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1.
Matthew A.LAZZARA Sophie A.ORENDORF Taylor P.NORTON Jordan G.POWERS David H.BROMWICH Scott CARPENTIER John J.CASSANO Steven R.COLWELL Arthur M.CAYETTE Kirstin WERNER 《大气科学进展》2020,37(5):423-430
<正>1.Overview In July 2018, the Antarctic community came together to meet at the 13th Workshop on Antarctic Meteorology and Climate (WAMC) in Madison, Wisconsin, USA (Fig. 1); and in the following year in June 2019, the 14th WAMC was held in 相似文献
2.
ABSTRACT
A critical event in the trajectory of a sand grain saltating in air is its interaction with the surface. We examine the phenomenon of grain-bed impacts in two dimensions using a combination of dynamical computer simulations, analytical models and physical reasoning. The results indicate that the grain-bed collisions can be treated as two-body collisions with the bed particle assuming an effective mass greater than its true mass. Also, the presence of geometrical surface irregularities has a strong bearing on the interaction between saltating and surface grain populations, as well as on the formation of small-scale bedforms. 相似文献
A critical event in the trajectory of a sand grain saltating in air is its interaction with the surface. We examine the phenomenon of grain-bed impacts in two dimensions using a combination of dynamical computer simulations, analytical models and physical reasoning. The results indicate that the grain-bed collisions can be treated as two-body collisions with the bed particle assuming an effective mass greater than its true mass. Also, the presence of geometrical surface irregularities has a strong bearing on the interaction between saltating and surface grain populations, as well as on the formation of small-scale bedforms. 相似文献
3.
The carbonate compaction law: a new tool 总被引:2,自引:0,他引:2
WERNER RICKEN 《Sedimentology》1987,34(4):571-584
Carbonate content, compaction, and porosity are evaluated from a large number of samples using micritic marl-limestone alternations from Germany, France, and Italy. Compaction is measured directly by utilizing both deformed, originally cylindrical bioturbation tubes and steinkerns of ammonites. Additionally, a method is developed to indirectly evaluate the total compaction of the rock matrix by using early, selectively cemented burrows and fossils. Plots representing measurements of compaction versus carbonate content display distinctly non-linear relationships which show increasing compaction with decreasing carbonate content. These relationships are found to clearly correspond with the carbonate compaction law. The compaction law is introduced as a theoretical derivation for sediments and rocks which calculates the carbonate and non-carbonate content, compaction, and porosity. It is based on the assumption that the non-carbonate fraction standardized to the primary sediment-volume remains constant during carbonate diagenesis. The compaction law is used to calculate the most commonly found sediment/rock transformations (e.g. mechanical compaction, cementation, and chemical compaction) and to simulate the diagenetic processes of given examples. Decompaction formulas are developed to evaluate the porosity and carbonate content of the primary sediment. An example of calculating decompaction and determining the original composition of the sediment is given utilizing carbonates spanning the Cretaceous-Tertiary boundary at Gubbio (Italy). 相似文献
4.
Nonlinear sweeps have often successfully been employed in the 1960s. However, this area of sweep technology has been neglected since the introduction of digital recording techniques in the Vibroseis system. Now the advent of computerized recording instruments yields a new economical possibility of forming approximately nonlinear sweeps by combining several linear sweeps with or without time gaps to a “Combisweep”. The total duration of a Combisweep may be as long as the maximum available recording time, for example 32 s. Beside the attenuation of correlation noise, the new method has further merits, such as the weighting of predetermined frequency ranges, in order to effect a certain kind of optimum filtering on the emitter side, or in order to compensate to some degree for frequency dependent absorption. In all these applications the Combisweep is considered as one signal in the correlation process. But by correlating with the individual sweeps or a partial combination of them and by applying automatic switching at predetermined times within the gaps between the individual sweeps additional possibilities arise, such as obtaining in one run with a twenty-four channel recording unit twenty-four traces with small distances between vibrators and geophones for shallow reflections and another twenty-four traces with larger distances for deeper reflections. Various Combisweeps and their applications are presented. 相似文献
5.
MICHAEL J. HAMBREY WERNER EHRMANN 《Boreas: An International Journal of Quaternary Research》2004,33(4):300-318
The Mount Cook area in the Southern Alps of New Zealand is heavily glacierized with numerous peaks over 3000 m a.s.l. feeding several large valley glaciers. The region is subject to rapid tectonic uplift and heavy precipitation (up to 15 m per year). This paper describes the clast roundness, clast shape and textural characteristics associated with five glaciers (Fox, Franz Josef, Hooker, Mueller and Tasman) in terms of inputs to the glacier system, transport by the glaciers and reworking following glacial deposition. Inputs include rockfall, alluvial fan and avalanche material delivered to the surface of valley glaciers. Basal debris, where observed at the terminus of two glaciers, consists mainly of incorporated fluvial material. Following deposition, reworking is mainly by subglacial and proglacial streams. The dominant facies are (i) boulder gravel with mainly angular clasts on the steep slopes above the glaciers, (ii) sandy boulder gravel, with mainly angular and subangular clasts, forming lateral and end moraines, and (iii) sandy boulder/cobble gravel with mainly subrounded clasts, and sand, which represent glacially transported sediment reworked by braided rivers. Diamicton is rare in the contemporary glacial environment. Since most sediment associated with glaciers in the Southern Alps lacks unambiguous indications of glacial transport, interpretation of similar sediments in the geological record should not necessarily exclude the involvement of glacial processes. 相似文献
6.
Combined Trace Element and Pb-Nd-Sr-O Isotope Evidence for Recycled Oceanic Crust (Upper and Lower) in the Iceland Mantle Plume 总被引:2,自引:0,他引:2
KOKFELT THOMAS FIND; HOERNLE KAJ; HAUFF FOLKMAR; FIEBIG JENS; WERNER REINHARD; GARBE-SCHONBERG DIETER 《Journal of Petrology》2006,47(9):1705-1749
We present the results of a comprehensive major element, traceelement and SrNdPbO isotopic study of post-glacialvolcanic rocks from the Neovolcanic zones on Iceland. The rocksstudied range in composition from picrites and tholeiites, whichdominate in the main rift systems, to transitional and alkalicbasalts confined to the off-rift and propagating rift systems.There are good correlations of rock types with geochemical enrichmentparameters, such as La/Sm and La/Yb ratios, and with long-termradiogenic tracers, such as SrNdPb isotope ratios,indicating a long-lived enrichment/depletion history of thesource region. 87Sr/86Sr vs 143Nd/144Nd defines a negative array.Pb isotopes define well-correlated positive arrays on both 206Pb/204Pbvs 207Pb/204Pb and 208Pb/204Pb diagrams, indicating mixing ofat least two major components: an enriched component representedby the alkali basalts and a depleted component represented bythe picrites. In combined SrNdPb isotopic spacethe individual rift systems define coherent mixing arrays withslightly different compositions. The enriched component hasradiogenic Pb (206Pb/204Pb > 19·3) and very similargeochemistry to HIMU-type ocean island basalts (OIB). We ascribethis endmember to recycling of hydrothermally altered upperbasaltic oceanic crust. The depleted component that is sampledby the picrites has unradiogenic Pb (206Pb/204Pb < 17·8),but geochemical signatures distinct from that of normal mid-oceanridge basalt (N-MORB). Highly depleted tholeiites and picriteshave positive anomalies in mantle-normalized trace element diagramsfor Ba, Sr, and Eu (and in some cases also for K, Ti and P),negative anomalies for Hf and Zr, and low 18Oolivine values(4·65·0) below the normal mantle range.All of these features are internally correlated, and we, therefore,interpret them to reflect source characteristics and attributethem to recycled lower gabbroic oceanic crust. Regional compositionaldifferences exist for the depleted component. In SW Icelandit has distinctly higher Nb/U (68) and more radiogenic 206Pb/204Pbratios (18·2818·88) compared with the NErift (Nb/U 47; 206Pb/204Pb = 18·0718·47).These geochemical differences suggest that different packagesof recycled oceanic lithosphere exist beneath each rift. A thirdand minor component with relatively high 87Sr/86Sr and 207Pb/204Pbis found in a single volcano in SE Iceland (Öræfajökullvolcano), indicating the involvement of recycled sediments inthe source locally. The three plume components form an integralpart of ancient recycled oceanic lithosphere. The slope in theuranogenic Pb diagram indicates a recycling age of about 1·5Ga with time-integrated Th/U ratios of 3·01. Surprisingly,there is little evidence for the involvement of North AtlanticN-MORB source mantle, as would be expected from the interactionof the Iceland plume and the surrounding asthenosphere in formof plumeridge interaction. The preferential samplingof the enriched and depleted components in the off-rift andmain rift systems, respectively, can be explained by differencesin the geometry of the melting regions. In the off-rift areas,melting columns are truncated deeper and thus are shorter, whichleads to preferential melting of the enriched component, asthis starts melting deeper than the depleted component. In contrast,melting proceeds to shallower depths beneath the main rifts.The longer melting columns also produce significant amountsof melt from the more refractory (lower crustal/lithospheric)component. KEY WORDS: basalts; trace element and Sr, Nd, Pb, O isotope geochemistry; Iceland plume; isotope ratios; oceanic crustal recycling; partial melting; plumeridge interaction 相似文献
7.
David H.BROMWICH Matthew A.LAZZARA Arthur M.CAYETTE Jordan G.POWERS Kirstin WERNER John J.CASSANO Steven R.COLWELL Scott CARPENTIER Xun ZOU 《大气科学进展》2022,39(3):536-542
1. Overview In June 2021, the 16th Workshop on Antarctic Meteorology and Climate (WAMC) and the 6th Year of Polar Prediction in the Southern Hemisphere (YOPP-SH) Meeting (http://polarmet.osu.edu/WAMC;021/) were held online and hosted by the Polar Meteorology Group at Byrd Polar and Climate Research Center, The Ohio State University, Columbus,Ohio (Fig. 1). 相似文献
8.
Located near the southeastern limit of Africa, the Lesotho‐Drakensberg and associated escarpment is the highest range of African mountains south of the massifs in Tanzania. At the escarpment summit and on the adjacent high peaks, the climate is generally interpreted as marginal periglacial yet few data, specifically rainfall and temperature, exist on record at these altitudes. Climatic data from two temporary field stations on the escarpment edge, one of which is the highest rainfall station yet on record in southern Africa, provide contemporary surface‐climate conditions. Mean annual rainfall recorded between 2001 and 2005 averages 767.8 mm at Sani Pass summit (three complete years), and 753.2 mm on Sentinel Peak (two complete years); these values are less than those recorded for the same period in the mountain foothills. Even though rainfall is slightly below long‐term rainfall averages for the area due to a marginally dry spell, the data show that earlier estimates of between 1000 mm and 2000 mm rainfall per annum on the escarpment are too high. A measured mean air temperature of 5.8°C at Sani Pass, however, falls within the range estimated for the escarpment summit. Frost cycles in air and at the soil surface are frequent in winter, but absent in soil for summer, and no long‐duration surface‐soil freeze was measured. Temperatures thus confirm the marginal periglacial nature as postulated for previously, but precipitation data indicate a dryer environment than anticipated. Palaeoenvironmental scenarios, notably arguments for former glaciation based on extrapolations from somewhat exaggerated contemporary precipitation values, thus require re‐consideration. 相似文献
9.
Video observations of the underside of arctic sea ice-features and morphology on medium and small scales 总被引:2,自引:0,他引:2
Morphological structures and the occurrence of sea-ice sediments and ice-related algae at the ice floe-water column interface were studied by video observations in summer 1995. Recordings at twelve stations in the northern Laptev Sea and the adjacent Arctic Ocean showed large variations. On a medium-scale (metres), level ice and deformed floes as well as whole rafted and stacked floes were found. At the underside of floes, small-scale structures (centimetres such as bulges, depressions and holes were observed. The surface and sides of rafted floes sometimes had downward running grooves. Sediment inclusions occurred in diffuse or concentrated forms as well as in parallel streaks. Ice-related algae were visible as green areas at the underside of floes or as threads haniging into the water column. The distribution of sediments and algae was patchy. Some processes which might lead to the observed structures are suggested. 相似文献
10.
The so-called 10- phase of the MgO-SiO2-H2O (MSH) system wassynthesized with 100% yields from a 3: 4 MgO/SiO2 gel at fluidpressure of 50 kb and 500 C, but only during runs of up to1 h and with total H2O contents near 50 wt. % in the sealedcapsules. The water contents determined in the run productsindicate a chemical composition Mg3Si4O10(OH)20.65 H2O, whichis different from the composition reported by Bauer & Sclar(1981), which had 1 H2O molecule per talc formula. The 10-phase has a = 5.293(3) , b = 9.194(3) , c = 10.044(3) , ß=96.10(8)its calculated density is pcalc.= 2.672 g/cm3; the refractiveindices measured are nx = 1.554. and nx = 1.574. The compatibilityof mean refractive index, calculated density, and chemical compositionfalls within the category excellent of Mandarino(1979). Runs of longer durations and with total H2O again near 50 wt.%, seeded with the less hydrous phase talc with the same Mg/Siratio, show that the 10- phase breaks down in the range 3070kb, 200700 C to form more talc. Thus it is not the stablehydrous high-pressure equivalent of talc as reported by Yamamoto& Akimoto (1977), but a metastable phase, which cannot playany role as a natural mineral of the mantle or of subductionzones. If the tie-line forsterite-H2O is stable in the MSH system,as it seems to be for the conditions of our experiments, mostof the hydrous, silica-poor, new high-pressure MSH phases maybe without significance for the Earth, except perhaps phaseA with as yet an ambiguous composition. 相似文献