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1.
Summary The discrepancy between measured (or estimated) visual range (V
g) and the one calculated from the drop size distribution (V
b), stated byTrappenberg on the basis of the measurements ofRittberger, is discussed. It is assumed that in the measurement of the drop size distribution the small droplets are discriminated. If the distributions are extrapolated to drop diameters of 2 or 1 ,V
b turns out to be in agreement withV
g.
Mit 1 Textabbildung 相似文献
Diskussionsbeitrag zur Frage der Sicht in Wolken
Zusammenfassung Die vonTrappenberg auf Grund der Messungen vonRittberger festgestellte Diskrepanz zwischen gemessener (oder geschätzter) SichtweiteV g und der aus der Tropfengrößenverteilung berechnetenV b wird diskutiert. Es wird angenommen, daß bei der Messung der Tropfengrößenverteilung die kleinen Tropfen nicht genügend zur Geltung kommen. Extrapoliert man die Verteilungen in zwangloser Weise bis zu Tropfendurchmessern von 2 oder 1 , so ergibt sich eine gute Übereinstimmung vonV b mitV g.
Résumé L'auteur discute la discrépance existant entre la visibilité mesurée (ou estimée)Vg et la visibilité calculéeV b au moyen de la répartition de la grosseur des gouttes, discrépance établie parTrappenberg en partant des mesures deRittberger. On admet alors que, lors de la mesure de la répartition de la grosseur des gouttes, les plus petites d'entre elles n'ont pas suffisament de poids. Si l'on extrapole cette répartition jusqu'à un diamètre des gouttes de 2 ou 1 , on constate alors une bonne concordance entreV b etV g.
Mit 1 Textabbildung 相似文献
2.
Gas hydrates in shallow deposits of the Amsterdam mud volcano, Anaximander Mountains, Northeastern Mediterranean Sea 总被引：2，自引：2，他引：0
Thomas Pape Sabine Kasten Matthias Zabel André Bahr Friedrich Abegg Hans-Jürgen Hohnberg Gerhard Bohrmann 《Geo-Marine Letters》2010,30(3-4):187-206
We investigated gas hydrate in situ inventories as well as the composition and principal transport mechanisms of fluids expelled at the Amsterdam mud volcano (AMV; 2,025 m water depth) in the Eastern Mediterranean Sea. Pressure coring (the only technique preventing hydrates from decomposition during recovery) was used for the quantification of light hydrocarbons in near-surface deposits. The cores (up to 2.5 m in length) were retrieved with an autoclave piston corer, and served for analyses of gas quantities and compositions, and pore-water chemistry. For comparison, gravity cores from sites at the summit and beyond the AMV were analyzed. A prevalence of thermogenic light hydrocarbons was inferred from average C1/C2+ ratios <35 and δ13C-CH4 values of ?50.6‰. Gas venting from the seafloor indicated methane oversaturation, and volumetric gas–sediment ratios of up to 17.0 in pressure cores taken from the center demonstrated hydrate presence at the time of sampling. Relative enrichments in ethane, propane, and iso-butane in gas released from pressure cores, and from an intact hydrate piece compared to venting gas suggest incipient crystallization of hydrate structure II (sII). Nonetheless, the co-existence of sI hydrate can not be excluded from our dataset. Hydrates fill up to 16.7% of pore volume within the sediment interval between the base of the sulfate zone and the maximum sampling depth at the summit. The concave-down shapes of pore-water concentration profiles recorded in the center indicate the influence of upward-directed advection of low-salinity fluids/fluidized mud. Furthermore, the SO 4 2? and Ba2+ pore-water profiles in the central part of the AMV demonstrate that sulfate reduction driven by the anaerobic oxidation of methane is complete at depths between 30 cm and 70 cm below seafloor. Our results indicate that methane oversaturation, high hydrostatic pressure, and elevated pore-water activity caused by low salinity promote fixing of considerable proportions of light hydrocarbons in shallow hydrates even at the summit of the AMV, and possibly also of other MVs in the region. Depending on their crystallographic structure, however, hydrates will already decompose and release hydrocarbon masses if sediment temperatures exceed ca. 19.3°C and 21.0°C, respectively. Based on observations from other mud volcanoes, the common occurrence of such temperatures induced by heat flux from below into the immediate subsurface appears likely for the AMV. 相似文献
3.
M. Adler C. Hensen S. Kasten H. D. Schulz 《International Journal of Earth Sciences》2000,88(4):641-654
Pore water concentration profiles of sediments at a site on the Amazon Fan were investigated and simulated with the numerical
model CoTReM (column transport and reaction model) to reveal the biogeochemical processes involved. The pore water profiles
for gravity core GeoB 4417-7 showed a distinct sulfate–methane transition zone in which deep sulfate reduction occurs. Only
a small sulfide peak could be observed at the reaction zone. Due to high amounts of iron minerals, the produced sulfide is
instantaneously precipitated in form of iron sulfides. We present a simulation which starts from a steady state system with
respect to pore water profiles for methane and sulfate. Furthermore, sulfide, iron, pH, pE, calcium and total inorganic carbon
(TIC) were included in the simulation. The program calculated mineral equilibria to mackinawite, iron sulfides (more stable
than mackinawite), iron hydroxides and calcite via saturation indices (SI) by a module incorporating the program PHREEQC (Parkhurst
1995). The measured sulfide and iron profiles are obtained in the simulation output by using a constant SI (=0) for mackinawite
and calcite, while a depth dependent SI distribution is applied for the PHREEQC phases “Pyrite” and “Fe(OH)3(a)”, representing
a composition and the kinetics of different iron sulfides and iron hydroxides. These SI distributions control the results
of sulfide and iron pore water profiles, especially conserving the sulfide profile at the reaction zone during the simulation.
The results suggest that phases of iron hydroxides are dissolved, mackinawite is precipitated within, and other iron sulfides
are precipitated below the reaction zone. The chemical reactivity of iron hydroxides corresponds to the rate of sulfide production.
The system H2O–CO2–CaCO3 is generally successfully maintained during the simulation. Deviations to the measured pH profile suggest that further processes
are active which are not included in the simulation yet.
Received: 9 November 1998 / Accepted: 26 October 1999 相似文献
4.
Biogeochemical controls on authigenic carbonate formation at the Chapopote “asphalt volcano”, Bay of Campeche 总被引：1，自引：0，他引：1
Thomas H. Naehr Daniel Birgel Gerhard Bohrmann Ian R. MacDonald Sabine Kasten 《Chemical Geology》2009,266(3-4):399-411
The Campeche Knolls in the Bay of Campeche, southern Gulf of Mexico, were investigated through detailed seafloor mapping, ROV surveys, and sediment and pore water sampling. The knolls are elongated, submarine hills created by salt tectonics with a positive relief of up to 800 m above the surrounding seafloor. Several of the knolls are associated with sea-surface oil slicks identified from satellite data, indicating the presence of hydrocarbon seeps on the seafloor. One of the knolls, named “Chapopote”, was studied in detail during two international research expeditions (SO174/2 and M67/2) and is characterized by extensive hydrocarbon seepage including large asphalt flows, oil and gas seeps, and seafloor gas hydrate deposits. Chemosymbiotic biological communities and authigenic carbonate deposits are associated with the seeps and are the result of both biogeochemical turnover and the interaction between downward-diffusing seawater and hydrocarbon-rich pore fluids at shallow sediment depth. Authigenic carbonates are characterized by aragonite, exhibit a porous texture, and are cemented by a matrix of microsparitic to sparitic aragonite. Macropores of the carbonates were completely filled with liquid oil. Carbonate microfabrics include peloidal or clotted fabrics that may indicate the existence of microenvironments resulting from microbial metabolism. Banded/botryoidal aragonite cements line the intra- and bioclasts and incompletely fill the pore spaces. The stable carbon isotopic composition of authigenic aragonite varies between − 28.6‰ and − 17.9‰ (PDB), identifying oil oxidation as the primary source of carbon to the DIC pool, while lipid biomarker data demonstrate the concurrent existence of microbial communities responsible for anaerobic oxidation of methane (AOM). These observations indicate the presence of additional, AOM-independent reactions responsible for carbon sequestration at hydrocarbon seeps and demonstrate the complexity of biogeochemical processes at seep sites in the Gulf of Mexico basin. Oxygen isotope data of authigenic aragonite vary from + 2.5‰ to + 3.8‰ (PDB), indicating carbonate precipitation in slight disequilibrium with the surrounding pore fluids. 相似文献
5.
6.
Redox sensitivity of P cycling during marine black shale formation: Dynamics of sulfidic and anoxic, non-sulfidic bottom waters 总被引：1，自引：0，他引：1
A high-resolution geochemical record of a 120 cm black shale interval deposited during the Coniacian-Santonian Oceanic Anoxic Event 3 (ODP Leg 207, Site 1261, Demerara Rise) has been constructed to provide detailed insight into rapid changes in deep ocean and sediment paleo-redox conditions. High contents of organic matter, sulfur and redox-sensitive trace metals (Cd, Mo, V, Zn), as well as continuous lamination, point to deposition under consistently oxygen-free and largely sulfidic bottom water conditions. However, rapid and cyclic changes in deep ocean redox are documented by short-term (∼15-20 ka) intervals with decreased total organic carbon (TOC), S and redox-sensitive trace metal contents, and in particular pronounced phosphorus peaks (up to 2.5 wt% P) associated with elevated Fe oxide contents. Sequential iron and phosphate extractions confirm that P is dominantly bound to iron oxides and incorporated into authigenic apatite. Preservation of this Fe-P coupling in an otherwise sulfidic depositional environment (as indicated by Fe speciation and high amounts of sulfurized organic matter) may be unexpected, and provides evidence for temporarily non-sulfidic bottom waters. However, there is no evidence for deposition under oxic conditions. Instead, sulfidic conditions were punctuated by periods of anoxic, non-sulfidic bottom waters. During these periods, phosphate was effectively scavenged during precipitation of iron (oxyhydr)oxides in the upper water column, and was subsequently deposited and largely preserved at the sea floor. After ∼15-25 ka, sulfidic bottom water conditions were re-established, leading to the initial precipitation of CdS, ZnS and pyrite. Subsequently, increasing concentrations of H2S in the water column led to extensive formation of sulfurized organic matter, which effectively scavenged particle-reactive Mo complexes (thiomolybdates). At Site 1261, sulfidic bottom waters lasted for ∼90-100 ka, followed by another period of anoxic, non-sulfidic conditions lasting for ∼15-20 ka. The observed cyclicity at the lower end of the redox scale may have been triggered by repeated incursions of more oxygenated surface- to mid-waters from the South Atlantic resulting in a lowering of the oxic-anoxic chemocline in the water column. Alternatively, sea water sulfate might have been stripped by long-lasting high rates of sulfate reduction, removing the ultimate source for HS− production. 相似文献
7.
Dr. Fritz Kasten 《Theoretical and Applied Climatology》1967,15(1-2):62-66
Summary A simple method is developed which allows for estimating the deviations of the relative optical air mass for a given vertical
air density profile from the relative optical air mass for the ARDC Model Atmosphere, 1959 which serves as standard. In case
of the mean profiles given byQuiroz [3] for middle latitudes, summer; middle latitudes, winter; arctic summer; and arctic winter the air mass deviations turn
out to be small.
Zusammenfassung Es wird eine einfache Methode entwickelt, um aus den Abweichungen eines gegebenen vertikalen Luftdichteprofils von der als Standard dienenden ARDC-Modell-Atmosph?re 1959 die entsprechenden Abweichungen in der relativen optischen Luftmasse abzusch?tzen. Im Fall der vonQuiroz [3] angegebenen mittleren Luftdichteprofile für mittlere Breiten, Sommer; mittlere Breiten, Winter; arktischen Sommer und arktischen Winter erweisen sich die Luftmassen-Abweichungen als gering.
Résumé On développe ici une méthode simple permettant d'estimer les déviations de la masse optique relative d'air pour un profil donné de la densité verticale de l'air en partant du modèle d'atmosphère ARDC 1959 pris pour référence. Dans le cas des profils moyens indiqués parQuiroz [3] pour les latitudes moyennes en été ou en hiver ainsi que pour l'arctique en été ou en hiver, les déviations dues aux différentes masses d'air sont faibles.相似文献
8.
Gas hydrate decomposition recorded by authigenic barite at pockmark sites of the northern Congo Fan 总被引：1，自引：0，他引：1
Sabine Kasten Kerstin N?then Christian Hensen Volkhard Spie? Martin Blumenberg Ralph R. Schneider 《Geo-Marine Letters》2012,32(5-6):515-524
The geochemical cycling of barium was investigated in sediments of pockmarks of the northern Congo Fan, characterized by surface and subsurface gas hydrates, chemosynthetic fauna, and authigenic carbonates. Two gravity cores retrieved from the so-called Hydrate Hole and Worm Hole pockmarks were examined using high-resolution pore-water and solid-phase analyses. The results indicate that, although gas hydrates in the study area are stable with respect to pressure and temperature, they are and have been subject to dissolution due to methane-undersaturated pore waters. The process significantly driving dissolution is the anaerobic oxidation of methane (AOM) above the shallowest hydrate-bearing sediment layer. It is suggested that episodic seep events temporarily increase the upward flux of methane, and induce hydrate formation close to the sediment surface. AOM establishes at a sediment depth where the upward flux of methane from the uppermost hydrate layer counterbalances the downward flux of seawater sulfate. After seepage ceases, AOM continues to consume methane at the sulfate/methane transition (SMT) above the hydrates, thereby driving the progressive dissolution of the hydrates “from above”. As a result the SMT migrates downward, leaving behind enrichments of authigenic barite and carbonates that typically precipitate at this biogeochemical reaction front. Calculation of the time needed to produce the observed solid-phase barium enrichments above the present-day depths of the SMT served to track the net downward migration of the SMT and to estimate the total time of hydrate dissolution in the recovered sediments. Methane fluxes were higher, and the SMT was located closer to the sediment surface in the past at both sites. Active seepage and hydrate formation are inferred to have occurred only a few thousands of years ago at the Hydrate Hole site. By contrast, AOM-driven hydrate dissolution as a consequence of an overall net decrease in upward methane flux seems to have persisted for a considerably longer time at the Worm Hole site, amounting to a few tens of thousands of years. 相似文献
9.
Florence Schubotz Julius S. Lipp Sabine Kasten Matthias Zabel Kai-Uwe Hinrichs 《Geochimica et cosmochimica acta》2011,75(16):4377-4415
At the Chapopote Knoll in the Southern Gulf of Mexico, deposits of asphalt provide the substrate for a prolific cold seep ecosystem extensively colonized by chemosynthetic communities. This study investigates microbial life and associated biological processes within the asphalts and surrounding oil-impregnated sediments by analysis of intact polar membrane lipids (IPLs), petroleum hydrocarbons and stable carbon isotopic compositions (δ13C) of hydrocarbon gases. Asphalt samples are lightly to heavily biodegraded suggesting that petroleum-derived hydrocarbons serve as substrates for the chemosynthetic communities. Accordingly, detection of bacterial diester and diether phospholipids in asphalt samples containing finely dispersed gas hydrate suggests the presence of hydrocarbon-degrading bacteria. Biological methanogenesis contributes a substantial fraction to the methane captured as hydrate in the shallow asphalt deposits evidenced by significant depletion in 13C relative to background thermogenic methane. In sediments, petroleum migrating from the subsurface stimulates both methanogenesis and methanotrophy at a sulfate-methane transition zone 6-7 m below the seafloor. In this zone, microbial IPLs are dominated by archaeal phosphohydroxyarchaeols and archaeal diglycosidic diethers and tetraethers. Bacterial IPLs dominate surface sediments that are impregnated by severely biodegraded oil. In the sulfate-reduction zone, diagnostic IPLs indicate that sulfate-reducing bacteria (SRB) play an important role in petroleum degradation. A diverse mixture of phosphohydroxyarchaeols and mixed phospho- and diglycosidic archaeal tetraethers in shallow oil-impregnated sediments point to the presence of anaerobic methane-oxidizing ANME-2 and ANME-1 archaea, respectively, or methanogens. Archaeal IPLs increase in relative abundance with increasing sediment depth and decreasing sulfate concentrations, accompanied by a shift of archaeol-based to tetraether-based archaeal IPLs. The latter shift is suggested to be indicative of a community shift from ANME-2 and/or methanogenic archaea in shallower sediments to ANME-1/methanogenic archaea and possibly benthic archaea in deeper sediments. 相似文献
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