δC variation in scallop shells: Increasing metabolic carbon contribution with body size?     

Anne Lorrain  Yves-Marie Paulet  Robert Dunbar  Michel Fontugne 《Geochimica et cosmochimica acta》2004,68(17):3509-3519

We examined δ¹³C values of shallow and deep-water scallop shells as well as δ¹³C of dissolved inorganic carbon (DIC) from the Bay of Brest in western Brittany. Time series of shell calcite δ¹³C do not reflect seasonal variation in seawater δ¹³C, but rather show a consistent pattern of decreasing δ¹³C with age, suggesting a metabolic effect rather than direct environmental control. This δ¹³C trend reflects an increasing contribution of metabolic CO₂ to skeletal carbonate throughout ontogeny, although this respired CO₂ does not seem to be the major source of skeletal carbon (contribution of only 10% over the first year of life). We propose a model of this effect that depends on the availability of metabolic carbon relative to the carbon requirements for calcification. A ratio of “respired to precipitated carbon” is calculated, and represents the amount of metabolic carbon available for calcification. Interestingly, this ratio increases throughout ontogeny suggesting a real increase of metabolic carbon utilization into the skeleton relative to carbon from seawater DIC. This ratio allows us to separate two different populations of Pecten maximus of different water depth. It is therefore suggested that shell δ¹³C might be used to track differences in the metabolic activity of scallops from different populations.  相似文献   

Mapping upper mantle anisotropy beneath SE France by SKS splitting indicates Neogene asthenospheric flow induced by Apenninic slab roll-back and deflected by the deep Alpine roots     

Guilhem Barruol  Anne Deschamps  Olivier Coutant   《Tectonophysics》2004,394(1-2):125-138

The presence of two regional seismic networks in southeastern France provides us high-quality data to investigate upper mantle flow by measuring the splitting of teleseismic shear waves induced by seismic anisotropy. The 10 three-component and broadband stations installed in Corsica, Provence, and western Alps efficiently complete the geographic coverage of anisotropy measurements performed in southern France using temporary experiments deployed on geodynamic targets such as the Pyrenees and the Massif Central. Teleseismic shear waves (mainly SKS and SKKS) are used to determine the splitting parameters: the fast polarization direction and the delay time. Delay times ranging between 1.0 and 1.5 s have been observed at most sites, but some larger delay times, above 2.0 s, have been observed at some stations, such as in northern Alps or Corsica, suggesting the presence of high strain zones in the upper mantle. The azimuths of the fast split shear waves define a simple and smooth pattern, trending homogeneously WNW–ESE in the Nice area and progressively rotating to NW–SE and to NS for stations located further North in the Alps. This pattern is in continuity with the measurements performed in the southern Massif Central and could be related to a large asthenospheric flow induced by the rotation of the Corsica–Sardinia lithospheric block and the retreat of the Apenninic slab. We show that seismic anisotropy nicely maps the route of the slab from the initial rifting phase along the Gulf of Lion (30–22 Ma) to the drifting of the Corsica–Sardinia lithospheric block accompanied by the creation of new oceanic lithosphere in the Liguro–Provençal basin (22–17 Ma). In the external and internal Alps, the pattern of the azimuth of the fast split waves follows the bend of the alpine arc. We propose that the mantle flow beneath this area could be influenced or perhaps controlled by the Alpine deep penetrative structures and that the Alpine lithospheric roots may have deflected part of the horizontal asthenospheric flow around its southernmost tip.  相似文献   

Geology, archaeology, and the ‘raging vortex of the “eolith” controversy’     

Anne O’Connor 《Proceedings of the Geologists' Association. Geologists' Association》2004,115(4):378

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Estimating historical in-lake alkalinity generation from sulfate reduction and its relationship to lake chemistry as inferred from algal microfossils   总被引：2，自引：4，他引：2  

Peter A. Siver  Richard Ricard  Richard Goodwin  Anne E. Giblin 《Journal of Paleolimnology》2003,29(2):179-197

Sediment cores were used to estimate in-lake alkalinity generation resulting from sulfate reduction relative to inferred changes in lakewater pH and trophic status over the last century in three Connecticut lakes. Despite being situated in geological settings with crystalline bedrock and thin, poorly buffered soils, and being impacted with high rates of acidic precipitation, none of the study lakes have declined in inferred pH based on scaled chrysophyte and diatom remains. In fact, the pH of one of the lakes, Coventry Lake, has significantly increased over the last century. Over the last 44 to 69 years the amount of sulfur stored in the sediments from each lake increased from ~two to three times resulting in mean rates of alkalinity generation ranging from 78 to 145 meq m^–2 yr^–1, significantly higher than the 45 to 48 meq m^–2 yr^–1 of hydrogen ions falling directly on the lake surfaces. In-lake alkalinity generation resulting from sulfate reduction has been sufficient to neutralize all of the acid falling directly onto the lake surfaces, as well as between 9% and 25% of the acid deposited onto the surrounding watersheds. Despite the increased importance of in-lake alkalinity generation, our findings support the hypothesis that significant amounts of alkalinity are also being generated in the catchments of the study lakes. The bulk of the increases in stored sulfur in all three lakes were as Fe sulfides and not in the form of organic sulfur, suggesting that the increases were the result of dissimilatory bacterial reduction of sulfate. As a result of the large increases in storage of Fe sulfides the ratio of total iron to chromium reducible sulfur (Fe:CRS) has declined in all cores over time. Despite the overall decline in Fe:CRS in recent sediments, values are still largely above 3 in more recent sediments of two of the lakes. However, values of Fe:CRS have dropped below 1 in surface sediments of Uncas Lake, suggesting that in-lake loading of phosphorus may be responsible for a recent shift in the algal flora towards a slightly more eutrophic condition.  相似文献   

Petrogenesis of olivine-phyric shergottites Sayh al Uhaymir 005 and Elephant Moraine A79001 lithology A     

Cyrena Anne Goodrich 《Geochimica et cosmochimica acta》2003,67(19):3735-3772

Martian meteorites Sayh al Uhaymir (SaU) 005 and lithology A of EETA79001 (EET-A) belong to a newly emerging group of olivine-phyric shergottites. Previous models for the origin of such shergottites have focused on mixing between basaltic shergottite-like magmas and lherzolitic shergottite-like material. Results of this work, however, suggest that SaU 005 and EET-A formed from olivine-saturated magmas that may have been parental to basaltic shergottites.SaU 005 and EET-A have porphyritic textures of large (up to ∼3 mm) olivine crystals (∼25% in SaU 005; ∼13% in EET-A) in finer-grained groundmasses consisting principally of pigeonite (∼50% in SaU 005; ∼60% in EET-A), plagioclase (maskelynite) and < 7% augite. Low-Ti chromite occurs as inclusions in the more magnesian olivine, and with chromian ulvöspinel rims in the more ferroan olivine and the groundmass. Crystallization histories for both rocks were determined from petrographic features (textures, crystal shapes and size distributions, phase associations, and modal abundances), mineral compositions, and melt compositions reconstructed from magmatic inclusions in olivine and chromite. The following observations indicate that the chromite and most magnesian olivine (Fo 74-70 in SaU 005; Fo 81-77 in EET-A) and pyroxenes (low-Ca pyroxene [Wo 4-6] of mg 77-74 and augite of mg 78 in SaU 005; orthopyroxene [Wo 3-5] of mg 84-80 in EET-A) in these rocks are xenocrystic. (1) Olivine crystal size distribution (CSD) functions show excesses of the largest crystals (whose cores comprise the most magnesian compositions), indicating addition of phenocrysts or xenocrysts. (2) The most magnesian low-Ca pyroxenes show near-vertical trends of mg vs. Al₂O₃ and Cr₂O₃, which suggest reaction with a magma. (3) In SaU 005, there is a gap in augite composition between mg 78 and 73. (4) Chromite cores of composite spinel grains are riddled with cracks, indicating that they experienced some physical stress before being overgrown with ulvöspinel. (5) Magmatic inclusions are absent in the most magnesian olivine, but abundant in the more ferroan, indicating slower growth rates for the former. (6) The predicted early crystallization sequence of the melt trapped in chromite (the earliest phase) in each rock produces its most magnesian olivine-pyroxene assemblage. However, in neither case is the total crystallization sequence of this melt consistent with the overall crystallization history of the rock or its bulk modal mineralogy.Further, the following observations indicate that in both SaU 005 and EET-A the fraction of solid xenocrystic or xenolithic material is small (in contrast to previous models for EET-A), and most of the material in the rock formed by continuous crystallization of a single magma (possibly mixed). (1) CSD functions and correlations of crystal size with composition show that most of the olivine (Fo 69-62 in SaU 005; Fo 76-53 in EET-A) formed by continuous nucleation and growth. (2) Groundmass pigeonites are in equilibrium with this olivine, and show continuous compositional trends that are typical for basalts. (3) The CSD function for groundmass pigeonite in EET-A indicates continuous nucleation and growth (Lentz and McSween, 2000). (4) The melt trapped in olivine of Fo 76 to 67 in EET-A has a predicted crystallization sequence similar to that inferred for most of the rock and produces an assemblage similar to its modal mineralogy. (5) Melt trapped in late olivine (Fo ∼ 64) in SaU 005 has a composition consistent with the inferred late crystallization history of the rock.The conclusion that only a small fraction of either SaU 005 or EET-A is xenocrystic or xenolithic implies that both rocks lost fractionated liquids in the late stages of crystallization. This is supported by: (1) high pigeonite/plagioclase ratios; (2) low augite contents; and (3) olivine CSD functions, which show a drop in nucleation rate at high degrees of crystallization, consistent with loss of liquid. For EET-A, this fractionated liquid may be represented by EET-B.  相似文献   

Simulation of digital earthquake accelerograms using the inverse discrete Fourier transform     

Hjrtur Thrinsson  Anne S. Kiremidjian 《地震工程与结构动力学》2002,31(12):2023-2048

Acceleration time histories of horizontal earthquake ground motion are obtained by inverting the discrete Fourier transform, which is defined by modelling the probability distribution of the Fourier phase differences conditional on the Fourier amplitude. The Fourier amplitude spectrum is modelled as a scaled, lognormal probability density function. Three parameters are necessary to define the Fourier amplitude spectrum. They are the total energy of the accelerogram, the central frequency, and the spectral bandwidth. The Fourier phase differences are simulated conditional on the Fourier amplitudes. The amplitudes are classified into three categories: small, intermediate and large. For each amplitude category, a beta distribution or a combination of a beta distribution and a uniform distribution are defined for the phase differences. Seven parameters are needed to completely define the phase difference distributions: two for each of the three beta distributions, and the weight of the uniform distribution for phase differences corresponding to small Fourier amplitudes. Approximately 300 uniformly processed horizontal ground motion records from recent California earthquakes are used to develop prediction formulas for the model parameters, as well as to validate the simulation model. The moment magnitude of the earthquakes ranges from 5.8 to 7.3. The source to site distance for all the records is less than 100 km. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

The fossil Coleoptera of the Two Creeks forest bed,Wisconsin     

Alan V. Morgan  Anne Morgan 《Quaternary Research》1979,12(2):226-240

A 21-kg sample of plant detritus from the Two Creeks forest bed at the junction of Kewaunee and Manitowoc Counties, Wisconsin, has produced a small, but well-preserved fauna of Coleoptera, Hymenoptera, and Diptera. Among the Coleoptera the majority of Carabidae (ground beetles) indicate moderately moist to fairly dry, open ground conditions with a sparsely vegetated substrate. Another significant beetle group is represented by the Scolytidae (bark beetles) nearly all of which inhabit spruce. The restricted number of Coleoptera species (21) is believed to represent an in situ assemblage and is part of about 50 taxa. Most of the Coleoptera identified to the species level have a transcontinental distribution, with the exception of two carabids which are extreme western forms, and nearly all reside within the boreal forest. The beetles indicate that the mean July temperature at Two Creeks approximately 11,850 yr B.P. was 14° to 16°C.  相似文献   

Stone movement through snow creep, 1963–75 mount twynam,snowy mountains,Australia     

J. N. Jennings  A. B. Costin 《地球表面变化过程与地形》1978,3(1):1-22

On the backwall of Twynam East Cirque selected stones moving through snow creep were marked and their movements from 1963 to 1975 measured. Their annual movements varied markedly between 1963 and 1970 but thereafter little. The percentage of stones failing to move varied reciprocally with snow thickness over a snow course in a comparable site near Spencers Creek. The annual mean movement, ranging from 7·6 to 36·3 cm, correlated strongly with Spencers Creek snow thickness. Frequent occurrence of annual movements of intermediate value characterise the process. Snow surface maps with 2m contours for 1964, 1974 and 1975 permitted determination of snow slope at the stone positions and of snow thickness by subtraction of ground heights. A 2 m contour ground surface map was also the basis for hillslope angles at stone positions. Basal area and area transverse to snow movement were calculated from measurements of the three principal axes of the stones. The vertical angles and directions of their abrasion tracks were measured. Rank correlation of stone movements with hillslope and snow slope was usually not significant but with track angle was so in most years. Track angle and direction are controlled partly by hillslope and partly by local rock geometry. Movements correlated inversely with stone basal area on which frictional drag depends. Correlation with stone transverse area was weak and inverse; this may be due to snow tending to move round larger stones. In most years there was significant correlation with snow thickness and basal stress (calculated from snow thickness and snow slope). However, the amount of ‘explanation’ associated with all the independent variables was small and the experiments revealed an importance of surface roughness at various scales in controlling stone movement which was much greater than expected from direct observation.  相似文献   

Reply to comment by G. E. Williams     

J.M. Bowler  G.S. Hope  J.N. Jennings  G. Singh  D. Walker 《Quaternary Research》1978,9(1):114-115

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Improvement of Fourier-Based Unconditional and Conditional Simulations for Band Limited Fractal (von Kármán) Statistical Models     

John A. Goff  James W. Jennings Jr. 《Mathematical Geology》1999,31(6):627-649

We evaluate the performance and statistical accuracy of the fast Fourier transform method for unconditional and conditional simulation. The method is applied under difficult but realistic circumstances of a large field (1001 by 1001 points) with abundant conditioning criteria and a band limited, anisotropic, fractal-based statistical characterization (the von Kármán model). The simple Fourier unconditional simulation is conducted by Fourier transform of the amplitude spectrum model, sampled on a discrete grid, multiplied by a random phase spectrum. Although computationally efficient, this method failed to adequately match the intended statistical model at small scales because of sinc-function convolution. Attempts to alleviate this problem through the covariance method (computing the amplitude spectrum by taking the square root of the discrete Fourier transform of the covariance function) created artifacts and spurious high wavenumber content. A modified Fourier method, consisting of pre-aliasing the wavenumber spectrum, satisfactorily remedies sinc smoothing. Conditional simulations using Fourier-based methods require several processing stages, including a smooth interpolation of the differential between conditioning data and an unconditional simulation. Although kriging is the ideal method for this step, it can take prohibitively long where the number of conditions is large. Here we develop a fast, approximate kriging methodology, consisting of coarse kriging followed by faster methods of interpolation. Though less accurate than full kriging, this fast kriging does not produce visually evident artifacts or adversely affect the a posteriori statistics of the Fourier conditional simulation.  相似文献