bluuebunny/crossref_metadata_2025_split huggingface dataset:
Biogeochemical Role of Subsurface Coherent Eddies in the Ocean: Tracer Cannonballs, Hypoxic Storms, and Microbial Stewpots?
Authors: Frenger Ivy , Bianchi Daniele , Stührenberg Carolin , Oschlies Andreas , Dunne John , Deutsch Curtis , Galbraith Eric , Schütte Florian 
Published: January 2018

Subsurface eddies are known features of ocean circulation, but the sparsity of observations prevents an assessment of their importance for biogeochemistry. Here we use a global eddying (0.1°) ocean‐biogeochemical model to carry out a census of subsurface coherent eddies originating from eastern boundary upwelling systems (EBUS) and quantify their biogeochemical effects as they propagate westward into the subtropical gyres. While most eddies exist for a few months, moving over distances of hundreds of kilometers, a small fraction (<5%) of long‐lived eddies propagates over distances greater than 1,000 km, carrying the oxygen‐poor and nutrient‐rich signature of EBUS into the gyre interiors. In the Pacific, transport by subsurface coherent eddies accounts for roughly 10% of the offshore transport of oxygen and nutrients in pycnocline waters. This “leakage” of subsurface waters can be a significant fraction of the transport by nutrient‐rich poleward undercurrents and may contribute to the well‐known reduction of productivity by eddies in EBUS. Furthermore, at the density layer of their cores, eddies decrease climatological oxygen locally by close to 10%, thereby expanding oxygen minimum zones. Finally, eddies represent low‐oxygen extreme events in otherwise oxygenated waters, increasing the area of hypoxic waters by several percent and producing dramatic short‐term changes that may play an important ecological role. Capturing these nonlocal effects in global climate models, which typically include noneddying oceans, would require dedicated parameterizations.
Addressing Pollution‐Related Global Environmental Health Burdens
Authors: Filippelli Gabriel M. , Taylor Mark P. 
Published: January 2018

AbstractNew analyses are revealing the scale of pollution on global health, with a disproportionate share of the impact borne by lower‐income nations, minority and marginalized individuals. Common themes emerge on the drivers of this pollution impact, including a lack of regulation and its enforcement, research and expertise development, and innovative funding mechanisms for mitigation. Creative approaches need to be developed and applied to address and overcome these obstacles. The existing “business as usual” modus operandi continues to externalize human health costs related to pollution, which exerts a negative influence on global environmental health.
An Argo‐Derived Background Diffusivity Parameterization for Improved Ocean Simulations in the Tropical Pacific
Authors: Zhu Yuchao , Zhang Rong‐Hua 
Published: January 2018

AbstractModel biases are substantial in ocean and coupled ocean‐atmosphere simulations in the tropical Pacific Ocean, including a too cold tongue and too diffuse thermocline. These biases can be partly attributed to vertical mixing parameterizations in which the background diffusivity depiction has great uncertainties. Here based on the fine‐scale parameterization, the Argo data are used to derive the spatially varying background diffusivity, with a magnitude of O(10−6 m2 s−1) in the most area of tropical Pacific. This new scheme is then employed into the version 5.1 of the Modular Ocean Model‐based ocean‐only and coupled models, resulting in substantial improvements in ocean simulations, including a more realistic cold tongue and equatorial thermocline. The improved simulations can be attributed to the reduced cooling effects induced by weakened equatorial upwelling. Additionally, the subsurface cooling effect is attributed to the reduced heat transfer from the upper layer to the subsurface layer and the convergence of the colder water from off the equator.
The North Atlantic Ocean Is in a State of Reduced Overturning
Authors: Smeed D. A. , Josey S. A. , Beaulieu C. , Johns W. E. , Moat B. I. , Frajka‐Williams E. , Rayner D. , Meinen C. S. , Baringer M. O. , Bryden H. L. , McCarthy G. D. 
Published: January 2018

AbstractThe Atlantic Meridional Overturning Circulation (AMOC) is responsible for a variable and climatically important northward transport of heat. Using data from an array of instruments that span the Atlantic at 26°N, we show that the AMOC has been in a state of reduced overturning since 2008 as compared to 2004–2008. This change of AMOC state is concurrent with other changes in the North Atlantic such as a northward shift and broadening of the Gulf Stream and altered patterns of heat content and sea surface temperature. These changes resemble the response to a declining AMOC predicted by coupled climate models. Concurrent changes in air‐sea fluxes close to the western boundary reveal that the changes in ocean heat transport and sea surface temperature have altered the pattern of ocean‐atmosphere heat exchange over the North Atlantic. These results provide strong observational evidence that the AMOC is a major factor in decadal‐scale variability of North Atlantic climate.
Top‐Down CO Emissions Based On IASI Observations and Hemispheric Constraints on OH Levels
Authors: Müller J.‐F. , Stavrakou T. , Bauwens M. , George M. , Hurtmans D. , Coheur P.‐F. , Clerbaux C. , Sweeney C. 
Published: January 2018

AbstractAssessments of carbon monoxide emissions through inverse modeling are dependent on the modeled abundance of the hydroxyl radical (OH) which controls both the primary sink of CO and its photochemical source through hydrocarbon oxidation. However, most chemistry transport models (CTMs) fall short of reproducing constraints on hemispherically averaged OH levels derived from methylchloroform (MCF) observations. Here we construct five different OH fields compatible with MCF‐based analyses, and we prescribe those fields in a global CTM to infer CO fluxes based on Infrared Atmospheric Sounding Interferometer (IASI) CO columns. Each OH field leads to a different set of optimized emissions. Comparisons with independent data (surface, ground‐based remotely sensed, aircraft) indicate that the inversion adopting the lowest average OH level in the Northern Hemisphere (7.8 × 105 molec cm−3, ∼18% lower than the best estimate based on MCF measurements) provides the best overall agreement with all tested observation data sets.
Ultrasonic Acoustic Velocities During Partial Melting of a Mantle Peridotite KLB‐1
Authors: Weidner Donald J. , Li Li , Whitaker Matthew L. , Triplett Richard 
Published: January 2018

AbstractKnowledge of the elastic properties of partially molten rocks is crucial for understanding low‐velocity regions in the interior of the Earth. Models of fluid and solid mixtures have demonstrated that significant decreases in seismic velocity are possible with small amounts of melt, but there is very little available data for testing these models, particularly with both P and S waves for mantle compositions. We report ultrasonic measurements of P and S velocities on a partially molten KLB‐1 sample at mantle conditions using a multi‐anvil device at a synchrotron facility. The P, S, and bulk sound velocities decrease as melting occurs. We find that the quantity, ∂lnVS/∂lnVB (where VB is the bulk sound velocity) is lower than mechanical models estimate. Instead, our data, as well as previous data in the literature, are consistent with a dynamic melting model in which melting and solidification interact with the stress field of the acoustic wave.
The Spectral Nature of Titan's Major Geomorphological Units: Constraints on Surface Composition
Authors: Solomonidou A. , Coustenis A. , Lopes R. M. C. , Malaska M. J. , Rodriguez S. , Drossart P. , Elachi C. , Schmitt B. , Philippe S. , Janssen M. , Hirtzig M. , Wall S. , Sotin C. , Lawrence K. , Altobelli N. , Bratsolis E. , Radebaugh J. , Stephan K. , Brown R. H. , Le Mouélic S. , Le Gall A. , Villanueva E. V. , Brossier J. F. , Bloom A. A. , Witasse O. , Matsoukas C. , Schoenfeld A. 
Published: January 2018

AbstractWe investigate Titan's low‐latitude and midlatitude surface using spectro‐imaging near‐infrared data from Cassini/Visual and Infrared Mapping Spectrometer. We use a radiative transfer code to first evaluate atmospheric contributions and then extract the haze and the surface albedo values of major geomorphological units identified in Cassini Synthetic Aperture Radar data, which exhibit quite similar spectral response to the Visual and Infrared Mapping Spectrometer data. We have identified three main categories of albedo values and spectral shapes, indicating significant differences in the composition among the various areas. We compare with linear mixtures of three components (water ice, tholin‐like, and a dark material) at different grain sizes. Due to the limited spectral information available, we use a simplified model, with which we find that each albedo category of regions of interest can be approximately fitted with simulations composed essentially by one of the three surface candidates. Our fits of the data are overall successful, except in some cases at 0.94, 2.03, and 2.79 μm, indicative of the limitations of our simplistic compositional model and the need for additional components to reproduce Titan's complex surface. Our results show a latitudinal dependence of Titan's surface composition, with water ice being the major constituent at latitudes beyond 30°N and 30°S, while Titan's equatorial region appears to be dominated partly by a tholin‐like or by a very dark unknown material. The albedo differences and similarities among the various geomorphological units give insights on the geological processes affecting Titan's surface and, by implication, its interior. We discuss our results in terms of origin and evolution theories.
A Combined (U‐Th)/He and Cosmogenic 3He Record of Landscape Armoring by Biogeochemical Iron Cycling
Authors: Monteiro H. S. , Vasconcelos P. M. P. , Farley K. A. 
Published: January 2018

Abstract(U‐Th)/He geochronology and cosmogenic 3He in iron oxides reveal mineral precipitation ages as old as 55 Ma and exposure ages greater than 5 Ma for canga‐cemented plateaus in the Quadrilátero Ferrífero, Brazil, showing that lateritic profiles overlying banded iron‐formation (BIF) landscapes in tropical regions have a long history of surface exposure. The long‐term erosion history obtained from cosmogenic 3He on BIF plateaus confirms that relic surfaces persist in the landscape for millions of years. Combined 3He and (U‐Th)/He dating shows that cangas are preferentially goethite cemented by biogeochemical reactions in the subsurface. Importantly, pebbles of hematite‐magnetite in colluvia or shallow creeks draining the canga‐cemented plateaus record a much longer exposure history than in situ canga blocks, showing that even older duricrusts, now eroded, once blanketed these plateaus. Physically stable but biogeochemically dynamic, cangas armor the landscape by pervasive and recurrent iron cycling and cementation, slowing down the delivery of weathered BIF or friable hematite–magnetite ore to erosion.
The Influence of Shallow Taliks on Permafrost Thaw and Active Layer Dynamics in Subarctic Canada
Authors: Connon Ryan , Devoie Élise , Hayashi Masaki , Veness Tyler , Quinton William 
Published: January 2018

AbstractMeasurements of active layer thickness (ALT) are typically taken at the end of summer, a time synonymous with maximum thaw depth. By definition, the active layer is the layer above permafrost that freezes and thaws annually. This study, conducted in peatlands of subarctic Canada, in the zone of thawing discontinuous permafrost, demonstrates that the entire thickness of ground atop permafrost does not always refreeze over winter. In these instances, a talik exists between the permafrost and active layer, and ALT must therefore be measured by the depth of refreeze at the end of winter. As talik thickness increases at the expense of the underlying permafrost, ALT is shown to simultaneously decrease. This suggests that the active layer has a maximum thickness that is controlled by the amount of energy lost from the ground to the atmosphere during winter. The taliks documented in this study are relatively thin (<2 m) and exist on forested peat plateaus. The presence of taliks greatly affects the stability of the underlying permafrost. Vertical permafrost thaw was found to be significantly greater in areas with taliks (0.07 m year−1) than without (0.01 m year−1). Furthermore, the spatial distribution of areas with taliks increased between 2011 and 2015 from 20% to 48%, a phenomenon likely caused by an anomalously large ground heat flux input in 2012. Rapid talik development and accelerated permafrost thaw indicates that permafrost loss may exhibit a nonlinear response to warming temperatures. Documentation of refreeze depths and talik development is needed across the circumpolar north.
Vertical Stratification of Peat Pore Water Dissolved Organic Matter Composition in a Peat Bog in Northern Minnesota
Authors: Tfaily Malak M. , Wilson Rachel M. , Cooper William T. , Kostka Joel E. , Hanson Paul , Chanton Jeffrey P. 
Published: January 2018

AbstractWe characterized dissolved organic matter (DOM) composition throughout the peat column at the Marcell S1 forested bog in northern Minnesota and tested the hypothesis that redox oscillations associated with cycles of wetting and drying at the surface of the fluctuating water table correlate with increased carbon, sulfur, and nitrogen turn over. We found significant vertical stratification of DOM molecular composition and excitation‐emission matrix parallel factor analysis components within the peat column. In particular, the intermediate depth zone (~ 50 cm) was identified as a zone where maximum decomposition and turnover is taking place. Surface DOM was dominated by inputs from surface vegetation. The intermediate depth zone was an area of high organic matter reactivity and increased microbial activity with diagenetic formation of many unique compounds, among them polycyclic aromatic compounds that contain both nitrogen and sulfur heteroatoms. These compounds have been previously observed in coal‐derived compounds and were assumed to be responsible for coal's biological activity. Biological processes triggered by redox oscillations taking place at the intermediate depth zone of the peat profile at the S1 bog are assumed to be responsible for the formation of these heteroatomic PACs in this system. Alternatively, these compounds could stem from black carbon and nitrogen derived from fires that have occurred at the site in the past. Surface and deep DOM exhibited more similar characteristics, compared to the intermediate depth zone, with the deep layer exhibiting greater input of microbially degraded organic matter than the surface suggesting that the entire peat profile consists of similar parent material at different degrees of decomposition and that lateral and vertical advection of pore water from the surface to the deeper horizons is responsible for such similarities. Our findings suggest that molecular composition of DOM in peatland pore water is dynamic and is a function of ecosystem activity, water table, redox oscillation, and pore water advection.
On Lack of Robustness in Hydrological Model Development Due to Absence of Guidelines for Selecting Calibration and Evaluation Data: Demonstration for Data‐Driven Models
Authors: Zheng Feifei , Maier Holger R. , Wu Wenyan , Dandy Graeme C. , Gupta Hoshin V. , Zhang Tuqiao 
Published: January 2018

AbstractHydrological models are used for a wide variety of engineering purposes, including streamflow forecasting and flood‐risk estimation. To develop such models, it is common to allocate the available data to calibration and evaluation data subsets. Surprisingly, the issue of how this allocation can affect model evaluation performance has been largely ignored in the research literature. This paper discusses the evaluation performance bias that can arise from how available data are allocated to calibration and evaluation subsets. As a first step to assessing this issue in a statistically rigorous fashion, we present a comprehensive investigation of the influence of data allocation on the development of data‐driven artificial neural network (ANN) models of streamflow. Four well‐known formal data splitting methods are applied to 754 catchments from Australia and the U.S. to develop 902,483 ANN models. Results clearly show that the choice of the method used for data allocation has a significant impact on model performance, particularly for runoff data that are more highly skewed, highlighting the importance of considering the impact of data splitting when developing hydrological models. The statistical behavior of the data splitting methods investigated is discussed and guidance is offered on the selection of the most appropriate data splitting methods to achieve representative evaluation performance for streamflow data with different statistical properties. Although our results are obtained for data‐driven models, they highlight the fact that this issue is likely to have a significant impact on all types of hydrological models, especially conceptual rainfall‐runoff models.
Impact of stroke mechanism in acute basilar occlusion with reperfusion therapy
Authors: Lee Woo‐Jin , Jung Keun‐Hwa , Ryu Young Jin , Kim Jeong‐Min , Lee Soon‐Tae , Chu Kon , Kim Manho , Lee Sang Kun , Sohn Chul‐Ho , Roh Jae‐Kyu 
Published: January 2018

AbstractObjectiveWe aimed to evaluate the impact of underlying mechanism of basilar artery (BA) occlusion on the outcomes after endovascular therapy (EVT) for reperfusion and the outcome factors associated with each mechanism, and to identify radiologic parameters enabling to distinguish the underlying mechanism.MethodsFrom a registry database, 194 consecutive patients with acute BA occlusion who underwent EVT were analyzed. Stroke mechanism, classified into in situ atherosclerotic thrombosis (ISAT) and embolism, clot sign location profiles in pre‐angiography magnetic resonance image (MRI), parameters of angiography and EVT, and reperfusion were assessed. Poor outcome was defined as a modified Rankin‐Scale score at 90 days of 3–6.ResultsThe mean age was 68.8±11.8 years (range 21–92 years) and seventy‐eight (40.2%) were female patients. 102 (52.6%) patients were classified into an embolism mechanism and 92 (47.4%) into an ISAT mechanism. Overall, ISAT mechanism compared with embolism was significantly associated with poor outcomes (P = 0.002), along with the NIHSS scores, reperfusion status, and collateral status. In the embolism group, reperfusion (P = 0.001), NIHSS scores (P < 0.001), and onset‐to‐treatment time (P = 0.030) were significant outcome factors. However, in the ISAT group, baseline collateral status (P = 0.001) and NIHSS scores (P < 0.001) were significant outcome factors. A clot sign at the distal BA segment on pre‐angiography MRI was strongly associated with embolism mechanism (P < 0.001).InterpretationStroke mechanism has a major influence on outcomes, and outcome predictors differ according to the underlying mechanism in acute BA occlusion with EVT. Clot sign profile on pre‐angiography MRI might be useful to determine the underlying mechanism.
Hydrolytic Stability of Boronate Ester‐Linked Covalent Organic Frameworks
Authors: Li Huifang , Li Haoyuan , Dai Qingqing , Li Hong , Brédas Jean‐Luc 
Published: January 2018

AbstractThe stability of covalent organic frameworks (COFs) is essential to their applications. However, the common boronate ester‐linked COFs are susceptible to attack by nucleophiles (such as water molecules) at the electron‐deficient boron sites. To provide an understanding of the hydrolytic stability of the representative boronate ester‐linked COF‐5 and of the associated hydrolysis mechanisms, density functional theory (DFT) calculations were performed to characterize the hydrolysis reactions of the molecule formed by the condensation of 1,4‐phenylenebis(boronic acid) (PBBA) and 2,3,6,7,10,11‐hexahydroxytriphenylene (HHTP) monomers; two cases were considered, one dealing with the freestanding molecule and the other with the molecule interacting with COF layers. It was found that the boronate ester (B–O) bond dissociation, which requires one H2O molecule, has a relatively high energy barrier of 22.3 kcal mol−1. However, the presence of an additional H2O molecule significantly accelerates hydrolysis by reducing the energy barrier by a factor of 3. Importantly, the hydrolysis of boronate ester bonds situated in a COF environment follows reaction pathways that are different and have increased energy barriers. These results point to an enhanced hydrolytic stability of COF‐5 crystals.
Anion–Cation Double Substitution in Transition Metal Dichalcogenide to Accelerate Water Dissociation Kinetic for Electrocatalysis
Authors: Tran Ngoc Quang , Bui Viet Q. , Le Hung M. , Kawazoe Yoshiyuki , Lee Hyoyoung 
Published: January 2018

AbstractUntil now, many works have shown that the hydrogen evolution reaction (HER) performance can be improved by anion or cation substitution into the crystal lattice of pyrite‐structure materials. However, the synergistic effects of anion–cation double substitution for overall enhancement of the catalytic activity remains questionable. Here, the simultaneous incorporation of vanadium and phosphorus into the CoS2 moiety for preparing 3D mesoporous cubic pyrite‐metal Co1‐xVxSP is presented. It is demonstrated that the higher catalytic activity of CoS2 after V incorporation can be primarily attributed to abundance active sites, whereas P substitution is responsible for improving HER kinetics and intrinsic catalyst. Interestingly, due to the synergistic effect of P–V double substitution, the 3D Co1‐xVxSP shows superior electrocatalysis toward the HER with a very small overpotential of 55 mV at 10 mA cm−2, a small Tafel slope of 50 mV dec−1, and a high turnover frequency of 0.45 H2 s−1 at 10 mA cm−2, which is very close to commercial 20% Pt/C. Density functional theory calculation reveals that the superior catalytic activity of the 3D Co1‐xVxSP is contributed by the reduced kinetic energy barrier of rate‐determining HER step as well as the promotion of the desorption H2 gas process.
Efficient Perovskite Solar Cells Fabricated by Co Partially Substituted Hybrid Perovskite
Authors: Xu Wenzhan , Zheng Luyao , Zhang Xiaotao , Cao Yu , Meng Tianyu , Wu Dezhen , Liu Lei , Hu Wenping , Gong Xiong 
Published: January 2018

AbstractIn the past years, hybrid perovskite materials have attracted great attention due to their superior optoelectronic properties. In this study, the authors report the utilization of cobalt (Co2+) to partially substitute lead (Pb2+) for developing novel hybrid perovskite materials, CH3NH3Pb1‐xCoxI3 (where x is nominal ratio, x = 0, 0.1, 0.2 and 0.4). It is found that the novel perovskite thin films possess a cubic crystal structure with superior thin film morphology and larger grain size, which is significantly different from pristine thin film, which possesses the tetragonal crystal structure, with smaller grain size. Moreover, it is found that the 3d orbital of Co2+ ensures higher electron mobilities and electrical conductivities of the CH3NH3Pb1‐xCoxI3 thin films than those of pristine CH3NH3Pb4 thin film. As a result, a power conversion efficiency of 21.43% is observed from perovskite solar cells fabricated by the CH3NH3Pb0.9Co0.1I3 thin film. Thus, the utilization of Co, partially substituting for Pb to tune physical properties of hybrid perovskite materials provides a facile way to boost device performance of perovskite solar cells.