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  • Wiley  (304,218)
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  • 101
    Publication Date: 2019
    Description: Abstract Pore fabrics define physical properties of a rock, such as permeability and elasticity, both of which are important to many geological, hydrological and environmental applications. Minerals and hence pores are often preferentially aligned, leading to anisotropy of physical properties and preferred flow directions. Preferred flow paths are defined by the shape and arrangement of pores, and a characterization of this pore fabric forms the basis for prediction of fluid flow directions. Magnetic pore fabrics (MPF), i.e., magnetic anisotropy measurements on ferrofluid‐impregnated samples, are a promising and fast way to characterize the pore fabric of connected pores in 3D, while analysing a large number of pores with sizes down to 10 nm, without the need for any a priori knowledge about fabric orientation. Empirical relationships suggest that MPF is related to the pore shape and orientation and approximates permeability anisotropy. This study uses models including shape and distribution anisotropy to better understand and quantify MPF, using simple pore shapes and pore assemblies measured in previous studies. The results obtained in this study show that (1) shape anisotropy reliably predicts the MPF of single pores, (2) both shape and distribution anisotropy are needed to predict MPF of pore assemblies, and (3) the anisotropy parameters P, L, and F are affected by the intrinsic susceptibility of the ferrofluid in addition to pore geometry. These findings can help explain some of the variability in empirical relationships, and are an important step towards a quantitative understanding and application of MPF in geological and environmental studies.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 102
    Publication Date: 2019
    Description: Abstract Rutile (TiO2) is a common U‐Th‐bearing accessory mineral in metamorphic and, to a lesser extent, igneous rocks. Its development as a (U‐Th)/He thermochronometer would diversify the lithologies dateable with the (U‐Th)/He technique. We report (U‐Th)/He dates for rutile with crystallization ages that vary from Cretaceous to Proterozoic from 8 samples with independent constraints on their thermal history to empirically calibrate the temperature sensitivity of the rutile (U‐Th)/He (RHe) system. The results document an analytical challenge for the Proterozoic rutile, where degassing at laser powers typical for zircon volatilized the parent isotopes while lower laser powers failed to consistently and completely extract all 4He from the crystals. In contrast, the 6 Phanerozoic samples were easily degassed without U‐Th loss. RHe dates for 5 of these samples are fairly reproducible (6‐22% dispersion) or yield positive RHe date‐eU correlations. RHe dates are older than or overlap with apatite (U‐Th)/He dates available for four of these samples and are younger than zircon (U‐Th)/He dates available for two of these samples. This implies that the He closure temperature (Tc) for these Phanerozoic rutile is between apatite (~70 °C) and lower‐damage zircon (~200°C). 4He diffusion experiment data are consistent with anisotropic He diffusion, suggest differing retentivities for the analyzed rutile, and yield Tc estimates of ~155‐159°C for diffusion parallel to the c‐axis (at a 10°C/Ma cooling rate). These results, the degassing patterns for Phanerozoic versus Proterozoic rutile, and the positive RHe date‐eU correlations in two samples imply that radiation damage increases rutile He retentivity.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 103
    Publication Date: 2019
    Description: Eskers are useful for reconstructing meltwater drainage systems of glaciers and ice sheets. However, our process understanding of eskers suffers from a disconnect between sporadic detailed morpho‐sedimentary investigations of abundant large‐scale ancient esker systems, and a small number of modern analogues where esker formation has been observed. This paper presents the results of detailed field and high‐resolution remote sensing studies into two esker systems that have recently emerged at Hørbyebreen, Svalbard, and one at Breiðamerkurjökull, Iceland. Despite the different glaciological settings (polythermal valley glacier vs. active temperate piedmont lobe), in all cases a distinctive planform morphology has developed, where ridges are orientated in two dominant directions corresponding to the direction of ice flow and the shape of the ice margin. These two orientations in combination form a cross‐cutting and locally rectilinear pattern. One set of ridges at Hørbyebreen is a hybrid of eskers and geometric ridges formed during a surge and/or jökulhlaup event. The other sets of ridges are eskers formed time‐transgressively at a retreating ice margin. The similar morphology of esker complexes formed in different ways on both glacier forelands implies equifinality, meaning that care should be taken when interpreting Quaternary esker patterns. The eskers at Hørbyebreen contain substantial ice‐cores with a high ice:sediment ratio, suggesting that they would be unlikely to survive after ice melt. The Breiðamerkurjökull eskers emerged from terrain characterized by buried ice that has melted out. Our observations lead us to conclude that eskers may reflect a wide range of processes at dynamic ice margins, including significant paraglacial adjustments. This work, as well as previous studies, confirms that constraints on esker morphology include: topographic setting (e.g. confined valley or broad plain); sediment and meltwater availability (including surges and jökulhlaups); position of formation (supraglacial, englacial or subglacial); and ice‐marginal dynamics such as channel abandonment, the formation of outwash heads or the burial and/or exhumation of dead ice.
    Print ISSN: 0300-9483
    Electronic ISSN: 1502-3885
    Topics: Geography , Geosciences
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  • 104
    Publication Date: 2019
    Description: Abstract A geophysical survey of the Ellice Basin, located in the south equatorial Pacific between the Ontong Java and Manihiki plateaus, revealed evidence for an extinct seafloor spreading system between the Pacific Plate and the Manihiki Plate. The spreading occurred during the Cretaceous Normal Superchron, the longest normal period of magnetic polarity from 121‐83 Ma, and therefore lacks magnetic‐isochron‐derived age and plate motion constraints. Utilizing high‐resolution bathymetric data acquired on survey KM1609 during December 2016 – January 2017, morphological and directional analyses were performed on the seafloor spreading fabric. Plate motion between the Pacific Plate and the Manihiki Plate during the Cretaceous Normal Superchron is described by three main stages of spreading. Stage 1 spreading was generally E‐W until a clockwise rotation of the spreading direction rotated transform faults by ~15 degrees and lengthened spreading ridges to form Stage 2 zed pattern rhomboids. An offset between Stage 2 fracture zones evidences the presence of a complex and short‐lived Stage 3. Reconstructions, with respect to the Pacific Plate, are created for each of the three stages. Our reconstructions show that there was an earlier opening history prior to Stage 1 that ultimately reconstructs the Ontong Java and Manihiki plateaus; its quantification will await high‐resolution multibeam bathymetry data closer to the two plateaus.
    Print ISSN: 0278-7407
    Electronic ISSN: 1944-9194
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 105
    Publication Date: 2019
    Description: Abstract The powerful HF/VHF radio emissions that occur during lightning flashes can be used as a signal of opportunity to study the bottom side ionosphere. The lightning emission is bright, broad spectrum, and short in duration, providing an ideal signal of opportunity for making ionograms. This study continues previous work in Obenberger et al. (2018), where the direct line of sight signal from lightning can be cross correlated with MHz frequency radio telescope observations to reveal ionogram traces created from the reflected lightning signals. This process was further developed to automate production of ionograms made from individual lightning flashes over the course of several hours, as well as create new techniques to detect the lightning signal using the all sky imaging mode. By using the Long Wavelength Array Sevilleta radio telescope as an interferometer, the point of reflection of the lightning signal for each frequency of the ionogram can be located in the ionosphere, instantaneously revealing density gradients within the ionosphere on minute time scales. We also explore the minimum size stations required for the application of this technique, which we found to be at least 32 antennas.
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
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  • 106
    Publication Date: 2019
    Description: Abstract Nitrogen (N) and phosphorus (P) deposition have increased rapidly during the past decades, which likely changes soil N and P availability. These soil resource variations will further affect N, P concentration and N:P ratio in different ecosystem pools (i.e. soil, leaf, litter, root and microbe). Various pools may show different stoichiometric responses to nutrient enrichment, with a further influence on ecosystem nutrient cycling. However, few studies have been conducted to fully examine the stoichiometric responses of different pools and their nutrient relationships in a given ecosystem. Here we established a two‐year experiment of N (10 g m‐2 yr‐1), P (10 g m‐2 yr‐1) and combined N+P addition in a temperate forest of Changbai Mountain. We found significantly different N:P stoichiometric responses among various ecosystem components under P addition, with the leaves showing a higher response than litter and root while microbe behaving the lowest response. The responses of N:P ratio to N+P addition were similar with those under P addition in all pools. In most cases, N addition did not significantly affect N:P ratio. These results indicate that N:P ratio response was mainly determined by changes in P rather than N concentration in this temperate forest ecosystem. Moreover, we found tighter N:P stoichiometric correlations than elements among diverse ecosystem components under nutrient addition. Overall, our research reveals different responses and tight links of element stoichiometric variations among various ecosystem components in face of nutrient enrichment. It calls our attention to considering stoichiometric changes in the whole‐ecosystem beyond individual plant organ or microbial components.
    Print ISSN: 2169-8953
    Electronic ISSN: 2169-8961
    Topics: Biology , Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 107
    Publication Date: 2019
    Description: Abstract This study examines the transport of chemical species to the upper troposphere/lower stratosphere (UTLS) by Typhoon Mireille (1991). We follow an integrated research approach, using in situ flight data when available and results from a high‐resolution chemical transport model. The Weather Research and Forecasting model coupled with chemistry (WRF‐Chem) was used with an innermost grid spacing of 3 km to explicitly resolve the convection being studied. Mireille was well simulated based on comparisons between the simulated fields and in situ chemical measurements from NASA's Pacific Exploratory Mission‐West A field project. Results from the simulated fields show that pollution from distant sources is ingested by Mireille and subsequently lofted by eyewall convection to the upper troposphere, enhancing concentrations in this region. Flux calculations suggest that a strong tropical cyclone (TC), such as Mireille, can impact UTLS chemistry as much as a continental middle latitude cyclone. Furthermore, overshooting convective cells in Mireille produced values of chemical flux density at tropopause level that are as much as 15‐30 times greater than that of the TC as a whole. Although overshooting tops comprise only a small area of the simulated total TC, they transport large quantities of gaseous species to the upper troposphere because of their strong updrafts.
    Print ISSN: 2169-897X
    Electronic ISSN: 2169-8996
    Topics: Geosciences , Physics
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  • 108
    Publication Date: 2019
    Description: Abstract The structure and evolution of the low‐level jet over the Orinoco River basin is characterized using finer horizontal, vertical, and temporal resolution than possible in previous studies via dynamical downscaling. The investigation relies on a 5‐month‐long simulation (November 2013 to March 2014) performed with the Weather Research and Forecasting model, with initial and boundary conditions provided by the Global Forecast System analysis. Dynamical downscaling is demonstrated to be an effective method to better resolve the horizontal and vertical characteristics of the Orinoco low‐level jet (OLLJ), improving not only the representation of small‐scale jet streaks within the broader region of low‐level wind enhancement but also its diurnal and austral‐summer evolution. The OLLJ is found to be a single stream tube over Colombia and Venezuela with wind speeds greater than 8 m/s and four distinctive cores varying in height under the influence of sloping terrain. The OLLJ has its maximum monthly mean wind speed (13 m/s) and largest spatial extent (2,100 km × 400 km) in January. The maximum mean wind speeds (13–17 m/s) in the diurnal cycle occur in the early morning, whereas wind speeds are a minimum (8–9 m/s) in the late afternoon when a deep, convective boundary layer is present. The intraseasonal variability of the wind speed and potential temperature only presents significant periodicity in the diurnal and semidiurnal scales, with no other meaningful cycles evident during the austral summer.
    Print ISSN: 2169-897X
    Electronic ISSN: 2169-8996
    Topics: Geosciences , Physics
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  • 109
    Publication Date: 2019
    Description: Abstract International Reference Ionosphere (IRI) is the international standard ionospheric climatic model. Since the original formation of the international task force in 1970s, the IRI model has been continuously improved by ingesting developments in research in ionosphere. The most current version, namely, IRI‐2016, is offered with International Radio Consultative Committee (CCIR) and International Union of Radio Science (URSI) model choices with “STORM” option for the F2 layer critical plasma frequency (foF2) and BSE‐1979, AMTB‐2013, and SHU‐2015 options for maximum ionization height, hmF2. Since these two parameters are the determining values for the other model outputs, the evaluation of the options offered by IRI‐2016 is critical for various applications. In this study, all foF2 and hmF2 model options offered online at irimodel.org are computed for winter and summer solstice and equinox seasons of 2011 and 2015 at the locations of all available ionosondes and for all measurement intervals. The ionosondes are grouped into northern and southern midlatitude, northern and southern high‐latitude and equatorial regions. Individual, regional and global model output foF2 and hmF2 values are compared with those of ionosondes in both root‐mean‐square (RMS) and normalized RMS (NRMS) senses. For foF2, “STORM ON” can be used any time and in any region. Equatorial and high‐latitude regions have larger RMS values due to the sparse ionosondes. In northern midlatitude and high‐latitude regions URSI, in all other regions CCIR is the better option. For hmF2, SHU‐2015 and BSE‐1979 options provide a better fit for all regions, seasons, and years.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
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  • 110
    Publication Date: 2019
    Description: Abstract Comprehensive pattern of ionospheric troughs' location in winter for all local times, longitudes, high (HSA), and low (LSA) solar activity, in both hemispheres, is at first investigated. Statistical analysis based on a large dataset of Interkosmos‐19, CHAMP, and Kosmos‐900 satellites was performed for quiet geomagnetic conditions Kp = 1–3. Three troughs were considered: high‐latitude trough (HLT) located inside the auroral oval, main ionospheric trough (MIT) located equatorward from the auroral oval, that is, at subauroral latitudes, and mid‐latitude ring ionospheric trough (RIT). The main purpose was to study the formation of the troughs' diurnal pattern in different conditions. The main problem was to distinguish MIT from RIT and MIT from HLT. For this purpose, early morning hours (04–06 LT), late morning hours (07–10 LT), day, evening, and night conditions were examined. In the early morning sector, RIT was separated from MIT and eliminated from the dataset. In the late morning sector, MIT and HLT were first clearly divided, although only for HSA. During the day, in the Northern Hemisphere under all conditions, HLT is mainly observed, in the Southern Hemisphere at poorly lit longitudes only the daytime MIT, and at well‐lit longitudes only the HLT is observed. The division of MIT and HLT was carried out according to the (statistical) position of the equatorial boundary of the auroral oval precipitation. At night, longitudinal variations in the MIT position determine the asymmetry of the hemispheres. Thus, the occurrence and position of MIT and HLT depend on the hemisphere, longitude, and solar activity.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
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  • 111
    Publication Date: 2019
    Description: Abstract We present observations of proton aurora at Mars made using the Imaging UltraViolet Spectrograph (IUVS) onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. Martian proton aurora display a prominent intensity enhancement in the hydrogen Lyman‐alpha (121.6 nm) emission between ~110‐150 km altitude. Using altitude‐intensity profiles from periapsis limb scan data spanning nearly two Martian years, we create a comprehensive database of proton aurora and characterize their phenomenology. Due to Mars’ lack of a global dipole magnetic field, Martian proton aurora are expected to form on the dayside via electron stripping and charge exchange between solar wind protons and the neutral corona. We observe proton aurora in ~14% of dayside periapsis profiles (with notable seasonal variability), making proton aurora the most commonly observed type of aurora at Mars. We determine that the primary factors influencing proton aurora occurrence rates are solar zenith angle (SZA) and season. The highest proton aurora occurrence rates are at low SZAs on the Mars dayside, consistent with known formation processes. Proton aurora have highest emission enhancements, peak intensities, peak altitudes, and occurrence rates (nearing 100%) around southern summer solstice. This time period corresponds with the seasonal inflation of the neutral lower atmosphere, the onset of Martian dust storm season, seasonally increased coronal hydrogen column densities, and higher atmospheric temperature and solar wind flux following perihelion. The results of our study provide a new understanding of the primary factors influencing proton aurora, and the long‐term variability of these phenomena as observed over multiple Mars years.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
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  • 112
    Publication Date: 2019
    Description: Abstract Forests provide a broad set of ecosystem services, including climate regulation. Other ecosystem services can be ecosystem dependent and are in part regulated by local‐scale decision‐making. In the southwestern United States, ongoing climate change is exacerbating a legacy of fire‐exclusion that has altered forest structure and increased high‐severity wildfire risk. Management can mitigate this risk by reducing forest density and restoring frequent surface fires, but at the cost of reduced carbon stocks. We sought to quantify the role of management in building adaptive capacity to projected climate and wildfires and the carbon consequences in a forested watershed. We simulated carbon dynamics under projected climate and wildfires and two management scenarios: prioritized and optimized. The prioritized scenario involved thinning and prescribed burning in areas selected by stakeholders to mitigate high‐severity wildfire risk. The optimized scenario used the probability of high‐severity wildfires to locate thinning treatments and increased prescribed fire area burned relative to the prioritized scenario. Both scenarios reduced wildfire severity and significantly increased net photosynthesis relative to no‐management. However, the optimized scenario decreased management‐related losses by 2.4 Mg • C • ha−1 and wildfire emissions by 2.9 Mg • C • ha−1 relative to the prioritized scenario. By decreasing the area thinned and increasing the area burned relative to the prioritized scenario, the optimized scenario halved the time to realize a net carbon benefit relative to no‐management. Given the increasing climatic and disturbance pressures impacting southwestern forests, management will play a critical role in building adaptive capacity and ensuring the continued provision of ecosystem services.
    Print ISSN: 2169-8953
    Electronic ISSN: 2169-8961
    Topics: Biology , Geosciences
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  • 113
    Publication Date: 2019
    Description: Abstract Geomagnetic pulsations in Pc5‐6 band (~3‐20 min) are persistent feature of ULF activity at dayside high latitudes. Magnetopause surface eigenmodes may be suggested as potential mechanism of these pulsations. One might expect the ground response of these modes to be near ionospheric projection of the open‐closed field line boundary (OCB). Using data from instruments located at Svalbard we study transient geomagnetic response to impulsive "intrusion" of magnetosheath plasma into the dayside magnetosphere. These intrusions are triggered by modest changes of interplanetary magnetic field to southward, and observed as sudden shifts of equatorward red aurora boundary to lower latitudes and green line emission intensification. Each auroral disturbance is accompanied by burst of ~1.7‐2.0 mHz geomagnetic pulsations. Near‐cusp latitudinal structure of ULF pulsations is compared with instant location of equatorward boundary of the red aurora, assumed to be a proxy of the OCB. Optical OCB latitude has been identified using data from the meridian scanning photometer. The latitudinal maximum of the transient geomagnetic response tends to be located near disturbed OCB proxy, within the error ~1o‐2o of the photometer and magnetometer methods. Recorded transient pulsations may be associated with the ground image of the magnetopause surface mode harmonic. Theoretical consideration indicates that after an initial excitation, surface large‐scale mode converts into localized Alfvén oscillations and thus can exist for limited time only. Therefore, MHD surface modes in realistic inhomogeneous plasma cannot be considered in isolation, but as a combined system of modes with discrete and continuous spectra with irreversible transformation between them.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
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  • 114
    Publication Date: 2019
    Description: ABSTRACT In this study, soil moisture data from two reanalysis datasets (ERA‐Interim, ERA5), a satellite soil moisture product from the European Space Agency (ESA) and three assimilation datasets from the Global Land Data Assimilation System (GLDAS), i.e., GLADS‐NOAH025, GLADS‐NOAH10, and GLDAS‐CLM were compared with the observed soil moisture data in Maqu and Maduo stations over the Three Rivers Source Region (TRSR) on the Tibetan Plateau in China. Comparative statistical parameters between the soil moisture observations and the products, including the root mean square error (RMSE), correlation coefficient (R), and standard deviation ratio (STR) were calculated to evaluate the products in different seasons. It was found that most products overestimated the soil moisture values, among which GLADS‐NOAH025 had relatively good consistency with the observations in the surface soil layer (0‐10 cm), whereas GLDAS‐CLM agreed well with the observations in the 10‐40 cm layer. Both ERA5 and ERA‐interim soil moisture overestimated soil moisture at all levels. The responses of soil moisture to regional climate change over the TRSR were also investigated by using the GLDAS‐NOAH025 soil moisture product, the ESA soil moisture product and the observations during the non‐freezing period. The results show that the trends of soil moisture are consistent with the precipitation changes in the main central part of the TRSR. A significant positive correlation was found between soil moisture and precipitation in most regions of the TRSR, which indicates that soil moisture increases with the increase of precipitation, except in the northwest TRSR, where the variation of soil moisture was possibly influenced by both the precipitation changes and the increase of evapotranspiration. This article is protected by copyright. All rights reserved.
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
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  • 115
    Publication Date: 2019
    Description: Abstract Substorm‐type evolution of the Earth's magnetosphere is investigated by mining more than two decades (1995‐2017) of spaceborne magnetometer data from multiple missions including the first two years (2016‐2017) of the Magnetospheric MultiScale mission. This investigation reveals interesting features of plasma evolution distinct from ideal MHD behavior: X‐lines, thin current sheets and regions with the tailward gradient of the equatorial magnetic field Bz. X‐lines are found to form mainly beyond 20 RE, but for strong driving, with the solar wind electric field exceeding ~ 5mV/m, they may come closer. For substorms with weaker driving, X‐lines may be preceded by redistribution of the magnetic flux in the tailward Bz gradient regions, similar to the magnetic flux release instability discovered earlier in PIC and MHD simulations as a precursor mechanism of the reconnection onset. Current sheets in the growth phase may be as thin as 0.2 RE, comparable to the thermal ions gyroradius, and at the same time, as long as 15 RE. Such an aspect ratio is inconsistent with the isotropic force balance for observed magnetic field configurations. These findings can help resolve kinetic mechanisms of substorm dipolarizations and adjust kinetic generalizations of global MHD models of the magnetosphere. They can also guide and complement micro‐scale analysis of non‐ideal effects.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
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  • 116
    Publication Date: 2019
    Description: Abstract Terrestrial gamma‐ray flashes (TGFs) are bright bursts of gamma rays produced by thunderstorms, typically observed by spacecraft in the low‐Earth orbit. Unfortunately, it has been difficult to disentangle the source altitude and the width and direction of the gamma‐ray beam using single point spacecraft measurements, which has hampered attempts to constrain TGF models. Polarimetry of astrophysical sources has been of interest for many decades which raises the question: Do TGFs and X‐rays from lightning have observable polarization, and if so, what would this polarization tell us about their source? REAM Monte Carlo code has been modified to record the linear polarization of X‐rays and gamma rays as a function of source altitude and beam geometry. It is found that polarization degree of a 20 km narrow beam of TGF is substantially different from a 15 km wide beam which could be used to constrain the source geometry of TGFs. However, due to the low fluence of these events in space, detecting this level of polarization would be challenging. It is also found that low‐altitude TGFs (source at 3.5 km) produce polarizations up to about 8%, however detectors need to be very close to the source region. Furthermore, very low‐altitude ground‐level TGFs and X‐rays showed a maximum polarization of 13% on the ground, of which the TGF's fluence was large enough for polarimetry. In addition, polarization reached its maximum further away from the z‐axis as the TGF's beam broadened. The dominant mechanism of the polarization was found to be Compton scattering.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
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  • 117
    Publication Date: 2019
    Description: Abstract Well‐exposed, vertically dipping, glacially polished outcrops of the Neoproterozoic Windermere Supergroup in the southern Canadian Cordillera include basin‐floor deposits of the Upper Kaza Group overlain by slope channel complexes of the Isaac Formation. Within the 2.5 km thick Kaza and Isaac succession is an up to 360 m thick interval composed of diverse deep‐water stratal elements including scour and interscour deposits, distributary channels, fine‐grained turbidites, terminal splays, mass‐transport deposits, erosional and levéed channels and avulsion splays, which collectively were formed during the development of an ancient passive‐margin channel‐lobe system. The proportion and vertical and lateral arrangement of stratal elements reveal three distinct complexes. The lower complex, consisting mostly of distributary channels and small and large scours, is interpreted to represent the detachment of lobes from an upflow levéed channel, wherein a well‐developed channel‐lobe transition zone was formed by efficient, siliciclastic flows during a period of sustained transport bypass and limited deposition coincident with the onset of falling relative sea level. The middle, comparatively thicker and more sandstone‐rich complex, comprises distributary channel fills, fine‐grained turbidites and lesser terminal splays that are interspersed with small scours, capped by a slope levéed channel filled with coarser‐grained siliciclastic. The abundance of basin‐floor elements suggests negligible separation between the levéed channel and lobe, and therefore a poorly‐developed channel‐lobe transition zone, resulting from inefficient, siliciclastic‐rich depositional flows that became dominant during lowstand and/or ensuing transgression. The stratal makeup of the upper complex resembles the lower detached complex, suggesting a return to efficient flows, and an abrupt change to mixed carbonate–siliciclastic sediments associated with highstand conditions. Accordingly, the stratigraphic architecture and stacking pattern of the Kaza‐Isaac interval, which relate to the formation of multiple channel‐lobe transition zones, were controlled by temporal changes in sediment supply and flow characteristics during the long‐term progradation of the Laurentian continental margin.
    Print ISSN: 0037-0746
    Electronic ISSN: 1365-3091
    Topics: Geosciences
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  • 118
    Publication Date: 2019
    Description: Abstract Climate is one of the main factors driving species distributions and global biodiversity patterns. Obtaining accurate predictions of species’ range shifts in response to ongoing climate change has thus become a key issue in ecology and conservation. Correlative species distribution models (cSDMs) have become a prominent tool to this aim in the last decade and have demonstrated good predictive abilities with current conditions, irrespective of the studied taxon. However, cSDMs rely on statistical association between species’ presence and environmental conditions and have rarely been challenged on their actual capacity to reflect causal relationships between species and climate. In this study, we question whether cSDMs can accurately identify if climate and species distributions are causally linked, a prerequisite for accurate prediction of range shift in relation to climate change. We compared the performance of cSDMs in predicting the distributions of 132 European terrestrial species, chosen randomly within five taxonomic groups (three vertebrate groups and two plant groups), and of 1,320 virtual species whose distribution is causally fully independent from climate. We found that i) for real species, the performance of cSDMs varied principally with range size, rather than with taxonomic groups and ii) cSDMs did not predict the distributions of real species with a greater accuracy than the virtual ones. Our results unambiguously show that the high predictive power of cSDMs can be driven by spatial autocorrelation in climatic and distributional data and does not necessarily reflect causal relationships between climate and species distributions. Thus, high predictive performance of cSDMs does not ensure that they accurately depict the role of climate in shaping species distributions. Our findings therefore call for strong caution when using cSDMs to provide predictions on future range shifts in response to climate change.
    Print ISSN: 0012-9658
    Electronic ISSN: 1939-9170
    Topics: Biology
    Published by Wiley on behalf of The Ecological Society of America (ESA).
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  • 119
    Publication Date: 2019
    Description: Abstract Rangelands are temporally and spatially complex socio‐ecological systems on which the predominant land use is livestock production. In North America, rangelands also contain approximately 80% of remaining habitat for grassland birds, a guild of species that has experienced precipitous declines since the 1970s. While livestock grazing management may benefit certain grassland bird species by generating the vegetation structure and density they prefer, these outcomes are poorly understood for avian species breeding in the shortgrass steppe. We evaluated how two grazing management systems – continuous, season‐long grazing and adaptive, rest‐rotational grazing – affected grassland bird abundance from 2013–2017 in Colorado’s shortgrass steppe. We examined grazing impacts in conjunction with ecological sites, which constitute unique soil and plant communities. When grazing management was evaluated in conjunction with spatial variation in ecological sites, we found three of our five focal bird species responded to grazing management. McCown’s longspur abundance decreased in pastures rested from grazing the previous year. The effect of grazing on horned lark and grasshopper sparrow depended on ecological site – horned lark density was highest in pastures that were intensively grazed and grasshopper sparrow density was highest in pastures that were rested the previous year in the least productive ecological site. In addition, densities of all species varied across ecological sites. Our results suggest consideration of soil and vegetation characteristics can inform how adaptive management is applied on a landscape to benefit the full suite of breeding grassland birds, including species that have seemingly contrasting habitat needs. For example, a manager could target adaptive drought mitigation practices, such as resting pastures for one year to generate grassbanks, in less productive soils to benefit grassland birds that prefer taller/denser vegetation structure, or could apply intensive, short‐duration grazing on less productive soils to benefit species preferring shorter/sparser vegetation. A single year of intensive, short‐duration grazing (i.e., one component of our rotational treatment) across the landscape, however, might not create sufficient habitat for species that prefer short/sparse vegetation in our system (e.g., McCown’s longspur). Ultimately, our study indicates how cattle production on rangelands can congruently support grassland bird populations in the shortgrass steppe.
    Print ISSN: 1051-0761
    Electronic ISSN: 1939-5582
    Topics: Biology
    Published by Wiley on behalf of The Ecological Society of America (ESA).
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  • 120
    Publication Date: 2019
    Description: Abstract Dynamic vegetation models (DVMs) are important tools to understand and predict the functioning and dynamics of terrestrial ecosystems under changing environmental conditions. In these models, uncertainty in the description of demographic processes, in particular tree mortality, is a persistent problem. Current mortality formulations lack realism and are insufficiently constrained by empirical evidence. It has been suggested that empirically estimated mortality submodels would enhance DVM performance, but due to the many processes and interactions within a DVM, the claim has rarely been tested.Here, we compare the performance of three alternative growth‐dependent tree mortality submodels in the DVM ForClim: (1) a mortality function with theoretical foundation (ForClim v3.3); (2) a mortality function with parameters directly estimated based on forest inventory data; and (3) the same function, but with parameters estimated using an inverse approach through Bayesian calibration (BC). Time series of inventory data from 30 ecologically distinct Swiss natural forest reserves collected over 35+ years, including the main tree species of Central Europe, were used for the calibration and subsequent validation of the mortality functions and the DVM.The recalibration resulted in mortality parameters that differed from the direct empirical estimates, particularly for the relationship between tree size and mortality. The calibrated parameters outperformed the direct estimates, and to a lesser extent the original mortality function, for predicting decadal‐scale forest dynamics at both calibration and validation sites. The same pattern was observed regarding the plausibility of their long‐term projections under contrasting environmental conditions. Our results demonstrate that inverse calibration may be useful even when direct empirical estimates of DVM parameters are available, as structural model deficiencies or data problems can result in discrepancies between direct and inverse estimates. Thus, we interpret the good performance of the inversely calibrated model for long‐term projections (which were not a calibration target) as evidence that the calibration did not compensate for model errors. Rather, we surmise that the discrepancy was mainly caused by a lack of representativeness of the mortality data. Our results underline the potential for learning more about elusive processes, such as tree mortality or recruitment, through data integration in DVMs.
    Print ISSN: 1051-0761
    Electronic ISSN: 1939-5582
    Topics: Biology
    Published by Wiley on behalf of The Ecological Society of America (ESA).
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  • 121
    Publication Date: 2019
    Description: Abstract High‐throughput sequencing has enabled robust shotgun metagenomic sequencing that informs our understanding of the genetic basis of important biogeochemical processes. Slower to develop, however, are the application of these tools in a controlled experimental framework that pushes the field beyond exploratory analysis toward hypothesis‐driven research. We performed flow‐through reactor experiments to examine how salt marsh sediments from varying depths respond to nitrate addition and linked biogeochemical processes to this underlying genetic foundation. Understanding the mechanistic basis of carbon and nitrogen cycling in salt marsh sediments is critical for predicting how important ecosystem services provided by marshes, including carbon storage and nutrient removal, will respond to global change. Prior to the addition of nitrate, we used metagenomics to examine the functional potential of the sediment microbial community that occurred along a depth gradient, where organic matter reactivity changes due to decomposition. Metagenomic data indicated that genes encoding enzymes involved in respiration, including denitrification, were higher in shallow sediments, and genes indicative of resource limitation were greatest at depth. After 92 d of nitrate enrichment, we measured cumulative increases in dissolved inorganic carbon production, denitrification, and dissimilatory nitrate reduction to ammonium; these rates correlated strongly with genes that encode essential enzymes in these important pathways. Our results highlight the importance of controlled experiments in linking biogeochemical rates to underlying genetic pathways. Furthermore, they indicate the importance of nitrate as an electron acceptor in fueling microbial respiration, which has consequences for carbon and nitrogen cycling and fate in coastal marine systems.
    Print ISSN: 0024-3590
    Electronic ISSN: 1939-5590
    Topics: Biology , Geosciences , Physics
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  • 122
    Publication Date: 2019
    Description: Abstract The enzyme carbonic anhydrase (CA) is crucial to many physiological processes involving CO2, from photosynthesis and respiration, to calcification and CaCO3 dissolution. We present new measurements of CA activity along a North Pacific transect, on samples from in situ pumps, sediment traps, discreet plankton samples from the ship's underway seawater line, plankton tows, and surface sediment samples from multicores. CA activity is highest in the surface ocean and decreases with depth, both in suspended and sinking particles. Subpolar gyre surface particles exhibit 10× higher CA activity per liter of seawater compared to subtropical gyre surface particles. Activity persists to 4700 m in the subpolar gyre, but only to 1000 m in the subtropics. All sinking CA activity normalized to particulate organic carbon (POC) follows a single relationship (CA/POC = 1.9 ± 0.2 × 10−7 mol mol−1). This relationship is consistent with CA/POC values in subpolar plankton tow material, suspended particles, and core top sediments. We hypothesize that most subpolar CA activity is associated with rapidly sinking diatom blooms, consistent with a large mat of diatomaceous material identified on the seafloor. Compared to the basin‐wide sinking CA/POC relationship, a lower subtropical CA/POC suggests that the inventory of subtropical biomass is different in composition from exported material. Pteropods also demonstrate substantial CA activity. Scaled to the volume within pteropod shells, first‐order CO2 hydration rate constants are elevated ≥ 1000× above background. This kinetic enhancement is large enough to catalyze carbonate dissolution within microenvironments, providing observational evidence for CA‐catalyzed, respiration‐driven CaCO3 dissolution in the shallow North Pacific.
    Print ISSN: 0024-3590
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  • 123
    Publication Date: 2019
    Description: Abstract In semi‐distributed hydrological modeling, sequential calibration usually refers to the calibration of a model by considering not only the flows observed at the outlet of a catchment, but also the different gauging points inside the catchment from upstream to downstream. While sequential calibration aims to optimize the performance at these interior gauged points, we show that it generally fails to improve performance at ungauged points. In this paper, we propose a regularization approach for the sequential calibration of semi‐distributed hydrological models. It consists in adding a priori information on optimal parameter sets for each modeling unit of the semi‐distributed model. Calibration iterations are then performed by jointly maximizing simulation performance and minimizing drifts from the a priori parameter sets. The combination of these two sources of information is handled by a parameter k to which the method is quite sensitive. The method is applied to 1305 catchments in France over 30 years of observed records. The leave‐one‐out validation shows that, at locations considered as ungauged, model simulations are significantly improved (over all the catchments, the median KGE criterion is increased from 0.75 to 0.83 and the first quartile from 0.35 to 0.66), while model performance at gauged points is not significantly impacted by the use of the regularization approach. Small catchments benefit most from this calibration strategy. These performances are however very similar with the performances obtained with a lumped model based on similar conceptualization.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 124
    Publication Date: 2019
    Description: Abstract Rivers are the fluvial conveyor belts routing sediment across the landscape. While there are proper techniques for continuous estimates of the flux of suspended solids, constraining bedload flux is much more challenging, typically involving extensive measurement infrastructure or labour‐intensive manual measurements. Seismometers are potentially valuable alternatives to in‐stream devices, delivering continuous data with high temporal resolution on the average behaviour of a reach. Two models exist to predict the seismic spectra generated by river turbulence and bedload flux. However, these models require estimating a large number of parameters and the spectra usually overlap significantly, which hinders straightforward inversion. We provide three functions contained in the R‐package 'eseis' that allow generic modelling of hydraulic and bedload transport dynamics from seismic data using these models. The underlying Monte Carlo approach creates lookup tables of potential spectra, which are compared against the empirical spectra to identify the best fitting solutions. The method is validated against synthetic data sets and independently measured metrics from the Nahal Eshtemoa, Israel, a flash flood dominated ephemeral gravel bed river. Our approach reproduces the synthetic time series with average absolute deviations of 0.01‐0.04 m (water depth, ranging between 0‐1 m) and 0.00‑0.04 kg/sm (bedload flux, ranging between 0‐4 kg/sm). The example flash flood water depths and bedload fluxes are reproduced with respective average deviations of 0.10 m and 0.02 kg/sm. Our approach thus provides generic, testable and reproducible routines for a quantitative description of key metrics, hard to collect by other techniques in a continuous and representative manner.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 125
    Publication Date: 2019
    Description: Abstract Satellite estimates of inland water quality have the potential to vastly expand our ability to observe and monitor the dynamics of large water bodies. For almost 50 years, we have been able to remotely sense key water quality constituents like Total Suspended Sediment (TSS), Dissolved Organic Carbon (DOC), Chlorophyll a, and Secchi Disk Depth (SDD). Nonetheless, remote sensing of water quality is poorly integrated into inland water sciences, in part due to a lack of publicly available training data and a perception that remote estimates are unreliable. Remote sensing models of water quality can be improved by training and validation on larger datasets of coincident field and satellite observations, here called matchups. To facilitate model development and deeper integration of remote sensing into inland water science, we have built AquaSat, the largest such matchup dataset ever assembled. AquaSat contains more than 600,000 matchups, covering 1984‐2019, of ground‐based TSS, DOC, Chlorophyll a, and SDD measurements paired with spectral reflectance from Landsat 5, 7, and 8 collected within +/‐1 day of each other. To build AquaSat, we developed open source tools in R and Python and applied them to existing public datasets covering the contiguous United States, including the Water Quality Portal, LAGOS‐NE, and the Landsat archive. In addition to publishing the dataset, we are also publishing our full code architecture to facilitate expanding and improving AquaSat. We anticipate that this work will help make remote sensing of inland water accessible to more hydrologists, ecologists, and limnologists while facilitating novel data‐driven approaches to monitoring and understanding critical water resources at large spatiotemporal scales.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 126
    Publication Date: 2019
    Description: Abstract This work reports auroral spots event observed by the SSUSI instruments on board the DMSP spacecraft between 22‐23 July 2009 during the recovery phase of a moderate magnetic storm. The spots were observed between 18:00 and 02:00 magnetic local time and stayed at ~60° magnetic latitude. They lasted for ~10 hours and corotated with ~64% of the Earth's rotational speed. In situ observations indicate that the isolated auroral spots were produced by energetic ions at energies between 10 keV and 240 keV, with significantly anisotropic electron (30 keV – 300 keV) precipitations. It is expected that the energetic ions originate from the ring current and can be scattered by the EMIC waves through cyclotron resonance. The energetic electrons can be precipitated by the non‐resonant interaction between the electrons and EMIC waves, which is suggested by previous works.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 127
    Publication Date: 2019
    Description: Abstract This is a personal perspective of how some significant upper‐atmosphere model developments were carried out from the mid‐1960s to the early 1990s, including modeling of the ionospheric wind dynamo, equatorial electrojet, two‐ and three‐dimensional thermospheric dynamics, the disturbance dynamo, interactive thermosphere/ionosphere dynamics and electrodynamics, and mapping of high‐latitude electric fields and currents through data assimilation. Well‐tested models enable exploration and prediction of a large number of phenomena.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
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  • 128
    Publication Date: 2019
    Description: Abstract The up‐looking total electron contents (TECs) from the GRACE, SWARM‐A, TerraSAR‐X and MetOp‐A satellites and in situ electron density (Ne) from SWARM‐A were utilized to investigate the topside ionospheric conditions during the 7‐8 September 2017 geomagnetic storm. The rate of TEC index (ROTI) and rate of density index (RODI), which are derivative indices of TEC and Ne respectively, were also used to characterize the topside ionospheric irregularities. The main results of this study are as follows: (1) There were significant enhancements seen in the up‐looking TEC during the first main phase of the storm. (2) The up‐looking TEC didn’t show similar unusual enhancement as observed by ground‐based TEC in the Asian‐Australian sector during the recovery phase of the storm on 11th September. (3) Prominent TEC hemispheric asymmetry at the middle and high latitudes was observed at both day and night sectors. (4) Long‐duration recovery of topside TEC with respect to the pre‐storm condition was also detected in this event. (5) Nighttime ROTI enhancements were presented in a wide latitudinal range from the equator to the poles during the main phases of the storm. (6) The ionospheric electric field disturbances associated with IMF‐Bz fluctuations probably played a very important role in triggering ionospheric irregularities during the relatively weak geomagnetic activity on 7th September, which implies that ionospheric irregularities do not necessarily occur under the severe geomagnetic conditions only.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
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  • 129
    Publication Date: 2019
    Description: Abstract Dissolved organic carbon (DOC) plays critical roles in marine carbon cycling, but its sources and sinks remain uncertain. In this study, we monitored DOC exudation rates of Sargassum natans under visible light (λ 〉390 nm) and solar radiation. DOC release rates ranged from 7 to 10 μg C g‐1biomass h‐1 (wet weight) under visible light, but increased to 23 to 41 μg C g‐1biomass h‐1 when exposed to natural sunlight. Results indicate that DOC released by Sargassum could amount to 0.3 to 1.2 Tg C yr‐1, potentially contributing significantly to the marine DOC pool in the Gulf of Mexico and Western North Atlantic. We employed the Folin‐Ciocalteu phenolic content method, nuclear magnetic resonance (NMR) spectroscopy, and ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR MS) to characterize the diverse pool of organic compounds exuded from Sargassum. Results from these complementary methods showed that Sargassum release large quantities of phlorotannins, a class of polyphenols that have very similar properties to terrestrial DOC. These phlorotannins and their oxygenated phenolic derivatives exhibit a high hydrogen deficiency and functionalization (i.e. 4 to 6 oxygen atoms per aromatic ring), representing 5 to 18% of the released DOC isolated by solid phase extraction. Thus, Sargassum is the largest biological source of open ocean polyphenols recorded to date. The amount of polyphenolic DOC released by Sargassum challenges previous beliefs that all polyphenols found within the oceans are remnants of terrestrial organic matter, although the stability of phlorotannins and their derivatives needs to be further evaluated.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 130
    Publication Date: 2019
    Description: Abstract Baseflow has become an important source of nitrate nonpoint source pollution in many intensive agricultural watersheds. Uncertainties in baseflow nutrient load separation are caused by the effects of hydrometeorological factors on both baseflow recession and baseflow nutrient load recession. These uncertainties have not been addressed well in the existing separating algorithms, which are based on simple baseflow rate–load relationships. In the present study, a recursive tracing source algorithm (RTSA) was developed based on a nonlinear reservoir algorithm and hydrometeorology‐corrected baseflow nutrient load recession parameter. This approach was used to reduce the uncertainty of baseflow nitrate load estimation caused by variations in different load recessions under varying climate conditions. RTSA validation in a typical rainy agricultural watershed yielded Nash‐Sutcliffe efficiency (NSE), root mean square error‐observation standard deviation ratio (RSR), and R2 values of 0.91, 0.30, and 0.91, respectively. The baseflow nitrate–nitrogen (N‐NO3–) loads from 2003 to 2012 in the Changle River watershed of eastern China were estimated with the RTSA. The results indicated that baseflow nitrate export accounted for 62.0% of the mean total annual N‐NO3– loads (18.0 kg/ha). The total baseflow N‐NO3– export was highest in spring (3.6 kg/ha), followed by summer (3.2 kg/ha), winter (2.3 kg/ha), and autumn (2.1 kg/ha). The contribution of baseflow to total nitrate in the stream decreased in the order of winter (69.88%) 〉 spring (66.59%) 〉 autumn (60.36%) 〉 summer (54.04%). The monthly baseflow N‐NO3– loads and flow‐weighted concentrations greatly increased during the research period (Mann‐Kendall test, Zs 〉 2.56, p 〈 0.01). Without proper countermeasures, baseflow nitrate may represent a serious long‐term risk for water surfaces in the future.
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 131
    Publication Date: 2019
    Description: Abstract Understanding the reliability of Global Climate Models (GCMs) to reproduce the historical surface wind fields is integral part of building robust projections of surface wind‐climate, and other wind‐dependent geophysical climatic variables. Understanding the skill of atmosphere‐only models (AGCM), coupled atmosphere–ocean models (AOGCM) and fully‐coupled Earth System Models (ESM) is likewise paramount to assess any systematic model improvements. In this paper, we systematically assess whether surface wind fields obtained from 28 CMIP5 GCMs can represent large‐scale spatial patterns and temporal variability of historical surface winds. We show that inter‐model uncertainty is typically 2–4 times larger than the uncertainty associated with GCM internal variability, although the latter can be significant within specific regions. We also find that CMIP5 models are typically capable of reliably reproducing large‐scale spatial patterns of historical near‐surface winds, but considerable uncertainty lies within the CMIP5 ensemble with strong latitudinal dependence. CMIP5 models show limitations in their ability to reliably represent inter‐annual and inter‐seasonal variability particularly within tropical‐cyclone affected regions. In further analysis, we quantify and intercompare historical wind bias from different types of models with different dynamical cores, based on multiple CMIP5 diagnostic experiments. We find that bias in surface wind fields are largely intrinsic to the atmospheric components of the models, and that the inclusion of carbon‐cycle dynamics has insignificant effect on simulated surface winds (at decadal time‐scales). Inconsistencies between atmosphere‐only and coupled atmosphere–ocean simulations are largely driven by errors in sea surface temperatures (SST); though such differences are not statistically significant relative to the inter‐model uncertainty within the CMIP5 ensemble. These results show that the dominant source of bias in simulated wind fields lies in the underlying physics of the atmospheric component of the models. This article is protected by copyright. All rights reserved.
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
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  • 132
    Publication Date: 2019
    Description: Ancient plant DNA in a lake sediment record from the Eastern Canadian Arctic constrains postglacial colonization of dwarf birch to 5,900 years ago, which was ~3,000 years after local deglaciation and at least 1,300 years after other tundra plants were established. We place this vegetation history into a climatic context using lipid biomarker paleothermometry, demonstrating that Betula colonization was delayed relative to peak postglacial warmth. This colonization timing is 〉2,000 years after birch pollen appears in adjacent lake sediment, highlighting the influence of exotic pollen fluxes on palynological records and underscoring the utility of sedimentary DNA for determining local plant presence. Abstract Arctic shrubification is an observable consequence of climate change, already resulting in ecological shifts and global‐scale climate feedbacks including changes in land surface albedo and enhanced evapotranspiration. However, the rate at which shrubs can colonize previously glaciated terrain in a warming world is largely unknown. Reconstructions of past vegetation dynamics in conjunction with climate records can provide critical insights into shrubification rates and controls on plant migration, but paleoenvironmental reconstructions based on pollen may be biased by the influx of exotic pollen to tundra settings. Here, we reconstruct past plant communities using sedimentary ancient DNA (sedaDNA), which has a more local source area than pollen. We additionally reconstruct past temperature variability using bacterial cell membrane lipids (branched glycerol dialkyl glycerol tetraethers) and an aquatic productivity indicator (biogenic silica) to evaluate the relative timing of postglacial ecological and climate changes at a lake on southern Baffin Island, Arctic Canada. The sedaDNA record tightly constrains the colonization of dwarf birch (Betula, a thermophilous shrub) to 5.9 ± 0.1 ka, ~3 ka after local deglaciation as determined by cosmogenic 10Be moraine dating and 〉2 ka later than Betula pollen is recorded in nearby lake sediment. We then assess the paleovegetation history within the context of summer temperature and find that paleotemperatures were highest prior to 6.3 ka, followed by cooling in the centuries preceding Betula establishment. Together, these molecular proxies reveal that Betula colonization lagged peak summer temperatures, suggesting that inefficient dispersal, rather than climate, may have limited Arctic shrub migration in this region. In addition, these data suggest that pollen‐based climate reconstructions from high latitudes, which rely heavily on the presence and abundance of pollen from thermophilous taxa like Betula, can be compromised by both exotic pollen fluxes and vegetation migration lags.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
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  • 133
    Publication Date: 2019
    Description: Abstract The Cretaceous and Cenozoic fill of the continental margins of southern Africa (South‐East Atlantic and Agulhas Margins) contains a continuous record of sediment supplied from the South African Plateau for the past 134 million years. Estimates of solid sediment volumes deposited offshore were calculated from isopach maps and extrapolated vertical cross‐sections derived from a large amount of industrial geophysical data. Solid phase volumes and accumulation rates were calculated for six epochs: Lower Cretaceous (134‐113 Ma), Mid Cretaceous (113‐93.5 Ma), Upper Cretaceous (93.5‐81 Ma and 81‐66 Ma), Paleogene (66‐25 Ma), Neogene (25‐0 Ma). Our new compilation demonstrates the existence of two periods of elevated flux. The most important one occurs in the late Cretaceous (93.5 to 66 Ma) and was synchronous with an acceleration of onshore denudation as shown by thermochronometric data. After a period of extremely low accumulation rate, the second phase of elevated flux started in the Oligocene (~30‐25 Ma) until present‐day. From these observations we suggest that the main phase of uplift of the South African Plateau took place during the Upper Cretaceous. Two mechanisms, namely uplift caused by lithospheric delamination or by dynamic topography caused by the continent moving over the African Superplume, are viable explanations for our observations. The more recent and lower amplitude episode of enhanced accumulation rates is likely to correspond to a second period of uplift, potentially associated with the onset of uplift and extension along the East African Rift System.
    Print ISSN: 0954-4879
    Electronic ISSN: 1365-3121
    Topics: Geosciences
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  • 134
    Publication Date: 2019
    Description: Abstract Ternary aluminum silicon carbide Al4SiC4 is a promising material not only in refractory applications, but also in electronics and photocatalysis. However, synthesis of Al4SiC4 requires high‐temperature heat treatment for several hours. In this work, we describe a new, fast and effective method to synthesize single‐phase Al4SiC4 powder. Our method is based on combustion synthesis reaction of Al, Si and C initiated under high‐frequency induction heating. Heating program was optimized to prevent separation of melted aluminum and provide uniform initiation, propagation and completion of the reaction. As a result, pure‐phase Al4SiC4 powder was synthesized in few minutes. Temperature profile of a sample measured during heating process showed appearance of two exothermic peaks, thus confirming propagation of a two‐step combustion reaction. Induction heating provided capability to finely and readily control external heating rate, which is considered to be one of the key factors to reach high‐purity Al4SiC4.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 135
    Publication Date: 2019
    Description: Abstract Lignocellulosic biomass has considerable potential for the production of fuels and chemicals as a promising alternative to conventional fossil fuels. However, the bioconversion of lignocellulosic biomass to desired products must be improved to reach economic viability. One of the main technical hurdles is the presence of inhibitors in biomass hydrolysates, which hampers the bioconversion efficiency by biorefinery microbial platforms such as Saccharomyces cerevisiae in terms of both production yields and rates. In particular, acetic acid, a major inhibitor derived from lignocellulosic biomass, severely restrains the performance of engineered xylose‐utilizing S. cerevisiae strains, resulting in decreased cell growth, xylose utilization rate, and product yield. In this study, the robustness of XUSE, one of the best xylose‐utilizing strains, was improved for the efficient conversion of lignocellulosic biomass into bioethanol under the inhibitory condition of acetic acid stress. Through adaptive laboratory evolution, we successfully developed the evolved strain XUSAE57, which efficiently converted xylose to ethanol with high yields of 0.43–0.50 g ethanol/g xylose even under 2–5 g/L of acetic stress. XUSAE57 not only achieved 2‐fold higher ethanol yields but also improved the xylose utilization rate by more than 2‐fold compared to those of XUSE in the presence of 4 g/L of acetic acid. During fermentation of lignocellulosic hydrolysate, XUSAE57 simultaneously converted glucose and xylose with the highest ethanol yield reported to date (0.49 g ethanol/g sugars). This study demonstrates that the bioconversion of lignocellulosic biomass by an engineered strain could be significantly improved through adaptive laboratory evolution for acetate tolerance, which could help realize the development of an economically feasible lignocellulosic biorefinery to produce fuels and chemicals.
    Print ISSN: 1757-1693
    Electronic ISSN: 1757-1707
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 136
    Publication Date: 2019
    Description: Abstract Fundamental understanding of pore‐scale methane hydrate dissociation in porous media is important to evaluate submarine slope stability and potential utilization of methane resources. In this paper, a general pore‐scale framework based on the lattice Boltzmann (LB) method is established for reactive transport coupled with non‐isothermal multiple physicochemical processes in porous media. The framework combines the gas hydrate dissociation kinetics model, the single‐phase flow LB model, the mass transport LB model and the conjugate heat transfer LB model. The pore‐scale framework is validated by several benchmark problems and then employed to investigate the endothermic dissociation process of methane hydrate with pore‐filling and grain‐coating habits in porous media. The methane hydrate endothermic dissociation behavior coupled with nonlinear non‐isothermal multiple physicochemical processes involving intrinsic dissociation dynamics, gas flow, mass transport, phase change heat transfer and conjugate heat transfer is well captured by the framework. The phase change of methane hydrate dissociation and pore structure evolution for different pore habits of hydrate are well depicted, and some insights about the dissociation front advancement and temperature distributions are also obtained. In addition, the effects of temperature field, inlet temperature, and inlet pressure on methane hydrate dissociation are investigated. The pore‐scale methane hydrate dissociation helps to advance our understanding of permeability‐saturation variation relation for continuum models.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 137
    Publication Date: 2019
    Description: Abstract Surface soil moisture measurements are typically correlated to some degree with changes in subsurface soil moisture. We calculate a hydrologic length scale, λ, which represents (1) the mean‐state estimator of total column water changes from surface observations, (2) an e‐folding length scale for subsurface soil moisture profile covariance fall‐off, and (3) the best 2nd‐moment mass‐conserving surface layer thickness for a simple bucket model, defined by the data streams of satellite soil moisture and precipitation retrievals. Calculations are simple, based on three variables: the autocorrelation and variance of surface soil moisture and the variance of the net flux into the column (precipitation minus estimated losses), which can be estimated directly from the soil moisture and precipitation time series. We develop a method to calculate the lag‐one autocorrelation for irregularly observed time series and show global surface soil moisture autocorrelation. λ is driven in part by local hydroclimate conditions and is generally larger than the 50 mm nominal radiometric length scale for the soil moisture retrievals, suggesting broad subsurface correlation due to moisture drainage. In all but the most arid regions, radiometric soil moisture retrievals provide more information about ecosystem‐relevant water fluxes than satellite radiometers can explicitly “see;” lower‐frequency radiometers are expected to provide still more statistical information about subsurface water dynamics.
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    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 138
    Publication Date: 2019
    Description: Abstract Changes in river flow may appear from shifts in land cover, constructions in the river channel, and climatic change, but currently there is a lack of understanding of the relative importance of these drivers. Therefore, we collected gauged river‐flow time‐series from 1961 to 2018 from across Sweden for 34 disturbed catchments to quantify how the various types of disturbances have affected river flow. We used trend analysis and the differences in observations versus hydrological modelling to explore the effects on river flow from: (1) land cover changes from wildfires, storms and urbanization; (2) dam constructions with regulations for hydropower production; and (3) climate‐change impact in otherwise undisturbed catchments. A mini model‐ensemble, consisting of three versions of the S‐HYPE model, was used and the three models gave similar results. We searched for changes in annual and daily stream flow, seasonal flow regime and flow duration curves. The results show that regulation of river flow has the largest impact, reducing spring floods with up to 100% and increasing winter flow by several orders of magnitude, with substantial effects transmitted far downstream. Climate changed the total river flow up to 20%. Tree removal by wildfires and storms has minor impacts at medium and large‐scales. Urbanization, on the contrary, showed a 20% increase in high flows also at medium scales. This study emphasizes the benefits of combining observed time‐series with numerical modelling to exclude the effect of varying weather conditions, when quantifying the effects of various drivers on long‐term streamflow shifts.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 139
    Publication Date: 2019
    Description: Abstract Accurate quantification of riverine water‐quality concentration and flux is challenging because monitoring programs typically collect concentration data at lower frequencies than discharge data. Statistical methods are often used to estimate concentration and flux on days without observations. One recently developed approach is the Weighted Regressions on Time, Discharge, and Season (WRTDS), which has been shown to provide among the most accurate estimates compared to other common methods. The main objective of this work was to improve WRTDS estimation by accounting for the autocorrelation structure of model residuals using the first‐order autoregressive model (AR1). This modified approach, called WRTDS‐Kalman Filter (WRTDS‐K), was compared with WRTDS for six constituents including nitrate‐plus‐nitrite (NOx), total phosphorus, total Kjeldahl nitrogen, soluble reactive phosphorus, suspended sediment, and chloride. Near‐daily concentration records at nine sites were used to generate subsets through Monte Carlo sampling for five different sampling scenarios. Results show that WRTDS‐K provided generally better daily estimates of concentration and flux than WRTDS under these sampling scenarios for all constituents, especially NOx. The degree of improvement is strongly affected by the underlying sampling scenario, with WRTDS‐K gaining more advantage when more samples are available, and hence more residuals can be exploited. The performance of WRTDS‐K depends on the AR1 coefficient (ρ) and that relationship varies with constituents and sampling scenarios. These results provided recommendations on the optimal ρ for each constituent and sampling scenario. Overall, WRTDS‐K has the potential for broad applications to monitoring records elsewhere, as demonstrated by a pilot application to Chesapeake Bay tributaries.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 140
    Publication Date: 2019
    Description: Abstract Elevated soil moisture and heavy precipitation contribute to landslides worldwide. These environmental variables are now being resolved with satellites at spatiotemporal scales that could offer new perspectives on the development of landslide warning systems. However, the application of these data to hydro‐meteorological thresholds (which account for antecedent soil moisture and rainfall) first need to be evaluated with respect to proven, direct measurement‐based thresholds that use rain gages and in situ soil moisture sensors. Here, we compare ground‐based hydrologic data to overlapping satellite‐based data before, during, and after a recent season of widespread shallow landsliding in the San Francisco Bay Area (California, USA). We then explore how the remotely sensed information could be used to empirically define hypothetical thresholds for shallow landsliding. We find that the ground‐based thresholds developed with a single monitoring station show superior performance because the in situ soil saturation data better reflect the gravity‐dominated subsurface flow conditions that are characteristic of hillslopes during the rainy season. Although the satellite‐based thresholds can identify most of the landslide days, they include a greater number of false alarms due to overestimates of soil moisture between major storm events. To avoid the type of false alarms that are characteristic of our satellite‐based thresholds, further post‐processing of the near‐surface hydrologic response data should be integrated into satellite‐based model outputs to better reflect gravity‐dominated drainage. Our results encourage further deployment of ground stations in landslide‐prone terrain and cautious exploration of satellite‐based hydro‐meteorological thresholds where in situ networks are nonexistent.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 141
    Publication Date: 2019
    Description: Abstract River discharge gauging is scarce in high mountainous regions, especially on the Tibetan Plateau, where rivers are widely distributed. Although remote sensing is an important mean of monitoring river discharge, previous methods are most suitable for large rivers, and the ability to monitor small rivers (with widths less than 100 m) is limited. To resolve this issue, a multiple pixel ratio (MPR) method is presented for monitoring the discharge of small rivers based on the relationship between river discharge and the near‐infrared reflectivity. Utilizing 281 Landsat images (1990‐2015), we monitored river discharges in two sub‐basins in the upstream region of the Heihe River located on the northeastern Tibetan Plateau. Our results indicate that the performance of the MPR method is more stable than the previous calibration/measurement (C/M) method. The monitoring accuracy was correlated with the length and location of the selected inundated river channel (SIRC). Using SIRC lengths between 300 and 600 m can provide better monitoring accuracy. The Nash‐Sutcliffe efficiency (NSE) of monitoring results (2013‐2014) of Qilian station was 0.82; the Zhamashike station (2015) was 0.45; the two stations multi‐years (1990‐2013) monitoring results was 0.32, 0.41, respectively; the ungauged basin was 0.45. Our results suggest that the MPR method can expand the ability of remote sensing to monitor discharge in small rivers with widths greater than 30 m on the Tibetan Plateau. In addition, the new method also has the potential to monitor the discharge of ungauged small rivers (with widths greater than 30 m).
    Print ISSN: 0043-1397
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  • 142
    Publication Date: 2019
    Description: Abstract This paper presents a 2×1 flower‐shaped (FS) multiple‐input multiple‐output (MIMO) monopole antenna with enhanced bandwidth and compact dimensions for modern wireless wideband applications. The proposed FS‐MIMO antenna is formed by merging multiple ellipses, each of which has a different value of semi‐major axis length and eccentricity. These ellipses are used to obtain resonances at different frequencies which cumulatively give a wideband behavior. The antenna characteristics such as reflection coefficient (S11), peak gain, surface current distribution at different resonating frequencies and 2‐D radiation patterns are investigated. The measured impedance bandwidth (for S11 below ‐10 dB) of the implemented antenna is around 126% (2.52‐11.12 GHz). The measured peak gain varies from 2.16 to 6.57 dB in the entire impedance bandwidth. Furthermore, the measured values of diversity performance parameters such as envelope correlation coefficient (ECC), diversity gain (DG), total active reflection coefficient (TARC), and mutual coupling (S21) are found within their acceptable limit. The more compact dimensions of 22×24 mm2 (or about 0.15λ0×0.16 λ0) as compared to the latest state‐of‐art along with the good diversity performance makes the proposed antenna a capable contender for antenna structures supporting wide impedance bandwidth wireless applications. The proposed antenna shows the good matching characteristics under various scenarios such as an extended ground plane, USB connector, and device housing (both vertical and horizontal).
    Print ISSN: 0048-6604
    Electronic ISSN: 1944-799X
    Topics: Geosciences , Physics
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  • 143
    Publication Date: 2019
    Description: Abstract Although prior studies have evaluated the role of sampling errors associated with local and regional methods to estimate peak flow quantiles (PFQs), the investigation of epistemic errors is more difficult because the underlying properties of the random variable have been prescribed using ad‐hoc characterizations of the regional distributions of peak flows. This study addresses this challenge using representations of regional peak flow distributions derived from a combined framework of Stochastic Storm Transposition, radar rainfall observations, and distributed hydrologic modeling. The authors evaluated four commonly‐used PFQ estimation methods using synthetic peak flows at 5,000 sites in the Turkey River watershed in Iowa, USA. They first used at‐site flood frequency analysis using the Pearson Type III distribution with L‐moments. The authors then pooled regional information using (1) the index flood method; (2) the quantile regression technique; and (3) parameter regression. This approach allowed quantification of error components stemming from epistemic assumptions, parameter estimation method, sample size, and, in the regional approaches, the number of “pooled” sites. The results demonstrate that the inability to capture the spatial variability of the skewness of the peak flows dominates epistemic error for regional methods. We concluded that, in the study basin, this variability could be partially explained by river network structure and the predominant orientation of the watershed. The general approach used in this study is promising in that it brings new tools and sources of data to the study of the old hydrologic problem of flood frequency analysis.
    Print ISSN: 0043-1397
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    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 144
    Publication Date: 2019
    Description: Abstract On the 21st August 2017 the eclipse shadow drastically changed the state of the ionosphere over the USA. This effect on the ionosphere is visible in the total electron content (TEC) measured by GNSS. The shadow moved with the supersonic speed of ~1000 m/s over Oregon to ~650 m/s over South Carolina. In order to exhaustively explore the ionospheric signature of the eclipse, we use data of total electron content (TEC) from ~3000 GNSS stations seeing multiple GPS and GLONASS satellites to visualize the phenomena. This tremendous dataset allows high‐resolution characterization of the frequency content and wavelengths ‐using an omega‐k analysis based on 3D Fast‐Fourier‐Transform (FFT)‐ of the eclipse signature in the ionosphere in order to fully identify traveling ionospheric disturbances (TIDs). We confirm the generation of TIDs associated with the eclipse including TIDs interpreted as bow waves in previous studies. Additionally we reveal, for the first time, short (50‐100 km) and long (500‐600 km) wavelength TIDs with periods between 30 and 65 min. The sources of the revealed short wavelength TIDs are co‐located with the regions of stronger gradient of the EUV related to sunspots. Our work confirms and describes physical properties of the waves observable in the ionosphere during the Great American Eclipse.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
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  • 145
    Publication Date: 2019
    Description: Abstract We explore the paradigm that Saturn's plasmapause marks the boundary between the magnetic flux tubes that have been circulating around the planet for some time, accumulating a dense load of Enceladus‐sourced material, and those that have recently undergone tail reconnection, shedding the bulk of the cold plasma and retaining a more tenuous, heated population. A centrifugally‐driven interchange instability should develop at this boundary, producing fingers of outward‐propagating dense plasma and of inward‐propagating hot, tenuous plasma. The plasmapause should thus be identifiable as a transition from mostly‐dense‐with‐some‐tenuous to mostly‐tenuous‐with‐some‐dense plasma populations. Electron densities from the Cassini CAPS/ELS instrument are used to identify the location of this transition for all of the low‐latitude (〈5° from the magnetic equator) passes through Saturn's inner/middle magnetosphere. The boundary is typically found near and somewhat beyond L=10 (i.e., at ~10 Rs from the planet), with a local time asymmetry such that it is closer to the planet on the night side than on the day side.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
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  • 146
    Publication Date: 2019
    Description: Abstract During the last deglaciation, a major global warming trend was punctuated by abrupt climate changes, likely related to Atlantic meridional overturning circulation (AMOC). One problem is that an abrupt increase in the AMOC during the Bølling‐Allerød (BA) transition occurred when the melting of Northern Hemisphere ice sheets was significant, which tended to weaken the AMOC. Here, from transient simulations of the last deglaciation using an atmosphere‐ocean general circulation model, we show that an abrupt increase in the AMOC during the BA transition could occur without reduction in glacial meltwater. The abrupt increase in the AMOC accompanied abrupt warming in Greenland and sea ice retreat in the North Atlantic, consistent with proxies and previous modeling studies. The results imply that abrupt BA warming during the middle stage of the last deglaciation was a response to gradual warming under the presence of meltwater from continental ice sheets.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 147
    Publication Date: 2019
    Description: Abstract Calving and submarine melt drive frontal ablation and sculpt the ice face of marine‐terminating glaciers. However, there are sparse observations of submarine termini, which limit estimates of spatially‐varying submarine melt. Here we present a detailed survey of a west Greenland glacier to reveal heterogeneity in submarine terminus morphology. We find that the majority of the terminus (~77%) is undercut, driven by calving in the upper water column and submarine melting at depth. The remaining ~23% of the terminus is overcut, driven by calving alone. We use observations of six subglacial discharge outlets, combined with a plume model, to estimate spatially‐varying discharge fluxes. While small discharge fluxes (〈43 m3 s‐1) feed numerous, deeply‐undercut outlets with subsurface plumes, ~70% of the net subglacial flux emerges at the terminus center, producing a vigorous, surface‐reaching plume. This primary outlet drives large, localized seasonal retreat that exceeds calving rates at secondary outlets.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 148
    Publication Date: 2019
    Description: Abstract Daily and sub‐daily homogenization of climate variables have been intensively investigated in the last decades, but to the best of our knowledge, this is the first study on homogenization of hourly temperature in Romania. This paper describes the creation of a homogenized hourly air temperature data set at a country scale by combining data from four independent meteorological networks. The air temperature measurements for the period 2009 and 2017 were obtained from the following networks: Romanian National Meteorological Administration (ANM), National Network for Monitoring Air Quality (RNMCA), Regional Basic Synoptic Network (RBSN), and Meteorological Terminal Aviation Routine Weather Report network (METAR). The climatological limits, persistence, temporal variation (step test), and spatial consistency were the quality control tests used to isolate the errors due to malfunctioning of the temperature sensors, data coding or transmission. The Climatol homogenization method was successfully applied for identifying and correcting any suspicious values. The missing data were filled by considering the similarities between each station and the reference series. Comparing the output with the original data, it is apparent that the removal of the breakpoints, correction and homogenization resulted in a new data set with statistical properties very similar to the raw data, but more reliable for climate research due to the increased homogeneity. Eventually, the procedure can be implemented in operational use for collecting more data from other networks. This article is protected by copyright. All rights reserved.
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
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  • 149
    Publication Date: 2019
    Description: Abstract The Asian‐Australian monsoon (AAM) plays a vital role in modulating the global and local climates. Current numerical models, including climate system models (CSMs) and atmospheric general circulation models (AGCMs), have difficulties in capturing the fundamental and intrinsic features of the AAM. By applying the stochastic multicloud model (SMCM) to the state‐of‐the‐art ECHAM6.3 atmosphere model, we investigated the impacts of SMCM on the simulation of AAM precipitation. Though the modified model with the SMCM improves simulations of the AAM precipitation in June‐July‐August‐September (JJAS) season, the solstice mode, the AAM domain, and the AAM precipitation intensity, deficiencies also exist in other aspects, i.e., simulations of rainfall in December‐January‐February‐March (DJFM) and April‐May (AM) seasons, and the equinox mode. Analyses also unraveled the modified model improves in simulating the spatial patterns of seasonal variation of precipitation in the Indian monsoon region, western North Pacific monsoon region, and Australian monsoon region in terms of pattern correlation coefficient and normalized root‐mean square error scores. The enhanced simulation of solar radiation in the modified model favors improving the performance of the simulated solstice mode. In addition, moisture budget analysis was applied to investigate physical processes that modulate the variations and distributions of AAM precipitation. Analyses revealed that variations and distributions of the vertical integral of moisture flux convergence is closely associated with changes in precipitation, while the stratification of vertical moist transport is associated with changes in precipitation over land in the AAM region. In addition, the modified model influences the AAM precipitation mainly through the variations of moisture flux convergence. The present work potentially provides a method to improve the simulated capability of AGCMs.
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
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  • 150
    Publication Date: 2019
    Description: Abstract Questions Spatial pattern analysis may be used to derive hypotheses on the processes that shape plant communities. Do different mature semidesert communities exhibit the same major spatial patterns, suggesting that similar processes shape them?. Location Nine localities in the Bolivian Andes. Methods We mapped all woody individuals at each locality. We performed uni‐, bi‐, and multivariate spatial analyses of nine Andean, mature semiarid plant communities to test for similarity in spatial patterns. Results We found that the nine communities exhibited, in most of the main spatial pattern attributes, close similarities (community aggregation, importance of plant interactions, life form differences, etc.). Some peculiarities were likely due to differences in life form or site history. Conclusions At least for Andean semiarid communities, the complete analysis of a representative plot conveys reliable information on spatial relationships and, hence, on potential underlying mechanisms. This shows that the use of 1‐2 representative plots can be used to extrapolate to similar communities within a given region. Our results can be used as a plausible hypothesis to be tested in other zones of the planet.
    Print ISSN: 1100-9233
    Electronic ISSN: 1654-1103
    Topics: Biology
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  • 151
    Publication Date: 2019
    Description: The Bulletin of the Ecological Society of America, EarlyView.
    Print ISSN: 0012-9623
    Electronic ISSN: 2327-6096
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering
    Published by Wiley on behalf of The Ecological Society of America (ESA).
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  • 152
    Publication Date: 2019
    Description: Journal of Industrial Ecology, EarlyView.
    Print ISSN: 1088-1980
    Electronic ISSN: 1530-9290
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 153
    Publication Date: 2019
    Description: Abstract Buildings represent a critical piece of a low‐carbon future, and their long lifetime necessitates urgent adoption of state‐of‐the‐art performance standards to avoid significant lock‐in risk regarding long‐lasting technology solution choices. Buildings, mobility, and energy systems are closely linked, and assessing their nexus by aiming for Zero Emission Neighborhoods (ZENs) provides a unique chance to contribute to climate change mitigation. We conducted a life‐cycle assessment of a Norwegian ZEN and designed four scenarios to test the influence of the house size, household size, and energy used and produced in the buildings as well as mobility patterns. We ran our scenarios with different levels of decarbonization of the electricity mix over a period of 60 years. Our results show the importance of the operational phases of both the buildings and mobility in the neighborhood's construction, and its decline over time induced by the decarbonization of the electricity mix. At the neighborhood end‐of‐life, embodied emissions then become responsible for the majority of the emissions when the electricity mix is decarbonized. The choice of functional unit is decisive, and we thus argue for the use of a primary functional unit “per neighborhood,” and a second “per person.” The use of a “per m2” functional unit is misleading as it does not give credits to the precautionary use of floor area. To best mitigate climate change, climate‐positive behaviors should be combined with energy efficiency standards that incorporate embodied energy, and absolute threshold should be combined with behavioral changes.
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    Electronic ISSN: 1530-9290
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 154
    Publication Date: 2019
    Description: Abstract The article examines degradation of a SiC‐based fiber composite containing Tyranno ZMI fibers in water vapor at elevated temperatures (800°C and 1100°C). Degradation is characterized through mechanical tests under cyclic and quasi‐static tensile loading in the near‐threshold regime, at stresses at or slightly above the matrix cracking limit. These tests are augmented by examinations of fracture surfaces and polished cross‐sections, measurements of fracture mirror radii, and measurements of interfacial debond toughness and sliding resistance. Degradation involves highly localized consumption of fibers through reactions of water vapor with the fibers and the BN coatings in regions adjacent to the few matrix cracks present at low stresses; the global hysteresis response and the average interfacial properties are minimally affected. Boria formed by oxidation of BN appears to play a fluxing role; it combines with silica on the fibers to form a non‐protective molten glass. Inhomogeneous fiber consumption leads to stress concentrations in the fibers and hence reduced fiber strength. Spatial variations in the degradation process occur at two length scales: at the macroscopic scale, because of cracking of the external CVI SiC overcoat and subsequent water ingress through the cracks, and at the tow‐scale, because of cracking of the CVI SiC around the tows. Parsing the kinetic processes over the two length scales remains a significant challenge.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 155
    Publication Date: 2019
    Description: ABSTRACT Improving the seismic time‐frequency resolution is a crucial step for identifying thin reservoirs. In this paper, we propose a new high‐precision time‐frequency analysis algorithm, synchroextracting generalized S‐transform, which exhibits superior performance at characterizing reservoirs and detecting hydrocarbons. This method first calculates time‐frequency spectra using generalized S‐transform; then, it squeezes all but the most smeared time‐frequency coefficients into the instantaneous frequency trajectory and finally obtains highly accurate and energy‐concentrated time‐frequency spectra. We precisely deduce the mathematical formula of the synchroextracting generalized S‐transform. Synthetic signal examples testify that this method can correctly decompose a signal and provide a better time‐frequency representation. The results of a synthetic seismic signal and real seismic data demonstrate that this method can identify some reservoirs with thincknesses smaller than a quarter wavelength and can be successfully applied for hydrocarbon detection. In addition, examples of synthetic signals with different levels of Gaussian white noise show that this method can achieve better results under noisy conditions. Hence, the synchroextracting generalized S‐transform has great application prospects and merits in seismic signal processing and interpretation. This article is protected by copyright. All rights reserved
    Print ISSN: 0016-8025
    Electronic ISSN: 1365-2478
    Topics: Geosciences , Physics
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  • 156
    Publication Date: 2019
    Description: Abstract For the first time, a transparent high‐entropy fluoride laser ceramic has been prepared and characterized. X‐ray diffraction (XRD) analysis of a CeNdCaSrBaF12 (CNCSBF) transparent ceramic consolidated by vacuum hot pressing (VHP) reveals that Ce3+, Nd3+, Ca2+, Sr2+, and Ba2+ have formed a single‐phased fluorite solid solution, with a lattice constant of 5.826 Å. Bulk density measurements produced a value of 6.15 g/cm3. Scanning electron microscopy (SEM) analysis of the ceramic revealed a uniform distribution of grain sizes in the material, with the average grain size being approximately 20 μm. The material exhibits a maximum in‐line transmittance of approximately 60% at 1000 nm. A near‐infrared range photoluminescence (PL) emission band was observed at 1057 nm, with a visible‐range PL emission band being located at 440 nm.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 157
    Publication Date: 2019
    Description: The five 3rd order depositional sequences interpreted in Albian do Campanian interval of Potiguar Basin, as well the system tracts, and its relation with the lithostratigraphic units. The Açu Formation, main oil‐bearing formation of the basin, in inserted in the Depositional Sequences 1 to 3 context. Abstract Five 3rd‐order depositional sequences are interpreted from the early Albian to late Campanian interval in the Potiguar Basin. An integrated analysis of seismic interpretations, well logs, cores and biostratigraphic data provides a stratigraphic framework composed by stratigraphic surfaces, systems tracts and sequences. Depositional Sequence 1 and 2 are, respectively, Albian and early to mid‐Cenomanian aged and are composed by the falling stage, low stand, transgressive and high stand systems tracts. Depositional Sequence 3 is late Cenomanian to mid‐Turonian aged and is composed by the transgressive and high stand systems tracts. Depositional sequences 4 and 5 are, respectively, late Turonian to mid‐Santonian and late Santonian to mid‐Campanian aged and are composed only by transgressive and high stand systems tracts. The lack of falling stage and low stand systems tracts in depositional sequences 3, 4 and 5, as well the increasing in transgressive and highstand systems tracts thickness as depositional sequences get younger, are reflection of an overall transgressive trend of a 2nd‐order sequence. The interpretation proposed in this paper correlates onshore with offshore deposits within a seismic scale (3rd‐order) sequence stratigraphy framework. This approach allows a better understanding of the Açu Formation, the primary oil‐bearing formation of the Potiguar Basin. The Açu Formation is part of depositional sequences 1, 2 and 3 and is characterized by lateral and vertical variations of depositional systems instead of being associated to a specific depositional system. This sequence stratigraphy analysis can be used as a low‐resolution framework for future high‐resolution (4th‐order scale) studies.
    Print ISSN: 0950-091X
    Electronic ISSN: 1365-2117
    Topics: Geosciences
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  • 158
    Publication Date: 2019
    Description: Abstract The Sample Analysis at Mars (SAM) experiment on the NASA Curiosity rover seeks evidence of organic compounds on the surface of Mars. Since the beginning of the mission, various organic molecules have been detected and identified. While several have been demonstrated to be indigenous to the Martian soil and rocks analyzed, others appear to have been produced from sources internal to the experiment. The objective of this study is to build an exhaustive molecular database to support the interpretation of SAM results by identifying all the chemical species produced from Tenax® adsorbents, by determining: (1) the thermal degradation byproducts of Tenax®, (2) the effect of Tenax® conditioning on the formation of Tenax® byproducts, (3) the impact of MTBSTFA or a mixture of MTBSTFA and DMF on Tenax® decomposition, and (4) the reaction between Tenax® and calcium perchlorate. Our results indicate that the by‐products of the SAM trap are due to the impact of trap heating, the impact of the derivatization reagent (MTBSTFA) and the presence of perchlorate in Martian soil. Some of these by‐products are observed in the SAM gas chromatograph mass spectrometer (GCMS) data from Mars.
    Print ISSN: 2169-9097
    Electronic ISSN: 2169-9100
    Topics: Geosciences , Physics
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  • 159
    Publication Date: 2019
    Description: Abstract Stable oxygen isotopes (δ18O) in the Bona‐Churchill (B‐C) ice core from southeast Alaska provide a valuable, high‐resolution history of climate variability and sea ice cover in the western Arctic over the last 800 years. Multiple ice cores have been collected from the Wrangell‐St. Elias Mountain Range; however, their δ18O records exhibit little consistency as each core offers a unique view on local, regional, and/or global climate variability. To explore the primary mechanisms influencing the isotopic signature at the B‐C site, we utilize isotope‐enabled model data, reanalysis data, and observations, which all indicate a strong connection between isotopes at the B‐C site and western Arctic climate, likely established by the location of the storm track in this region. Enriched B‐C δ18O reflects increased southerly flow and warmer waters in the Bering Sea, which modulates the heat flux through the Bering Strait and into the Arctic, thereby affecting sea ice cover in the western Arctic. The B‐C δ18O paleorecord shares some remarkable similarities (r = −0.80, p 〈 .001) with the duration of western arctic sea ice cover reconstructed from a Chukchi Sea sediment core. Interestingly, during the Little Ice Age, enriched δ18O and reduced western Arctic sea ice are observed and may be indicative of prolonged periods of the warm Arctic/cold continents pattern and a northwestward shift of the North Pacific storm track.
    Print ISSN: 2169-897X
    Electronic ISSN: 2169-8996
    Topics: Geosciences , Physics
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  • 160
    Publication Date: 2019
    Description: Abstract The Tien Shan is the largest independent latitudinal mountain ranges in Eurasia, but due to a lack of long‐term instrumental data, knowledge of past temperature variability in the Tien Shan is limited. In this paper, a maximum latewood density (MXD) chronology of Schrenk spruce (Picea schrenkiana) was constructed from the Tien Shan, Central Asia. Correlation analyses indicate that the MXD variations of spruce trees in the Tien Shan are mainly limited by summer temperature variations. The July‐August mean temperature was reconstructed for the Tien Shan back to 1615 CE. The temperature reconstruction explained 42.9% of the instrumental variance (1930–2005). This reconstruction successfully captured the past temperature variabilities in the Tien Shan and enabled visualization of the cool climate before 1850s and the climatic warming after the 1850s. Agreement among the temperature series of the Tien Shan and regional temperature records based on MXDs from Eurasia suggested that our reconstruction had good reliability, captured some warm/cold periods, and first principal component (PC1) of these MXD records showed that there are strong large‐scale temperature forcings in Eurasia. Our study also showed that there is a linkage between temperature changes in Central Asia and the atmospheric circulations of the middle‐high latitude westerly region and the sea surface temperatures of both the Pacific Ocean and the Atlantic Ocean. The positive correlations among the PC1 time series of regional temperature reconstructions based on MXDs and Northern Hemisphere temperature reconstructions revealed that the MXD chronologies from Central Asia have the potential for developing large‐scale temperature reconstruction.
    Print ISSN: 2169-897X
    Electronic ISSN: 2169-8996
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 161
    Publication Date: 2019
    Description: Abstract The characteristics of global electron density variations in the ionosphere during a geomagnetic storm on November 7 and 8, 2004, were investigated using total electron content (TEC) obtained from the global navigation satellite system (GNSS). The regions of enhanced TEC over North America, Europe, and Japan first appeared in the mid‐latitude regions. The TEC enhancements over North America showed a rapid longitudinal expansion and reached a wide longitudinal extent during the initial and main phases of the geomagnetic storm. TEC enhancements were simultaneously observed in both North America and Japan at 05:00 UT on November 8. Observation data from the Defense Meteorological Satellite Program showed a slight enhancement of electron density at 850 km below the equatorward boundary of the mid‐latitude trough (45–48°N in geomagnetic latitude) over the Pacific Ocean. This electron density variation may correspond to the TEC enhancements observed in both Japan and North America. These results imply that an enhanced TEC region existed between North America and Japan. The TEC enhancement in Japan appeared with a magnetic conjugacy in the Southern hemisphere, indicating one of the characteristics of storm‐enhanced density (SED). Moreover, TEC enhancements simultaneously appeared from Japan to Central Asia at 11:00 UT on November 8, corresponding to the early recovery phase of the geomagnetic storm. From the above results, it is suggested that SED phenomena can be simultaneously generated over a wide longitudinal width (~100°). The longitudinal extent of this SED event is 2.5–5.0 times longer than those reported by previous studies.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 162
    Publication Date: 2019
    Description: Abstract Impact bombardment changes target properties, and topographic degradation increases crater diameters. These effects potentially change the shape of lunar production function (PF), which is usually assumed to be constant with time. Using crater scaling laws, we model PFs (MPFs) formed by near‐Earth objects on two‐layer target models that have increasing regolith thickness with time. Model‐derived MPFs show a significantly elevated production rate for small lunar craters, which is consistent with a high regolith production rate during the last ~1 Ma. Further integrating the effect of topographic degradation, we model the time‐dependent observable PFs (MOPFs) from the MPFs. Comparing among MOPFs, MPFs, and the prevailing Neukum PF suggests that, for D = 10–1,000 m simple craters, applying MPFs and Neukum PF may cause the derived cumulative density of D 〉 1 km craters (i.e., N(1)) to differ from its real value by a factor up to ~3 and ~10, respectively.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 163
    Publication Date: 2019
    Description: Abstract Studying spatial and temporal trends in volcanic gas compositions and fluxes is crucial to both volcano monitoring and to constrain the origin and recycling efficiency of volatiles at active convergent margins. New compositions and fluxes are here reported for Nevado del Ruiz, Galeras and Purace, the most persistently degassing volcanoes in the Colombian Arc Segment (CAS) of the Northern Volcanic Zone (NVZ). At Nevado del Ruiz, from 2014 to 2017, plume emissions showed an average molar CO2/ST ratio of 3.9 ± 1.6 (ST is total sulfur, S). Contemporary, fumarolic chemistry at Galeras progressively shifted towards low‐temperature, S‐depleted gas discharges with an average CO2/ST ratio in excess of 10 (6.0 – 46.0, 2014‐2017). This shift in volcanic gas compositions was accompanied by a concurrent decrease in SO2 emissions, confirmed on the 21 March 2017 by high‐resolution UV camera‐based SO2 fluxes of ~2.5 kg s‐1 (~213t d‐1). For comparison, SO2 emissions remained high at Nevado del Ruiz (weighted average of 8 kg s‐1) between 2014 and 2017, while Puracé maintained rather low emission levels (〈1 kg s‐1 of SO2, CO2/SO2 ≈ 14). We here estimate carbon dioxide fluxes for Nevado del Ruiz, Galeras and Puracé of ~23, 30 and 1 kg s‐1, respectively. These, combined with recent CO2 flux estimates for Nevado del Huila of ~10 kg s‐1 (~860 t d‐1), imply that this arc segment contributes about 50% to the total subaerial CO2 budget of the Andean Volcanic Belt. Furthermore, our work highlights the northward increase in carbon‐rich sediment input into the mantle wedge via slab fluids and melts that is reflected in magmatic CO2/ST values far higher than those reported for Southern Volcanic Zone (SVZ) and Central Volcanic Zone (CVZ) volcanoes. We estimate that about 20% (~1.3 Mt C/y) of the C being subducted (~6.19 Mt C/y) gets resurfaced through subaerial volcanic gas emissions in Colombia (Nevado del Ruiz ~0.7 Mt C/y). As global volcanic volatile fluxes continue to be quantified and refined, the contribution from this arc segment should not be underestimated.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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  • 164
    Publication Date: 2019
    Description: Abstract Salt marshes often undergo rapid changes in lateral extent, the causes of which lack common explanation. We combine hydrological, sedimentological and climatological data with analysis of historical maps and photographs to show that long‐term patterns of lateral marsh change can be explained by large‐scale variation in sediment supply and its wave‐driven transport. Over 150 years, northern marshes in Great Britain expanded while most southern marshes eroded. The cause for this pattern was a north to south reduction in sediment flux and fetch‐driven wave sediment resuspension and transport. Our study provides long‐term and large‐scale evidence that sediment supply is a critical regulator of lateral marsh dynamics. Current global declines in sediment flux to the coast are likely to diminish the resilience of salt marshes and other sedimentary ecosystems to sea level rise. Managing sediment supply is not common‐place, but may be critical to mitigating coastal impacts from climate change.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 165
    Publication Date: 2019
    Description: Abstract Question As a result of recent and substantial digitization efforts, herbaria are becoming important sources of data for vegetation scientists. Are such datasets appropriate to describe composition gradients and β‐diversity? When compared with phytosociological data, what are the differences in terms of composition (co‐occurrence) gradients depending on the considered scale? Location Páramos (Neo‐tropical alpine ecosystems) of Colombia. Methods We compared vegetation patterns from phytosociological relevés and reconstructed pseudo‐communities from herbarium collections in the Colombian high elevation páramo ecosystem using diversity partitioning and Mantel correlations. Results Species composition differed in the two datasets, which could be explained by taxonomic bias toward charismatic species and over‐representation of rare species in the herbarium dataset, whereas common species were more frequently represented in the phytosociological dataset. The two datasets showed a similarly preponderant importance of large‐scale differences when we looked at species accumulation across different scales. Small scale richness contributed more to total richness for the phytosociological dataset, while richness at intermediate scales was more important in the herbarium dataset. Finally, pairwise β‐diversity analyses did not show correlations between datasets, and common species showed similar ecological distribution patterns. Conclusions We recommend caution to researchers who wish to describe β‐diversity patterns in local communities using only herbarium data. However, since the two datasets showed some complementarity in their composition patterns, we suggest that combining data from relevés (or plots) and occurrence data (herbarium records, citizen science, etc.) could be an efficient strategy for describing broader diversity patterns. We discuss the circumstances under which it could be advantageous to work with such combined datasets, in particular in relation to conservation issues.
    Print ISSN: 1100-9233
    Electronic ISSN: 1654-1103
    Topics: Biology
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  • 166
    Publication Date: 2019
    Description: Abstract Despite similar geological and tectonic setting along the Himalayan orogen, distinct thermochronological/exhumational and seismicity variability exists between the Kumaun and the Garhwal regions of the NW‐ Himalaya. The processes responsible for such variability are still debated. To understand this, published thermochronological ages from several traverses across the Higher Himalayan Crystalline (HHC) and Lesser Himalayan Crystalline (LHC) have been correlated with the seismicity pattern in both Garhwal and Kumaun segments. The seismicity pattern coincides with the zone of rapid uplift and exhumation. The profiles of seismicity across the Kumaun and the Garhwal regions agree with the existence of the Main Himalayan Thrust (MHT) underlying the regions and reflect its geometry and architecture. Slip along the MHT is responsible for occurrence of seismicity on decade time‐scale and exhumation pattern on Myr time‐scale of the Himalaya.
    Print ISSN: 0954-4879
    Electronic ISSN: 1365-3121
    Topics: Geosciences
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  • 167
    Publication Date: 2019
    Description: Abstract Digging animals may alter many characteristics of their environment as they disrupt and modify the ground’s surface by creating foraging pits or burrows. Extensive disturbance to the soil and litter layer changes litter distribution and availability, potentially altering fuel loads. In many landscapes, including peri‐urban areas, fire management to reduce fuel loads is complex and challenging. The reintroduction of previously common digging animals, many of which are now threatened, may have the added benefit of reducing fuel loads. We experimentally examined how the reintroduction of a marsupial bandicoot, quenda (Isoodon fusciventer), altered surface fuel loads in an urban bush reserve in Perth, Western Australia. Foraging activities of quenda (where they dig for subterranean food) were substantial throughout the reserve, creating a visibly patchy distribution in surface litter. Further, in open plots where quenda had access, compared to fenced plots where quenda were excluded, quenda foraging significantly reduced litter cover and litter depth. Similarly, estimated surface fuel loads were nearly halved in open plots where quenda foraged compared to fenced plots where quenda were absent (3.6 c.f. 6.4 tonnes ha‐1). Fire behaviour modelling, using the estimated surface fuel loads, indicated the predicted rate of spread of fire were significantly lower for open plots where quenda foraged compared to fenced plots under both low (29.2 c.f. 51.4 m hr‐1; total fuels) and high (74.3 c.f. 130.4 m hr‐1; total fuels) fire conditions. Although many environments require fire, including the bushland where this study occurred, fire management can be a considerable challenge in many landscapes, including urban bushland reserves which are usually small and close to human infrastructure. The reintroduction of previously common digging species may have potential value as a complimentary tool for reducing fuel loads, and potentially, fire risk.
    Print ISSN: 1051-0761
    Electronic ISSN: 1939-5582
    Topics: Biology
    Published by Wiley on behalf of The Ecological Society of America (ESA).
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  • 168
    Publication Date: 2019
    Description: Abstract Functional responses describe how changing resource availability affects consumer resource use, thus providing a mechanistic approach to prediction of the invasibility and potential damage of invasive alien species (IAS). However, functional responses can be context‐dependent, varying with resource characteristics and availability, consumer attributes, and environmental variables. Identifying context‐dependencies can allow invasion and damage risk to be predicted across different ecoregions. Understanding how ecological factors shape the functional response in agro‐ecosystems can improve predictions of hotspots of highest impact and inform strategies to mitigate damage across locations with varying crop types and availability. We linked heterogeneous movement data across different agro‐ecosystems to predict ecologically‐driven variability in the functional responses. We applied our approach to wild pigs (Sus scrofa), one of the most successful and detrimental IAS worldwide where agricultural resource depredation is an important driver of spread and establishment. We used continental‐scale movement data within agro‐ecosystems to quantify the functional response of agricultural resources relative to availability of crops and natural forage. We hypothesized that wild pigs would selectively use crops more often when natural forage resources were low. We also examined how individual attributes such as sex, crop type, and resource stimulus such as distance to crops altered the magnitude of the functional response. There was a strong agricultural functional response where crop use was an accelerating function of crop availability at low density (Type III) and was highly context‐dependent. As hypothesized, there was a reduced response of crop use with increasing crop availability when non‐agricultural resources were more available, emphasizing that crop damage levels are likely to be highly heterogeneous depending on surrounding natural resources and temporal availability of crops. We found significant effects of crop type and sex – with males spending 20% more time and visiting crops 58% more often than females, and both sexes showing different functional responses depending on crop type. Our application demonstrates how commonly collected animal movement data can be used to understand context‐dependencies in resource use to improve our understanding of pest foraging behavior, with implications for prioritizing spatio‐temporal hotspots of potential economic loss in agro‐ecosystems.
    Print ISSN: 1051-0761
    Electronic ISSN: 1939-5582
    Topics: Biology
    Published by Wiley on behalf of The Ecological Society of America (ESA).
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  • 169
    Publication Date: 2019
    Description: Abstract Exotic invasive plants threaten ecosystem integrity, and their success depends on a combination of abiotic factors, disturbances, and interactions with existing communities. In dryland ecosystems, soil biocrusts (communities of lichens, bryophytes and microorganisms) can limit favorable microsites needed for invasive species establishment, but the relative importance of biocrusts for landscape‐scale invasion patterns remains poorly understood. We examine effects of livestock grazing in habitats at high risk for invasion to test the hypothesis that disturbance indirectly favors exotic annual grasses by reducing biocrust cover. We present some of the first evidence that biocrusts increase site resistance to invasion at a landscape scale and mediate the effects of disturbance. Biocrust species richness, which is reduced by livestock grazing, also appears to promote native perennial grasses. Short mosses, as a functional group, appeared to be particularly valuable for preventing invasion by exotic annual grasses. Our study suggests that maintaining biocrust communities with high cover, species richness, and cover of short mosses can increase resistance to invasion. These results highlight the potential of soil surface communities to mediate invasion dynamics and suggest promising avenues for restoration in dryland ecosystems.
    Print ISSN: 1051-0761
    Electronic ISSN: 1939-5582
    Topics: Biology
    Published by Wiley on behalf of The Ecological Society of America (ESA).
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  • 170
    Publication Date: 2019
    Description: Abstract Over the past two decades, the Gulf of California (GOC) has experienced three strong El Niño events (1997–1998, 2009–2010, and 2015–2016), each of which was followed by a drastic reduction in mantle length of mature Humboldt squid, Dosidicus gigas (from 〉60 cm to 〈20 cm). However, it is unclear how the oceanographic changes associated with strong El Niño events affected the midwater organisms on which D. gigas feed, limiting our ability to assess the relative importance of temperature and food availability in the phenotypic response of D. gigas to environmental variability. We quantified the diet of D. gigas in the GOC before, during, and following the past three El Niño events and found that although its diet varied little across a large range of body sizes (8–85 cm), significant and predictable diet variability was observed with respect to sea surface temperature and chlorophyll‐a concentration. Consumption of large numbers of relatively small, high calorie prey in both relatively cool (anchovies) and relatively warm, productive conditions (myctophids) is likely necessary to support growth to large body sizes before maturation. When warm, unproductive conditions prevailed in the GOC, only small squid were present and had diets dominated by euphausiids and pteropods, prey with relatively low caloric value. Using a time series of diet data, this work provides unique insights into the response of a midwater forage community to oceanographic variability and the effects of environmental variability on the trophic ecology of an oceanic predator.
    Print ISSN: 0024-3590
    Electronic ISSN: 1939-5590
    Topics: Biology , Geosciences , Physics
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  • 171
    Publication Date: 2019
    Description: An example of a zoning policy whereby development has been focused onto flood safe areas combined with land‐use changes. Abstract One commonly proposed method to limit flood risk is land‐use or zoning policies which regulates construction in high‐risk areas, in order to reduce economic exposure and its vulnerability to flood events. Although such zoning regulations can be effective in limiting trends in flood risk, they also have adverse impacts on society, for instance by limiting local development of areas near the water. In order to judge whether proposed land‐use or zoning policies are a net benefit to society, they should be accepted or rejected based on a societal cost–benefit analysis (CBA). However, conducting a CBA of zoning regulation is complex and comprehensive guidelines of how to do such an analysis are lacking. We offer guidelines for good practice. In order to assess the costs and benefits of zoning as a climate change adaption strategy, they should be assessed at a societal level in order to account for public good features of flood risk reduction strategies, and because costs in one area can be benefits in another region. We propose a multistep process: first, determine the spatial extent of the zoning policy and how interconnected the zoned area is to other locations; second, conduct a CBA using monetary costs and benefits estimated from an integrated hydro‐economic model to investigate if total benefits exceed total costs; third, conduct a sensitivity analysis regarding the main assumptions; fourth, conduct a multicriteria analysis (MCA) of the normative outcomes of a zoning policy. A desirable policy is preferred in both the CBA and MCA. This article is categorized under: Engineering Water 〉 Planning Water Human Water 〉 Value of Water Science of Water 〉 Water Extremes Human Water 〉 Methods
    Electronic ISSN: 2049-1948
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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  • 172
    Publication Date: 2019
    Description: Abstract North‐eastern Romania is frequently affected by storms that produce annual floods with catastrophic effects upon agriculture areas. The implementation of the 2007/60/ EC Directive, which aims, among other things, to assess and manage flood risk, is currently being carried out by means of rough hydrological risk maps. Additionally, the limits of the potentially floodable areas generated on digital elevation models with 30 points/m resolution (SRTM) do not correspond to the current topographic reality. Three tests (T1, T2, and T3) for modelling the floodplains and the comparative assessment of potential damages in the case of 30 localities in the study area (Başeu River basin) were carried out in this study. The results indicate that official data (T1) underestimate potential damage in the case of hydrological events with a recurrence interval probability of 1% (100‐year). The T2 [1%] (100‐year) results also highlight the role of hydro‐technical works in mitigating floods. In T3, the hydrological risk areas were generated with an accuracy of 0.5 m, evaluating the probable damage in cases of events with probabilities of 3% (33.3‐year), 1% (100‐year), and 0.1% (1,000‐year) recurrence intervals. The accuracy of the official hydrological hazard maps (T1) was improved using high‐density LiDAR data and HEC‐RAS software (T3).
    Electronic ISSN: 1753-318X
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
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  • 173
    Publication Date: 2019
    Description: Abstract Barotropic variability plays an important role in a variety of extratropical atmospheric processes, such as annular modes, teleconnections, and baroclinic life cycles, which occur on a wide range of timescales. Extratropical dynamics is dominated by high‐frequency (periods shorter than 10 days) transient waves, which drive barotropic variability through baroclinic life cycle events. However, other types of waves (e.g. low‐frequency, with periods longer than 10 days, and stationary waves) also play an important role in shaping extratropical dynamics on various timescales. This study uses reanalysis data in the context of the zonal momentum budget to address the relative importance of stationary, low‐frequency and high‐frequency waves in driving barotropic variability at high (synoptic) and low (subseasonal‐to‐seasonal) frequencies both locally in storm track regions and in the zonal mean in both hemispheres. The analysis reveals that the eddy forcing of barotropic variability on synoptic timescales is dominated by the interaction between low‐frequency (and stationary) and high‐frequency waves, and not by high‐frequency self‐interactions. On longer (subseasonal‐to‐seasonal) timescales the picture is more complex, with increased importance of low‐frequency self‐interactions but still largely negligible high‐frequency self‐interactions. A better understanding of the mechanisms driving barotropic variability on subseasonal‐to‐seasonal timescales may help advancing predictability on these timescales. This article is protected by copyright. All rights reserved.
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
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  • 174