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1.
The effects of sedimentation and compaction on oceanic heat flow 总被引:1,自引:0,他引:1
Iain Hutchison 《Geophysical Journal International》1985,82(3):439-459
Summary. The estimation of environmental effects forms an important part of the interpretation of oceanic heat flow measurements. In particular, the perturbations associated with sedimentation and surface temperature changes must be taken into account. Analytical solutions can be obtained only for individual, simplified versions of these problems, whereas any real example is complicated by the process of sediment compaction which changes the bulk thermal properties with depth. A physical model is developed which uses sediment porosity trends to predict the thermal parameters and material advection rates for an evolving sediment/basement system. These values are then used in a numerical solution to the heat flow equation to give estimates of the perturbed surface heat flux through time. In addition to variations in sedimentation rate, sediment type, radioactive heat production and surface temperature changes are considered. Heat flow corrections may vary by up to a factor of 2 according to sediment type while radioactive heat production can offset the effects of sedimentation by as much as 40 per cent. The results also indicate that alterations determined from simple analytical models tend to over-estimate the true perturbation to the flux. 相似文献
2.
3.
Tuff deposits of the Koko Crater group consist largely of alkali basalt glass, either fresh or palagonitized. Most of the deposits are progressively palagonitized at depth, and topographic relations of palagonite on Koko Crater indicate that the palagonite was formed after the cone had been deeply eroded.The principal authigenic minerals in the palagonite tuffs were deposited in following sequence: phillipsite, chabazite, analcime, montmorillonite together with opal, and calcite. The amount of authigenic minerals in a given sample is generally proportional to the amount of palagonite, indicating that the authigenic minerals are produced in palagonitization of glass.Chemical analyses of sideromelane and associated palagonite by the electron microprobe show that about a quarter of the SiO2, half of the Al2O3 and MgO, and three quarters or more of the CaO, Na2O, and K2O are lost in converting sideromelane to an equal volume of palagonite. A substantial proportion of these components lost from the sideromelane are precipitated nearby in zeolites, montmorillonite, opal, and calcite.Reaction of sideromelane with percolating ground water at low temperatures accounts for the vertical zoning from relatively fresh tuffs down into palagonite tuffs. The pH and ionic strength of percolating water probably increased with depth by solution and hydrolysis of glass, and where the pH and ionic strength became sufficiently high, the glass reacted to form palagonite and zeolites. Palagonite was formed by a microsolution-precipitation mechanism rather than by hydration or devitrification. 相似文献
4.
Drivers of ecosystem and climate change in tropical West Africa over the past ∼540 000 years 下载免费PDF全文
5.
A model magneto-atmosphere is used to discuss the behavior of the group velocity for magnetoacoustic-gravity (MAG) waves as a function of their angular frequency. The qualitative frequency/time history of a signal generated by a source differs significantly from the case where the magnetic field is zero, for which a clear distinction may be made between the acoustic and gravity components of the signal. 相似文献
6.
Xiaoxian Zhang A. Glyn Bengough John W. Crawford Iain M. Young 《Journal of Hydrology》2002,260(1-4):75-87
The non-linear solvers in numerical solutions of water flow in variably saturated soils are prone to convergence difficulties. Many aspects can give rise to such difficulties and in this paper we address the gravity term and the prescribed-flux boundary in the Picard iteration. The problem of the gravity term in the Picard iteration is iteration-to-iteration oscillation as the gravity term is treated, by analogy with the time-step advance technique, ‘explicitly’ in the iteration. The proposed method for the gravity term is an improvement of the ‘implicit’ approach of Zhang and Ewen [Water Resour. Res. 36 (2000) 2777] by extending it to heterogeneous soil and approximating the inter-nodal hydraulic conductivity in the diffusive term and the gravity term with the same scheme. The prescribed-flux boundary in traditional methods also gives rise to iteration-to-iteration oscillation because there is no feedback to the flux in the solution at the new iteration. To reduce such oscillation, a new method is proposed to provide such a feedback to the flux. Comparison with traditional Picard and Newton iteration methods for a wide range of problems show that a combination of these two proposed methods greatly improves the stability and consequently the computational efficiency, making the use of small time step and/or under-relaxation solely for convergence unnecessary. 相似文献
7.
Regional variation in maturation of sandeels in the North Sea 总被引:1,自引:0,他引:1
8.
Wolf Uwe Reimold Iain McDonald Ralf‐Thomas Schmitt Birgit Hansen Juliane Jacob Christian Koeberl 《Meteoritics & planetary science》2013,48(9):1531-1571
Suevite and melt breccia compositions in the boreholes Enkingen and Polsingen are compared with compositions of suevites from other Ries boreholes and surface locations and discussed in terms of implications for impact breccia genesis. No significant differences in average chemical compositions for the various drill cores or surface samples are noted. Compositions of suevite and melt breccia from southern and northeastern sectors of the Ries crater do not significantly differ. This is in stark contrast to the published variations between within‐crater and out‐of‐crater suevites from northern and southern sectors of the Bosumtwi impact structure, Ghana. Locally occurring alteration overprint on drill cores—especially strong on the carbonate‐impregnated suevite specimens of the Enkingen borehole—does affect the average compositions. Overall, the composition of the analyzed impact breccias from Ries are characterized by very little macroscopically or microscopically recognized sediment‐clast component; the clast populations of suevite and impact melt breccia are dominated consistently by granitic and intermediate granitoid components. The Polsingen breccia is significantly enriched in a dioritic clast component. Overall, chemical compositions are of intermediate composition as well, with dioritic‐granodioritic silica contents, and relatively small contributions from mafic target components. Selected suevite samples from the Enkingen core have elevated Ni, Co, Cr, and Ir contents compared with previously analyzed suevites from the Ries crater, which suggest a small meteoritic component. Platinum‐group element (PGE) concentrations for some of the enriched samples indicate somewhat elevated concentrations and near‐chondritic ratios of the most immobile PGE, consistent with an extraterrestrial contribution of 0.1–0.2% chondrite‐equivalent. 相似文献
9.
Peter Jenniskens Emmanuel Jehin Remi A. Cabanac Christophe O. Laux Iain D. Boyd 《Meteoritics & planetary science》2004,39(4):609-616
Abstract— A meteor spectrum was recorded serendipitously at the European Southern Obrervatory (ESO) Very Large Telescope (VLT) during a long exposure in long‐slit spectroscopic mode with FORS1. The ?8 magnitude fireball crossed the narrow 1Î × 7î slit during the observation of a high z supernova in normal service mode operation on May 12, 2002. The spectrum covered the range of 637–1050 nm, where the meteor's air plasma emissions from N2, N, and O dominate. Carbon atom emission was not detected in the relatively unexplored wavelength range above 900 nm, but the observed upper limit was only 3 sigma less than expected from the dissociation of atmospheric CO2. The meteor trail was resolved along the slit, and the emission had a Gaussian distribution with a dimension of FWHM = 7.0 (±0.4) * sin(α) * H (km)/90 m, where α is the unknown angle between the orientation of the meteor path and slit and H the assumed altitude of the meteor in km. To our knowledge, this is the first observation of a spatially resolved spectrum across a meteor trail. Unlike model predictions, the plasma excitation temperature varied only from about 4,300 to 4,365 K across the trail, based on the ratio of atomic and molecular nitrogen emissions. Unfortunately, we conclude that this was because the meteor at 100 km altitude was out of focus. 相似文献
10.
Andrew?SwalesEmail author Iain?T.?MacDonald Malcolm?O.?Green 《Estuaries and Coasts》2004,27(2):225-243
Isolated patches ofSpartina anglica (cordgrass) at two sites on a wave-exposed mid-intertidal flat of the 340 km2 Manukau Harbor (Auckland, New Zealand) have developed very differently since being planted in the mid-1970s. Although the
two sites are only 0.5 km apart and at the same intertidal elevation,Spartina patches at the easternmost site (site 1) have as much as an order of magnitude higher biomass and accumulated sediment volume
thanSpartina patches at site 2. A field experiment was conducted to characterize waves and associated sediment dynamics at each site,
which might explain whySpartina patches at the two sites have developed so differently over the past 25 yr or so. Suspended sediments were measured and wave
characteristics were inferred from subsurface pressure data measured for 5 wk at bothSpartina sites and at an intermediate location. Bed-orbital speeds and frictional wave-energy dissipation were consistently lower
at the easternmost site with the largerSpartina patches. The west-to-east reduction in wave energy is due to the spatial arrangement of theSpartina sites relative to the predominant wind fetches. The wave-energy gradient is maintained by tidal-cycle variations in fetch
and bed friction and results in a west-to-east reduction in sand suspension. Silt, which is largely resuspended under southwest
winds, is redeposited in the low wave-energy conditions in and around the larger site 1Spartina patches. Shell accumulation bySpartina patches at site 1 occurs infrequently, during southwest winds >10 m s−1 and water depths >0.7 m, when waves are least attenuated by bed friction. Large between-site differences in the growth of
and sediment accumulation by theSpartina patch are consistent with the observed wave-energy gradient. The resulting spatial patterns of silt, sand, and shell resuspension
and deposition directly influence the rate of sediment accumulation bySpartina patches and the composition of accumulated sediment on this wave-exposed intertidal flat. 相似文献