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121.
We report chemical compositions (major and trace components including light hydrocarbons), hydrogen, oxygen, helium and nitrogen
isotope ratios of volcanic and geothermal fluids of Mutnovsky volcano, Kamchatka. Several aspects of the geochemistry of fluids
are discussed: chemical equilibria, mixing of fluids from different sources, evaluation of the parent magmatic gas composition
and contributions to magmatic vapors of fluids from different reservoirs of the Kamchatkan subduction zone. Among reactive
species, hydrogen and carbon monoxide in volcanic vapors are chemically equilibrated at temperatures >300°C with the SO2-H2S redox-pair. A metastable equilibrium between saturated and unsaturated light hydrocarbons is attained at close to discharge
temperatures. Methane is disequilibrated. Three different sources of fluids from three fumarolic fields in the Mutnovsky craters
can be distinguished: (1) magmatic gas from a large convecting magma body discharging through Active Funnel, a young crater
with the hottest fumaroles (up to 620°C) contributing ~80% to the total volcanic gas output; (2) volcanic fluid from a separate
shallow magma body beneath the Bottom Field of the main crater (96–280°C fumaroles); and (3) hydrothermal fluid with a high
relative and absolute concentrations of CH4 from the Upper Field in the main crater (96–285°C fumaroles). The composition of the parent magmatic gas is estimated using
water isotopes and correlations between He and other components in the Active Funnel gases. The He-Ar-N2 systematics of volcanic and hydrothermal fluids of Mutnovsky are consistent with a large slab-derived sedimentary nitrogen
input for the nitrogen inventory, and we calculate that only ~1% of the magmatic N2 has a mantle origin and <<1% is derived from the arc crust. 相似文献
122.
We shall consider diffusion or single-phase flow in a multiscale porous medium which represents an infinite set of self-similar double-porosity media. At each scale, the medium consists of a highly permeable network of connected channels and low-permeable blocks. The characteristic scale of heterogeneity is ε at the highest level of hierarchy, wherein ε is a small parameter. The ratio between the channel and block permeability at each scale is ε 2. The process analyzed is described using a diffusion equation with an oscillating multiscale diffusion parameter. The macroscale behavior is of interest. The transition to the macroscale is performed by means of the two-scale homogenization procedure. One step of averaging at each level of hierarchy leads to the appearance of the memory terms in the averaged equation. The successive averaging steps lead to progressive memory accumulation, so at each step of averaging, the macroscale model changes its type, and even the result of the second step is unknown a priori. The objective was to determine the macroscopic limit model for the infinite number of scales. By the method of induction, we obtained the macroscale model for an arbitrary number of scales and its limit for the infinite hierarchy. The limit model represents the system of two equations with memory terms. The kernel of the memory operator is the solution of a nonlinear integro-differential equation. Its solution is obtained through Laplace transform. 相似文献
123.
Abstract– We present the geology and interpreted shock features of the Suavjärvi circular structure. Suavjärvi is a circular feature (illustrated by satellite imagery, topography, and magnetic data) located in the central part of the Karelian Craton (lat. 63°07′N, long. 33°23′E). To date, little information on the geologic and impact features of the Suavjärvi structure is available in the literature. The structure is characterized by gravity and magnetic lows and disruption of the regional magnetic fabric. In the northeastern and southwestern parts of the structure, several erosional remnants of highly disturbed rocks occur referred to as monomict and polymict megabreccia. These comprise blocks of both basement granitoids and supracrustal greenstone rocks. The impact origin of polymict megabreccia and therefore of the Suavjärvi structure is confirmed by observations of closely spaced planar microstructures at angles consistent with planes that have Miller indices indicative of impact shock effects, mostly of ω{10¯13}. The Suavjärvi is considered to be a remnant of a deeply eroded and metamorphosed impact structure, which has a diameter of 16 km and was formed during the Paleoproterozoic (older than 2.2 Ga); this is inferred from the age of the overlying volcanic‐sedimentary Jatulian sequence. Suavjärvi underwent regional metamorphism that resulted in obliteration or transformation of shock metamorphic effects. Massive sulfides occur within megabreccia; originating probably from postimpact redeposition of pre‐existing mineralization. 相似文献
124.
125.
Slope steaks are one of the most intriguing modern phenomena observed on Mars. They have been mostly interpreted as some specific type of granular flow. We propose another mechanism for slope streak formation on Mars. It involves natural seasonal formation of a modest amount of highly concentrated chloride brines within a seasonal thermal skin, and runaway propagation of percolation fronts. Given the current state of knowledge of temperature regimes and the composition and structure of the surface layer in the slope streak regions, this mechanism is consistent with the observational constraints; it requires an assumption that a significant part of the observed chlorine to be in form of calcium and ferric chloride, and a small part of the observed hydrogen to be in form of water ice. This “wet” mechanism has a number of appealing advantages in comparison to the widely accepted “dry” granular flow mechanism. Potential tests for the “wet” mechanism include better modeling of the temperature regime and observations of the seasonality of streak formation. 相似文献
126.
Results of studying characteristic features of variability of the water surface temperature fields of Lake Ladoga during the
open water period are presented. Anomalies and extreme deviations of real spatial distributions from those typical of the
scales of synoptic variability are estimated. Typical surface temperature distribution of Lake Ladoga during an open water
period occupies not more than 20% of the lake area. The near-shore shallow water area is characterized as an area of most
anomalous water temperature distribution. The abnormality extent changes from month to month. July is the most anomalous month
of the open water period. 相似文献
127.
Background insect herbivory, in addition to insect outbreaks, can have an important long term influence on the performance
of tree species. Since a projected warmer climate may favour insect herbivores, we use a dynamic ecosystem model to investigate
the impacts of background herbivory on vegetation growth and productivity, as well as distribution and associated changes
in terrestrial ecosystems of northern Europe. We used the GUESS ecosystem modelling framework and a simple linear model for
including the leaf area loss of Betula pubescens in relation to mean July temperature. We tested the sensitivity of the responses of the simulated ecosystems to different,
but realistic, degrees of insect damage. Predicted temperature increases are likely to enhance the potential insect impacts
on vegetation. The impacts are strongest in the eastern areas, where potential insect damage to B. pubescens can increase by 4–5%. The increase in insect damage to B. pubescens results in a reduction of total birch leaf area (LAI), total birch biomass and birch productivity (Net Primary Production).
This effect is stronger than the insect damage to leaf area alone would suggest, due to its second order effect on the competition
between tree species. The model's demonstration that background herbivory may cause changes in vegetation structure suggests
that insect damage, generally neglected by vegetation models, can change predictions of future forest composition. Carbon
fluxes and albedo are only slightly influenced by background insect herbivory, indicating that background insect damage is
of minor importance for estimating the feedback of terrestrial ecosystems to climate change. 相似文献
128.
Naumenko M. A. Guzivaty V. V. Nesterov N. A. Sybetto D. A. 《Doklady Earth Sciences》2019,486(1):585-587
Doklady Earth Sciences - A digital bathymetric model with a 10 × 10 m spatial resolution was created on the basis of the depth sounding on the southwestern slope of Valaam Island with the use... 相似文献
129.
The measured sky twilight brightness of a site is believed to be connected with main factors such as geographical latitude, elevation of the site above sea level, the season of observations and the aerosol pollution. These factors may decrease the sky twilight brightness and thus improve the crescent visibility limits. The effect of these factors on the visibility conditions to see the new Moon are investigated in the present work. The results show that the visibility conditions has improved at sites situated at higher northern geographical latitudes and higher elevation above sea level. The conditions to see the new Moon in winter season is better than the summer season. The aerosol pollution has a great effect on the visibility of the new Moon at sun's depression 5°, while for sun's depression greater than 5° the aerosol pollution has a small effect. 相似文献
130.
By analysing records made in the northern taiga forests of the Lapland Reserve (Kola Peninsula, Russia) during 1930–1998, we unexpectedly discovered a decline in the length of the snow-free and ice-free periods by 15–20 days due to both delayed spring and advanced autumn/winter. Respective seasonal temperatures best explained the dates of all phenological phases: 1 °C shift in temperature was approximately equal to 2–5 day shift in phenology. However the phenological shiftsduring the observation period are much larger than could be expected from the slight (0.56 °C) drop in temperatures during August–September, suggesting that the biotic effects of a very slight cooling have been enhanced by one or more unknown factors. Although emissions of sulphur dioxide from the nickel-copper smelter at Monchegorsk may have contributed to the observed trend (via changes in regional radiative budget), we found no evidence of direct pollution impact on dates of birch autumnal coloration or birch leaf fall, which exhibited the largest (22 days) shift between 1930 and 1998. The detected phenological trends agree with an increase in winter (snow) precipitation in the study area by 44%; however, effects of precipitation on any of the investigated phenological phases were far from significant. Our results highlight the importance of phenological records for the assessment of past regional environmental changes, and demonstrates that the prediction of even the simplest biotic responses to the Global Changes requires a profound understanding of the interactive impact of abiotic factors on the ecosystem. 相似文献