Can sand dunes be used to study historic storm events?

Knowing the long‐term frequency of high magnitude storm events that cause coastal inundation is critical for present coastal management, especially in the context of rising sea levels and potentially increasing frequency and severity of storm events. Coastal sand dunes may provide a sedimentary archive of past storm events from which long‐term frequencies of large storms can be reconstructed. This study uses novel portable optically stimulated luminescence (POSL) profiles from coastal dunes to reconstruct the sedimentary archive of storm and surge activity for Norfolk, UK. Application of POSL profiling with supporting luminescence ages and particle size analysis to coastal dunes provides not only information of dunefield evolution but also on past coastal storms. In this study, seven storm events, two major, were identified from the dune archive spanning the last 140 years. These appear to correspond to historical reports of major storm surges. Dunes appear to be only recording (at least at the sampling resolution used here) the highest storm levels that were associated with significant flooding. As such the approach seems to hold promise to obtain a better understanding of the frequency of large storms by extending the dune archive records further back to times when documentation of storm surges was sparse. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

Turbulent Heating in the Accelerating Region Using a Multishell Model

Solar energetic particles (SEPs) are released into the heliosphere by solar flares and coronal mass ejections (CMEs). They are mostly protons, with smaller amounts of heavy ions from helium to iron, and lesser amounts of species heavier than iron. The spectra of heavy ions have been previously studied mostly by using the fluence of the particles in an event-integrated spectrum in a small number of spectral snapshots. In this article, we analyze the temporal evolution of the heavy-ion spectra using two large SEP events (27 January 2012 and 7 January 2014) from the Solar TErrestrial Relations Observatory (STEREO) era using Advanced Composition Explorer (ACE) Solar Isotope Spectrometer (SIS) and Ultra Low Energy Isotope Spectrometer (ULEIS), Energetic Particles: Acceleration, Composition and Transport (EPACT) onboard Wind, and the STEREO-A (Ahead) and -B (Behind) Low-Energy Telescope (LET) and Suprathermal Ion Telescope (SIT) instruments, taking a large number of snapshots covering the temporal evolution of the event. We find large differences in the spectra of the ions after the main flux enhancement in terms of the grouping of similar species, but also in terms of the location of the instruments. Although it is somewhat less noticeable than in the case of the temporal evolution of protons (Doran and Dalla, Solar Phys. 291, 2071, 2016), we observe a wave-like pattern travelling through the heavy ion spectra from the highest energies to the lowest, creating an “arch” structure that later straightens into a power law after 18 to 24 hours.

     

土体触探静力加载试验的FLAC模拟模型选择

本文将触探静力加载试验作为轴对称问题处理,建立了两种不同FLAC轴对称模型,等荷载模型和等位移模型。研究表明,两种模型的FLAC模拟结果基本一致,一般条件下,应用简化的、运算速度快的等荷载模型可以满足试验要求。     

Dispersant Use and a Bioremediation Strategy as Alternate Means of Reducing Impacts of Large Oil Spills on Mangroves: The Gladstone Field Trials

Over a three-year period (1995–1998), we studied short-term effects of dispersant use and a bioremediation strategy in two consecutive field trials in sub-tropical Australian mangroves. In each case, weathered oil was applied, and a large spill simulated, in mature Rhizophora stylosa trees around 4–9 m tall. In the first trial, we used Gippsland light crude oil with or without dispersant, Corexit 9527. In the second, a bioremediation strategy followed application of Gippsland oil or Bunker C fuel oil. Bioremediation involved forced aeration with supplemental application of nutrients. Dispersant use had an overall positive benefit shown as reduced tree mortality. By contrast, there was no apparent reduction in mortality of trees with bioremediation. However, one year after oiling, leaf densities of surviving trees were greater in bioremediation plots than in controls, and less in oil-only plots. These and other results have been incorporated into spill response management strategies in Australia.     

Fish assemblages as indicators of water quality in the middle Thames estuary, England (1980–1989)

Fish abundance and environmental data collected over ten years (1980–1989) from the middle Thames estuary, England, were analyzed to detect temporal trends in fish populations and relationship with environmental parameters, and to assess water quality. Fish were collected from the cooling water intake screens of West Thurrock power station, situated 35.5 km below London Bridge, in the mid-estuary. Marine species abundance were highly seasonal, with peaks in December–March for herring (Clupea harengus), sprat (Sprattus sprattus), 3-spined-stickleback (Gasterosteus aculeatus), and poor cod (Trisopterus minutus); July–August for flounder (Platichthys flesus); and September–December for sand goby (Pomatoschistus minutus), whiting (Merlangius merlangus), bass (Dicentrarchus labrax), plaice (Pleuronectes platessa), and dab (Limanda limanda). Bimodal seasonal patterns of peaks or unclear seasonality in abundance characterized marine estuarine-dependent sole (Solea solea), Nilsson's pipefish (Syngnathus rostelattus) (April/May and September/October), and pouting (Trisopterus luscus) (May and November/December); the estuarine smelt (Osmerus eperlanus) (October and January) and the catadromous eel (Anguilla anguilla) (June and October). There was substantial variation in the abundance of common species over the period of ten years, with herring, sand goby, flounder, and plaice showing a stable abundance in 1980–1984, increasing sharply in 1985–1986, and then decreasing successively through the remainder of the decade (1987–1989). The first half of the decade was a period of higher abundance for less tolerant species such as smelt, sprat, and poor cod, while the second half showed higher abundances of species tolerant to harsh environmental conditions such as sand goby, flounder, eel, and plaice. A general pattern of stable fish populations with a slight trend of deterioration was found to emerge over the years, related to the number of species and quantities of common species. Multivariate techniques of principal component and canonical correspondence ordinations were used for assessing relationships between fish populations abundance and environmental variables. The most significant environmental variables correlated with fish species were temperature and dissolved oxygen. High abundances of flounder were associated with high temperature, while high abundance of poor cod, sprat, herring, and 3-spined-stickleback were associated with high dissolved oxygen, flow, ammonical nitrogen, and low temperature. Plaice, whiting, sand goby, bass, and dab were preferentially found in high salinity and suspended solids, while smelt and sole were likely to prefer average values or showed no clear preferences.     

AMG preconditioning for sedimentary basin simulations in Temis calculator

Basin modelling aims at reconstructing the time evolution of a sedimentary basin in order to make quantitative predictions of geological phenomena leading to hydrocarbon accumulations. It accounts for porous medium compaction, heat transfer, hydrocarbon generation and migration. These physical phenomena are modelled by partial differential equations [Schneider, F., Wolf, S., Faille, I., Pot, D. 2000. A 3D basin model for hydrocarbon potential evaluation: application to Congo offshore. Oil and Gas Science Technologie, Rev-IFP 55, 3–13] representing the mass balances of solid, fluids (water and oil) coupled with Darcy's law and a compaction law. These equations are discretized using a cell-centered Finite Volume method in space and an implicit Euler integration in time. At each time step, the resulting nonlinear system is solved using Newton's method ending up at each Newton iteration with the solution of a linear system which represents the most cpu-time-consuming part of the basin simulator.     

Kinetics of nutrient and metal release from decomposing lake sediments

Rates of anaerobic decomposition of Lake Erie sediments were determined for seven depth intervals at three temperatures. Sealed sediment sections were incubated under anoxic conditions and the interstitial waters were serially sampled over a period of approximately 200 days. Concentration increases of bicarbonate, phosphate, ammonium, Ca, Mg, Fe and Mn in pore water within any given depth interval followed zero order kinetics over the sampling period and exhibited Arrhenius temperature dependency. Rates of release to the pore waters were proportional to the concentrations in the solid phases, indicating first order kinetics overall.The rates and temperature dependencies of these fermentation reactions were only slightly less than those reported from sediments undergoing sulfate reduction. The observed release rates decreased exponentially with depth in the sediment due to a corresponding decrease in the amount of metabolizable organic matter and acid hydrolyzable mineral phases.A stoichiometric model was constructed utilizing the observed release rates and assumed chemical reactions to predict the stoichiometry of the decomposing organic matter and the nature of the hydrogen buffer. The modeling indicates that 60% of the observed bicarbonate release is the direct result of organic decomposition, that 20% of the release is from the dissolution of calcium carbonate mineral phases, and that the remaining 20% of the release is from the dissolution of magnesium, iron und manganese carbonate mineral phases.Kinetic modeling of the observed production rates accurately predicts the vertical profiles of Ca, Mg, Fe and Mn, but cannot quantitatively account for all the concentration differences of the nutrient elements C, N and P. This implies that in addition to decomposition, increased depositional flux also accounts for the significant changes in concentrations of the nutrient elements in the near surface sediments.     

Assimilation of preexisting Pleistocene intrusions at Long Valley by periodic magma recharge accelerates rhyolite generation: rethinking the remelting model

Rhyolite flows and tuffs from the Long Valley area of California, which were erupted over a two-million-year time period, exhibit systematic trends in Nd, Hf, and Pb isotopes, trace element composition, erupted volume, and inferred magma residence time that provide evidence for a new model for the production of large volumes of silica-rich magma. Key constraints come from geochronology of zircon crystal populations combined with a refined eruption chronology from Ar–Ar geochronology; together these data give better estimates of magma residence time that can be evaluated in the context of changing magma compositions. Here, we report Hf, Nd, and Sr isotopes, major and trace element compositions, ⁴⁰Ar/³⁹Ar ages, and U–Pb zircon ages that combined with existing data suggest that the chronology and geochemistry of Long Valley rhyolites can be explained by a dynamic interaction of crustal and mantle-derived magma. The large volume Bishop Tuff represents the culmination of a period of increased mantle-derived magma input to the Long Valley volcanic system; the effect of this input continued into earliest postcaldera time. As the postcaldera evolution of the system continued, new and less primitive crustal-derived magmas dominated the system. A mixture of varying amounts of more mafic mantle-derived and felsic crustal-derived magmas with recently crystallized granitic plutonic materials offers the best explanation for the observed chronology, secular shifts in Hf and Nd isotopes, and the apparently low zircon crystallization and saturation temperatures as compared to Fe–Ti oxide eruption temperatures. This scenario in which transient crustal magma bodies remained molten for varying time periods, fed eruptions before solidification, and were then remelted by fresh recharge provides a realistic conceptual framework that can explain the isotopic and geochemical evidence. General relationships between crustal residence times and magma sources are that: (1) precaldera rhyolites had long crustal magma residence times and high crustal affinity, (2) the caldera-related Bishop Tuff and early postcaldera rhyolites have lower crustal affinity and short magma residence times, and (3) later postcaldera rhyolites again have stronger crustal signatures and longer magma residence times.     

周边地区对北京地面SO2影响的初步研究

采用Lagrangian传输、扩散、沉降模式计算了1994年9、10月份(非采暖期)、1995年1月和2000年1月(采暖期)北京地区SO2的变化规律,并分别计算了北京市不同类型的排放源以及周边地区污染源对平均地面SO2浓度的贡献.计算结果与实际观测资料对比表明,模式能够较好地模拟北京地区SO2的浓度量级和逐日变化趋势.北京地区地面SO2浓度受天气条件的影响较大.采暖期,北京当地排放源的影响相对较大;但在大气条件有利输送的背景下,来自周边地区污染排放源的影响不容忽视.     

First GOCE gravity field models derived by three different approaches

Three gravity field models, parameterized in terms of spherical harmonic coefficients, have been computed from 71 days of GOCE (Gravity field and steady-state Ocean Circulation Explorer) orbit and gradiometer data by applying independent gravity field processing methods. These gravity models are one major output of the European Space Agency (ESA) project GOCE High-level Processing Facility (HPF). The processing philosophies and architectures of these three complementary methods are presented and discussed, emphasizing the specific features of the three approaches. The resulting GOCE gravity field models, representing the first models containing the novel measurement type of gravity gradiometry ever computed, are analysed and assessed in detail. Together with the coefficient estimates, full variance-covariance matrices provide error information about the coefficient solutions. A comparison with state-of-the-art GRACE and combined gravity field models reveals the additional contribution of GOCE based on only 71 days of data. Compared with combined gravity field models, large deviations appear in regions where the terrestrial gravity data are known to be of low accuracy. The GOCE performance, assessed against the GRACE-only model ITG-Grace2010s, becomes superior at degree 150, and beyond. GOCE provides significant additional information of the global Earth gravity field, with an accuracy of the 2-month GOCE gravity field models of 10?cm in terms of geoid heights, and 3?mGal in terms of gravity anomalies, globally at a resolution of 100?km (degree/order 200).