Climate-related cyclic deposition of carbonate and organic matter in Holocene lacustrine sediment,Lower Michigan,USA     

Jennifer A. Nelson  Kathy Licht  Catherine Yansa  Gabriel Filippelli 《Journal of Paleolimnology》2010,43(1):1-13

Records from lake sediment cores are critical for assessing the relative stability of climate and ecosystems over the Holocene. Duck Lake in south-central Lower Michigan, USA, was the focus of a study that identified how changes in the geochemical variables in lake sediments relate to variations in regional climate and local land use during the Holocene. More than 8.5 m of lacustrine sediment were recovered using Livingston and freeze corers and analyzed for organic carbon, inorganic (carbonate) carbon, total nitrogen, and trace metals. Repeating packages of sediment (1–10 cm thick) that grade from light (inorganic carbon-rich) to dark (organic carbon-rich) were found from the surface to a depth of about 8 m. Variations in the high-resolution gray scale data from core X-radiographs are highly correlated to the relative amount of inorganic carbon. Geochemical analyses of the upper 8.5 m of sediment revealed a wide range of values: 0.05–10.6% for inorganic carbon (i.e. 0.5–89% calcium carbonate) and 1.1–28% for organic carbon (i.e. 2.7–70% organic matter). Organic carbon to nitrogen ratios indicate that most of the sediment organic matter is produced within the lake. A core chronology based on eight AMS radiocarbon dates shows low sediment accumulation rates (0.05 cm/year) from 10,000 to 3,800 cal year BP and higher sediment accumulation rates (0.1–0.3 cm/year) from 3,800 cal year BP to present. We suggest that carbonate accumulates during relatively dry times, whereas organic matter accumulation dominates when nutrient input to the lake is enhanced by wetter climate. The Duck Lake core records a distinct low point in inorganic carbon deposition that may be related to the 8.2 ka cooling event now documented from several sites in North America. Spectral analysis of gray scale values shows significant ~200-year periodicities over the past 8,000 years, hypothesized to result from climate changes induced by solar forcing. Concentrations of trace metals (e.g. lead, iron, copper, zinc) indicate the onset of regional anthropogenic influence about 150 cal year BP.  相似文献   

Characterization of error dynamics in a 3D coastal model of the Catalan sea using stochastic modelling     

Gabriel Jordà  Pierre De Mey 《Continental Shelf Research》2010

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Velocity and Temperature Dissimilarity in the Surface Layer Uncovered by the Telegraph Approximation     

Huang  Kelly Y.  Katul  Gabriel G.  Hultmark  Marcus 《Boundary-Layer Meteorology》2021,179(3):385-401

We consider the Janjic (NCEP Office Note 437:61, 2001) boundary-layer model, which is one of the most widely used in numerical weather prediction models. This boundary-layer model is based on a number of length scales that are, in turn, obtained from a master length multiplied by constants. We analyze the simulation results obtained using different sets of constants with respect to measurements using sonic anemometers, and interpret these results in terms of the turbulence processes in the atmosphere and of the role played by the different length scales. The simulations are run on a virtual machine on the Chameleon cloud for low-wind-speed, unstable, and stable conditions.

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Bias correction method of high-resolution satellite-based precipitation product for Peninsular Malaysia     

Iqbal  Zafar  Shahid  Shamsuddin  Ahmed  Kamal  Wang  Xiaojun  Ismail  Tarmizi  Gabriel  Hamza Farooq 《Theoretical and Applied Climatology》2022,148(3-4):1429-1446

Theoretical and Applied Climatology - Satellite-based precipitation (SBP) is emerging as a reliable source for high-resolution rainfall estimates over the globe. However, uncertainty in SBP is...  相似文献   

Impact of fire on long-term vegetation dynamics of ombrotrophic peatlands in northwestern Québec,Canada     

Gabriel Magnan  Martin Lavoie  Serge Payette 《Quaternary Research》2012,77(1):110-121

A 7000-year record of local fire history was reconstructed from three ombrotrophic peatlands in the James Bay lowlands (northwestern Québec, Canada) using a high-resolution analysis of macroscopic charcoal (long axis ≥ 0.5 mm). The impact of fire on vegetation changes was evaluated using detailed analysis of plant macrofossils. Compared to upland boreal forest, fire incidence in these Sphagnum-dominated bogs is rather low. Past fire occurrence seems to have been controlled primarily by internal processes associated with local hydroseral succession. Size of the peatland basin and distance from the well-drained forest soils also appear to be factors controlling fire occurrence. The impact of peatland fires on long-term vegetation succession appears negligible except in a forested bog, where it initiated the replacement of Sphagnum by mosses. In some circumstances, fire caused marked changes in the bryophyte assemblages over many decades. However, ombrotrophic peatland vegetation is generally resilient to surface fire.  相似文献   

Passive ocean acoustic tomography     

O. A. Godin  V. V. Goncharov  N. A. Zabotin 《Doklady Earth Sciences》2012,444(1):606-609

The possibility to apply natural acoustic ocean noise in the ocean and noise of distant vessels as sounding signals in order to determine the physical parameters of a water layer is considered in this paper. We developed the methods making it possible to suppress the non-diffuse components of noise produced, e.g., by local vessels and to account for hydrophone motion. These methods are applied to the noise records obtained in the course of a year-long experiment on long-range sound propagation in the Pacific Ocean. We confirmed experimentally our theoretical predictions as to the possibility of retrieving deterministic acoustic ray travel times in a nonuniform environment from a mutual correlation function of imperfectly diffuse (gradually anisotropic and spatially nonuniform) noise without invoking any data on its source. We performed passive measurements of sound velocity in the ocean with a relative error of about 0.1% by correlation of noise fields recorded with vertical aerials. This accuracy approaches that needed for oceanological applications. Further investigations are necessary to study the feasibility of passive acoustic tomography and thermometry in the ocean at distances of tens and hundreds of kilometers and the possibility to use simpler arrays not equipped with hydrophone positioning systems.  相似文献   

Exponential time integrators for stochastic partial differential equations in 3D reservoir simulation     

Sebastian Geiger  Gabriel Lord  Antoine Tambue 《Computational Geosciences》2012,16(2):323-334

The transport of chemically reactive solutes (e.g. surfactants, CO₂ or dissolved minerals) is of fundamental importance to a wide range of applications in oil and gas reservoirs such as enhanced oil recovery and mineral scale formation. In this work, we investigate exponential time integrators, in conjunction with an upwind weighted finite volume discretisation in space, for the efficient and accurate simulation of advection–dispersion processes including non-linear chemical reactions in highly heterogeneous 3D oil reservoirs. We model sub-grid fluctuations in transport velocities and uncertainty in the reaction term by writing the advection–dispersion–reaction equation as a stochastic partial differential equation with multiplicative noise. The exponential integrators are based on the variation of constants solution and solve the linear system exactly. While this is at the expense of computing the exponential of the stiff matrix representing the finite volume discretisation, the use of real Léja point or the Krylov subspace technique to approximate the exponential makes these methods competitive compared to standard finite difference-based time integrators. For the deterministic system, we investigate two exponential time integrators, the second-order accurate exponential Euler midpoint (EEM) scheme and exponential time differencing of order one (ETD1). All our numerical examples demonstrate that our methods can compete in terms of efficiency and accuracy compared with standard first-order semi-implicit time integrators when solving (stochastic) partial differential equations that model mixing and chemical reactions in 3D heterogeneous porous media. Our results suggest that exponential time integrators such as the ETD1 and EEM schemes could be applied to typical 3D reservoir models comprising tens to hundreds of thousands unknowns.  相似文献   

Temperature Dependence of Oxygen Dynamics and Community Metabolism in a Shallow Mediterranean Macroalgal Meadow (Caulerpa prolifera)     

Raquel Vaquer-Sunyer  Carlos M. Duarte  Gabriel Jordà  Sergio Ruiz-Halpern 《Estuaries and Coasts》2012,35(5):1182-1192

Hypoxia is emerging as a major threat to marine coastal biota. Predicting its occurrence and elucidating the driving factors are essential to set successful management targets to avoid its occurrence. This study aims to elucidate the effects of warming on the likelihood of hypoxia. High-frequency dissolved oxygen measurements have been used to estimate gross primary production (GPP), net ecosystem production (NEP) and community respiration (CR) in a shallow macroalgae (Caulerpa prolifera) ecosystem in a highly human-influenced closed Mediterranean bay. Daily averaged GPP and CR ranged from 0 to 1,240.9 and 51.4 to 1,297.3?mmol?O₂?m^?2?day^?1, respectively. The higher GPP and CR were calculated for the same day, when daily averaged water temperature was 28.3?°C, and resulted in a negative NEP of ?56.4?mmol?O₂?m^?2?day^?1. The ecosystem was net heterotrophic during the studied period, probably subsidized by allochthonous organic inputs from ground waters and from the surrounding town and boating activity. Oxygen dynamics and metabolic rates strongly depend on water temperature, with lower oxygen content at higher temperatures. The probability of hypoxic conditions increased at a rate of 0.39?% °C^?1 (±0.14?% °C^?1). Global warming will increase the likelihood of hypoxia in the bay studied, as well as in other semi-enclosed bays.  相似文献   

A simple model accounting for the uptake,transport, and deposition of wind‐eroded mineral particles in the hyperarid coastal Atacama Desert of northern Chile     

Stephane C. Alfaro  Valentina Flores‐Aqueveque  Gilles Foret  Sandrine Caquineau  Gabriel Vargas  Jose A. Rutllant 《地球表面变化过程与地形》2011,36(7):923-932

As previously observed in marine sediments collected downwind of African or South American continental sources, recent studies of sediment cores collected at the bottom of Mejillones Bay in north Chile (23°S) show a laminated structure in which the amount of particles of aeolian origin and their size create significant differences between the layers. This suggests inter‐annual to inter‐decadal variations in the strength of the local southerly winds responsible for (1) the erosion of the adjacent hyperarid surface of the Mejillones Pampa, and (2) the subsequent transport of the eroded particles towards the bay. A simple model accounting for the vertical uptake, transport, and deposition of the particles initially set into motion by wind at the surface of the pampa is proposed. This model, which could be adapted to other locations, assumes that the initial rate of (vertical) uptake is proportional to the (horizontal) saltation flux quantified by means of White's equation, that particles are lifted to a height (H), increasing with the magnitude of turbulence, and that sedimentation progressively removes the coarsest particles from the air column as it moves towards the bay. In this model, the proportionality constant (A) linking the vertical flux of particles with the horizontal flux, and the injection height (H) control the magnitude and size distribution of the deposition flux in the bay. Their values are determined using the wind speed measured over the pampa and the size distribution of particles collected in sediment traps deployed in the bay as constraints. After calibration, the model is used to assess the sensitivity of the deposition flux to the wind intensity variations. The possibility of performing such quantitative studies is necessary for interpreting precisely the variability of the aeolian material in the sediment cores collected at the bottom of Mejillones Bay. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987111000405   总被引：1，自引：0，他引：1  

Jean de la Paix Mupenzi  Lanhai Li  Jiwen Ge  Achal Varenyam  Gabriel Habiyaremye  Nzayisenga Theoneste  Kamanzi Emmanuel 《地学前缘(英文版)》2011,2(4):599-607

This study has focused on the processes of soil degradation and chemical element concentration in tea-growing regions of Rwanda, Africa. Soil degradation accelerated by erosion is caused not only by topography but also by human activities. This soil degradation involves both the physical loss and reduction in the amount of topsoil associated with nutrient decline. Soil samples were collected from eleven tropical zones in Rwanda and from variable depth within each collecting site. Of these, Samples from three locations in each zone were analyzed in the laboratory, with the result that the pH of all soil samples is shown to be less than 5 (pH < 5) with a general average of 4.4. The elements such as iron (Fe), copper (Cu), manganese (Mn), and zinc (Zn) are present in high concentration levels. In contrast calcium (Ca) and sodium (Na) are present at low-level concentrations and carbon (C) was found in minimal concentrations. In addition, elements derived from fertilizers, such as nitrogen (N), phosphorous (P), and potassium (K) which is also from minerals such as feldspar, are also present in low-level concentrations. The results indicate that the soil in certain Rwandan tea plantations is acidic and that this level of pH may help explain, in addition to natural factors, the deficiency of some elements such as Ca, Mg, P and N. The use of chemical fertilizers, land use system and the location of fields relative to household plots are also considered to help explain why tea plantation soils are typically degraded.  相似文献