bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Impact of Variable Phytoplankton Stoichiometry on Projections of Primary Production, Food Quality, and Carbon Uptake in the Global Ocean
Authors: Kwiatkowski Lester , Aumont Olivier , Bopp Laurent , Ciais Philippe 
Published: March 2018

AbstractOcean biogeochemical models are integral components of Earth system models used to project the evolution of the ocean carbon sink, as well as potential changes in the physical and chemical environment of marine ecosystems. In such models the stoichiometry of phytoplankton C:N:P is typically fixed at the Redfield ratio. The observed stoichiometry of phytoplankton, however, has been shown to considerably vary from Redfield values due to plasticity in the expression of phytoplankton cell structures with different elemental compositions. The intrinsic structure of fixed C:N:P models therefore has the potential to bias projections of the marine response to climate change. We assess the importance of variable stoichiometry on 21st century projections of net primary production, food quality, and ocean carbon uptake using the recently developed Pelagic Interactions Scheme for Carbon and Ecosystem Studies Quota (PISCES‐QUOTA) ocean biogeochemistry model. The model simulates variable phytoplankton C:N:P stoichiometry and was run under historical and business‐as‐usual scenario forcing from 1850 to 2100. PISCES‐QUOTA projects similar 21st century global net primary production decline (7.7%) to current generation fixed stoichiometry models. Global phytoplankton N and P content or food quality is projected to decline by 1.2% and 6.4% over the 21st century, respectively. The largest reductions in food quality are in the oligotrophic subtropical gyres and Arctic Ocean where declines by the end of the century can exceed 20%. Using the change in the carbon export efficiency in PISCES‐QUOTA, we estimate that fixed stoichiometry models may be underestimating 21st century cumulative ocean carbon uptake by 0.5–3.5% (2.0–15.1 PgC).
Regional Variation in Gravel Riverbed Mobility, Controlled by Hydrologic Regime and Sediment Supply
Authors: Pfeiffer Allison M. , Finnegan Noah J. 
Published: March 2018

AbstractThe frequency and intensity of riverbed mobility are of paramount importance to the inhabitants of river ecosystems as well as to the evolution of bed surface structure. Because sediment supply varies by orders of magnitude across North America, the intensity of bedload transport varies by over an order of magnitude. Climate also varies widely across the continent, yielding a range of flood timing, duration, and intermittency. Together, the differences in sediment supply and hydroclimate result in diverse regimes of bed surface stability. To quantitatively characterize this regional variation, we calculate multidecadal time series of estimated bed surface mobility for 29 rivers using sediment transport equations. We use these data to compare predicted bed mobility between rivers and regions. There are statistically significant regional differences in the (a) exceedance probability of bed‐mobilizing flows (W* > 0.002), (b) maximum bed mobility, and (c) number of discrete bed‐mobilizing events in a year.
ISR Spectra Simulations With Electron‐Ion Coulomb Collisions
Authors: Longley William J. , Oppenheim Meers M. , Fletcher Alex C. , Dimant Yakov S. 
Published: March 2018

AbstractIncoherent scatter radars (ISR) rely on Thomson scattering of very high frequency or ultrahigh frequency radio waves off electrons in the ionosphere and measure the backscattered power spectra in order to estimate altitude profiles of plasma density, electron temperature, ion temperature, and ion drift speed. These spectra result from the collective behavior of coupled ion and electron dynamics, and, for most cases, existing theories predict these well. However, when the radar points nearly perpendicular to the Earth's magnetic field, the motion of the plasma across the field lines becomes complex and Coulomb collisions between electrons and ions become important in interpreting ISR measurements. This paper presents the first fully kinetic, self‐consistent, particle‐in‐cell simulations of ISR spectra with electron‐ion Coulomb collisions. We implement a grid‐based Coulomb collision algorithm in the Electrostatic Parallel Particle‐in‐Cell simulator and obtain ISR spectra from simulations both with and without collisions. For radar directions greater than 5° away from perpendicular to the magnetic field, both sets of simulations match collisionless ISR theory well. For angles between 3° and 5°, the collisional simulation is well described by a simplified Brownian motion collision process. At angles less than 3° away from perpendicular the Brownian motion model fails, and the collisional simulation qualitatively agrees with previous single particle simulations. For radar directions exactly perpendicular to the magnetic field the simulated collisional spectra match those from the Brownian motion collision theory, in agreement with previous single particle simulations.
Depressurization‐Induced Fines Migration in Sediments Containing Methane Hydrate: X‐Ray Computed Tomography Imaging Experiments
Authors: Han Gyeol , Kwon Tae‐Hyuk , Lee Joo Yong , Kneafsey Timothy J. 
Published: March 2018

AbstractDepressurization of hydrate‐bearing sediments (HBS) can cause the movement of fine particles, and in turn, such fines migration affects fluid flow and mechanical behavior of sediments, ultimately affecting long‐term hydrocarbon production and wellbore stability. This study investigated how and to what extent depressurization of HBS causes fines migration using X‐ray computed tomography (CT) imaging. Methane hydrate was synthesized in sediments with 10% fines content (FC), composed of sands with silt and/or clay, and the hydrate‐bearing samples were stepwisely depressurized while acquiring CT images. The CT images were analyzed to quantify the spatial changes in FC in the host sediment and thus to capture the fines migration during depressurization. It was found that the FC changes began occurring from the hydrate dissociation regions. This confirms that the multiphase flow caused by depressurization accompanies fines migration. Depressurization of HBS with a hydrate saturation of ~20–40% caused FC reduction from ~10% to ~6–9%, and the extent of fines migration differed with the particle sizes of the host sands and the types of fines. It was found that fines migration was more pronounced with coarse sands and with silty fines. Such observed level of FC reduction is estimated to increase sediment permeability by several factors based on the Kozeny‐type permeability model. Our results support the notion that the extent of fines migration and its effect on fluid flow behavior need to be assessed in consideration of physical properties of host sediment and fine particles to identify optimum depressurization strategies.
Active Seafloor Seepage Along Hydraulic Fractures Connected to Lateral Stress From Salt‐Related Rafting: Regab Pockmark, Congo Fan
Authors: Wenau S. , Spiess V. 
Published: March 2018

AbstractSeafloor seepage is a widespread phenomenon within salt‐influenced basins as the deformation provides pathways for hydrocarbons to reach the seafloor. However, only minor attention has been given to the distal parts of such systems where the impact of salt tectonic deformation is relatively unpronounced. The stress put on the sedimentary column by moving salt on a continental margin may influence fluid flow systems even outside of the salt province. This stress may lead to overpressure formation within reservoirs and determine the orientation of overpressure‐induced fractures. Seepage in the Congo Fan has been discovered in such a distal position at the Regab pockmark, about 35 km west of the salt front, and its geology and biology have been studied extensively in recent years. We present high‐resolution multichannel seismic data from the Regab pockmark that reveal the underlying migration pathways from a buried channel flank 300 m below seafloor to the seafloor via hydraulic fractures in the sealing overburden. Local doming of the reservoir and the remobilization and uplift of sedimentary strata along the migration pathways are interpreted as the result of overpressure within the reservoir. The orientation of the hydraulic fractures is WSW‐ENE, and the fracture outline corresponds to the area of most intense seepage activity within the seafloor pockmark. Along with a similar orientation of other fractures in the vicinity, we propose that this alignment is due to the stress imposed on the sedimentary column in the fan by the seaward moving salt and rafting sedimentary packages of the salt province further east.
Hydrologically Induced Karst Deformation: Insights From GPS Measurements in the Adria‐Eurasia Plate Boundary Zone
Authors: Serpelloni E. , Pintori F. , Gualandi A. , Scoccimarro E. , Cavaliere A. , Anderlini L. , Belardinelli M. E. , Todesco M. 
Published: March 2018

AbstractWe apply a blind source separation algorithm to the ground displacement time series recorded at continuous Global Positioning System (GPS) stations in the European Eastern Alps and Northern Dinarides. As a result, we characterize the temporal and spatial features of several deformation signals. Seasonal displacements are well described by loading effects caused by Earth surface mass redistributions. More interestingly, we highlight a horizontal, nonseasonal, transient deformation signal, with spatially variable amplitudes and directions. The stations affected by this signal reverse the sense of movement with time, implying a sequence of dilatational and compressional deformation that is oriented normal to rock fractures in karst areas. The temporal evolution of this deformation signal is correlated with the history of cumulated precipitations at monthly time scales. This transient horizontal deformation can be explained by pressure changes associated with variable water levels within vertical fractures in the vadose zones of karst systems. The water level changes required to open or close these fractures are consistent with the fluctuations of precipitation and with the dynamics of karst systems.
Effects of Melt Percolation on Zn Isotope Heterogeneity in the Mantle: Constraints From Peridotite Massifs in Ivrea‐Verbano Zone, Italian Alps
Authors: Huang Jian , Chen Sha , Zhang Xing‐Chao , Huang Fang 
Published: March 2018

AbstractWe determined Zn isotopic compositions of 21 orogenic peridotites from the Baldissero and Balmuccia peridotite massifs in Ivrea‐Verbano Zone, Italian Alps, to investigate Zn isotope behaviors during partial melting and melt percolation in the mantle. The samples include lherzolites, harzburgites, and dunites. Lherzolites are strongly depleted in light rare earth element relative to middle and heavy rare earth element with (La/Sm)PM from 0.009 to 0.265 and (La/Yb)PM from 0.003 to 0.125, which can be explained by 5–15% fractional melting of a primitive mantle source. Harzburgites and dunites with nearly identical Mg# (molar 100 * Mg/(Mg + Fe) = 90.2–91.0) have (La/Sm)PM and (La/Yb)PM higher than but Zn contents similar to or lower than those of the parental lherzolites, suggesting that they were influenced by Zn‐depleted silicate melt percolation. Lherzolites have δ66Zn from 0.13 to 0.27‰ showing no correlations with indicators of melt extraction (e.g., Al2O3, Mg#, and La/Yb) and Zn contents. Three sulfide melt‐affected lherzolites show similar δ66Zn to the other normal ones. These observations indicate that 5–15% partial melting and sulfide melt percolation cause limited Zn isotope variations in the mantle. The metasomatic harzburgites and dunites display high δ66Zn (up to 0.46‰) negatively correlated with Zn contents. Such correlations are attributed to kinetic effect during silicate melt percolation, whereby 64Zn preferentially diffuses out from mantle minerals (e.g., olivine) to the percolating silicate melts. A diffusion model suggests that the negative correlation between δ66Zn and Zn contents in dunites can be explained by an empirical βZn (i.e., βZn‐exponent in D66Zn/D64Zn = (m64Zn/m66Zn)βZn) of 0.05–0.06 in olivine.
The Microphysical Properties of Convective Precipitation Over the Tibetan Plateau by a Subkilometer Resolution Cloud‐Resolving Simulation
Authors: Gao Wenhua , Liu Liping , Li Jian , Lu Chunsong 
Published: March 2018

AbstractThe microphysical properties of convective precipitation over the Tibetan Plateau are unique because of the extremely high topography and special atmospheric conditions. In this study, the ground‐based cloud radar and disdrometer observations as well as high‐resolution Weather Research and Forecasting simulations with the Chinese Academy of Meteorological Sciences microphysics and four other microphysical schemes are used to investigate the microphysics and precipitation mechanisms of a convection event on 24 July 2014. The Weather Research and Forecasting‐Chinese Academy of Meteorological Sciences simulation reasonably reproduces the spatial distribution of 24‐hr accumulated rainfall, yet the temporal evolution of rain rate has a delay of 1–3 hr. The model reflectivity shares the common features with the cloud radar observations. The simulated raindrop size distributions demonstrate more of small‐ and large‐size raindrops produced with the increase of rain rate, suggesting that changeable shape parameter should be used in size distribution. Results show that abundant supercooled water exists through condensation of water vapor above the freezing layer. The prevailing ice crystal microphysical processes are depositional growth and autoconversion of ice crystal to snow. The dominant source term of snow/graupel is riming of supercooled water. Sedimentation of graupel can play a vital role in the formation of precipitation, but melting of snow is rather small and quite different from that in other regions. Furthermore, water vapor budgets suggest that surface moisture flux be the principal source of water vapor and self‐circulation of moisture happen at the beginning of convection, while total moisture flux convergence determine condensation and precipitation during the convective process over the Tibetan Plateau.
A Simple Ensemble Simulation Technique for Assessment of Future Variations in Specific High‐Impact Weather Events
Authors: Taniguchi Kenji 
Published: March 2018

AbstractTo investigate future variations in high‐impact weather events, numerous samples are required. For the detailed assessment in a specific region, a high spatial resolution is also required. A simple ensemble simulation technique is proposed in this paper. In the proposed technique, new ensemble members were generated from one basic state vector and two perturbation vectors, which were obtained by lagged average forecasting simulations. Sensitivity experiments with different numbers of ensemble members, different simulation lengths, and different perturbation magnitudes were performed. Experimental application to a global warming study was also implemented for a typhoon event. Ensemble‐mean results and ensemble spreads of total precipitation, atmospheric conditions showed similar characteristics across the sensitivity experiments. The frequencies of the maximum total and hourly precipitation also showed similar distributions. These results indicate the robustness of the proposed technique. On the other hand, considerable ensemble spread was found in each ensemble experiment. In addition, the results of the application to a global warming study showed possible variations in the future. These results indicate that the proposed technique is useful for investigating various meteorological phenomena and the impacts of global warming. The results of the ensemble simulations also enable the stochastic evaluation of differences in high‐impact weather events. In addition, the impacts of a spectral nudging technique were also examined. The tracks of a typhoon were quite different between cases with and without spectral nudging; however, the ranges of the tracks among ensemble members were comparable. It indicates that spectral nudging does not necessarily suppress ensemble spread.
Observed Responses of Mesospheric Water Vapor to Solar Cycle and Dynamical Forcings
Authors: Remsberg Ellis , Damadeo Robert , Natarajan Murali , Bhatt Praful 
Published: March 2018

AbstractThis study focuses on responses of mesospheric water vapor (H2O) to the solar cycle flux at Lyman‐α wavelength and to dynamical forcings according to the multivariate El‐Nino/Southern Oscillation (ENSO) index. The zonal‐averaged responses are for latitudes from 60°S to 60°N and pressure‐altitudes from 0.01 to 1.0 hPa, as obtained from multiple linear regression analyses of time series of H2O from the Halogen Occultation Experiment for July 1992 to November 2005. The results compare very well with those from a separate simultaneous temporal and spatial (STS) method that also confirms that there are no significant sampling biases affecting both sets of results. Distributions of the seasonal amplitudes for temperature and H2O are in accord with the seasonal net circulation. In general, the responses of H2O to ENSO are anticorrelated with those of temperature. H2O responses to multivariate ENSO index are negative in the upper mesosphere and largest in the Northern Hemisphere; responses in the lower mesosphere are more symmetric with latitude. H2O responses to the Lyman‐α flux (Lya) vary from strong negative values in the uppermost mesosphere to very weak, positive values in the tropical lowermost mesosphere. However, the effects of those H2O responses to the solar activity extend to the rest of the mesosphere via dynamical processes. Profiles of the responses to ENSO and Lya also agree reasonably with published results for H2O at the low latitudes from the Microwave Limb Sounder.
Lower Ionosphere Effects on Narrowband Very Low Frequency Transmission Propagation: Fast Variabilities and Frequency Dependence
Authors: Koh Kuang Liang , Liu Zhongjian , Füllekrug Martin 
Published: March 2018

AbstractThe man‐made narrowband very low frequency transmission from Rhauderfehn, Germany, is studied using high accuracy, microsecond time resolution measurements in Bath, UK. The high time resolution enables a novel comparison of the measurements with a detailed simulation of the transmitted signal. It is found that the wave propagation frequency response exhibits nonlinear amplitude and phase changes with frequency over the narrow transmission bandwidth during the time of the measurements (13 May 2011 15:00:03–15:00:09 UTC). The high time resolution also enables measurements of fast variabilities in the wave propagation <5 ms. The fast propagation variabilities are likely to originate from integrated ionospheric variability over the propagation path or fast ionospheric processes. The wave propagation frequency response measurement has potential benefits in the study of the lower ionosphere, in particular during highly variable perturbations such as those caused by lightning.
Optimization of Large‐Scale Daily Hydrothermal System Operations With Multiple Objectives
Authors: Wang Jian , Cheng Chuntian , Shen Jianjian , Cao Rui , Yeh William W.‐G. 
Published: March 2018

AbstractThis paper proposes a practical procedure for optimizing the daily operation of a large‐scale hydrothermal system. The overall procedure optimizes a monthly model over a period of 1 year and a daily model over a period of up to 1 month. The outputs from the monthly model are used as inputs and boundary conditions for the daily model. The models iterate and update when new information becomes available. The monthly hydrothermal model uses nonlinear programing (NLP) to minimize fuel costs, while maximizing hydropower production. The daily model consists of a hydro model, a thermal model, and a combined hydrothermal model. The hydro model and thermal model generate the initial feasible solutions for the hydrothermal model. The two competing objectives considered in the daily hydrothermal model are minimizing fuel costs and minimizing thermal emissions. We use the constraint method to develop the trade‐off curve (Pareto front) between these two objectives. We apply the proposed methodology on the Yunnan hydrothermal system in China. The system consists of 163 individual hydropower plants with an installed capacity of 48,477 MW and 11 individual thermal plants with an installed capacity of 12,400 MW. We use historical operational records to verify the correctness of the model and to test the robustness of the methodology. The results demonstrate the practicability and validity of the proposed procedure.
Approximate Solutions for Ideal Dam‐Break Sediment‐Laden Flows on Uniform Slopes
Authors: Ni Yufang , Cao Zhixian , Borthwick Alistair , Liu Qingquan 
Published: March 2018

AbstractShallow water hydro‐sediment‐morphodynamic (SHSM) models have been applied increasingly widely in hydraulic engineering and geomorphological studies over the past few decades. Analytical and approximate solutions are usually sought to verify such models and therefore confirm their credibility. Dam‐break flows are often evoked because such flows normally feature shock waves and contact discontinuities that warrant refined numerical schemes to solve. While analytical and approximate solutions to clear‐water dam‐break flows have been available for some time, such solutions are rare for sediment transport in dam‐break flows. Here we aim to derive approximate solutions for ideal dam‐break sediment‐laden flows resulting from the sudden release of a finite volume of frictionless, incompressible water‐sediment mixture on a uniform slope. The approximate solutions are presented for three typical sediment transport scenarios, i.e., pure advection, pure sedimentation, and concurrent entrainment and deposition. Although the cases considered in this paper are not real, the approximate solutions derived facilitate suitable benchmark tests for evaluating SHSM models, especially presently when shock waves can be numerically resolved accurately with a suite of finite volume methods, while the accuracy of the numerical solutions of contact discontinuities in sediment transport remains generally poorer.
The Role of Narratives in Sociohydrological Models of Flood Behaviors
Authors: Leong Ching 
Published: March 2018

AbstractWhile current efforts to model sociohydrologic phenomena provide crucial insight, critics argue that these do not fully reflect the complexity one observes empirically in the real world. The policy sciences, with its focus on the interaction between human agency and the institutions that constrain public choice, can complement such efforts by providing a narrative approach. This paper demonstrates this complementarity by investigating the idea of resilience in a community response to floods. Using the quantitative Q methodology, we trace the dynamics of a common sociohydrologic hypothesis—the “memory effect” and how it decreases vulnerability and, more crucially, the instances when such memory effects do not obtain. Our analysis of a floodprone maladaptive community in Assam, India, finds four distinct narrative types: the Hardened Preparer, the Engineer, Discontent, and the Pessimist. This paper put forward an explicitly sociohydrological conception of resilience which takes into account the role of sociological indicators such as narrative types and perceptions. Such contextual understandings and narrative types can form the basis of generic resilience indicators which complement the anticipated outcomes of sociohydrologic models generally.