bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mercury Sourcing and Sequestration in Weathering Profiles at Six Critical Zone Observatories
Authors: Richardson Justin B. , Aguirre Arnulfo A. , Buss Heather L. , Toby O'Geen A. , Gu Xin , Rempe Daniella M. , Richter Daniel de B. 
Published: August 2018

AbstractMercury sequestration in regolith (soils + weathered bedrock) is an important ecosystem service of the critical zone. This has largely remained unexplored, due to the difficulty of sample collection and the assumption that Hg is predominantly sequestered within surface soils (here we define as 0–0.3 m). We measured Hg concentrations and inventories in weathering profiles at six Critical Zone Observatories (CZOs): Boulder Creek in the Front Range of Colorado, Calhoun in the South Carolina Piedmont, Eel River in coastal northern California, Luquillo in the tropical montane forest of Puerto Rico, Shale Hills of the valley and ridges of central Pennsylvania, and Southern Sierra in the Sierra Nevada range of California. Surface soils had higher Hg concentrations than the deepest regolith samples, except for Eel River, which had lower Hg concentrations in surface soils compared to regolith. Using Ti normalization, CZOs with <12% rock‐derived Hg (Boulder Creek, Calhoun, and Southern Sierra) had Hg peaks between 1.5 and 8.0 m in depth. At CZOs with >50% rock‐derived Hg, Eel River Hg concentrations and pools were greatest at >4.0 m in the weathering profile, while Luquillo and Shale Hills had peaks at the surface that diminished within 1.0 m of the surface. Hg and total organic C were only significantly correlated in regolith at Luquillo and Shale Hills CZOs, suggesting that Hg sorption to organic matter may be less dominant than clays or Fe(II) sulfides in deeper regolith. Our results demonstrate the importance of Hg sequestration in deep regolith, below typical soil sampling depths.
On the Origin of STEVE: Particle Precipitation or Ionospheric Skyglow?
Authors: Gallardo‐Lacourt B. , Liang J. , Nishimura Y. , Donovan E. 
Published: August 2018

AbstractOne of the recent developments in ionospheric research was the introduction of a subauroral spectacle called STEVE (Strong Thermal Emission Velocity Enhancement). Although STEVE has been documented by amateur night sky watchers for decades, it is an exciting new upper atmospheric phenomenon for the scientific community. Observed first by amateur auroral photographers, STEVE appeared as a narrow luminous structure across the night sky. Currently, only one scientific study has focused on STEVE, revealing that it corresponds to a narrow (tens of kilometers in north‐south extent) and long (thousands of kilometers in east‐west direction) structure located in the subauroral region. An important and fundamental question that arises from this study is the origin of STEVE; more specifically, does STEVE correspond to a new ionospheric phenomenon or is it due to particle precipitation? In this letter, we analyze a STEVE event on 28 March 2008 observed by Time History of Events and Macroscale Interactions during Substorms (THEMIS) ground‐based All‐Sky Imagers and a Polar Orbiting Environmental Satellite (POES). The POES‐17 satellite crossed STEVE at the center of the All‐Sky Imager field‐of‐view, allowing us to collect particle data simultaneously. These concurrent measurements show that STEVE might not be associated with particle precipitation (electrons or ions). Therefore, this event suggests that STEVE's skyglow (which we defined to be unrelated to aurora or airglow) could be generated in the ionosphere.
Lake Surface Water Temperature Change Over the Tibetan Plateau From 2001 to 2015: A Sensitive Indicator of the Warming Climate
Authors: Wan W. , Zhao L. , Xie H. , Liu B. , Li H. , Cui Y. , Ma Y. , Hong Y. 
Published: August 2018

AbstractThe Tibetan Plateau (TP) plays a significant role in the Earth's climate system. This letter examines the nighttime lake surface water temperature (LSWT) of 374 lakes (≥10 km2 each) over the TP for the past 15 years (2001–2015). An overall warming trend (0.037 °C/year) is found and it is consistent with the warming air temperature (0.036 °C/year) over the TP, with the vast majority of the lakes (70%, with 28% of which are significant) showing warming (0.076 °C/year) and the rest (30%, with 37% of which are significant) showing cooling (−0.053 °C/year). This astonishing contrast was controlled by different water sources recharging these lakes: (1) warming LSWT due to increased precipitation (central and northern TP) or permafrost degradation (northwestern TP) and (2) cooling LSWT due to increased glacier meltwater (southwestern TP), revealing LSWT a sensitive indicator to climate change that triggered different regional responses in precipitation, permafrost, and glacier changes over the TP. This study helps improve our understanding of high‐altitude lakes and their changing mechanisms under the warming climate.
Temporal‐Scale Analysis of Environmental Controls on Sea Spray Aerosol Production Over the South Pacific Gyre
Authors: Dror Tom , Lehahn Yoav , Altaratz Orit , Koren Ilan 
Published: August 2018

AbstractAn understanding of sea spray aerosol (SSA) production is needed to better assess its influence on climate. Using satellite data, we investigated the production of the coarse mode of aerosol optical depth (AODc), a proxy for SSA, over the pristine South Pacific Gyre. The analysis was done on three time scales: daily, seasonal, and interannual. Scale‐dependent links were shown between the AODc and wind speed (W). AODc and W were positively correlated on both daily and interannual time scales but were significantly anticorrelated on the seasonal time scale. Seasonality of the AODc − W link suggests contribution of other environmental factors. The main variable that could statistically explain trends in AODc on the seasonal time scale was chlorophyll a concentration, which showed a clear negative correlation with AODc. The AODc yield per W unit was clearly reduced when chlorophyll a concentration was high, suggesting a secondary, but important influence of marine biological activity on SSA production.
Quantifying the Stress of the Saturnian Magnetosphere During the Cassini Era
Authors: Staniland N. R. , Dougherty M. K. , Masters A. 
Published: August 2018

AbstractWe quantify the magnetospheric stress state of Saturn, revealing the nature of the planetary environment and its current systems. The complete magnetic field data set collected by the Cassini spacecraft is used to track the global behavior of the Saturnian magnetosphere during the Cassini era. Variations in the magnetodisc current model parameter μoIo determine when the system is stretched, compressed, or near the ground state. Of the 111 orbits that pass through our chosen region, 69 are well described by the model, indicating a steady state current sheet during this interval. While the stress state displays a dependence on local time, it is also shown to vary temporally. We conclude that the Saturnian magnetosphere remained in a quiet state for a significant period of the Cassini orbital mission at Saturn, with occasional large‐scale deviations observed.
Azimuth Estimations From a Small Aperture Infrasonic Array: Test Observations at Stromboli Volcano, Italy
Authors: Yamakawa Kazuya , Ichihara Mie , Ishii Kyoka , Aoyama Hiroshi , Nishimura Takeshi , Ripepe Maurizio 
Published: August 2018

AbstractWe tested the performance of an infrasonic array consisting of three microphones with a 20‐m aperture at Stromboli volcano, Italy. There were four active vents separated by ∼10∘. We employed multiple signal classification (MUSIC) to estimate direction of arrival (DOA) of the detected signals. Using test signals of which the source vents were identified by visual observation, the resolution of DOA estimation of MUSIC is compared with those of Capon beamforming, grid search, and semblance. We confirmed that MUSIC and grid search gave better resolution of DOA than the other two methods. Also, MUSIC provided the best resolutions in time and frequency. It was shown that the DOA switched between different vents or fluctuated in short time scales and can vary with frequency, which indicate multiple active sources. Possible DOA estimation errors were evaluated. A small aperture infrasonic array combined with MUSIC will become a powerful tool for studying and monitoring active volcanoes.
Standing Alfvén Waves in Jupiter's Magnetosphere as a Source of ∼10‐ to 60‐Min Quasiperiodic Pulsations
Authors: Manners H. , Masters A. , Yates J. N. 
Published: August 2018

AbstractEnergy transport inside the giant magnetosphere at Jupiter is poorly understood. Since the Pioneer era, mysterious quasiperiodic (QP) pulsations have been reported. Early publications successfully modeled case studies of ∼60‐min (rest‐frame) pulsations as standing Alfvén waves. Since then, the range of periods has increased to ∼10–60 min, spanning multiple data sets. More work is required to assess whether a common QP modulation mechanism is capable of explaining the full range of wave periods. Here we have modeled standing Alfvén waves to compute the natural periods of the Jovian magnetosphere, for varying plasma sheet thicknesses, field line lengths, and Alfvén speeds. We show that variability in the plasma sheet produces eigenperiods that are consistent with all the reported observations. At least the first half‐dozen harmonics (excluding the fundamental) may contribute but are indistinguishable in our analysis. We suggest that all QP pulsations reported at Jupiter may be explained by standing Alfvén waves.
On the Responses of Mesosphere and Lower Thermosphere Temperatures to Geomagnetic Storms at Low and Middle Latitudes
Authors: Li Jingyuan , Wang Wenbin , Lu Jianyong , Yuan Tao , Yue Jia , Liu Xiao , Zhang Kedeng , Burns Alan G. , Zhang Yongliang , Li Zheng 
Published: August 2018

AbstractObservations from lidars and satellites have shown that large neutral temperature increases and decreases occur in the middle and low latitudes of the mesosphere and lower thermosphere region during geomagnetic storms. Here we undertake first‐principles simulations of mesosphere and lower thermosphere temperature responses to storms using the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model to elucidate the nature and causes of these changes. Temperature variations were not uniform; instead, nighttime temperatures changed earlier than daytime temperatures, and temperatures changed earlier at high latitudes than at low ones. Furthermore, temperatures increased in some places/times and decreased in others. As the simulation behaves similar to observations, it provides an opportunity to understand physical processes that drive the observed changes. Our analysis has shown that they were produced mainly by adiabatic heating/cooling that was associated with vertical winds resulting from general circulation changes, with additional contributions from vertical heat advection.
Extratropical Cyclone Precipitation Life Cycles: A Satellite‐Based Analysis
Authors: Booth James F. , Naud Catherine M. , Jeyaratnam Jeyavinoth 
Published: August 2018

AbstractAlthough extratropical cyclones are the most common midlatitude storms, the relationship between their precipitation life cycle and dynamical strength life cycle has not been thoroughly analyzed. Given that thermodynamic heat exchanges associated with precipitation impact cyclone circulation, there is a need to understand the precipitation/dynamics relationship. Based on Integrated Multi‐satellitE Retrievals for Global Precipitation MeasurementGPM precipitation and Lagrangian cyclone tracks, the precipitation maximum occurs prior to the dynamical strength maximum 70% of the time. The lag in timing is consistent with the difference in cyclone precipitable water vapor at the two peaks. Conditional subsetting of the cyclone composites shows that if the precipitable water vapor distribution is constrained to be equal throughout the composite life cycle, the precipitation peak occurs very near the time of the peak in cyclone dynamical strength. Thus, the boost in dynamical strength caused by latent heat associated with precipitation manifest itself with little to no time lag.
ENSO's Changing Influence on Temperature, Precipitation, and Wildfire in a Warming Climate
Authors: Fasullo J. T. , Otto‐Bliesner B. L. , Stevenson S. 
Published: August 2018

AbstractOn interannual to decadal time scales, the climate mode with many of the strongest societal impacts is the El Niño–Southern Oscillation (ENSO). However, quantifying ENSO's changes in a warming climate remains a formidable challenge, due to both the noise arising from internal variability and the complexity of air‐sea feedbacks in the tropical Pacific Ocean. In this work, we use large (≥30‐member) ensembles of climate simulations to show that anthropogenic climate change can produce systematic increases in ENSO teleconnection strength over many land regions, driving increased interannual variability in regional temperature extremes and wildfire frequency. As the spatial character of this intensification exhibits strong land‐ocean contrasts, a causal role for land‐atmosphere feedbacks is suggested. The identified increase in variance occurs in multiple model ensembles, independent of changes in sea surface temperature variance. This suggests that in addition to changes in the overall likelihoods of heat and wildfire extremes, the variability in these events may also be a robust feature of future climate.
Dynamic Vegetation Simulations of the Mid‐Holocene Green Sahara
Authors: Lu Zhengyao , Miller Paul A. , Zhang Qiong , Zhang Qiang , Wårlind David , Nieradzik Lars , Sjolte Jesper , Smith Benjamin 
Published: August 2018

AbstractThe “Green Sahara” is a period when North Africa was characterized by vegetation cover and wetlands. To qualitatively identify the orbital‐climatic causation of the Green Sahara regime, we performed dynamic vegetation model (LPJ‐GUESS) simulations, driven by climate forcings from coupled general circulation model (EC‐Earth) simulations for the mid‐Holocene, in which the vegetation is prescribed to be either modern desert or artificially vegetated with a reduced dust load. LPJ‐GUESS simulates a vegetated Sahara covered by both herbaceous and woody vegetation types consistent with proxy reconstructions only in the latter scenario. Sensitivity experiments identify interactions required to capture the northward extension of vegetation. Increased precipitation is the main driver of the vegetation extent changes, and the temperature anomalies determine the plant functional types mainly through altered fire disturbance. Furthermore, the simulated vegetation composition also depends on the correct representation of soil texture in a humid environment like Green Sahara.
Devonian Crustal Stretching in the Northern Tasmanides (Australia) and Implications for Oroclinal Bending
Authors: Abdullah Rashed , Rosenbaum Gideon 
Published: August 2018

AbstractThe Tasmanides in eastern Australia exhibit a number of orogenic curvatures (oroclines), and possibly, a continental‐scale bend that defines the continuation of the Delamerian Orogen with the Thomson Orogen. We provide an insight into the geodynamic processes associated with the origin of this orocline. We present interpretations of seismic reflection profiles and potential field data from the Thomson Orogen, which provide information on the crustal architecture and unravel major structures and kinematic relationships. Results show that a large area in the northern Tasmanides is underlain by thinned crust, bounded in the north and south by ~E‐W trending geophysical features with apparent sinistral and dextral sense of kinematics, respectively. Within the highly extended crust of the Thomson Orogen, there is evidence for widespread Devonian basins bounded by normal faults. In stark contrast to the southern Tasmanides, where rocks show evidence for an earlier (Silurian) episode of extension and Devonian contractional deformation, no evidence for Silurian synrift sedimentation is observed in the Thomson Orogen. Evidence for ~E‐W trending sinistral and dextral crustal‐scale shear zones in the northern and southern boundaries of the Thomson Orogen, respectively, may represent tear faults, which were active during the Early Devonian and were possibly accompanied by tear‐related magmatism. We suggest that crustal stretching in the northern Tasmanides was associated with Devonian back‐arc extension in response to trench retreat, bounded by zones of slab‐tearing and crustal segmentation that ultimately led to the development of the Delamerian‐Thomson Orocline.
A Mechanism for Pacific Interdecadal Resonances
Authors: Skákala Jozef , Bruun John T. 
Published: August 2018

AbstractPacific interdecadal variability (PIV) is an important large‐scale climate phenomenon. There is growing evidence that PIV contains three spectral resonances: a decadal (13 ± 1‐year) spectral peak, bidecadal (20 ± 5‐year) resonance, and a pentadecadal (60 ± 10‐year) resonance. Although much has been clarified about mechanisms behind PIV, there are still many open questions about the origin of these resonant modes (especially the pentadecadal mode). We describe dynamics in the Pacific basin by a toy (delayed oscillator) model that sheds light on the nature of these resonant peaks. The model suggests that unlike the bidecadal resonance, which results from local atmosphere‐ocean coupling in the extratropics, the pentadecadal and possibly also decadal resonances result from atmospheric and oceanic teleconnections between the extratropics and tropics. We show that a tiny coupling between extratropics and tropics through the ocean tunnel is sufficient to trigger the pentadecadal oscillation in the Pacific basin. Our model also explains (a) the observed three‐period locking between the bidecadal and pentadecadal modes and (b) the synchronization of anomalies in the central eastern tropics and central North Pacific with the opposite relative sign. We conclude that the role of oceanic teleconnections is probably underestimated in the current literature on PIV.
Particulate Trace Metal Composition and Sources in the Kuroshio Adjacent to the East China Sea: The Importance of Aerosol Deposition
Authors: Liao Wen‐Hsuan , Ho Tung‐Yuan 
Published: August 2018

AbstractThe Kuroshio, flowing through the eastern end of the East China Sea, transports terrestrial material to the Northwestern Pacific Ocean. Along the Kuroshio path, we collected size‐fractionated suspended particles in the upper 200 m to investigate the composition and sources of particulate trace metals. Demonstrated by Al‐ and P‐normalized elemental ratios, we found that anthropogenic aerosol deposition was the major source of most particulate trace metals in the Kuroshio region although the impact of bottom resuspension and riverine input may be significant at some specific regions. As seen in our previous studies in the South China Sea and the Western Philippine Sea, this study concluded that anthropogenic aerosol deposition is the dominant particulate trace metal source in the surface water of the Northwestern Pacific Ocean and its marginal seas. Compared to particulate trace metal composition obtained in other open oceans, we found that the distribution patterns of particulate trace metal composition in the surface waters are closely associated with aerosol deposition fluxes. In regions with low deposition, the particulate trace metal concentrations were extremely low and metal to P ratios were all comparable to their intracellular quota previously proposed. In regions with high deposition, metal to P ratios were highly elevated in comparison to their intracellular quota and metal to Al ratios were deviated from lithogenic ratios to various extents. The globally consistent distribution patterns validate trace metal stoichiometry concept in plankton intracellularly and the primary role of aerosol deposition on deciding particulate trace metal composition in oceanic surface water globally.
SO2 Oxidation Kinetics Leave a Consistent Isotopic Imprint on Volcanic Ice Core Sulfate
Authors: Gautier Elsa , Savarino Joel , Erbland Joseph , Farquhar James 
Published: August 2018

AbstractThis work presents measurements of time‐resolved mass‐independently fractionated sulfate of volcanic origin from Antarctic ice core records that cover the last 2,600 years. These measurements are used to evaluate the time dependence of the deposited isotopic signal and to extract the isotopic characteristics of the reactions yielding sulfate from stratospheric volcanic eruptions in the modern atmosphere. Time evolution of the signal in snow (years) with respect to the fast SO2 oxidation in the stratosphere suggests that photochemically produced condensed phase is rapidly and continuously separated from the gas phase and preserved during transportation and deposition on the polar ice cap. On some eruptions, a nonzero isotopic mass balance highlights that a part of the signal can be lost during transport and/or deposition. The large number of volcanic events studied allows the Δ33S versus Δ36S and δ34S versus Δ33S slopes to be constrained at −1.56 (1σ = 0.25) and 0.09 (1σ = 0.02), respectively. The Δ33S versus Δ36S slope refines a prior determinations of Δ36S/Δ33S = −4 and overlaps the range observed for sulfur seen in early Earth samples (Archean). In recent volcanogenic sulfate, the Δ33S versus δ34S differs, however, from the Archean record. The similitude for Δ36S/Δ33S and the difference for Δ33S/δ34S suggest similar mass‐independently fractionated sulfate processes to the Archean atmosphere. Using a simple model, we highlight that a combination of several mechanisms is needed to reproduce the observed isotopic trends and suggest a greater contribution from mass‐dependent oxidation by OH in the modern atmosphere.
Diel Stream Temperature Effects on Nitrogen Cycling in Hyporheic Zones
Authors: Zheng Lizhi , Bayani Cardenas M. 
Published: August 2018

AbstractStream temperature often varies diurnally and seasonally, and these variations propagate into hyporheic zones (HZs), forming dynamic and heterogeneous thermal patterns. The complex thermal distribution creates potential biogeochemical hotspots and hot moments. Yet, how diel temperature variations affect HZ nitrogen cycling is unknown. We thus conducted a series of multiphysics numerical simulations of nonisothermal fluid flow and multicomponent reactive solute transport to investigate this problem. We imposed a sinusoidally varying stream temperature representing diel warming and cooling and studied the effects of different temperature means and amplitudes on HZ nitrate removal efficiency inside a streambed with a dune. The results showed that the time‐variable nitrification, denitrification, and nitrate removal efficiency responded differently to the diel stream temperature signal. The temporal variation of spatially averaged nitrification rate tracks the stream temperature signal, whereas the spatially averaged denitrification variation pattern has a more complex connection to temperature. We observed a persistent hotspot where significant denitrification rates are present over the 24‐hr period. We further evaluated and estimated the bulk nitrate removal efficiency calculated by time integration of spatially averaged reaction rates over a day. For denitrification‐dominant systems, the bulk nitrate removal efficiency for cases with dynamic stream temperature was effectively the same as those with an equivalent constant mean temperature. Therefore, the bulk removal efficiency of a thermally dynamic diel system may be represented by an equivalent isothermal system given stable flow conditions. However, since large instantaneous variations in various rates were observed, the results imply that randomly timed field measurements are unlikely to be representative. This has to be considered for both past and future synoptic observational studies.