Variations in the composition of particulate organic matter in a time-series sediment trap     

Cindy Lee  Stuart G. Wakeham  John W. Farrington 《Marine Chemistry》1983,13(3):181-194

A time-series sediment trap was used to collect material for organic geochemical analyses as part of the Sediment Trap Intercomparison Experiment. The flux of particulate matter was more likely related to a change in current direction during the course of the experiment than to small-scale changes in surface productivity. Of the compounds measured, the n-alkanes reflected this change most dramatically, decreasing with the change in current direction.Amino acid and lipid components were measured in the samples. Amino acids made up 15–35% of the total organic carbon flux and 35–75% of the total organic nitrogen flux collected in the traps. Specific amino acids indicative of bacterial biomass or activity suggested that microbial growth occurred in the traps, probably as a result of incomplete poisoning by NaN₃. However, the effect of this growth on the bulk composition of particulate matter appeared to be minimal.The amino acid distribution of particulate organic material collected by large volume filtration (LVF) was not significantly different from the sediment trap material, except that the LVF material did not appear to be affected by bacterial growth.  相似文献   

The polarization of P-waves in anisotropic media     

Stuart Crampin  Ralph A. Stephen  Robert McGonigle 《Geophysical Journal International》1982,68(2):477-485

Summary. The paper examines P -wave propagation in anisotropic solids, and demonstrates the effect of anisotropy on the polarizations of quasi P -waves. The deviation of the polarization of the quasi P -wave from the propagation vector may be significant, but is in almost the same direction as the deviation of the group-velocity vector. Since the group-velocity, or energy propagation, vector follows seismic ray paths, the apparent deviation is the difference of the polarization and group-velocity deviations and is small. Consequently, it may be easily overlooked, hidden by noise, or attributed to the effects of inhomogeneity.  相似文献   

The countryside: planning and change: Blacksell,M. and Gilg,A. London: Allen and Unwin, 1981. 262 pp.     

Paul White 《Applied geography (Sevenoaks, England)》1983,3(2):161-163

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Effective anisotropic elastic constants for wave propagation through cracked solids   总被引：19，自引：0，他引：19  

Stuart Crampin 《Geophysical Journal International》1984,76(1):135-145

Summary. Theoretical developments of Hudson demonstrate how to calculate the variations of velocity and attenuation of seismic waves propagating through solids containing aligned cracks. The analysis can handle a wide variety of crack configurations and crack geometries. Hudson associates the velocity variations with effective elastic constants. In this paper we associate the variation of attenuation with the imaginary parts of complex effective elastic constants. These complex elastic constants permit the simulation of wave propagation through two-phase materials by the calculation of wave propagation through homogeneous anisotropic solids.  相似文献   

X-ray and extreme ultraviolet (1–400 Å) spectroscopy of the sun,from OSO-III     

W. M. Neupert  W. A. White  W. J. Gates  M. Swartz  R. M. Young 《Solar physics》1969,6(2):183-192

X-ray spectra of the sun have been obtained during solar flares. New emission lines are observed in the spectral range from 1.3 Å to 3 Å, and 8 Å–20 Å, the most intense of the new emission features being tentatively attributed to optical transitions in high stages of ionization of iron (Fexxv through Fexx). Studies of the variability of these lines during flares provide new information of the development of a hot plasma in the initial stages of the flare event.  相似文献   

The IGU commission on man and environment     

Gilbert F. White 《Geoforum》1976,7(2):143-147

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The Žermanice sill: new insights into the mineralogy,petrology, age,and origin of the teschenite association rocks in the Western Carpathians,Czech Republic     

Matýsek  Dalibor  Jirásek  Jakub  Skupien  Petr  Thomson  Stuart N. 《International Journal of Earth Sciences》2018,107(7):2553-2574

International Journal of Earth Sciences - The Žermanice locality represents the best-exposed example of the meta-basaltoid/meta-gabbroic rock type of the teschenite association. It forms a...  相似文献   

Late Pleistocene to Holocene vegetation and climate changes in northwestern Chukotka (Far East Russia) deduced from lakes Ilirney and Rauchuagytgyn pollen records     

Andrei A. Andreev  Elena Raschke  Boris K. Biskaborn  Stuart A. Vyse  Jeremy Courtin  Thomas Böhmer  Kathleen Stoof-Leichsenring  Stefan Kruse  Lyudmila A. Pestryakova  Ulrike Herzschuh 《Boreas: An International Journal of Quaternary Research》2021,50(3):652-670

This paper presents two new pollen records and quantitative climate reconstructions from northern Chukotka documenting environmental changes over the last 27.9 ka. Open tundra- and steppe-like habitats dominated between 27.9 and 18.7 cal. ka BP. Betula and Alnus shrubs might have grown in sheltered microhabitats but disappeared after 18.7 cal. ka BP. Although the climate was rather harsh, local herb-dominated communities supported herbivores as is evident by the presence of coprophilous spores in the sediments. The increase in Salix and Cyperaceae ~16.1 cal. ka BP suggests climate amelioration. Shrub Betula appeared ~15.9 cal. ka BP, and became dominant after ~15.52 cal. ka BP, whilst typical steppe communities drastically reduced. Very high presence of Botryococcus in the Lateglacial sediments reflects widespread shallow habitats, probably due to lake level increase. Shrub Alnus became common after ~13 cal. ka BP reflecting further climate amelioration. Simultaneously, herb communities gradually decreased in the vegetation reaching a minimum ~11.8 cal. ka BP. A gradual decrease of algae remains suggests a reduction of shallow-water habitats. Shrubby and graminoid tundra was dominant ~11.8–11.1 cal. ka BP, later Salix stands significantly decreased. The forest-tundra ecotone established in the Early Holocene, shortly after 11.1 cal. ka BP. Low contents of green algae in the Early Holocene sediments likely reflect deeper aquatic conditions. The most favourable climate conditions were between ~10.6 and 7 cal. ka BP. Vegetation became similar to the modern after ~7 cal. ka BP but Pinus pumila came to the Ilirney area at about 1.2 cal. ka BP. It is important to emphasize that the study area provided refugia for Betula and Alnus during MIS 2. It is also notable that our records do not reflect evidence of Younger Dryas cooling, which is inconsistent with some regional environmental records but in good accordance with some others.  相似文献   

The effect of multiple particle sizes on cooling rates of chondrules produced in large‐scale shocks in the solar nebula          下载免费PDF全文

Melissa A. Morris  Stuart J. Weidenschilling  Steven J. Desch 《Meteoritics & planetary science》2016,51(5):870-883

Chondrules represent one of the best probes of the physical conditions and processes acting in the early solar nebula. Proposed chondrule formation models are assessed based on their ability to match the meteoritic evidence, especially experimental constraints on their thermal histories. The model most consistent with chondrule thermal histories is passage through shock waves in the solar nebula. Existing models of heating by shocks generally yield a good first‐order approximation to inferred chondrule cooling rates. However, they predict prolonged heating in the preshock region, which would cause volatile loss and isotopic fractionation, which are not observed. These models have typically included particles of a single (large) size, i.e., chondrule precursors, or at most, large particles accompanied by micron‐sized grains. The size distribution of solids present during chondrule formation controls the opacity of the affected region, and significantly affects the thermal histories of chondrules. Micron‐sized grains evaporate too quickly to prevent excessive heating of chondrule precursors. However, isolated grains in chondrule‐forming regions would rapidly coagulate into fractal aggregates. Preshock heating by infrared radiation from the shock front would cause these aggregates to melt and collapse into intermediate‐sized (tens of microns) particles. We show that inclusion of such particles yields chondrule cooling rates consistent with petrologic and isotopic constraints.  相似文献   

Techniques for measuring rock weathering: application to a dated fan segment sequence in southern Tunisia     

Kevin White  Rob Bryant  Nick Drake 《地球表面变化过程与地形》1998,23(11):1031-1043

There are a number of techniques for estimating the amount of weathering a clast has undergone. These usually have the objective of establishing an ordinal chronology of geomorphological surfaces, or investigation of site-specific conditions affecting weathering rates. Three such techniques are applied to a dated sequence of alluvial fan segments in southern Tunisia. Two of these techniques depend on measuring surface roughness (the micro-roughness meter and a displacement approach) and one uses the structural weakening of the rock fabric (Schmidt hammer). The micro-roughness meter enables calculation of standard deviation of surface height variation, root mean square roughness and surface autocorrelation function. Of these techniques, Schmidt hammer rebound values, standard deviation, root mean square roughness and the displacement technique show systematic changes on the three fan segments which are statistically significant at the 0·05 level. However, the amount of variance in all datasets is very large, indicating the need for caution in application of these techniques for relative dating. © 1998 John Wiley & Sons, Ltd.  相似文献