–25 total Mn2O3, 0.6–4 MgO and 20–24 wt.% CaO. Reconnaissance experiments using a starting material of synthetic Ca2Mn3+Al2Si3O12(OH)-piemontite at 300 MPa and temperatures of 250, 300, 400 and 500 °C indicate that Mn-rich pumpellyite can crystallize
from piemontite at lower temperatures than the stability field of piemontite. The Mn-rich pumpellyite was accompanied by garnet,
wollastonite and alleghanyite. The chemical compositions of the Mn-pumpellyites are 32–36 SiO2, 18–27 Al2O3, 8–18 total Mn2O3 and 20–23 wt.% CaO. This study shows that the stability fields of piemontite, piemontite+Mn-pumpellyite, and Mn-pumpellyite
range in this order with decreasing temperature under high fO2 conditions. The maximum stability temperature of Mn-rich pumpellyite lies between 400 and 500 °C at 200–400 MPa in high fO2 conditions.
Received March 3, 2000; revised version accepted December 28, 2001 相似文献
13.
Nitrate contamination of groundwater in an agroecosystem in Zhangye Oasis,Northwest China 总被引:5,自引:2,他引:3
In order to assess the extent of groundwater contamination by nitrate (NO3
−–N) and to provide information about the deterioration of the groundwater quality in Zhangye Oasis, Northwest China, a study
was conducted in this area. The mean value of NO3
−–N concentrations in groundwater samples was 10.66 ± 0.19 mg l−1. NO3
−–N concentrations exceeding 10 mg l−1 (the threshold for drinking water set by the World Health Organization) were found in 32.4% of 71 wells, and were 13, 33.3,
52.4 and 50.0% in the groundwater samples from drinking wells, irrigation wells, hand-pumping wells and groundwater table
observation wells, respectively. The result showed that the groundwater samples that had NO3
−–N concentrations exceeding the threshold for drinking water were mostly collected from a depth of less than 20 m. Groundwater
NO3
−–N concentrations in areas used for the cultivation of vegetables, seed maize and intercropped maize were significantly higher
than those in urban or paddy areas. NO3
−–N contamination of groundwater in areas with sandy soil was more severe than in those with loam soil. 相似文献
14.
V. S. N. Murty V. Ramesh Babu L. V. G. Rao Charuta V. Prabhu V. Tilvi 《Journal of Earth System Science》2000,109(2):267-277
Time-series data on upper-ocean temperature, Vessel-Mounted Acoustic Doppler Current Profiler (VM-ADCP) measured currents
and surface meteorological parameters have been obtained for the first time in the southern Bay of Bengal at 7‡N, 10‡N, and
13‡N locations along 87‡E during October–November, 1998 under BOBMEX-Pilot programme. These data have been analysed to examine
the diurnal variability of upper oceanic heat budget and to estimate the eddy diffusivity coefficient of heat in the upper
layer. Diurnal variation of near-surface temperature is typical at northern location (13‡N) with a range of 0.5‡C while the
diurnal range of temperature is enhanced to 0.8‡C at the central location (10‡N) due to intense solar radiation (1050 W/m2), clear skies and low wind speeds. At the southern location (7‡N), the diurnal variation of temperature is atypical with
the minimum temperature occurring at 2000 hrs instead of at early morning hours. In general, the diurnal curve of temperature
penetrated up to 15 to 20 m with decreasing diurnal range with depth. The VM-ADCP measured horizontal currents in the upper
ocean were predominantly easterly/northeasterly at southern location, north/northerly at central location and northwesterly
at northern location, thus describing a large-scale cyclonic gyre with the northward meridional flow along 87‡E. The magnitudes
of heat loss at the surface due to air-sea heat exchanges and in the upper 50 m layer due to vertical diffusion of heat are
highest at the southern location where intense convective activity followed by overcast skies and synoptic disturbance prevailed
in the lower atmosphere. This and the estimated higher value (0.0235 m2/s) of eddy diffusivity coefficient of heat in the upper ocean (0–50 m depth) suggest that 1-D processes controlled the upper
layer heat budget at the southern location. On the other hand, during the fair weather conditions, at the central and northern
locations, the upper layer gained heat energy, while the sea surface lost (gained) heat energy at northern (central) location.
This and lower values of eddy diffusivity coefficient of heat (0.0045 and 0.0150 m2/s) and the northward intensification of horizontal currents at these locations suggest the greater role of horizontal heat
advection over the 1-D processes in the upper ocean heat budget at these two locations. 相似文献
15.
Tracing the sources of nitrate in karstic groundwater in Zunyi,Southwest China: a combined nitrogen isotope and water chemistry approach 总被引:1,自引:0,他引:1
Si-Liang Li Cong-Qiang Liu Yun-Chao Lang Zhi-Qi Zhao Zhi-Hua Zhou 《Environmental Earth Sciences》2010,60(7):1415-1423
Nitrate (NO3
−) is major pollutant in groundwater worldwide. Karst aquifers are particularly vulnerable to nitrate contamination from anthropogenic
sources due to the rapid movement of water in their conduit networks. In this study, the isotopic compositions (δ15N–NO3
−, δ15N–NH4
+) and chemical compositions(e.g., NO3
−, NH4
+, NO2
−, K+) were measured in groundwater in the Zunyi area of Southwest China during summer and winter to identify the primary sources
of contamination and characterize the processes affecting nitrate in the groundwater. It was found that nitrate was the dominant
species of nitrogen in most of the water samples. In addition, the δ15N–NO3
− values of water samples collected in summer were lower than those collected in winter, suggesting that the groundwater received
a significant contribution of NO3
− from agricultural fertilizer during the summer. Furthermore, the spatial variation in the concentration of nitrate and the
δ15N–NO3
− value indicated that some of the urban groundwater was contaminated with pollution from point sources. In addition, the distribution
of δ15N–NO3
− values and the relationship between ions in the groundwater indicated that synthetic and organic fertilizers (cattle manure)
were the two primary sources of nitrate in the study area, except in a few cases where the water had been contaminated by
urban anthropogenic inputs. Finally, the temporal and spatial variation of the water chemistry and isotopic data indicated
that denitrification has no significant effect on the nitrogen isotopic values in Zunyi groundwater. 相似文献
16.
K. Kusaka K. Hagiya M. Ohmasa Y. Okano M. Mukai K. Iishi N. Haga 《Physics and Chemistry of Minerals》2001,28(3):150-166
The structures of Ca2CoSi2O7, Ca2MgSi2O7, and Ca2(Mg0.55Fe0.45)Si2O7 have been determined in the temperature range between 297 and 773 K with arbitrary intervals. The structures of the incommensurate
phase of the three compounds are characterized by the presence of the six-, seven-, and eight-coordinated Ca–O polyhedra and
of the bundles along the c-axes consisting of four arrays of the six-coordinated Ca–O polyhedra and an array of T1O4 (T1: Co, Mg, or Mg–Fe) tetrahedra in the structures. The number of bundles in each material decreases at elevated temperatures.
The incommensurate phase undergoes a phase transition into the normal phase at 493 K in Ca2CoSi2O7, at 360 K in Ca2MgSi2O7, and at 510 K in Ca2(Mg0.55Fe0.45)Si2O7. The features of the structures of the normal phase are almost the same as those found in the basic structures (the averaged
structures of the incommensurate structures), and this fact implies that the characteristics of the structures, such as the
six-coordinated Ca–O polyhedra or fragments of the bundles, should be partially preserved at higher temperatures both in the
incommensurate structures and also in the structures of the normal phase. Analyses of anisotropic displacement parameters
clarified that disorder of the modulation waves is developed in the structures at higher temperatures. The evolution of a
disorder in the structures was ascertained by observation of the circular diffuse streaks in the vicinity of the transition
temperature between the incommensurate and normal phases.
Received: 3 July 2000 / Accepted: 26 October 2000 相似文献
17.
M. Zhang G. J. Redhammer E. K. H. Salje M. Mookherjee 《Physics and Chemistry of Minerals》2002,29(9):609-616
Synthetic aegirine LiFeSi2O6 and NaFeSi2O6 were characterized using infrared spectroscopy in the frequency range 50–2000 cm−1, and at temperatures between 20 and 300 K. For the C2/c phase of LiFeSi2O6, 25 of the 27 predicted infrared bands and 26 of 30 predicted Raman bands are recorded at room temperature. NaFeSi2O6 (with symmetry C2/c) shows 25 infrared and 26 Raman bands. On cooling, the C2/c–P21/c structural phase transition of LiFeSi2O6 is characterized by the appearance of 13 additional recorded peaks. This observation indicates the enlargement of the unit
cell at the transition point. The appearance of an extra band near 688 cm−1 in the monoclinic P21/c phase, which is due to the Si–O–Si vibration in the Si2O6 chains, indicates that there are two non-equivalent Si sites with different Si–O bond lengths. Most significant spectral
changes appear in the far-infrared region, where Li–O and Fe–O vibrations are mainly located. Infrared bands between 300 and
330 cm−1 show unusually dramatic changes at temperatures far below the transition. Compared with the infrared data of NaFeSi2O6 measured at low temperatures, the change in LiFeSi2O6 is interpreted as the consequence of mode crossing in the frequency region. A generalized Landau theory was used to analyze
the order parameter of the C2/c–P21/c phase transition, and the results suggest that the transition is close to tricritical.
Received: 21 January 2002 / Accepted: 22 July 2002 相似文献
18.
Mario Tribaudino Fabrizio Nestola Marco Bruno Tiziana Boffa Ballaran Christian Liebske 《Physics and Chemistry of Minerals》2008,35(5):241-248
The high temperature volume and axial parameters for six C2/c clinopyroxenes along the NaAlSi2O6–NaFe3+Si2O6 and NaAlSi2O6–CaFe2+Si2O6 joins were determined from room T up to 800°C, using integrated diffraction profiles from in situ high temperature single crystal data collections. The thermal
expansion coefficient was determined by fitting the experimental data according to the relation: ln(V/V
0) = α(T − T
0). The thermal expansion coefficient increases by about 15% along the jadeite–hedenbergite join, whereas it is almost constant
between jadeite and aegirine. The increase is related to the Ca for Na substitution into the M2 site; the same behaviour was
observed along the jadeite–diopside solid solution, which presents the same substitution at the M2 site. Strain tensor analysis
shows that the major deformation with temperature occurs in all samples along the b axis; on the (010) plane the higher deformation occurs in jadeite and aegirine at a direction almost normal to the tetrahedral–octahedral
planes, and in hedenbergite along the projection of the longer M2–O bonds. The orientation of the strain ellipsoid with temperature
in hedenbergite is close to that observed with pressure in pyroxenes. Along the jadeite–aegirine join instead the high-temperature
and high-pressure strain are differently oriented. 相似文献
19.
Jürgen Konzett Daniel J. Frost Alexander Proyer Peter Ulmer 《Contributions to Mineralogy and Petrology》2008,155(2):215-228
Experiments have been conducted in the P-T range 2.5–15 GPa and 850–1,500°C using bulk compositions in the systems SiO2–TiO2–Al2O3–Fe2O3–FeO–MnO–MgO–CaO–Na2O–K2O–P2O5 and SiO2–TiO2–Al2O3–MgO–CaO–Na2O to investigate the Ca-Eskola (CaEs Ca0.5□0.5AlSi2O6) content of clinopyroxene in eclogitic assemblages containing garnet + clinopyroxene + SiO2 ± TiO2 ± kyanite as a function of P, T, and bulk composition. The results show that CaEsss in clinopyroxene increases with increasing T and is strongly bulk composition dependent whereby high CaEs-contents are favoured by bulk compositions with high normative
anorthite and low diopside contents. In this study, a maximum of 18 mol% CaEsss was found at 6 GPa and 1,350°C in a kyanite-eclogite assemblage garnet + clinopyroxene + kyanite + rutile + coesite. By comparison,
no significant increase in CaEsss with increasing P could be observed. If the formation of oriented SiO2-rods frequently observed in eclogititc clinopyroxenes is due to the retrogressive breakdown of a CaEs-component then these
textures are a cooling rather than a decompression phenomenon and are most likely to be found in kyanite-bearing eclogites
cooled from temperatures ≥750°C. The presence of clinopyroxene with approx. 4 mol% CaEsss in an experiment conducted at 2.5 GPa/850°C confirms earlier suggestions based on field data that vacancy-rich clinopyroxenes
are not necessarily restricted to ultrahigh pressure metamorphic conditions.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
20.
Justus E. E. van Beusekom Dirk Mengedoht Christina B. Augustin Mario Schilling Maarten Boersma 《International Journal of Earth Sciences》2009,98(2):251-260
From March 2002 to until April 2003 we investigated the seasonal nutrient and phytoplankton dynamics in the central Bornholm
Basin (Baltic Sea) within the framework of the German GLOBEC Project. We choose a nested approach consisting of vertical fluorescence
profiles, phytoplankton counts and nutrient analyses. The Fluoroprobe (MultiProbe, BBE Moldaenke) is capable of distinguishing
four algal groups (Cryptophyceae, Cyanophyceae, Chlorophyceae, Bacillariophyceae + Dinophyceae). Winter nutrient concentrations
were about 5 μM NO3 and 0.5 μM PO4 in the central Basin. The spring phytoplankton bloom was dominated by the diatom Skeletonema sp. and reached a maximum of about 270 μg C/l before the onset of the seasonal stratification. Protozooplankton was dominated
by the Mesodinium rubrum (a phototrophic ciliate = Myrionecta rubra) and reached a maximum biomass of about 200–300 μg C/l about 2 weeks after the demise of the diatom spring bloom. During summer,
the water column was stratified and a subsurface maximum developed near the thermocline consisting of Bacillariophyceae, Cryptophycea
and other phototrophic flagellates. Phytoplankton and protozooplankton biomass was generally low. Nutrient concentrations
point towards a nitrogen limitation during this period. The stratification period ended during September and surface nutrient
concentrations increased again. Protozooplankton reached a second maximum during September. With the Fluoroprobe small scale
structures in the plankton community could be detected like a subsurface Cryptophyceae maximum near the thermocline that however,
could not be confirmed by cell counts. The chlorophyll a estimate of the Fluoroprobe was in good agreement with the phytoplankton
biomass estimated from counts. We conclude that only by combining modern sensing technology with microscopy, the small-scale
dynamics and taxonomic spectrum of the plankton can be fully captured. 相似文献