bluuebunny/crossref_metadata_2025_split huggingface dataset:
High‐Pressure Geophysical Properties of Fcc Phase FeHX
Authors: Thompson E. C. , Davis A. H. , Bi W. , Zhao J. , Alp E. E. , Zhang D. , Greenberg E. , Prakapenka V. B. , Campbell A. J. 
Published: January 2018

AbstractFace centered cubic (fcc) FeHX was synthesized at pressures of 18–68 GPa and temperatures exceeding 1,500 K. Thermally quenched samples were evaluated using synchrotron X‐ray diffraction (XRD) and nuclear resonant inelastic X‐ray scattering (NRIXS) to determine sample composition and sound velocities to 82 GPa. To aid in the interpretation of nonideal (X ≠ 1) stoichiometries, two equations of state for fcc FeHX were developed, combining an empirical equation of state for iron with two distinct synthetic compression curves for interstitial hydrogen. Matching the density deficit of the Earth's core using these equations of state requires 0.8–1.1 wt % hydrogen at the core‐mantle boundary and 0.2–0.3 wt % hydrogen at the interface of the inner and outer cores. Furthermore, a comparison of Preliminary Reference Earth Model (PREM) to a Birch's law extrapolation of our experimental results suggests that an iron alloy containing ∼0.8–1.3 wt % hydrogen could reproduce both the density and compressional velocity (VP) of the Earth's outer core.
Zircon (U‐Th)/He Thermochronometric Constraints on Himalayan Thrust Belt Exhumation, Bedrock Weathering, and Cenozoic Seawater Chemistry
Authors: Colleps Cody L. , McKenzie N. Ryan , Stockli Daniel F. , Hughes Nigel C. , Singh Birendra P. , Webb A. Alexander G. , Myrow Paul M. , Planavsky Noah J. , Horton Brian K. 
Published: January 2018

AbstractShifts in global seawater 187Os/188Os and 87Sr/86Sr are often utilized as proxies to track global weathering processes responsible for CO2 fluctuations in Earth history, particularly climatic cooling during the Cenozoic. It has been proposed, however, that these isotopic records instead reflect the weathering of chemically distinctive Himalayan lithologies exposed at the surface. We present new zircon (U‐Th)/He thermochronometric and detrital zircon U‐Pb geochronologic evidence from the Himalaya of northwest India to explore these contrasting interpretations concerning the driving mechanisms responsible for these seawater records. Our data demonstrate in‐sequence southward thrust propagation with rapid exhumation of Lesser Himalayan strata enriched in labile 187Os and relatively less in radiogenic 87Sr at ∼16 Ma, which directly corresponds with coeval shifts in seawater 187Os/188Os and 87Sr/86Sr. Results presented here provide substantial evidence that the onset of exhumation of 187Os‐enriched Lesser Himalayan strata could have significantly impacted the marine 187Os/188Os record at 16 Ma. These results support the hypothesis that regional weathering of isotopically unique source rocks can drive seawater records independently from shifts in global‐scale weathering rates, hindering the utility of these records as reliable proxies to track global weathering processes and climate in deep geologic time.
Dynamical and Thermodynamic Elements of Modeled Climate Change at the East African Margin of Convection
Authors: Giannini Alessandra , Lyon Bradfield , Seager Richard , Vigaud Nicolas 
Published: January 2018

AbstractWe propose a dynamical interpretation of model projections for an end‐of‐century wetting in equatorial East Africa. In the current generation of global climate models, increased atmospheric moisture content associated with warming is not the dominant process explaining the increase in rainfall, as the regional circulation is only weakly convergent even during the rainy seasons. Instead, projected wetter future conditions are generally consistent with the El Niño‐like trend in tropical Pacific sea surface temperatures in climate models. In addition, a weakening in moisture convergence over the adjacent Congo Basin and Maritime Continent cores of convection results in the weakening of near‐surface winds, which increases moisture advection from the Congo Basin core toward the East African margin. Overall confidence in the projections is limited by the significant biases in simulation of the regional climatology and disagreement between observed and modeled tropical Pacific sea surface temperature trends to date.
First Observation of Lion Roar Emission in Saturn's Magnetosheath
Authors: Píša D. , Sulaiman A. H. , Santolík O. , Hospodarsky G. B. , Kurth W. S. , Gurnett D. A. 
Published: January 2018

AbstractWe present an observation of intense emissions in Saturn's magnetosheath as detected by the Cassini spacecraft. The emissions are observed in the dawn sector (magnetic local time ∼06:45) of the magnetosheath over a time period of 11 h before the spacecraft crossed the bow shock and entered the unshocked solar wind. They are found to be narrow‐banded with a peak frequency of about 0.16 fce, where fce is the local electron gyrofrequency. Using plane wave propagation analysis, we show that the waves are right hand circularly polarized in the spacecraft frame and propagate at small wave normal angles (<10∘) with respect to the ambient magnetic field. Electromagnetic waves with the same properties known as “lion roars” have been reported by numerous missions in the terrestrial magnetosheath. Here we show the first evidence such emission outside the terrestrial environment. Our observations suggest that lion roars are a solar‐system‐wide phenomenon and capable of existing in a broad range of parameter space. This also includes 1 order of magnitude difference in frequencies. We anticipate our result to provide new insight into such emissions in a new parameter regime characterized by a higher plasma beta (owing to the substantially higher Mach number bow shock) compared to Earth.
Inferring Fault Frictional and Reservoir Hydraulic Properties From Injection‐Induced Seismicity
Authors: Jagalur‐Mohan Jayanth , Jha Birendra , Wang Zheng , Juanes Ruben , Marzouk Youssef 
Published: January 2018

AbstractCharacterizing the rheological properties of faults and the evolution of fault friction during seismic slip are fundamental problems in geology and seismology. Recent increases in the frequency of induced earthquakes have intensified the need for robust methods to estimate fault properties. Here we present a novel approach for estimation of aquifer and fault properties, which combines coupled multiphysics simulation of injection‐induced seismicity with adaptive surrogate‐based Bayesian inversion. In a synthetic 2‐D model, we use aquifer pressure, ground displacements, and fault slip measurements during fluid injection to estimate the dynamic fault friction, the critical slip distance, and the aquifer permeability. Our forward model allows us to observe nonmonotonic evolutions of shear traction and slip on the fault resulting from the interplay of several physical mechanisms, including injection‐induced aquifer expansion, stress transfer along the fault, and slip‐induced stress relaxation. This interplay provides the basis for a successful joint inversion of induced seismicity, yielding well‐informed Bayesian posterior distributions of dynamic friction and critical slip. We uncover an inverse relationship between dynamic friction and critical slip distance, which is in agreement with the small dynamic friction and large critical slip reported during seismicity on mature faults.
Plant Wax n‐Alkane and n‐Alkanoic Acid Signatures Overprinted by Microbial Contributions and Old Carbon in Meromictic Lake Sediments
Authors: Makou Matthew , Eglinton Timothy , McIntyre Cameron , Montluçon Daniel , Antheaume Ingrid , Grossi Vincent 
Published: January 2018

AbstractSpecific n‐alkanes and n‐alkanoic acids are commonly used as biomarkers in paleoenvironmental reconstruction, yet any individual homologue may originate from multiple biological sources. Here we improve source and age controls for these compounds in meromictic systems by measuring the radiocarbon (14C) ages of specific homologues preserved in twentieth century Lake Pavin (France) sediments. In contrast to many studies, 14C ages generally decreased with increasing carbon chain length, from 7.3 to 2.6 ka for the C14‐C30 n‐alkanoic acids and from 9.2 to 0.3 ka for the C21‐C33 n‐alkanes. Given a known hard water effect, these values suggest that aquatic microbial sources predominate and contributed to most of the homologues measured. Only the longest chain n‐alkanes exclusively represent inputs of higher plant waxes, which were previously sequestered in soils over centennial to millennial timescales prior to transport and deposition. These findings suggest that biomarker source and age should be carefully established for lacustrine settings.
Distinguishing Subauroral Ion Drifts From Birkeland Current Boundary Flows
Authors: Archer W. E. , Knudsen D. J. 
Published: January 2018

AbstractThe Swarm satellites regularly observe latitudinally narrow ion velocity jets exceeding 1 km/s relative to the surrounding plasma at high latitude. Two distinct categories of duskward directed flow channels are observed. The most common are situated between the Region 1 and Region 2 currents, are observed primarily during quiet geomagnetic conditions, and are called Birkeland current boundary flows. During active conditions, a second type of duskward directed ion velocity jet is observed at the equatorward edge of the Region 2 currents, colocated with a sharp poleward directed plasma density gradient, consistent with subauroral ion drifts. Pedersen current and electric field estimates from the Swarm satellites show both types of flow channel to be associated with low height‐integrated Pedersen conductivity relative to the surrounding plasma. In this study we show two cases in which the Swarm satellites passed through both types of event on the same orbit, as well as the average ion velocity, field‐aligned current, and plasma density surrounding 57 of these events. Some field‐aligned current morphologies previously associated with subauroral ion drifts suggest that they may have instead been Birkeland current boundary flows. In this study we provide a comparative description of both phenomena to facilitate their distinction in future studies.
Effects of High‐Latitude Forcing Uncertainty on the Low‐Latitude and Midlatitude Ionosphere
Authors: Pedatella N. M. , Lu G. , Richmond A. D. 
Published: January 2018

AbstractEnsemble simulations are performed using the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM) in order to understand the role of high‐latitude forcing uncertainty on the low‐latitude and midlatitude ionosphere response to the April 2010 geomagnetic storm. The ensemble is generated by perturbing either the high‐latitude electric potential or auroral energy flux in the assimilative mapping for ionosphere electrodynamics (AMIE). Simulations with perturbed high‐latitude electric potential result in substantial intraensemble variability in the low‐latitude and midlatitude ionosphere response to the geomagnetic storm, and the ensemble standard deviation for the change in NmF2 reaches 50–100% of the mean change. Such large intraensemble variability is not seen when perturbing the auroral energy flux. In this case, the effects of the forcing uncertainty are primarily confined to high latitudes. We therefore conclude that the specification of high‐latitude electric fields is an important source of uncertainty when modeling the low‐latitude and midlatitude ionosphere response to a geomagnetic storm. A multiple linear regression analysis of the results indicates that uncertainty in the storm time changes in the equatorial electric fields, neutral winds, and neutral composition can all contribute to the uncertainty in the ionosphere electron density. The results of the present study provide insight into the possible uncertainty in simulations of the low‐latitude and midlatitude ionosphere response to geomagnetic storms due to imperfect knowledge of the high‐latitude forcing.
Exploring Wave‐Wave Interactions in a General Circulation Model
Authors: Nystrom Virginia , Gasperini Federico , Forbes Jeffrey M. , Hagan Maura E. 
Published: January 2018

AbstractNonlinear interactions involving Kelvin waves with (periods, zonal wave numbers) = (3.7d, s =− 1) (UFKW1) and = (2.4d, s =− 1) (UFKW2) and s = 0 and s = 1 quasi 9 day waves (Q9DW) with diurnal tides DW1, DW2, DW3, DE2, and DE3 are explored within a National Center for Atmospheric Research (NCAR) thermosphere‐ionosphere‐mesosphere electrodynamics general circulation model (TIME‐GCM) simulation driven at its ∼30 km lower boundary by interpolated 3‐hourly output from Modern‐Era Retrospective Analysis for Research and Applications (MERRA). The existence of nonlinear wave‐wave interactions between the above primary waves is determined by the presence of secondary waves (SWs) with frequencies and zonal wave numbers that are the sums and differences of those of the primary (interacting) waves. Focus is on 10–21 April 2009, when the nontidal dynamics in the mesosphere‐lower thermosphere (MLT) region is dominated by UFKW and when identification of SW is robust. Fifteen SWs are identified in all. An interesting triad is identified involving UFKW1, DE3, and a secondary UFKW4 = (1.5d, s =− 2): The UFKW1‐DE3 interaction produces UFKW4, the UFKW4‐DE3 interaction produces UFKW1, and the UFKW1 interaction with UFKW4 produces DE3. At 120 km the dynamic range of the reconstructed latitude‐longitude zonal wind field due to all of the SW is roughly half that of the primary waves, which produced them. This suggests that nonlinear wave‐wave interactions could significantly modify the way that the lower atmosphere couples with the ionosphere.
Resolving Horizontal Rupture Directivity of Moderate Crustal Earthquake in Sparse Network With Ambient Noise Location
Authors: He X. , Ni S. 
Published: January 2018

AbstractEarthquake rupture directivity can remove fault plane ambiguity in earthquake moment tensor solutions; thus, it is helpful to improve reliability of shake map and understanding the seismogenic processes. In this paper, we propose an algorithm to resolve the horizontal rupture directivity of moderate crustal earthquakes in two steps. The first step is to determine the two candidate fault planes from focal mechanism inversion. Then, rupture directivity is estimated via the difference between the hypocenter and the centroid location which is constrained on the candidate fault planes. Accurate centroid location is determined with ambient noise location method, in which the noise cross‐correlation functions (NCFs) provide a stable calibration for the path effects. This technique is applied to the 2011 Oklahoma earthquake, and the estimated centroid location is about 2–4 km southwest to the hypocenter, indicating that the mainshock ruptured along the 234° plane for about 4–8 km. The result is consistent with directivity estimation using a foreshock as reference event and also agrees with early aftershock distribution as well as finite fault inversion. More applications to the 2004 Parkfield earthquake and the 2014 Napa earthquake are performed to explore the effectiveness and limitation of this method. This method is helpful for determining rupture directivity of earthquakes in sparse network but requiring one or two nearby stations. Alternatively, temporary stations can be installed in the area of high seismic hazard, then a library of NCFs and path calibrations would be available for rapidly determining rupture directivity of future earthquakes.
Magma Mixing in a Granite and Related Rock Association: Insight From Its Mineralogical, Petrochemical, and “Reversed Isotope” Features
Authors: Jiang Ding‐Sheng , Xu Xi‐Sheng , Xia Yan , Erdmann Saskia 
Published: January 2018

AbstractMagma mixing commonly takes place between isotopically depleted mafic and enriched felsic magmas. Here we present isotopic evidence exhibiting the opposite behavior in the Early Cretaceous Siling complex (south China), which is composed of gabbro, quartz diorite, granodiorite, and alkali feldspar granite with locally many mafic microgranular enclaves. Field observations and zircon U‐Pb dating indicate that all of the rock units crystallized contemporaneously at ca. 127–129 Ma. Mineralogical and petrochemical analyses indicate that the Siling quartz diorite and granodiorite crystallized from hybrid magmas of temporally and spatially coexisting gabbroic and granitic melts. The Siling gabbro, characterized by variable yet enriched Sr‐Nd‐Hf isotopic compositions [(87Sr/86Sr)i = 0.70788 to 0.70833; ɛNd(t) = −7.6 to −3.5; ɛHf(t) = −6.8 to −1.9], exhibits Th/Nb, Nb/Nb*, and Sm/Yb versus εNd(t) correlations, indicating that the gabbro represents variable mixing of magmas derived from deep‐level pyroxenite and shallow‐level peridotite sources. The Siling alkali feldspar granite, which has typical A‐type characteristics, exhibits less enriched Sr‐Nd‐Hf isotopic signatures [(87Sr/86Sr)i = 0.70650; εNd(t) = −3.2 to −2.5; ɛHf(t) = −1.3] than the coexisting gabbro, indicating its derivation from the remelting of juvenile lower crust. “Reversed isotope” feature of the Siling gabbro and alkali feldspar granite means that the quartz diorite and granodiorite recorded “reversed isotope” mixing between isotopically enriched mafic and relatively depleted felsic magmas. The results indicate that the injection of mantle‐derived mafic magma does not necessarily imprint relatively depleted isotopic signatures on the host felsic melt and that the vertical growth of the continental crust by the input of isotopically enriched magma should be concerned.
Sediment Suspension by Straining‐Induced Convection at the Head of Salinity Intrusion
Authors: Zhang Qianjiang , Wu Jiaxue 
Published: January 2018

AbstractThe tidal straining can generate convective motions and exert a periodic modification of turbulence and sediment transport in estuarine and coastal bottom boundary layers. However, the evidence and physics of convection and sediment suspension induced by tidal straining have not been straightforward. To examine these questions, mooring and transect surveys have been conducted in September 2015 in the region of the Yangtze River plume influence. Field observations and scaling analyses indicate an occurrence of convective motions at the head of saline wedge. Theoretical analyses of stratification evolution in the saline wedge show that unstable stratification and resultant convection are induced by tidal straining. Vertical turbulent velocity and eddy viscosity at the head of saline wedge are both larger than their neutral counterparts in the main body, largely enhancing sediment suspension at the head of saline wedge. Moreover, sediment suspension in both neutral and convection‐affected flows is supported by the variance of vertical turbulent velocity, rather than the shearing stress. Finally, the stability correction functions in the Monin‐Obukhov similarity theory can be simply derived from the local turbulent kinetic energy balance to successfully describe the effects of tidal straining on turbulent length scale, eddy viscosity, and sediment diffusivity in the convection‐affected flow. These recognitions may provide novel understanding of estuarine turbidity maxima, and the dynamical structure and processes for coastal hypoxia.
Evaluation of Water Residence Time, Submarine Groundwater Discharge, and Maximum New Production Supported by Groundwater Borne Nutrients in a Coastal Upwelling Shelf System
Authors: Luo Xin , Jiao Jiu Jimmy , Liu Yi , Zhang Xiaolang , Liang Wenzhao , Tang Danling 
Published: January 2018

AbstractThe biogeochemical processes in the continental shelf systems are usually extensively influenced by coastal upwelling and submarine groundwater discharge (SGD). Using eastern Hainan upwelling shelf system as an example, this study fully investigates SGD and coastal upwelling and their effects on the coastal nutrient loadings to the mixing layer of eastern Hainan shelf. Based on the spatial distributions of 223Ra and 228Ra, water residence time is estimated to be 16.9 ± 8.9 days. Based on the mass balance models of 226Ra and 228Ra, the total SGD of the eastern Hainan shelf is estimated to be 0.8 × 108 and 1.4 × 108 m3 d−1, respectively. The groundwater borne dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphate (DIP) are estimated to be up to 1121.8 and 20.4 μM m2 d−1. The coastal upwelling delivers 2741.8 μM m2 d−1 DIN and 217.7 μM m2 d−1 DIP into the mixing layer, which are predominant in all the exogenous nutrient inputs. The groundwater borne DIN will support a maximum new production of 7.5 mM C m2 d−1, about up to 24.0% of the total new production in the study area. SGD‐derived nutrient could be significant as a missing DIN to support the new production in the mixing layer of eastern Hainan shelf. The findings contribute to a better understanding of biogeochemical processes under the influences of SGD and coastal upwelling in the study area and other similar coastal upwelling systems.
Variability of the Labrador Sea Surface Eddy Kinetic Energy Observed by Altimeter From 1993 to 2012
Authors: Zhang Weiwei , Yan Xiao‐Hai 
Published: January 2018

AbstractA merged along track altimeter data set is used to study the variability of eddy kinetic energy (EKE) in the Labrador Sea from 1993 to 2012. The EKE near the west Greenland current (WGC) has strong interannual variability without long‐term trend from 1993 to 2012. The propagation direction of the Irminger Rings (IRs) originating from the WGC can be inferred from the EKE derived from altimeter, and the southward propagation of the IRs varies interannually. The central Labrador Sea EKE increases significantly from 1993 to 2012. The central Labrador Sea temperature difference between the end and the beginning of the winter convections is defined as restratification index to measure the restratification strengths. The relation between the central Labrador Sea EKE and the restratification index shows that the enhanced eddy activity originating from the west of the central Labrador Sea may cool the central Labrador Sea significantly. The interannual variability of the WGC EKE is likely to be driven by the large scale Subpolar Gyre (SPG) circulation variability and the North Atlantic Oscillation (NAO). The NAO also affects the central Labrador Sea EKE through its fingerprint in the local wind stress and surface heat flux. The NAO affects the WGC EKE by changing the SPG circulation strength, which will subsequently affect the WGC EKE through unknown physical processes.