A Three-Dimensional Global Model Study of Carbonyl Sulfide in the Troposphere and the Lower Stratosphere   总被引：4，自引：0，他引：4  

Erik Kjellström 《Journal of Atmospheric Chemistry》1998,29(2):151-177

Global distributions of carbonyl sulfide and carbon disulfide have been calculated with a three-dimensional global model of the atmospheric general circulation (ECHAM). The model calculates a global sink strength for carbonyl sulfide of 0.3 Tg S yr^-1, with vegetation uptake being the largest sink. With this sink strength, the sources have to be close to the lower limit of the present estimate in the literature. The calculated mixing ratios are higher in the Southern Hemisphere than in the Northern Hemisphere. This interhemispheric gradient is the opposite of what is observed demonstrating that the present knowledge of the distribution of sinks and sources is not fully adequate. The model calculations support the idea that the open oceans could act as a net sink of carbonyl sulfide. The calculated stratospheric photolysis of carbonyl sulfide constitutes about 4% of the total sink of carbonyl sulfide. A stratospheric production of sulfate from carbonyl sulfide of 0.013 Tg S yr^-1 is obtained, which is 3 to 12 times less than what is needed to maintain the stratospheric sulfate aerosol layer. Although these results are associated with uncertainties, due to the low upper boundary and coarse vertical resolution of the model, they support recent findings of a low stratospheric production of sulfate from carbonyl sulfide. Instead, sulfur dioxide transported from the troposphere is calculated to be the most important precursor for the stratospheric sulfate aerosol layer.  相似文献   

Determination of predevelopment denudation rates of an agricultural watershed (Cayaguás River, Puerto Rico) using in-situ-produced Be in river-borne quartz     

Erik Thorson Brown  Robert F. Stallard  Matthew C. Larsen  Didier L. Bourls  Grant M. Raisbeck  Franoise Yiou 《Earth and Planetary Science Letters》1998,160(3-4):723-728

Accurate estimates of watershed denudation absent anthropogenic effects are required to develop strategies for mitigating accelerated physical erosion resulting from human activities, to model global geochemical cycles, and to examine interactions among climate, weathering, and uplift. We present a simple approach to estimate predevelopment denudation rates using in-situ-produced cosmogenic ¹⁰Be in fluvial sediments. Denudation processes in an agricultural watershed (Cayaguás River Basin, Puerto Rico) and a matched undisturbed watershed (Icacos River Basin) were compared using ¹⁰Be concentrations in quartz for various size fractions of bed material. The coarse fractions in both watersheds bear the imprint of long subsurface residence times. Fine material from old shallow soils contributes little, however, to the present-day sediment output of the Cayaguás. This confirms the recent and presumably anthropogenic origin of the modern high denudation rate in the Cayaguás Basin and suggests that pre-agricultural erosional conditions were comparable to those of the present-day Icacos.  相似文献   

Refractional influences in astrometry and geodesy     

Prof. Erik Tengström 《Journal of Geodesy》1978,52(4):329-334

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Meeting of the Special Study Group V.49 of IAG on “Use of Geodetic Data for Studies of the Earth-moon System”     

Prof. Erik Tengström 《Journal of Geodesy》1978,52(4):335-336

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Vertebrate use of muskrat lodges and burrows     

Erik Kiviat 《Estuaries and Coasts》1978,1(3):196-200

The literature is reviewed and analysis made of references to more than 60 vertebrates that use lodges or bank burrows built by the muskrat,Ondatra zibethicus L. Muskrat homes are important to turtles, waterfowl, terns, carnivores, rodents, and other species for shelter, nesting, getting above the water, or seeking food. No use is obligate but the availability of muskrat homes may limit some species. Effects on vertebrate associates should be considered when muskrat populations are manipulated.  相似文献   

On the consequences of a long-term perspective for coastal management     

Erik M. Horstman  Kathelijne M. Wijnberg  Alfons J. Smale  Suzanne J.M.H. Hulscher 《Ocean & Coastal Management》2009,52(12):593-611

The potential impacts of climate change on coastal zones combined with the ever increasing number of people living in these areas, motivate a more long-term perspective in coastal management. To explore whether such a perspective raises the need for developing coastal management strategies at larger spatial scales, this paper presents a case study for the dune-protected Holland coast. Long-term (200 years) coastal management strategies are set-up at different levels of spatial aggregation, accounting for specific characteristics of the coast itself and for types of land use in the hinterland. Using a combination of multi-criteria analysis and cost-benefit analysis the new coastal management strategies are compared to the long-term continuation of present coastal management practice. It appears that the large uncertainties that inevitably accompany a long-term perspective do not preclude the comparison of long-term coastal management strategies. Additionally, it appears that a long-term perspective favors solutions for coastal defense enhancement that are more spatially extended and alongshore uniform than those emerging from continuing today's coastal management practice for two centuries.  相似文献   

Volatile retention from cometary impacts on the Moon     

Lissa Ong  Erik I. Asphaug  Robert F. Coker 《Icarus》2010,207(2):578-589

Impacts of comets and asteroids play an important role in volatile delivery on the Moon. We use a novel method for tracking vapor masses that reach escape velocity in hydrocode simulations of cometary impacts to explore the effects of volatile retention. We model impacts on the Moon to find the mass of vapor plume gravitationally trapped on the Moon as a function of impact velocity. We apply this result to the impactor velocity distribution and find that the total impactor mass retained on the Moon is approximately 6.5% of the impactor mass flux. Making reasonable assumptions about water content of comets and the comet size-frequency distribution, we derive a water flux for the Moon. After accounting for migration and stability of water ice at the poles, we estimate a total 1.3×10⁸-4.3×10⁹ metric tons of water is delivered to the Moon and remains stable at the poles over 1 Ga. A factor of 30 uncertainty in the estimated cometary impact flux is primarily responsible for this large range of values. The calculated mass of water is sufficient to account for the neutron fluxes poleward of 75° observed by Lunar Prospector. A similar analysis for water delivery to the Moon via asteroid impacts shows that asteroids provide six times more water mass via impacts than comets.  相似文献   

Degradation of dissolved organic monomers and short-chain fatty acids in sandy marine sediment by fermentation and sulfate reduction     

Thomas Valdemarsen  Erik Kristensen 《Geochimica et cosmochimica acta》2010,74(5):1593-1605

The decay of a wide range of organic monomers (short-chain volatile fatty acids (VFA’s), amino acids, glucose and a pyrimidine) was studied in marine sediments using experimental plug flow-through reactors. The reactions were followed in the presence and absence of 10 mM SO₄²⁻. Degradation stoichiometry of individual monomers (inflow concentration of 6 mM organic C) was traced by measuring organic (VFA’s, amino acids) and inorganic (CO₂, NH₄⁺, SO₄²⁻) compounds in the outflow. Fermentation of amino acids was efficient and complete during passage through anoxic sediment reactors. Aliphatic amino acids (alanine, serine and glutamate) were primarily recovered as CO₂ (24-34%), formate (3-22%) and acetate (41-83%), whereas only ∼1/3 of the aromatic amino acid (tyrosine) was recovered as CO₂ (13%) and acetate (20%). Fermentation of glucose and cytosine was also efficient (78-86%) with CO₂ (30-35%), formate (3%) and acetate (28-33%) as the primary products. Fermentation of VFA’s (acetate, propionate and butyrate), on the other hand, appeared to be product inhibited. The presence of SO₄²⁻ markedly stimulated VFA degradation (29-45% efficiency), and these compounds were recovered as CO₂ (17% for butyrate to 100% for acetate) and acetate (51% and 82% for propionate and butyrate, respectively). When reaction stoichiometry during fermentation is compared with compound depletion during sulfate reduction, the higher proportion CO₂ recovery is consistent with lower acetate and formate accumulation. Our results therefore suggest that fermentation reactions mediate the initial degradation of added organic compounds, even during active sulfate reduction. Fermentative degradation stoichiometry also suggested significant H₂ production, and >50% of sulfate reduction appeared to be fuelled by H₂. Furthermore, our results suggest that fermentation was the primary deamination step during degradation of the amino acids and cytosine.  相似文献   

Devitrite (Na2Ca3Si6O16)—structural, spectroscopic and computational investigations on a crystalline impurity phase in industrial soda-lime glasses     

Volker Kahlenberg  Daniela Girtler  Erik Arroyabe  Reinhard Kaindl  Daniel M. Többens 《Mineralogy and Petrology》2010,100(1-2):1-9

Single crystals of devitrite (Na₂Ca₃Si₆O₁₆) were synthesized as pale-yellow transparent needle shaped crystals using a Na₂MoO₄-flux. Experiments aiming to prepare the K-equivalent of devitrite from the corresponding K₂MoO₄-flux were unsuccessful. The crystal structure of devitrite was determined from single-crystal X-ray diffraction data (Mo-K_α radiation, 2θ_max.?=?25.34°, R_int?=?2.66%) and refined in space group P $ \bar{1} $ (no. 2) to R(|F|)?=?3.08% using 2,513 observed reflections with I?>?2σ(I). Unit-cell parameters are: a?=?7.2291(8), b?=?10.1728(12), c?=?10.6727(12) Å, α?=?95.669(9), β?=?109.792(10), γ?=?99.156(9)°, V?=?719.19(14) ų, Z?=?2. The structure belongs to the group of multiple chain silicates consisting of dreier quadruple chains, i.e. the crystallochemical formula can be written as $ {\hbox{N}}{{\hbox{a}}_2}{\hbox{C}}{{\hbox{a}}_3}\left\{ {{\mathbf{uB}}{,4}_\infty^1} \right\}\left[ {^3{\hbox{S}}{{\hbox{i}}_6}} \right.\left. {{{\hbox{O}}_{16}}} \right\} $ . Linkage between the bands running along [100] is provided by double chains of edge sharing CaO₆-octahedra as well as additional more irregularly coordinated Na- and Ca-cations located in the tunnel-like cavities of the mixed tetrahedral-octahedral framework. Structural investigations were completed by Raman and infrared spectroscopical studies. The allocation of the bands to certain vibrational species was aided by density functional theory (DFT) calculations.  相似文献   

Towards a 4D topographic view of the Norwegian sea margin   总被引：1，自引：1，他引：0  

Morten Smelror  John Dehls  Jrg Ebbing  Eiliv Larsen  Erik R. Lundin   ystein Nordgulen  Per Terje Osmundsen  Odleiv Olesen  Dag Ottesen  Christophe Pascal  Thomas F. Redfield  Leif Rise 《Global and Planetary Change》2007,58(1-4):382

The present-day topography/bathymetry of the Norwegian mainland and passive margin is a product of complex interactions between large-scale tectonomagmatic and climatic processes that can be traced back in time to the Late Silurian Caledonian Orogeny. The isostatic balance of the crust and lithosphere was clearly influenced by orogenic thickening during the Caledonian Orogeny, but was soon affected by post-orogenic collapse including overprinting of the mountain root, and was subsequently affected by a number of discrete extensional events eventually leading to continental break-up in Early Eocene time. In the mid-Jurassic the land areas experienced deep erosion in the warm and humid climate, forming a regional paleic surface. Rift episodes in the Late Jurassic and Early Cretaceous, with differential uplift along major fault zones, led to more pronounced topographic contrasts during the Cretaceous, and thick sequences of clastic sediments accumulated in the subsiding basins on the shelf. Following renewed extension in the Late Cretaceous, a new paleic surface developed in the Paleocene. Following break-up the margin has largely subsided thermally, but several Cenozoic shortening events have generated positive contraction structures. On the western side of the on-shore drainage divide, deeper erosion took place along pre-existing weakness zones, creating the template of the present day valleys and fjords. In the Neogene the mainland and large portions of the Barents Sea were uplifted. It appears that this uplift permitted ice caps to nucleate and accumulate during the Late Pliocene northern hemisphere climatic deterioration. The Late Pliocene to Pleistocene glacial erosion caused huge sediment aprons to be shed on to the Norwegian Sea and Barents Sea margins. Upon removal of the ice load the landmass adjusted isostatically, and this still continues today.  相似文献