Reconstructing seawater δO from paired coral δO and Sr/Ca ratios: Methods, error analysis and problems, with examples from Tahiti (French Polynesia) and Timor (Indonesia)     

Sri Yudawati Cahyarini  Miriam Pfeiffer  Oliver Timm  Dieter Garbe Schönberg 《Geochimica et cosmochimica acta》2008,72(12):2841-2853

We compare several statistical routines that may be used to calculate δ¹⁸O_sw and SSS from paired coral Sr/Ca and δ¹⁸O measurements. Typically, the δ¹⁸O_coral-SST relationship is estimated by linear regression of coral δ¹⁸O vs. SST. If this method is applied, evidence should be given that at a particular site SST and SSS do not co-vary. In the tropical oceans, SST and δ¹⁸O_sw (SSS) often co-vary, and this will bias the estimate of the regression slope of δ¹⁸O_coral-SST. Using a stochastic model, we show that covariance leads to a bias in the coefficients of the univariate regression equations. As the slope of the δ¹⁸O_coral-SST relationship has known, we propose to insert this value for γ₁ in the regression models. This requires that the constants of the regression equations are removed. To omit the constants, we propose to center the regression equations (i.e., to remove the mean values from the variables). The statistical error propagation is calculated to assess our ability to resolve past variations in δ¹⁸O_sw (SSS). At Tahiti, we find that the combined analytical uncertainties of coral δ¹⁸O and Sr/Ca equal the amplitude of the seasonal cycle of δ¹⁸O_sw (SSS). Therefore, we cannot resolve the seasonal cycle of SSS at Tahiti. At Timor, the error of reconstructed δ¹⁸O_sw (SSS) is lower than the magnitude of seasonal variations of δ¹⁸O_sw (SSS), and the seasonal cycle of δ¹⁸O_sw (SSS) can be resolved.  相似文献   

Effects of the forced resettlement of a community from an agricultural settlement to a high-rise building     

Miriam Billig 《GeoJournal》2016,81(1):123-137

The objective of this study was to understand the implications of forced displacement and resettlement of a rural community to an extremely different built environment in urban setting. Based on the Inglehart’s theory of cultural shifts we were able to delineate the process by which changes in physical environment caused significant changes in the community social structure and community members’ cultural identities. The collective characteristics that had once united and strengthened the community’s social structure began to dwindle. Meanwhile, a growing tendency towards individualistic characteristics gradually increased, causing the weakening and eventual dissolution of both the community and its social structure. The gradual process of community changes was reflected in the subjective narratives presented by community residents in a series of in-depth interviews conducted 4 years after the evacuation, in their new homes. Till that time, the community finally broke up, most of its members spreading out to live in various other areas. The study findings will be incorporated into a framework for resettlement policy on appropriate housing for resettled communities.  相似文献   

Groundwater flow in the transition zone between freshwater and saltwater: a field-based study and analysis of measurement errors     

Vincent E. A. Post  Eddie Banks  Miriam Brunke 《Hydrogeology Journal》2018,26(6):1821-1838

The quantification of groundwater flow near the freshwater–saltwater transition zone at the coast is difficult because of variable-density effects and tidal dynamics. Head measurements were collected along a transect perpendicular to the shoreline at a site south of the city of Adelaide, South Australia, to determine the transient flow pattern. This paper presents a detailed overview of the measurement procedure, data post-processing methods and uncertainty analysis in order to assess how measurement errors affect the accuracy of the inferred flow patterns. A particular difficulty encountered was that some of the piezometers were leaky, which necessitated regular measurements of the electrical conductivity and temperature of the water inside the wells to correct for density effects. Other difficulties included failure of pressure transducers, data logger clock drift and operator error. The data obtained were sufficiently accurate to show that there is net seaward horizontal flow of freshwater in the top part of the aquifer, and a net landward flow of saltwater in the lower part. The vertical flow direction alternated with the tide, but due to the large uncertainty of the head gradients and density terms, no net flow could be established with any degree of confidence. While the measurement problems were amplified under the prevailing conditions at the site, similar errors can lead to large uncertainties everywhere. The methodology outlined acknowledges the inherent uncertainty involved in measuring groundwater flow. It can also assist to establish the accuracy requirements of the experimental setup.  相似文献   

Early and Middle Pleistocene Faunal and hominins dispersals through Southwestern Asia     

Ofer Bar-Yosef  Miriam Belmaker 《Quaternary Science Reviews》2011,30(11-12):1318-1337

This review summarizes the paleoecology of the Early and Middle Pleistocene of southwestern Asia, based on both flora and fauna, retrieved from a series of ‘windows’ provided by the excavated sites. The incomplete chrono-stratigraphy of this vast region does not allow to accept the direct chronological correlation between the available sites and events of faunal and hominin dispersals from Africa. It also demonstrates that hominins survived in a mixed landscape of open parkland with forested surrounding hills. In addition, the prevailing environmental conditions are not sufficient to explain successful adaptations to new ecological niches away from the African savanna of the bearers of ‘core and flake’ and the Acheulian industries, The differences in knapping and secondary shaping of stone artifacts probably reflect the learned traditions of different groups of hominins. The current distribution of lithic industries across Eurasia is undoubtedly incomplete due to lack of cultural continuities as well as paucity of field research in several sub-regions. This observation supports the contention that what we view as a constant stream of migrants was actually interrupted many times. The continuous occupation of southwestern Asia by the makers of the Acheulian is in contrast with neighboring regions such as the Iranian plateau and Eastern Europe. A more complex model is required to explain the recorded Eurasian archaeological–cultural mosaic.  相似文献   

A model for the bite mechanics in the herbivorous dinosaur Stegosaurus (Ornithischia, Stegosauridae)     

Miriam Reichel 《Swiss Journal of Geoscience》2010,103(2):235-240

Although the herbivorous dinosaur Stegosaurus (Ornithischia, Stegosauridae) is a well-described Late Jurassic taxon, little is known about the feeding habits and biomechanics of its homodont dentition. The presence of a rhamphotheca has been suggested, but it is still unknown how much such structure would have participated in the foraging behaviour of Stegosaurus. To better understand the feeding mechanism of this taxon, three-dimensional models of a Stegosaurus tooth were created, using the software ZBrush^®. One model was simple and lacked serrations, whereas the other model included serrations. Those models were then transferred to the software Strand7^®, where finite element analyses took place. The models were given material properties of enamel, based on studies done with crocodilian and mammalian teeth. In addition to that, bite forces were calculated for Stegosaurus, based on skull proportions. The results show little difference between the force distributions on the serrated and non-serrated models, indicating an efficient mechanism of stress dissipation that avoids high stresses being transferred to the jaw bones during biting. Digital plant models were also created to test the calculated bite forces in Stegosaurus, which suggests this animal was capable of biting through smaller branches. Computer modelling and analyses provide additional information about feeding habits and plant preferences for Stegosaurus, and can be adapted for studying other comparable herbivorous taxa.  相似文献   

Beyond El Niño: Decadal and Interdecadal Climate Variability     

Miriam Steinitz Kannan 《Journal of Paleolimnology》2001,25(4):548-550

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Ship structure loads and stresses     

Sonderforschungsbereich  O. Grim  D. Hachmann  H. -J. Hansen  J. Isensee  S. Kastner  H. Keil  J. Laudan  K. -Y. Lee  P. N. Misra  E. Ple  D. Prange  H. Sding  G. Soproni 《Ocean Engineering》1980,7(5):571-658

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Recent observations of the WR central star of the planetary nebula LMC-N66     

Miriam Peña  Manuel Peimbert  Silvia Torres-Peimbert  Maria Teresa Ruiz  Jose Maza 《Astrophysics and Space Science》1996,238(1):55-58

The recent evolution of the central star of the planetary nebula LMC-N66 is presented. Before 1987, it showed a weak continuum with aT _eff120 000 K andL _bol25 000L and in a few years it developed strong WR features (P Cygni line profiles in N v at 124.0 nm and C IV at 155.0 nm, wide Heii emission, etc.) typical of a WN 4.5. Additionally the stellar continuum increased by a large factor and the absolute visual magnitude of the star changed from + 1.24 in 1987 to–2.57 in January, 1995. The WR features and enhanced continuum, evidencing a powerful mass-loss event remained with small variations for more than 5 years. Recent ultraviolet and optical data shows that the mass-loss seems to have diminished abruptly in the last three months.  相似文献   

Proximal impact deposits at the Cretaceous-Tertiary boundary in the Gulf of Mexico: a restudy of DSDP Leg 77 Sites 536 and 540     

Alvarez W  Smit J  Lowrie W  Asaro F  Margolis SV  Claeys P  Kastner M  Hildebrand AR 《Geology》1992,20(8):697-700

Restudy of Deep Sea Drilling Project Sites 536 and 540 in the southeast Gulf of Mexico gives evidence for a giant wave at Cretaceous-Tertiary boundary time. Five units are recognized: (1) Cenomanian limestone underlies a hiatus in which the five highest Cretaceous stages are missing, possibly because of catastrophic K-T erosion. (2) Pebbly mudstone, 45 m thick, represents a submarine landslide possibly of K-T age. (3) Current-bedded sandstone, more than 2.5 m thick, contains anomalous iridium, tektite glass, and shocked quartz; it is interpreted as ejecta from a nearby impact crater, reworked on the deep-sea floor by the resulting tsunami. (4) A 50-cm interval of calcareous mudstone containing small Cretaceous planktic foraminifera and the Ir peak is interpreted as the silt-size fraction of the Cretaceous material suspended by the impact-generated wave. (5) Calcareous mudstone with basal Tertiary forams and the uppermost tail of the Ir anomaly overlies the disturbed interval, dating the impact and wave event as K-T boundary age. Like Beloc in Haiti and Mimbral in Mexico, Sites 536 and 540 are consistent with a large K-T age impact at the nearby Chicxulub crater.  相似文献   

Diagenesis of siliceous oozes—I. Chemical controls on the rate of opal-A to opal-CT transformation—an experimental study     

M. Kastner  J.B. Keene  J.M. Gieskes 《Geochimica et cosmochimica acta》1977,41(8):1041-1059

Evidence from deep-sea sediments supports the following diagenetic maturation sequence: opal-A (siliceous ooze) → opal-CT (porcelanite) → chalcedony or cryptocrystalline quartz (chert). A solution-redeposition mechanism is involved in the opal-A to opal-CT transformation. Exceptions to the overall maturation sequence are numerous, suggesting that temperature and time are not the only important factors controlling these mineralogical transformations. The rates of the above transformations are strongly affected by the composition of the solution and of the host sediments ; in Mesozoic clayey sediments, opal-CT predominates, while in carbonate sediments quartz is most common.Experiments at 25 and 150°C over a period of one day to six months show that the transformation rate of opal-A to opal-CT is much higher in carbonate than in clay-rich sediments, and that opal-CT lepisphere formation is aided by the precipitation of nuclei with magnesium hydroxide as an important component. The role of carbonate is explained as follows : in carbonate-rich sediments, the dissolution of carbonate provides the necessary alkalinity, and sea water provides the magnesium for the magnesium hydroxide in the nuclei. In contrast, in clay-rich sediments the clay minerals compete with opal-CT formation for the available alkalinity from sea water. As a result, the clays are enriched in Mg, and the rate of opal-CT formation is strongly reduced. This mechanism also bears on the common observation of carbonate replacement by silica.  相似文献