bluuebunny/crossref_metadata_2025_split huggingface dataset:
Three‐Dimensional Spatially Constrained Sulfur Isotopes Highlight Processes Controlling Sulfur Cycling in the Near Surface of the Iheya North Hydrothermal System, Okinawa Trough
Authors: LaFlamme C. , Hollis S. P. , Jamieson J. W. , Fiorentini M. L. 
Published: August 2018

AbstractModern seafloor hydrothermal systems are unique environments in which many of the Earth's reservoirs, including the hydrosphere, biosphere, and geosphere, dynamically interact. Analysis of spatially constrained sulfur isotope compositions from fluids and hydrothermal precipitates within the discharge zone of a volcanogenic system can be used to trace the interactions between the various isotopically distinct sulfur reservoirs that result in the formation of hydrothermal massive sulfide deposits. Here we present in situ sulfur isotope results from laterally and vertically constrained euhedral hydrothermal pyrite from the Iheya North hydrothermal system in the Okinawa Trough, which was investigated during the Integrated Ocean Drilling Program Expedition 331. Hydrothermal pyrite at the North Big Chimney yields δ34S values of ~+11.9 ± 1.1‰ (1σ), which are near identical to the δ34S composition of the vent fluid. Outward, ~150 and ~450 m from North Big Chimney, hydrothermal pyrite within drill core yields δ34S equal to +10.9 ± 1.3‰ (1σ) and +7.0 ± 3.8‰ (1σ), respectively, showing a shift in isotopic composition away from the main vent site. This evolution to a lighter and more scattered isotopic signature of hydrothermal pyrite (which is easily identifiable from biogenic pyrite) is interpreted to indicate that the hydrothermal fluid leached sulfides (formed previously by biogenic processes) from the surrounding sedimentary strata. As the most significant metal enrichments (Fe, Zn, Cu, Bi, Tl, and Cd) are associated with samples that contain average hydrothermal pyrite δ34S values similar to δ34S of the vent fluid, we demonstrate that sulfur isotopes can vector toward metals in seafloor massive sulfide deposits.
Frictional Behavior of Input Sediments to the Hikurangi Trench, New Zealand
Authors: Rabinowitz H. S. , Savage H. M. , Skarbek R. M. , Ikari M. J. , Carpenter B. M. , Collettini C. 
Published: August 2018

AbstractThe Hikurangi subduction zone hosts shallow slow‐slip events, possibly extending to the seafloor. The mechanisms allowing for this behavior are poorly understood but are likely a function of the frictional properties of the downgoing seafloor sediments. We conducted friction experiments at a large range of effective stresses, temperatures, and velocities on incoming sediment to the Hikurangi subduction zone to explore the possible connection of frictional properties to slow‐slip events. These experiments were conducted on multiple apparatuses, allowing us to access a wider range of deformation conditions than is available on any one machine. We find that the material frictionally weakens and becomes less velocity strengthening with increasing effective stress, whereas temperature has only a small effect on both friction and frictional stability. When driven at the plate convergence rate, the sediment exhibits velocity‐weakening behavior. These results imply that the frictional properties of the sediment package subducting at Hikurangi could promote slow‐slip events at the pressures, temperatures, and strain rates expected along the plate boundary thrust up to 10‐km depth without requiring elevated pore fluid pressures. The transition to velocity‐strengthening behavior at faster slip rates could provide a mechanism for limiting unstable slip to slow‐sliding velocities, rather than accommodating deformation through ordinary earthquakes.
Shear Wave Splitting Beneath Eastern North American Continent: Evidence for a Multilayered and Laterally Variable Anisotropic Structure
Authors: Chen Xiaoran , Li Yiran , Levin Vadim 
Published: August 2018

AbstractEastern North America records a tectonic history of over 3 Ga in duration. Much of this record is preserved within the lithosphere and may be unraveled by detailed studies of its interior structure. Past episodes of tectonic activity likely left their imprints in the form of anisotropy‐forming rock fabric presently preserved in the lithosphere of the continent. We perform shear wave splitting measurements using observations of core‐refracted waves collected from a ~1,300‐km‐long array extending from James Bay in Quebec to the Fundy basin in Maine, with lateral spacing of 10–100 km between instruments. Close spacing of instruments helps us associate anisotropic properties with geological boundaries. We find that the fast polarizations concentrate between N60°E and N90°E with an average of N80°E and change systematically with backazimuth. In addition, we observe a lateral increase in delay time from 0.56 ±0.25 s at the NW end of the array to 0.90 ± 0.41 s at the SE end. The location of lateral change in delay time does not match geological boundaries on the surface but seems to match the geophysical boundary at depth of 160 km. We interpret this boundary in splitting values to be the edge of cratonic lithosphere at depth. Our observations suggest that the anisotropic structure beneath our study area is complex and possibly both multilayered and laterally variable.
Distinct Geologic Settings of Opal‐A and More Crystalline Hydrated Silica on Mars
Authors: Sun Vivian Z. , Milliken Ralph E. 
Published: August 2018

AbstractOpaline silica deposits have been identified on Mars from orbital near‐infrared (NIR) reflectance spectra, but opal types (e.g., −A,/CT) have not yet been conclusively determined due to insufficient laboratory spectra acquired at Mars‐relevant conditions. NIR reflectance spectra of siliceous deposits acquired by the Compact Reconnaissance Imaging Spectrometer for Mars instrument are compared with new laboratory spectra of terrestrial opal samples that we measured under Mars‐relevant conditions. Opal‐A occurrences on Mars are commonly associated with bedrock exposures, whereas more crystalline hydrated silica (opal‐CT and quartz/chalcedony) is primarily observed in unconsolidated sediments. These differences suggest some opal‐bearing deposits may have experienced prolonged interaction with near‐surface water or diagenetic fluids, and bedrock exposures dominated by opal‐A may have experienced less post‐formation diagenesis compared with those containing more crystalline hydrated silica. NIR data thus provide a useful tool to assess opal maturity and relative potential for biosignature preservation for different siliceous deposits on Mars.
Organic Carbon Aging During Across‐Shelf Transport
Authors: Bao Rui , Uchida Masao , Zhao Meixun , Haghipour Negar , Montlucon Daniel , McNichol Ann , Wacker Lukas , Hayes John M. , Eglinton Timothy I. 
Published: August 2018

AbstractCompound‐specific radiocarbon analysis was performed on different grain‐size fractions of surficial sediments to examine and compare lateral transport times (LTTs) of organic carbon. 14C aging of long‐chain leaf wax fatty acids along two dispersal pathways of fluvially derived material on adjacent continental margins implies LTTs over distances of ~30 to 500 km that range from hundreds to thousands of years. The magnitude of aging differs among grain size fractions. Our finding suggests that LTTs vary both temporally and spatially as a function of the specific properties of different continental shelf settings. Observations suggest that 14C aging is widespread during lateral transport over continental shelves, with hydrodynamic particle sorting inducing age variations among organic components residing in different grain sizes. Consideration of these phenomena is of importance for understanding carbon cycle processes and interpretation on sedimentary records on continental margins.
Weakening of Nonlinear ENSO Under Global Warming
Authors: Kohyama Tsubasa , Hartmann Dennis L. , Battisti David S. 
Published: August 2018

AbstractThe amplitude response of the El Niño–Southern Oscillation (ENSO) to global warming is examined in two global climate models with realistic ENSO nonlinearity. Geophysical Fluid Dynamics Laboratory Earth System Model Version 2M (GFDL‐ESM2M) and Model for Interdisciplinary Research on Climate version 5 (MIROC5) are the two models that exhibit realistic ENSO nonlinearity. With quadrupled atmospheric carbon dioxide, the ENSO amplitude of GFDL‐ESM2M decreases by about 40%, whereas that of MIROC5 remains almost constant. Because GFDL‐ESM2M exhibits stronger climatological thermal stratification than MIROC5, greenhouse gas forcing increases the upper ocean stability and causes the thermocline to be less sensitive to wind perturbations. The stiffer thermocline inhibits the nonlinear variations of sea surface temperature so that the ENSO amplitude substantially weakens. Idealized nonlinear recharge oscillator model experiments further support climatological thermal stratification as a determinant of the warming response. Observations exhibit stronger thermal stratification than both models, which suggests that the real world may terminate strong, nonlinear El Niños sooner than model‐based projections.
Structures of Hall Fields in Asymmetric Magnetic Reconnection
Authors: Dai Lei 
Published: August 2018

AbstractUnlike a quadrupolar Hall magnetic field in symmetric magnetic reconnection, a bipolar or quadrupolar Hall magnetic field occurs in asymmetric reconnection as indicated by recent observations from the Magnetospheric Multiscale (MMS) mission. Here we present analytic calculations of the structures of Hall magnetic fields in asymmetric reconnection. The Hall magnetic fields are analyzed in terms of kinetic Alfvén wave eigenmodes of the reconnection layer. The bipolar and quadrupolar patterns of Hall magnetic fields correspond to a dominance of the n = 0 and n = 1 kinetic Alfvén wave eigenmode, respectively. The asymmetry of Hall fields is linked to the asymmetry of the Alfvé speed profile. The Hall magnetic fields are shifted toward and enhanced on the low Alfvén speed side of the reconnection layer. The asymmetry in the magnetic field strength of the reconnection layer has a major effect on the structures of Hall magnetic fields.
Comparison of Variations of TEC at Disturbed and Quiet Time Using Nonlinear Dynamics Tools
Authors: Eapen Suja , Asokan K. , Kumar K. Satheesh , Ramamohan T. R. , Kumar Anil 
Published: August 2018

AbstractWe analyze the underlying dynamics at three different latitudes of ionosphere through total electron content‐series for 4 months. The global dynamics reconstructed from the data is shown to be deterministic with low dimensional chaotic attractors at all the locations, and the dynamics is seen to be less complex at the midlatitude station with smaller dimension of correlation (CD) and maximum Lyapunov exponent (MLE). The influence of geomagnetic storms on the ionospheric dynamics is studied, by analyzing the local dynamics during disturbed and quiet periods, reconstructed from segments of total electron content‐series of shorter duration. With positive MLEs and smaller CDs, the local dynamics is seen to be deterministic and chaotic at the low latitude, midlatitude, and high latitude during both the disturbed and quiet days. However, it is interesting to observe that the dynamics is less chaotic and complex during the disturbed days of the entire period of observation compared to the adjacent quiet days at the three locations. This is further evidenced by sample predictions made using nonlinear tools, yielding better predictions during storms. The smaller CD value during disturbed periods indicates that the geomagnetic activities tend to make a few of the variables dominant enough to control the essential dynamics of the system. Further, the MLEs of the disturbed days are found to increase nearly in a linear fashion from beginning to end of the observation period at all the locations considered. This is an indication of the strong influence of geomagnetic activities on the ionosphere and might have caused the restructuring of the ionospheric dynamics.
Reply to Comment on the Article “Parametric Instability Induced by X‐Mode Wave Heating at EISCAT” by Wang et al. (2016)
Authors: Wang Xiang , Zhou Chen , Honary Farideh 
Published: August 2018

AbstractThis paper is a response to the comment by Blagoveshchenskaya et al. (2017, https://doi.org/10.1002/2017JA023880) on the paper by Wang et al. (2016, https://doi.org/10.1002/2016JA023070). Although we disagree with Blagoveshchenskaya et al. (2017), nevertheless, we do thank them for their comments, since they have given us the opportunity to clarify some points.
Geodetically Inferred Locking State of the Cascadia Megathrust Based on a Viscoelastic Earth Model
Authors: Li Shaoyang , Wang Kelin , Wang Yanzhao , Jiang Yan , Dosso Stan E. 
Published: August 2018

AbstractIn a viscoelastic Earth, stresses slowly built up due to fault locking are relaxed concurrently during the entire interseismic period. This interseismic stress relaxation causes crustal deformation much farther away from the locked fault than can be explained using elastic models that neglect the relaxation. Here we develop a viscoelastic geodetic inversion model to address this problem at Cascadia. We invert ~500 horizontal velocity vectors based on continuous and campaign geodetic measurements over the past two decades. Ambiguities arising from long‐term rotation of upper‐plate crustal blocks are addressed by test‐correcting the geodetic velocities with two different block‐motion models. Fault back slip (i.e., slip deficit) Green's functions are derived using a Maxwell viscoelastic finite element model with realistic subduction zone structure and megathrust geometry. The preferred model features a narrow and shallow megathrust locked zone, consistent with earlier thermorheological reasoning. For an elastic model to fit the data to the same fidelity, megathrust locking has to extend to much greater depths. However, even with the viscoelastic model, the land‐based geodetic data still cannot resolve whether there is some creep (incomplete locking) in the shallowest part of the megathrust far offshore. Neither can the land data fully resolve along‐strike variations of the locking state. These ambiguities can be resolved only when adequate seafloor geodetic data are obtained.
A Tensile Origin for Fault Rock Pulverization
Authors: Griffith W. Ashley , St. Julien Rene C. , Ghaffari Hamed O. , Barber Troy J. 
Published: August 2018

AbstractThe origin of highly fragmented, but weakly strained rocks found along major strike‐slip faults has been enigmatic since their first recognition. These so‐called pulverized rocks occur up to 100 m away from the principal slip zone of seismogenic faults around the world. Previous dynamic compression experiments have suggested that rock pulverization occurs at strain rates on the order of 102 s−1, pointing to a coseismic origin; however, strain rates during earthquake rupture 100 m from faults is expected to be 4 orders of magnitude smaller. We present evidence from new modified Split‐Hopkinson Pressure Bar experiments that instead supports a tensile origin for coseismic rock pulverization. In the new experimental configuration, the axial compressive load from the Split‐Hopkinson Pressure Bar induces radially isotropic tension in a Westerly Granite disk bonded between two lead cylinders. The isotropic tensile state of stress results in the formation of polygonal fracture arrays that bound axis‐parallel columnar fragments. The tensile strength of Westerly Granite measured at strain rates between ~5 and 50 s−1 bridges the gap between low strain rate and shock strengths reported previously, supporting an interpretation that highly fragmented rocks may form in a state of isotropic tension. The resulting fragment size is independent of strain rate and instead appears to be controlled by elastic strain energy, a strong function of material strength, and fracture toughness. Our results provide a solution to the strain rate‐distance scaling problem between laboratory experiments and field observations of pulverized rocks and also explain the asymmetric distribution of pulverized fault rocks about strike‐slip faults.
Olivine Grain Size Distributions in Faults and Shear Zones: Evidence for Nonsteady State Deformation
Authors: Aupart Claire , Dunkel Kristina G. , Angheluta Luiza , Austrheim Håkon , Ildefonse Benoit , Malthe‐Sørenssen Anders , Jamtveit Bjørn 
Published: August 2018

AbstractThe grain size distribution of deformed rocks may provide valuable information about their deformation history and the associated mechanisms. Here we present a unique set of olivine grain size distributions from ultramafic rocks deformed under a wide range of stress and strain rate conditions. Both experimentally deformed and naturally deformed samples are included. We observe a surprisingly uniform behavior, and most samples show power law grain size distributions. Convincing lognormal distributions across all scales were only observed for samples experimentally deformed at high temperature (1200 °C) and for some mantle‐deformed natural samples. Single power law distributions were observed for natural samples deformed by brittle mechanisms and by samples deformed experimentally in the regime of low‐temperature plasticity. Most natural samples show a crossover in power law scaling behavior near the median grain size from a steep slope for the larger grain fraction to a more gentle slope for the smaller grains. The small grain fraction shows a good data collapse when normalized to the crossover length scale. The associated power law slope indicates a common grain size controlling process. We propose a model that explains how such a scaling behavior may arise in the dislocation creep regime from the competition between the rate involved in the dislocation dynamics and the imposed strain rate. The common departure from lognormal distributions suggests that naturally deformed samples often have a deformation history that is far from a steady state scenario and probably reflects deformation under highly variable stress and strain rates.
A Pedogenic Model for the Magnetic Enhancement of Late Miocene Fluvial‐Lacustrine Sediments From the Xining Basin, NE Tibetan Plateau
Authors: Zan Jinbo , Kang Jian , Yan Maodu , Fang Xiaomin , Li Xiaojing , Guan Chong , Zhang Weilin , Fang Yahui 
Published: August 2018

AbstractContinuous sequences of Cenozoic fluvial‐lacustrine sediments are well preserved in the northeastern edge of the Tibetan Plateau (TP), and they provide a good opportunity to improve our understanding of the tectonic uplift and paleoenvironmental evolution of the NE TP. To date, however, the factors controlling the variations in the magnetic properties of these fluvial‐lacustrine sediments remain complex and ambiguous. Here we systematically assess the contribution of pedogenesis to the magnetic enhancement of late Miocene fluvial‐lacustrine sediments in the Xining Basin, using a combination of rock magnetic, diffuse reflectance spectroscopy, and geochemical methods. Our results demonstrate that the magnetic concentration parameters show a long‐term increasing trend since the late Miocene, with two dramatic increases at ~11 and 9 Ma. Based on the examination of several factors that may affect the magnetic properties of fluvial‐lacustrine sediments in the NE TP, we argue that an accelerated drying process in waterlogged environments, induced by late Miocene global cooling or/and tectonic uplift, may have caused the changes from anaerobic to aerobic conditions and resulted in the observed stepwise increases in pedogenic intensity. The two dramatic increases in magnetic parameters are closely related to intensified aridification and tectonic activity in the NE TP at ~11 and 9 Ma, respectively. These observations suggest that the pedogenic magnetic enhancement model, caused by the disappearance of a waterlogged and reducing pedogenic environment since the late Miocene, should be reconsidered as a possible factor explaining the magnetic properties of fluvial‐lacustrine sediments in the NE TP.
Delayed and Quasi‐Synchronous Response of Tropical Atlantic Surface Salinity to Rainfall
Authors: Grodsky Semyon A. , Carton James A. 
Published: August 2018

AbstractZonally elongated patterns of tropical Atlantic rainfall variability associated with the Atlantic meridional (dipole) and the El Niño‐Southern Oscillation (ENSO) modes extend over the ocean and adjacent land and lead to a complex sea surface salinity (SSS) response. SSS response to local ocean rainfall is quasi‐instantaneous, while SSS response to land rainfall is delayed through river hydrology. Amazon rainfall associated with the Atlantic meridional mode concentrates over coastal north‐east Brazil and results in a fast Amazon response. In contrast, ENSO rainfall occupies vast inland areas and results in 3‐ to 7‐month delayed Amazon discharge response. Although ocean profile analyses represent well interannual SSS forced by open ocean rainfall, they miss interannual SSS in the plume. Including thermosalinograph transect data improves the representation of plume SSS, but its dynamic is better captured by ocean reanalyses. In Simple Ocean Data Assimilation, the plume SSS anomaly persists several months following the peak of land rainfall and is mixed out by seasonally accelerating winds in boreal winter. Its discharge‐correlated magnitude is only a modest few tenths of PSU. Perhaps, such weak projection of continental discharge variations on simulated SSS is not surprising due to other factors contributing in this dynamically active western boundary area. Significant transient variability in local currents not associated with rainfall/discharge variability is a factor explaining why ocean analyses based on occasional profile observations fail in resolving the rain‐induced SSS in the Amazon plume.
Role of SST Patterns on Surface Wind Modulation of a Heavy Midlatitude Precipitation Event
Authors: Meroni Agostino N. , Parodi Antonio , Pasquero Claudia 
Published: August 2018

AbstractThe mechanisms controlling the influence of the sea surface temperature (SST) structure on the surface winds are studied by means of numerical simulations run with a nonhydrostatic fully compressible state‐of‐the‐art numerical model in a realistic midlatitudes setup, leading to the 9 October 2014 Genoa heavy rainfall event. Starting from a simulation with high‐resolution submesoscale eddy‐permitting SST field, the surface temperature boundary conditions are changed to enhance, reduce, or smooth the SST gradient. It is found that the marine atmospheric boundary layer responds to the submesoscale SST forcing structures over time scales of the order of hours. In particular, through the downward momentum mixing mechanism, the presence of SST horizontal gradients impacts the spatial structure of the surface wind convergence, which can displace the convective heavy rain bands that develop over the sea.