Dramatic decrease of pelagic carbonate production by nannoplankton across the Early Toarcian anoxic event (T-OAE)     

Emanuela Mattioli  Bernard Pittet  Laurent Petitpierre  Samuel Mailliot 《Global and Planetary Change》2009,65(3-4):134-145

In this account we present estimates of nannofossil fluxes in four sections and one borehole all belonging to the Early Jurassic western Tethys. This study aims to map the distribution of pelagic carbonate production across the Early Toarcian anoxic event (T-OAE), and to understand which environmental parameters did control such production. Our results indicate important changes in carbonate production by nannoplankton occurring within the western Tethys and its variations through time. Nannofossil fluxes (specimens per m² per year) are extremely low during the T-OAE in all the studied settings. Higher fluxes are encountered in the westernmost part of the Tethys Ocean before the T-OAE, whilst pelagic carbonate production shifted towards the northern margin of the Tethys after the recovery from anoxic conditions. The dramatic decrease in nannoplankton production during the T-OAE has been interpreted in previous works as a biocalcification crisis related to high pCO₂ in the atmosphere/hydrosphere system. Although a high pCO₂ may have lowered the carbonate saturation state of Early Jurassic oceans and finally hampered biocalcification, we speculate that the most important effects of CO₂ increase were indirect, and affected pelagic producers via changes on climate and sea-level. Namely, it seems that precipitation/evaporation budgets and continental runoff that controlled nutrient levels and salinity in surface oceanic waters were important factors for pelagic biocalcifiers.  相似文献   

Probability distributions for carbon emissions and atmospheric response     

Clifford E. Singer  T. S. Gopi Rethinaraj  Samuel Addy  David Durham  Murat Isik  Madhu Khanna  Brandon Kuehl  Jianding Luo  Wilma Quimio  Kothavari Rajendran  Donna Ramirez  Ji Qiang  Jürgen Scheffran  T. Nedjla Tiouririne  Junli Zhang 《Climatic change》2008,88(3-4):309-342

Probability distributions for carbon burning, atmospheric CO₂, and global average temperature are produced by time series calibration of models of utility optimization and carbon and heat balance using log-linear production functions. Population growth is used to calibrate a logistically evolving index of development that influences production efficiency. Energy production efficiency also includes a coefficient that decreases linearly with decreasing carbon intensity of energy production. This carbon intensity is a piecewise linear function of fossil carbon depletion. That function is calibrated against historical data and extrapolated by sampling a set of hypotheses about the impact on the carbon intensity of energy production of depleting fluid fossil fuel resources and increasing cumulative carbon emissions. Atmospheric carbon balance is determined by a first order differential equation with carbon use rates and cumulative carbon use as drivers. Atmospheric CO₂ is a driver in a similar heat balance. Periodic corrections are included where required to make residuals between data and model results indistinguishable from independently and identically distributed normal distributions according to statistical tests on finite Fourier power spectrum amplitudes and nearest neighbor correlations. Asymptotic approach to a sustainable non-fossil energy production is followed for a global disaggregation into a tropical/developing and temperate/more-developed region. The increase in the uncertainty of global average temperature increases nearly quadratically with the increase in the temperature from the present through the next two centuries.  相似文献   

Characterization of manganese oxide precipitates from Appalachian coal mine drainage treatment systems     

Hui Tan  Gengxin Zhang  Peter J. Heaney  Samuel M. Webb  William D. Burgos 《Applied Geochemistry》2010

The removal of Mn(II) from coal mine drainage (CMD) by chemical addition/active treatment can significantly increase treatment costs. Passive treatment for Mn removal involves promotion of biological oxidative precipitation of manganese oxides (MnO_x). Manganese(II) removal was studied in three passive treatment systems in western Pennsylvania that differed based on their influent Mn(II) concentrations (20–150 mg/L), system construction (±inoculation with patented Mn(II)-oxidizing bacteria), and bed materials (limestone vs. sandstone). Manganese(II) removal occurred at pH values as low as 5.0 and temperatures as low as 2 °C, but was enhanced at circumneutral pH and warmer temperatures. Trace metals such as Zn, Ni and Co were removed effectively, in most cases preferentially, into the MnO_x precipitates. Based on synchrotron radiation X-ray diffraction and Mn K-edge extended X-ray absorption fine structure spectroscopy, the predominant Mn oxides at all sites were poorly crystalline hexagonal birnessite, triclinic birnessite and todorokite. The surface morphology of the MnO_x precipitates from all sites was coarse and “sponge-like” composed of nm-sized lathes and thin sheets. Based on scanning electron microscopy (SEM), MnO_x precipitates were found in close proximity to both prokaryotic and eukaryotic organisms. The greatest removal efficiency of Mn(II) occurred at the one site with a higher pH in the bed and a higher influent total organic C (TOC) concentration (provided by an upstream wetland). Biological oxidation of Mn(II) driven by heterotrophic activity was most likely the predominant Mn removal mechanism in these systems. Influent water chemistry and Mn(II) oxidation kinetics affected the relative distribution of MnO_x mineral assemblages in CMD treatment systems.  相似文献   

Characterizing the U–Pb systematics of baddeleyite through chemical abrasion: application of multi-step digestion methods to baddeleyite geochronology     

Matthew Rioux  Samuel Bowring  Frank Dudás  Richard Hanson 《Contributions to Mineralogy and Petrology》2010,160(5):777-801

U–Pb baddeleyite geochronology has become a major tool for dating mafic rocks, especially dikes associated with Large Igneous Provinces. However, in many cases, post-crystallization Pb-loss and intergrowth of baddeleyite and zircon limit the precision and/or accuracy of crystallization ages. We present results from multi-step digestion experiments designed to understand and reduce these effects. Experiments were carried out on Neoproterozoic baddeleyites with zircon inter- and over-growths from the Gannakouriep dike swarm, Namibia, and on fragments of a large Paleoproterozoic baddeleyite from the Phalaborwa carbonatite, South Africa. Multi-step digestion experiments on annealed Phalaborwa baddeleyite were designed to test whether the recently developed chemical abrasion technique for U–Pb zircon geochronology can be applied to baddeleyite. The experiments generated complex results—individual digestion steps were both normally and reversely discordant suggesting that U and Pb were decoupled in the multi-step digestions—and indicate that the current form of multi-step chemical abrasion is not an effective method for reducing the impact of Pb-loss in baddeleyite. A separate set of experiments on the Gannakouriep baddeleyite focused on isolating the zircon and baddeleyite components in composite grains. Conventional single-step digestion experiments for this sample resulted in a discordant suite of analyses with significant scatter attributed to inter- and over-grown zircon and highlight the difficulty of obtaining precise and accurate ages from composite grains. To isolate the baddeleyite and zircon in these grains, a two-step HCl–HF chemical abrasion procedure for annealed grains was developed. This technique was successful at selectively dissolving the baddeleyite and zircon components. Secondary zircon inter- and over-growths of baddeleyite can occur in samples affected by low-temperature alteration to granulite facies metamorphism, and the new HCl–HF chemical abrasion procedure provides a method for resolving both the igneous and metamorphic history of these composite grains.  相似文献   

Amplification of gravitational waves in scalar-tensor accelerating lambda-Universes     

Marcelo Samuel Berman 《Astrophysics and Space Science》2010,325(2):283-286

After reviewing the scalar-tensor lambda-accelerating power-law solutions by Berman (Astrophys. Space Sci. 323:103, 2009a), we obtain solutions for the amplification of gravitational waves in the models. The solutions consider a perfect gas equation of state, with cosmic pressure proportional to the energy density, the proportionality constant being smaller than −2/3.  相似文献   

Tropical glacier fluctuations in the Cordillera Blanca,Peru between 12.5 and 7.6 ka from cosmogenic 10Be dating     

Neil F. Glasser  Samuel Clemmens  Christoph Schnabel  Cassandra R. Fenton  Lanny McHargue 《Quaternary Science Reviews》2009,28(27-28):3448-3458

We report cosmogenic surface exposure ¹⁰Be ages of 21 boulders on moraines in the Jeullesh and Tuco Valleys, Cordillera Blanca, Peru (～10°S at altitudes above 4200 m). Ages are based on the sea-level at high-latitude reference production rate and scaling system of Lifton et al. (2005. Addressing solar modulation and long-term uncertainties in scaling secondary cosmic rays for in situ cosmogenic nuclide applications. Earth and Planetary Science Letters 239, 140–161) in the CRONUS-Earth online calculator of Balco et al. (2008. A complete and easily accessible means of calculating surface exposure ages or erosion rates from ¹⁰Be and ²⁶Al measurements. Quaternary Geochronology 3, 174–195). Using the Lifton system, large outer lateral moraines in the Jeullesh Valley have a ¹⁰Be exposure age of 12.4 ka, inside of which are smaller moraine systems dated to 10.8, 9.7 and 7.6 ka. Large outer lateral moraines in the Tuco Valley have a ¹⁰Be exposure age of 12.5 ka, with inner moraines dated to 11.3 and 10.7 ka. Collectively, these data indicate that glacier recession from the Last Glacial Maximum (LGM) in the Cordillera Blanca was punctuated by three to four stillstands or minor advances during the period 12.5–7.6 ka, spanning the Younger Dryas Chronozone (YDC; ～12.9–11.6 ka) and the cold event identified in Greenland ice cores and many other parts of the world at 8.2 ka. The inferred fluctuations of tropical glaciers at these times, well after their withdrawal from the LGM, indicate an increase in precipitation or a decrease in temperature in this region. Although palaeoenvironmental records show regional and temporal variability, comparison with proxy records (lacustrine sediments and ice cores) indicate that regionally this was a cold, dry period so we ascribe these glacier advances to reduced atmospheric temperature rather than increased precipitation.  相似文献   

Advance,deglacial and sea‐level chronology for Foxe Peninsula,Baffin Island,Nunavut          下载免费PDF全文

Daniel J. Utting  John C. Gosse  Samuel E. Kelley  Kayla J. Vickers  Brent C. Ward  Michelle S. Trommelen 《Boreas: An International Journal of Quaternary Research》2016,45(3):439-454

The impact of the Laurentide Ice Sheet (LIS) deglaciation on Northern Hemisphere early Holocene climate can be evaluated only once a detailed chronology of ice history and sea‐level change is established. Foxe Peninsula is ideally situated on the northern boundary of Hudson Strait, and preserves a chronostratigraphy that provides important glaciological insights regarding changes in ice‐sheet position and relative sea level before and after the 8.2 ka cooling event. We utilized a combination of radiocarbon ages, adjusted with a new locally derived ΔR, and terrestrial in‐situ cosmogenic nuclide (TCN) exposure ages to develop a chronology for early‐Holocene events in the northern Hudson Strait. A marine limit at 192 m a.s.l., dated at 8.1–7.9 cal. ka BP, provides the timing of deglaciation following the 8.2 ka event, confirming that ice persisted at least north of Hudson Bay until then. A moraine complex and esker morphosequence, the Foxe Moraine, relates to glaciomarine outwash deltas and beaches at 160 m a.s.l., and is tightly dated at 7.6 cal. ka BP with a combination of shell dates and exposure ages on boulders. The final rapid collapse of Foxe Peninsula ice occurred by 7.1–6.9 cal. ka BP (radiocarbon dates and TCN depth profile age on an outwash delta), which supports the hypothesis that LIS melting contributed to the contemporaneous global sea‐level rise known as the Catastrophic Rise Event 3 (CRE‐3).  相似文献   

Evaluation of probabilistic flow in two unsaturated soils     

Samuel Boateng 《Hydrogeology Journal》2001,9(6):543-554

A variably saturated flow model is coupled to a first-order reliability algorithm to simulate unsaturated flow in two soils. The unsaturated soil properties are considered as uncertain variables with means, standard deviations, and marginal probability distributions. Thus, each simulation constitutes an unsaturated probability flow event. Sensitivities of the uncertain variables are estimated for each event. The unsaturated hydraulic properties of a fine-textured soil and a coarse-textured soil are used. The properties are based on the van Genuchten model. The flow domain has a recharge surface, a seepage boundary along the bottom, and a no-flow boundary along the sides. The uncertain variables are saturated water content, residual water content, van Genuchten model parameters alpha (α) and n, and saturated hydraulic conductivity. The objective is to evaluate the significance of each uncertain variable to the probabilistic flow. Under wet conditions, saturated water content and residual water content are the most significant uncertain variables in the sand. For dry conditions in the sand, however, the van Genuchten model parameters α and n are the most significant. Model parameter n and saturated hydraulic conductivity are the most significant for the wet clay loam. Saturated water content is most significant for the dry clay loam. Electronic Publication  相似文献   

From the Hagedoorn imaging technique to Kirchhoff migration and inversion   总被引：1，自引：0，他引：1  

Norman Bleistein  Samuel H. Gray 《Geophysical Prospecting》2001,49(6):629-643

The seminal 1954 paper by J.G. Hagedoorn introduced a heuristic for seismic reflector imaging. That heuristic was a construction technique – a 'string construction' or 'ruler and compass' method – for finding reflectors as an envelope of equal traveltime curves defined by events on a seismic trace. Later, Kirchhoff migration was developed. This method is based on an integral representation of the solution of the wave equation. For decades Kirchhoff migration has been one of the most popular methods for imaging seismic data. Parallel with the development of Kirchhoff wave-equation migration has been that of Kirchhoff inversion, which has as its objectives both structural imaging and the recovery of angle-dependent reflection coefficients. The relationship between Kirchhoff migration/inversion and Hagedoorn's constructive technique has only recently been explored. This paper addresses this relationship, presenting the mathematical structure that the Kirchhoff approach adds to Hagedoorn's constructive method and showing the relationship between the two.  相似文献   

NLS EQUATION OF INTERNAL WAVES IN WEAKLY STRATIFIED OCEAN   总被引：1，自引：0，他引：1  

徐肇廷  楼顺里  田纪伟 《中国海洋湖沼学报》1996,14(2):121-127

The NLS (Non-Linear Schr(?)dinger) equation of internal waves in a wekly stratified ocean is der-ived in phase coordnates in terms of the RPM (Reductive Perturbation Method). It was shown thatwhen AB>0 there exist modulation forms of envelope soliton and dn, and tha when AB<0 there arethree modulation forms dark soliton, sn and cn. Only if K~2>B/A(?) . the side-band perturbation is stable,otherwise unstable. For the stable side-band perturbation there ekisis a modulation form of MdV soliton.  相似文献