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1.
Studies of the extreme solar proton event of January 20, 2005 intensified the contest over of a long-standing problem: are solar cosmic rays arriving at the Earth accelerated by solar flares or by shocks preceding rapidly moving coronal mass ejections? Among the most important questions is the relationship between the energy spectra of the solar cosmic rays and the frequency spectra of flare microwave bursts. Some studies of previous solar-activity cycles have shown that such a relationship does exist, in particular, for protons with energies of tens of MeV. The present work analyzes this relation using data for 1987–2008. For flare events observed in the western half of the disk, there is a significant correlation between the index δ, which is equivalent to the power-law index of the integrated energy spectrum of 10–100 MeV protons detected near the Earth’s orbit, and radio burst parameters such as a ratio of peak fluxes S at two frequencies (for example, at 9 and 15 GHz) and a microwave peak frequency f m . Proton fluxes with hard (flat) energy spectra (δ ≤ 1.5) correspond to hard microwave frequency spectra (S 9/S 15 ≤ 1 and f m ≥ 15 GHz), while flares with soft radio spectra (S 9/S 15 ≥ 1.5 and f m ≤ 5 GHz) result in proton fluxes with soft (steep) energy spectra (δ ≥ 1.5–2). It is also shown that powerful high-frequency bursts with the hardest radio spectra (f m ≈ 30 GHz) can point at acceleration of significant proton fluxes in flares occurring in strong magnetic fields. These results argue that solar cosmic rays (or at least their initial impulses) are mainly accelerated in flares associated with impulsive and post-eruptive energy release, rather than in shocks driven by coronal mass ejections.  相似文献   

2.
Spring wheat (Triticum aestivum Linn.) is an important crop for food security in the desert-oasis farmland in the middle reaches of the Heihe River in northwestern China. We measured fluxes using eddy covariance and meteorological parameters to explore the energy fluxes and the relationship between CO2 flux and climate change in this region during the wheat growing seasons in 2013 and 2014. The energy balance closures were 70.5% and 72.7% in the 2013 and 2014 growing season, respectively. The wheat ecosystem had distinct seasonal and diurnal dynamics of CO2 fluxes with U-shaped curves. The accumulated net ecosystemic CO2 exchanges (NEE) were -111.6 and -142.2 g C/m2 in 2013 and 2014 growing season, respectively. The ecosystem generally acted as a CO2 sink during the growing season but became a CO2 source after the wheat harvest. A correlation analysis indicated that night-time CO2 fluxes were exponentially dependent on air temperature and soil temperature at a depth of 5 cm but were not correlated with soil-water content, water-vapour pressure, or vapour-pressure deficit. CO2 flux was not correlated with the meteorological parameters during daytime. However, irrigation and precipitation, may complicate the response of CO2 fluxes to other meteorological parameters.  相似文献   

3.
This paper gives a review on the topic of the mean radiant temperature T mrt , the most important parameter influencing outdoor thermal comfort during sunny conditions. T mrt summarizes all short wave and long wave radiation fluxes reaching the human body, which can be very complex (variable in spatial and also in temporal manner) in urban settings. Thermal comfort researchers and urban planners need easy and sound methodological approaches to assess T mrt . After the basics of the T mrt calculation some of the methods suitable for obtaining T mrt also in urban environments will be presented.. Two of the discussed methods are based on instruments which measure the radiation fluxes integral (globe thermometer, pyranometer-pyrgeometer combination), and three of the methods are based on modelling the radiation environment with PC software (RayMan, ENVI-met and SOLWEIG).  相似文献   

4.
A suite of metabasite dykes, emplaced within the Albee Formation, east-central Vermont, preserves evidence of interaction with a CO2-bearing hydrous fluid during Acadian metamorphism. Coupled advective and diffusive cross-layer fluxes of CO2 are recorded by forwards progress of the hydration-carbonation reaction: 3 amphibole + 2 epidote + 8 H2O + 10 CO2 = 3 chlorite + 10 calcite + 21 quartz Advection, diffusion and mineral reaction rates are modelled from reaction progress data through application of an analytical solution to the 1-D mass conservation equation for linear reaction kinetics (Lichtner 1988; Lasaga and Rye 1993; Skelton et al. in press). Dimensionless Peclet (Pe) and Damköhler (ND) numbers which describe the ratios of advection to diffusion and reaction rate to advection are thus resolved, from which time-integrated fluid fluxes are calculated. Small Pe (<10), large ND (>10) and small time-integrated fluid fluxes (<5 m3/m2) are obtained, predicting that cross-layer fluxes of CO2 are largely diffusive. It follows that, within the Albee schists, fluid flow must have been layer parallel. Where fluid flow is layer parallel, it is both interesting and informative to consider the geometry of fluid flow at a fold hinge. For layer-parallel fluid flow to be maintained, the flow direction must reverse which is difficult to justify with regards to the driving force. It is perhaps more reasonable that fluid should “escape” through the fold hinge (cf. Skelton et al. 1995), either via close-spaced microveins (cf. Cole and Graham 1994) or macro-scale axial-planar quartz veins (Ferry 1992, 1994). At present, the Albee schists are ～ vertical and strike ～ N–S. This reflects: (1) E–W recumbent folding of strata (early Acadian “nappe-stage” deformation; D1); (2) N–S arching of strata (late Acadian “dome-stage” deformation; D2). In the Strafford Quadrangle, east-central Vermont, curious “Coarse Garnet Schists” occur in the axial regions of D1 fold closures. On the basis of this spatial association, crystal morphologies, reaction textures and chemical zoning profiles, it is postulated that the Coarse Garnet Schists developed in response to structurally focused fluid escape. That fluid flow was syn-D1 is implicit to this argument. As such, layer-parallel fluid flow must have been ～ horizontal. Although this conclusion is in close agreement with that of Ferry (1994), up-temperature fluid flow is not implicated.  相似文献   

5.
Time variation of surface fluxes of heat, moisture and momentum over a sea station (20°N 89°E) in the north Bay of Bengal has been computed by profile method for the period 18th–25th August 1990 using meteorological data of MONTBLEX-90 from ORVSagarkanya. The fluxes showed synoptic and diurnal variations which are marked during depression (20th–21st August) compared to their variation prior to and after this period. Variations of heat and water vapour fluxes were in phase. Night time fluxes are relatively high compared to day time. Average momentum transfer during depression was two to three times large. Variations in Bowen ratio were relatively large during day time. During depression, it varied between 0·2 in day time and about 0·3 at night and in the undisturbed period between ?0·1 and 0·2 during day time and 0·2 and 0·25 at night. The study shows that the assumptionC D=CH=CE of the exchange coefficients normally used in estimating the fluxes by the bulk aerodynamic method is not appropriate becauseC H/CD≈2,C E/CD≈1·5 andC H/CE≈1·4.  相似文献   

6.
The first and possibly only major rise of atmospheric oxygen, from pO2 ≤ 0.1% PAL (the present atmospheric level) to pO2 ≥ 10% PAL, appears to have occurred sometime before 2 Ga ago, although the exact time of and the cause(s) for the rise have been hotly debated. Equally important questions on the atmospheric oxygen concern its stability, especially the mechanisms regulating the atmospheric pO2 level and the causes and magnitude of pO2 variations since the first major rise of atmospheric oxygen. Previous efforts to model the pO2 variation during the Phanerozoic time have typically relied on secondary information, such as the carbon and sulfur isotopic records of sedimentary rocks, and on simple dynamics of the geochemical cycles of O, C, S, and P based on box-type models. As a result, many kinetic questions about the variation and stability of atmospheric oxygen could not have been answered. Here we quantitatively evaluate the dynamics and stability of atmospheric O2 and CO2, using recent experimental data, field observations, and a new model for the C-O coupled geochemical cycles. We examine the change with time in the fluxes of various compounds (O2, CO2, phosphate, organic C, carbonate C, C-bearing reduced volcanic gases, and C-free reduced volcanic gases) among the various reservoirs (atmosphere, soil, surface ocean, deep ocean, the lower crust and mantle, and upper crust) under a variety of scenarios. Our model does not assume steady-state fluxes for any of the reservoirs. Rather, the model incorporates the kinetic experimental data on oxidation of coal, a proxy for kerogen, the dynamics of soil formation and erosion, the kinetics of decomposition of organic matter in the Oceans by aerobic and anaerobic bacteria, the equilibrium ocean-atmosphere carbonate model, the observed relationships among the organic burial flux, dissolved O2 content of deep ocean, and sedimentation rates, and the three-box model ocean. The important parameters that strongly influence the dynamics of atmospheric O2, are found to be (a) the total area of soil formation on Earth; (b) the average soil depth; (c) the average rate of physical erosion of soils, which is linked to the average rate of accumulation of clastic sediments in the oceans; (d) the composition and flux of volcanic gas; and (e) the level of atmospheric CO2. We develop kinetic equations linking these parameters to the production and consumption fluxes of atmospheric oxygen and also to stable pO2 values. Considering the likely ranges of variations in these parameters in geologic history, we suggest that the atmospheric pO2 level is likely to have stayed within a very narrow range of 0.6-2 PAL and that the entire ocean, except for local euxinic basins, is likely to have been basically oxygenated since the first major rise of atmospheric oxygen more than 2 Ga ago.  相似文献   

7.
Much uncertainty exists in spatial and temporal variations of nitrous oxide (N2O) emissions from coastal marshes in temperate regions. To investigate the spatial and temporal variations of N2O fluxes and determine the environmental factors influencing N2O fluxes across the coastal marsh dominated by Suaeda salsa in the Yellow River estuary, China, in situ measurements were conducted in high marsh (HM), middle marsh (MM), low marsh (LM), and mudflat (MF) in autumn and winter during 2011–2012. Results showed that mean N2O fluxes and cumulative N2O emission indicated intertidal zone of the examined marshes as N2O sources over all sampling seasons with range of 0.0051 to 0.0152 mg N2O m?2 h?1 and 7.58 to 22.02 mg N2O m?2, respectively. During all times of day and the seasons measured, N2O fluxes from the intertidal zone ranged from ?0.0004 to 0.0644 mg N2O m?2 h?1. The freeze/thaw cycles in sediments during early winter (frequent short-term cycle) and midwinter (long-term cycle) were one of main factors affecting the temporal variations of N2O emission. The spatial variations of N2O fluxes in autumn were mainly dependent on tidal fluctuation and plant composition. The ammonia-nitrogen (NH4 +–N) in sediments of MF significantly affected N2O emissions (p < 0.05), and the high concentrations of Fe in sediments might affect the spatial variation of N2O fluxes. This study highlighted the large spatial variation of N2O fluxes across the coastal marsh (coefficient of variation (CV) = 127.86 %) and the temporal variation of N2O fluxes during 2011–2012 (CV = 137.29 %). Presently, the exogenous C and N loadings of the Yellow River estuary are increasing due to human activities; thus, the potential effects of exogenous C and N loadings on N2O emissions during early winter should be paid more attention as the N2O inventory is assessed precisely.  相似文献   

8.
New empirical relations are derived for source parameters of the Koyna–Warna reservoir-triggered seismic zone in Western India using spectral analysis of 38 local earthquakes in the magnitude range M L 3.5–5.2. The data come from a seismic network operated by the CSIR-National Geophysical Research Institute, India, during March 2005 to April 2012 in this region. The source parameters viz. seismic moment, source radius, corner frequency and stress drop for the various events lie in the range of 1013–1016 Nm, 0.1–0.4 km, 2.9–9.4 Hz and 3–26 MPa, respectively. Linear relationships are obtained among the seismic moment (M 0), local magnitude (M L), moment magnitude (M w), corner frequency (fc) and stress drop (?σ). The stress drops in the Koyna–Warna region are found to increase with magnitude as well as focal depths of earthquakes. Interestingly, accurate depths derived from moment tensor inversion of earthquake waveforms show a strong correlation with the stress drops, seemingly characteristic of the Koyna–Warna region.  相似文献   

9.
Gulf of Aqaba is recognized as an active seismic zone where many destructive earthquakes have occurred. The estimation of source parameters and coda Q attenuation are the main target of this work. Fifty digital seismic events in eight short-period seismic stations with magnitude 2.5–5.2 are used. Most of these events occurred at hypocentral depths in the range of 7–20 km, indicating that the activity was restricted in the upper crust. Seismic moment, M o, source radius, r, and stress drop, Δσ, are estimated from P- and S-wave spectra using the Brune’s seismic source model. The average seismic moment generated by the whole sequence of events was estimated to be 4.6E?+?22 dyne/cm. The earthquakes with higher stress drop occur at 10-km depth. The scaling relation between the seismic moment and the stress drop indicates a tendency of increasing seismic moment with stress drop. The seismic moment increases with increasing the source radius. Coda waves are sensitive to changes in the subsurface due to the wide scattering effects generating these waves. Single scattering model of local earthquakes is used to the coda Q calculation. The coda with lapse times 10, 20, and 30 s at six central frequencies 1.5, 3, 6, 12, 18, 24 Hz are calculated. The Q c values are frequency dependent in the range 1–25 Hz, and are approximated by a least squares fit to the power law [ $ {Q_c}(f) = {Q_o}{(f/{f_o})^\eta } $ ]. The average of Q c values increases from 53?±?10 at 1.5 Hz to 700?±?120 at 24 Hz. The average of Q o values ranges from 13?±?1 at 1.5 Hz to 39?±?4 at 24 Hz. The frequency exponent parameter η ranges between 1.3?±?0.008 and 0.9?±?0.001.  相似文献   

10.
Theoretical spectral energy distributions for Sakurai's object at 300–1000 nm are derived. A model-atmosphere grid with T eff=5000–6250 K and logg=0.0–1.0 is computed for the chemical composition of Sakurai's object using opacity sampling including molecular and atomic absorption. Opacity due to absorption in 20 band systems of diatomic molecules is computed using the JOLA technique. The theoretical fluxes are compared with the observed energy distribution in a spectrum of Sakurai's object taken in April 1997. It is shown that (a) the theoretical energy distributions agree well qualitatively with the observed spectrum and depend strongly on the effective temperature; (b) C2 and CN molecular bands are dominant in the visible and near-infrared spectrum, while atomic absorption is important at UV and blue wavelengths; and (c) comparison of the observed and computed spectra yields an effective temperature for Sakurai's object in April 1997 T eff≈5250–5500 K. The dependence of the computed spectra at 300–1000 nm on the input parameters and adopted approximations is also discussed.  相似文献   

11.
Mud volcanoes are important pathways for CH4 emission from deep buried sediments; however, the importance of gas fluxes have hitherto been neglected in atmospheric source budget considerations. In this study, gas fluxes have been monitored to examine the stability of their chemical compositions and fluxes spatially, and stable C isotopic ratios of CH4 were determined, for several mud volcanoes on land in Taiwan. The major gas components are CH4 (>90%), “air” (i.e. N2 + O2 + Ar, 1–5%) and CO2 (1–5%) and these associated gas fluxes varied slightly at different mud volcanoes in southwestern Taiwan. The Hsiao-kun-shui (HKS) mud volcano emits the highest CH4 concentration (CH4 > 97%). On the other hand, the Chung-lun mud volcano (CL) shows CO2 up to 85%, and much lower CH4 content (<37%). High CH4 content (>90%) with low CO2 (<0.2%) are detected in the mud volcano gases collected in eastern Taiwan. It is suggestive that these gases are mostly of thermogenic origin based on C1 (methane)/C2 (ethane) + C3 (propane) and δ13CCH4 results, with the exception of mud volcanoes situated along the Gu-ting-keng (GTK) anticline axis showing unique biogenic characteristics. Only small CH4 concentration variations, <2%, were detected in four on-site short term field-monitoring experiments, at Yue-shi-jie A, B, Kun-shui-ping and Lo-shan A. Preliminary estimation of CH4 emission fluxes for mud volcanoes on land in Taiwan fall in a range between 980 and 2010 tons annually. If soil diffusion were taken into account, the total amount of mud volcano CH4 could contribute up to 10% of total natural CH4 emissions in Taiwan.  相似文献   

12.
Study of the 26 December 2011 Aswan earthquake,Aswan area,South of Egypt   总被引：1，自引：1，他引：0  
The source process and parameters for a moderate earthquake of magnitude Ml 4.1 that occurred on the Kalabsha fault at the Aswan area are analyzed. The derived focal mechanisms of this event and other two aftershocks using polarities of P, SV, and SH waves show strike-slip fault with minor vertical movement of normal type. The solutions give two nodal planes trending ENE–WSW and NNW–SSE in close agreement with the surface traces of the faults crossing the area. The movement is right lateral along the first plane while left lateral along the second one. The rupture process characterization of this event has been investigated by using the empirical Green’s function deconvolution method. By inversion only for the P wave part of the records of these three events (main and other two aftershocks), the source time function for the master events and the azimuthally variations in the (RSTF) pulse amplitude are retrieved for estimating the rupture directivities. The estimated rupture direction is combined with the P-wave focal mechanisms for the three events to identify the fault plane solution for these earthquakes. Based on the width, amplitudes, and numbers of the isolated source time functions, a complex bi-lateral rupture of the studied earthquake is delineated. The source parameters of the master event is calculated and the derived corner frequencies f o for P-wave spectra show a value of 6.6 Hz; the seismic moment (M o ) is 4.2?×?1022 Nm; the average displacement (U) is 0.5 m; fault radius (r) 40 m; the average value of the stress drops (Δσ) is 0.6 Mpa, and the moment magnitude (M w ) is 4.4.  相似文献   

13.
We calculated the quality factor, Qc, at frequencies from 6 to 24 Hz using coda waves of 97 aftershocks of the Petatlan, Mexico, earthquake (March 14, 1979; MS=7.6). The data were recorded parallel (between Acapulco and Playa Azul) and perpendicular (between Petatlan and Mexico City) to the coast. The results are the following: at 12 and 24 Hz there is no significant difference in the attenuation (Qc−1) along the two paths; at 6 Hz, Qc−1 has a large scatter in both directions. This observation indicates strong site effects at this frequency; average Qc−1 is slightly higher between Petatlan–Acapulco (toward SE) than between Petatlan–Playa Azul (toward NW); and at high frequencies, Qc−1 remains essentially constant perpendicular to the coast. These results show that the large seismic wave amplifications in Mexico City are caused by shallow site effects.  相似文献   

14.
《Comptes Rendus Geoscience》2003,335(6-7):577-595
This article focuses on the contribution of natural ecosystems (forests, grasslands) and agrosystems to carbon sequestration either in biomass or in soil. Carbon stocks are important (650 Gt in biomass, 1500 to 2000 Gt in soils as compared with 750 for atmospheric CO2), and also fluxes that led to CO2 emissions in the past (due to deforestation or cultivation) and which now turn to carbon sequestration (2 GtC/year). This article shows great spatial variations in stocks and fluxes and great measurement difficulties, especially for stock variations. Anthropic actions such as reforestation (mainly in the North), changes in land use or in crop management, can increase carbon sequestration in biomass or soil, with a residence time of several decades, which is not insignificant with respect to the Kyoto protocol and which also has other environmental benefits. To cite this article: M. Robert, B. Saugier, C. R. Geoscience 335 (2003).  相似文献   

15.
Tibetan Plateau (TP) is the highest and most extensive plateau in the world and has been known as the roof of the world, and it is sensitive to climate change. The researches of CO2 fluxes (F C) in the TP region play a significant role in understanding regional and global carbon balance and climate change. Eddy covariance flux measurements were conducted at three sites of south-eastern TP comprising Dali (DL, cropland ecosystem), LinZhi (LZ, alpine meadow ecosystem) and Wenjiang (WJ, cropland ecosystem); amongst those DL and LZ are located in plateau region, while WJ is in plain region. Dynamics of F C and influences of vegetation, meteorological (air temperature, photosynthetically active radiation, soil temperature and soil water content) and terrain factors (altitude) were analysed on the basis of data taken during 2008. The results showed that, in the cool sub-season (March, April, October and December), carbon sink appeared even in December with fluxes of (?0.021 to ?0.05) mg CO2 m?2 s?1 and carbon source only in October (0.03 ± 0.0048) mg CO2 m?2 s?1 in DL and WJ site. In LZ site, carbon sink was observed in April: (?0.036 ± 0.0023) mg CO2 m?2 s?1 and carbon sources in December and March (0.008–0.010 mg CO2 m?2 s?1). In the hot sub-season (May–August), carbon source was observed only in May with (0.011 ± 0.0022), (0.104 ± 0.0029) and (0.036 ± 0.0017) fluxes in LZ, DL and WJ site, respectively, while carbon sinks with (?0.021 ± 0.0041), (?0.213 ± 0.0007) and (?0.110 ± 0.0015) mg CO2 m?2 s?1 fluxes in LZ, DL, and WJ, respectively. Comparing with plain region (WJ), carbon sinks in plateau region (DL and LZ) lasted for a longer time, and the absorption sum was large and up to (–357.718 ± 0.0054) and (?371.111 ± 0.0039) g C m?2 year?1, respectively. The LZ site had the weakest carbon sink with (?178.547 ± 0.0070) g C m?2 year?1. Multivariate analysis of covariance showed that altitude (AL) as an independent factor explained 39.5 % of F C (P < 0.026). F C had a quadratic relationship with Normalized difference vegetation index (NDVI) (R 2 ranges from 0.485 to 0.640 for three sites), an exponential relationship with soil temperature at 5-cm depth (ST 5) at night time and a quadratic relationship with air temperature (T a) at day time. Path analysis indicated that photosynthetically active radiation (PAR), sensible heat fluxes (H) and other factors all had direct or indirect effects on F C in all of the three tested sites around the south-eastern TP.  相似文献   

16.
Observations of eclipses of the radio pulsar B1259-63 by the disk of its Be-star companion SS 2883 provide an excellent opportunity to study the winds of stars of this type. The eclipses lead to variations in the radio flux (due to variations in the free-free absorption), dispersion measure, rotation measure, and linear polarization of the pulsar. We have carried out numerical modeling of the parameters of the Be-star wind and compared the results with observations. The analysis assumes that the Be-star wind has two components: a disk wind in the equatorial plane of the Be star with a power-law fall-off in the electron density n e with distance from the center of the star \(\rho (n_e \sim \rho ^{ - \beta _o } )\), and a spherical wind above the poles. The parameters for a disk model of the wind are estimated. The disk is thin (opening angle 7.5°) and dense (electron density at the stellar surface n0e ～ 1012 cm?3, β0 = 2.55). The spherical wind is weak (n0e ? 109 cm?3, β0 = 2). This is the first comparison of calculated and observed fluxes of the pulsating radio emission.  相似文献   

17.
Carbon dioxide (CO2) emission from the river-type reservoir is an hotspot of carbon cycle within inland waters. However, related studies on the different types of reservoirs are still inadequate. Therefore, we sampled the Three Gorges Reservoir (TGR), a typical river-type reservoir having both river and lake characteristics, using an online system (HydroCTM/CO2) and YSI-6600v2 meter to determine the partial pressure of carbon dioxide (pCO2) and physical chemical parameters in 2013. The results showed that the CO2 flux from the mainstream ranged from 26.1 to 92.2 mg CO2/m2 h with average CO2 fluxes of 50.0 mg/m2 h. The CO2 fluxes from the tributary ranged from ?10.91 to 53.95 mg CO2/m2 h with area-weighted average CO2 fluxes of 11.4 mg/m2 h. The main stream emits CO2 to the atmosphere the whole year; however, the surface water of the tributary can sometimes act as a sink of CO2 for the atmosphere. As the operation of the TGR, the tributary became more favorable to photosynthetic uptake of CO2 especially in summer. The total CO2 flux was estimated to be 0.34 and 0.03 Tg CO2/year from the mainstream and the tributaries, respectively. Our emission rates are lower than previous estimates, but they are in agreement with the average CO2 flux from temperate reservoirs estimated by Barros et al. (Nat Geosci 4(9):593–596, 2011).  相似文献   

18.
In order to better understand the spatiotemporal variations and interrelationships of greenhouse gases (GHG), monthly surface fluxes and profile concentrations of GHG (CO2, N2O and CH4) in karst areas in the Guizhou Province, southwest China, were measured from June 2006 to May 2007. GHG fluxes showed high variability, with a range of 460.9?C1,281.2?mg?m?2?h?1 for CO2, ?25.4 to 81.5???g?m?2?h?1 for N2O and ?28.7 to ?274.9???g?m?2?h?1 for CH4, but no obvious seasonal change trends of the fluxes existed. Profile concentrations of CO2, N2O and CH4 varied between 0.5 and 31.5?mL?L?1, 0.273 and 0.734, and 0.1 and 3.5???L?L?1, respectively. In general, concentrations of CO2 and N2O increased with depth, while CH4 had an inverse trend. However, in October, November and January, the reversal of depth patterns of GHG concentrations took place below 15?cm, close to the soil?Crock interface. The spatiotemporal distribution of CO2 in soil profile was significantly positively correlated with that of N2O (p?<?0.05?C0.01) and negatively correlated with that of CH4 (p?<?0.01). The correlation analysis showed that soil temperature and moisture may be responsible for GHG dynamics in the soils, rather than the exchange of GHG between land and atmosphere.  相似文献   

19.
A data base for the composition and emission rates of more than 100 thermal manifestations including boiling geothermal systems and 23 volcanoes along the 1900 km long Kamchatka-Kuril (KK) arc is presented. These results were used to estimate mean fluxes of volatiles from the KK arc. The fluxes from the KK arc are compared with the fluxes from the best studied Central American (CA) arc and with the compiled literature data on global fluxes. The error ranges and the OUT/IN (in)balance calculations are also discussed. The estimated fluxes of volatiles from volcanic fumaroles and the observed, normalized to the Cl content, fluxes from hydrothermal systems are very close, with the higher hydrothermal flux from Kuril Islands due to a larger number of the acidic Cl-SO4 springs on the Islands and their outflow rates. The total volcanic SO2 flux from the whole KK arc is estimated to be higher than 3000 t/d. The measured S and C fluxes from hydrothermal systems are much lower than the volcanic output due to the loss of these components in the upper crust (mineral precipitation). The Cl/3He ratio is inferred to be a stable indicator of the arc setting for hydrothermal and volcanic fluids with a mean value of (2 ± 4) × 109. Comparison of the obtained volcano-hydrothermal fluxes with fluxes calculated from the erupted solid volcanic products at Kamchatka and Kurils during Holocene time reveals that the total estimated volatile output from the KK arc is compatible with the total magmatic output if the intruded to erupted ratio is close to 7, i.e. almost the same as assumed for the Central American arc. Calculated fluxes as well as the ratios for OUT/IN fluxes (volcanic + hydrothermal output/slab + mantle input) for CO2, S, H2O, Cl, N2, 4He and 3He from the KK arc normalized to the arc length are in general close to the global estimates. The fractions of CO2 and S in the total volatile output at KK arc derived directly from the mantle wedge are 18% and 16% (mole basis), respectively. Fractions of mantle derived H2O, N2 and Cl are much lower, less that 5% of their output.  相似文献   

20.
Community Oxygen and Nutrient Fluxes in Seagrass Beds of Florida Bay, USA   总被引：1，自引：0，他引：1  
We used clear, acrylic chambers to measure in situ community oxygen and nutrient fluxes under day and night conditions in seagrass beds at five sites across Florida Bay five times between September 1997 and March 1999. Underlying sediments are biogenic carbonate with porosities of 0.7–0.9 and with low organic content (<1.6%). The seagrass communities always removed oxygen from the water column during the night and produced oxygen during daylight, and sampling date and site significantly affected both night and daytime oxygen fluxes. Net daily average fluxes of oxygen (?4.9 to 49 mmol m?2 day?1) ranged from net autotrophy to heterotrophy across the bay and during the 18-month sampling period. However, the Rabbit Key Basin site, located in the west-central bay and covered with a dense Thalassia testudinum bed, was always autotrophic with net average oxygen production ranging from 4.8 to 49 mmol m?2 day?1. In November 1998, three of the five sites were strongly heterotrophic and oxygen production was least at Rabbit, suggesting the possibility of hypoxic conditions in fall. Average ammonium (NH4) concentrations in the water column varied widely across the bay, ranging from a mean of 6.9 μmol l?1 at Calusa in the eastern bay to a mean of 0.6 μmol l?1 at Rabbit Key for the period of study. However, average NH4 fluxes by site and date (?240 to 110 μmol m?2 h?1) were not correlated with water column concentrations and did not vary in a consistent diel, seasonal, or spatial pattern. Concentrations of dissolved organic nitrogen (DON) in the water column, averaged by site (15–25 μmol l?1), were greater than mean NH4 concentrations, and the range of day and night DON fluxes (?920 to 1,300 μmol m?2 h?1), averaged by site and date, was greater than the range of mean NH4 fluxes. Average DON fluxes did not vary consistently from day to night, seasonally or spatially. Mean silicate fluxes ranged from ?590 to 860 μmol m?2 h?1 across all sites and dates, but mean net daily fluxes were less variable and most of the time contributed small amounts of silicate to the water column. Mean concentrations of filterable reactive phosphorus (FRP) in the water column across the bay were very low (0.021–0.075 μmol l?1); but site average concentrations of dissolved organic phosphorus (DOP) were higher (0.04–0.15 μmol l?1) and showed a gradient of increasing concentration from east to west in the bay. A pronounced gradient in average surficial sediment total phosphorus (1.1–12 μmol g DW?1) along an east-to-west gradient was not reflected in fluxes of phosphorus. FRP fluxes, averaged by site and date, were low (?5.2 to 52 μmol m?2 h?1), highly variable, and did not vary consistently from day to night or across season or location. Mean DOP fluxes varied over a smaller range (?8.7 to 7.4 μmol m?2 h?1), but also showed no consistent spatial or temporal patterns. These small DOP fluxes were in sharp contrast to the predominately organic phosphorus pool in surficial sediments (site means?=?0.66–7.4 μmol g DW?1). Significant correlations of nutrient fluxes with parameters related to seagrass abundance suggest that the seagrass community may play a major role in nutrient recycling. Integrated means of net daily fluxes over the area of Florida Bay, though highly variable, suggest that seagrass communities might be a source of DOP and NH4 to Florida Bay and might remove small amounts of FRP and potentially large amounts of DON from the waters of the bay.  相似文献   

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