bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reef‐Scale‐Dependent Response of Massive Porites Corals From the Central Indian Ocean to Prolonged Thermal Stress: Evidence From Coral Sr/Ca Measurements
Authors: Leupold Maike , Pfeiffer Miriam , Garbe‐Schönberg Dieter , Sheppard Charles 
Published: February 2019

AbstractHere we present coral Sr/Ca data of biweekly resolution from three modern coral cores drilled from living Porites corals from two different reef settings at Chagos (tropical Indian Ocean). Chagos lies at the eastern margin of the Seychelles‐Chagos thermocline ridge and features open ocean upwelling. In situ temperatures have been recorded by temperature loggers since 2006. High‐resolution satellite temperatures closely track the logger data. Two cores were collected from a patch reef in the lagoon of Peros Banhos, a site characterized by high mean temperatures and low‐temperature variability. An open ocean core was collected at the outer reef slope of Diego Garcia, which experiences larger temperature fluctuations related to open ocean upwelling. The open ocean core shows clear seasonal cycles in Sr/Ca that closely track the satellite temperatures. The Sr/Ca records from the two lagoon corals show good reproducibility. Between 2007 and 2010, Sr/Ca tracks satellite temperatures. However, between 2003 and 2006 the Sr/Ca curves are almost flat and annual coral growth rates are low. During these years, warm sea surface temperatures and coral bleaching have been observed at Chagos. It is likely that the observed reduction in coral growth rates is a response to prolonged warming events, adding to the growing evidence that seemingly healthy and surviving corals are affected by thermal stress. Further, the high correlation between the Sr/Ca records of the two lagoon cores suggests that this effect is not limited to single coral colonies but may affect the entire reef setting.
Striations in Marginal Seas and the Mediterranean Sea
Authors: Zhang Y. , Guan Y. P. 
Published: February 2019

AbstractStriations, which are jet‐like structures comprising alternating ridges and furrows within large‐scale circulations, are widely studied in the open ocean, although it is unclear whether they exist in marginal or semiclosed seas. Based on an appropriate choice of averaging time scale and cutoff wavelength, our analysis reveals striations in marginal seas, including the South China Sea (SCS), Sea of Japan, and Gulf of Mexico, and in the Mediterranean Sea (MS). Compared with the open ocean, these striations have a narrower bandwidth (about 60 km in marginal seas and 100 km in the MS), fewer zonal orientations, stronger baroclinic structure, and deeper intensification. Striations in the open ocean are usually barotropic; however, within the South China Sea and MS, they are baroclinic in the upper 1,000 m and intensified at depths greater than 3,000 m.
Wind Power on Oceanic Near‐Inertial Oscillations in the Global Ocean Estimated From Surface Drifters
Authors: Liu Yongzheng , Jing Zhao , Wu Lixin 
Published: February 2019

AbstractWind power on oceanic near‐inertial oscillations is thought to play an important role in furnishing the diapycnal mixing in the ocean. Yet their global distribution and magnitude have not been quantified based on observations. In this study, we use hourly ocean current records derived from surface drifters to compute the global near‐inertial wind power during 1993–2016, with a combination of surface wind measurements obtained from satellites. The climatological near‐inertial wind power integrated between 60°S and 60°N is estimated to be 0.3–0.6 TW. The strongest energy flux occurs in the 30–60° latitude band during the winter season as a result of energetic storm activities. Ocean current imprint on wind stress has a significant impact on the estimated global near‐inertial wind power from drifters. Neglecting this imprint overestimates the near‐inertial wind power locally by 25–120% and its global mean value by 60%.
Aerosol Indirect Effects in Marine Stratocumulus: The Importance of Explicitly Predicting Cloud Droplet Activation
Authors: Bulatovic I. , Ekman A. M. L. , Savre J. , Riipinen I. , Leck C. 
Published: February 2019

AbstractClimate models generally simulate a unidirectional, positive liquid water path (LWP) response to increasing aerosol number concentration. However, satellite observations and large‐eddy simulations show that the LWP may either increase or decrease with increasing aerosol concentration, influencing the overall magnitude of the aerosol indirect effect (AIE). We use large‐eddy simulation to investigate the LWP response of a marine stratocumulus cloud and its dependence on different parameterizations for obtaining cloud droplet number concentration (CDNC). The simulations confirm that the LWP response is not always positive—regardless of CDNC treatment. However, the AIE simulated with the model version with prescribed CDNC is almost 3 times larger compared to the version with prognostic CDNC. The reason is that the CDNC in the prognostic scheme varies in time due to supersaturation fluctuations, collection, and other microphysical processes. A substantial spread in simulated AIE may thus arise simply due to the CDNC treatment.
The Extra‐Magnetospheric Ion Environment as Observed by the Magnetospheric Multiscale Mission Hot Plasma Composition Analyzer (MMS‐HPCA)
Authors: Gomez R. G. , Fuselier S. A. , Mukherjee J. , Gonzalez C. A. , Burch J. L. , Strangeway R. J. , Starkey M. J. 
Published: February 2019

AbstractObservations within the solar wind (SW) environment outside of the Earth's magnetosphere were conducted on 6 December 2016, by the Hot Plasma Composition Analyzer of the Magnetospheric Multiscale mission. At the time of measurement, the SW was in a compressed state with a southbound interplanetary magnetic field of 9 nT and corresponding increases in proton density and dynamic pressure. High time resolution measurements of pickup ions in this region were made during the time when the Earth is situated in a solar gravitational focusing cone for interstellar neutrals. Proton measurements revealed a suprathermal ion population traveling with a maximum velocity that is two and a half times that of the SW velocity (Vsw). Helium ions exhibited pitch angle scattering that was uncorrelated with changes in the interplanetary magnetic field orientation. The time‐of‐flight measurements exhibited expected contributions from both protons and singly charged helium. Because the Magnetospheric Multiscale spacecraft are in the SW, counts from heavy SW ions (possibly Fe7+ or Fe8+) with M/Q = 8 AMU/e are observed with a mean energy/charge (E/Q) of 5.75 keV/e.
The Impact of Rheology on the Transition From Stick‐Slip to Creep in a Semibrittle Analog
Authors: Birren T. , Reber J. E. 
Published: February 2019

AbstractFaults can release energy via a variety of different slip mechanisms ranging from steady creep to fast and destructive earthquakes. Tying the rheology of the crust to various slip dynamics is important for our understanding of plate tectonics and earthquake generation. Here we propose that the interplay of fractures and viscous flow leads to a spectrum between stick‐slip and creep. We use an elasto‐visco‐plastic rock analog (Carbopol U‐21) where we vary the yield stress to investigate its impact on slip dynamics in shear experiments. The experiments are performed using a simple shear apparatus, which provides distributed shear across the entire width of the experiment and allows in situ observations of deformation. We record force and displacement during deformation and use time lapse photography to document fracture development. A low yield stress (25 Pa) leads to creep dynamics in the absence of fractures. An intermediate yield stress (144 Pa) leads to the development and interaction of opening (mode I) and shear (mode II) fractures. This interaction leads to a spectrum in slip dynamics ranging from creep to stick‐slip. A high yield stress (357 Pa) results in the development of many mode I fractures and a deformation signal dominated by stick‐slip. These results show that bulk yield stress, fracture formation, and slip dynamics are closely linked and can lead to a continuum between creep and stick‐slip. We suggest that rheology should be considered as an additional mechanism to explain the broad range of slip dynamics in natural faults.
The Structure and Entrainment Characteristics of Partially Confined Gravity Currents
Authors: Kelly R. W. , Dorrell R. M. , Burns A. D. , McCaffrey W. D. 
Published: February 2019

AbstractSeafloor channels are the main conduit for turbidity currents transporting sediment to the deep ocean, and they can extend for thousands of kilometers along the ocean floor. Although it is common for channel‐traversing turbidity currents to spill onto levees and other out‐of‐channel areas, the associated flow development and channel‐current interaction remain poorly understood; much of our knowledge of turbidity current dynamics comes from studies of fully confined scenarios. Here we investigate the role that partial lateral confinement may play in affecting turbidity current dynamics. We report on laboratory experiments of partially confined, dilute saline flows of variable flux rate traversing fixed, straight channels with cross‐sectional profiles representative of morphologies found in the field. Complementary numerical experiments, validated against high‐resolution laboratory velocity data, extend the scope of the analysis. The experiments show that partial confinement exerts a first‐order control on flow structure. Overbank and downstream discharges rapidly adjust over short length scales, providing a mechanism via which currents of varying sizes can be tuned by a channel and conform to a given channel geometry. Across a wide range of flow magnitudes and states of flow equilibration to the channel, a high‐velocity core remains confined within the channel with a constant ratio of velocity maximum height to channel depth. Ongoing overbank flow prevents any flow thickening due to ambient entrainment, allowing stable downstream flow evolution. Despite dynamical differences, the entrainment rates of partially confined and fully confined flows remain comparable for a given Richardson number.
Modeling the Transition to High Sediment Concentrations as a Response to Channel Deepening in the Ems River Estuary
Authors: Dijkstra Yoeri M. , Schuttelaars Henk M. , Schramkowski George P. , Brouwer Ronald L. 
Published: February 2019

AbstractMany estuaries are strongly modified by human interventions, including substantive channel deepening. In the Ems River Estuary (Germany and Netherlands), channel deepening between the 1960s and early 2000s coincided with an increase in the maximum near‐bed suspended sediment concentration from moderate (∼1 kg/m3) to high (>10 kg/m3). In this study the observed transition in the suspended sediment concentration in the Ems is qualitatively reproduced by using an idealized width‐averaged iFlow model. The model is used to reproduce observations from 1965 and 2005 by only changing the channel depth between the years. Model results show an increase in sediment concentrations from approximately 1–2 kg/m3 to 20–30 kg/m3 near the bed between 1965 and 2005 if the river discharge is below 70 m3/s, which holds approximately 60% of the time. Thereby, this study for the first time provides strong evidence for earlier published hypotheses that channel deepening was the main driver of the increased sediment concentrations in the Ems. The results are explained using two aspects: sediment transport (longitudinal processes) and local resuspension (vertical processes). The magnitude of the sediment import increased, because a combination of channel deepening and sediment‐induced damping of turbulence increased the M2–M4 tidal asymmetry. This effect is particularly strong, because the M4 tide evolved to a state close to resonance. All imported sediment is kept in suspension when it is assumed that resuspension is sufficiently efficient, which depends on the value of the erosion parameter used and inclusion of hindered settling in the model.
Variability of Surface Water pCO2 in the Canadian Arctic Archipelago From 2010 to 2016
Authors: Ahmed M. , Else B. G. T. , Burgers T. M. , Papakyriakou T. 
Published: February 2019

AbstractThis study provides 6 years of high‐resolution underway measurements of the sea surface partial pressure of CO2 (pCO2sw), sea surface temperature, and salinity across the Canadian Arctic Archipelago (CAA). Observed pCO2sw varied regionally, with the northern and central channels of the CAA undersaturated in pCO2sw (with respect to the atmosphere), while the western regions were typically saturated to supersaturated in pCO2sw. This apparent spatial variability was caused to some extent by the timing of our ship transit through the CAA, as we also found a general seasonal trend of pCO2sw being undersaturated in the early summer, followed by saturation to supersaturation in late summer, and a return to undersaturation during the autumn. Sea surface temperature was significantly correlated with pCO2sw at various locations across the CAA, but we also observed the effects of other regional processes like upwelling, primary production, riverine input, and sea ice melt. These processes are linked to each other, and hence, it is impossible to pinpoint only one dominant factor controlling pCO2sw variability in the CAA. However, we found that sea ice dominates the seasonal cycle of all these processes, thus making the timing of sea ice breakup a useful predictor of pCO2sw variability in the CAA. We calculated an average net oceanic sink of 14 mmol CO2 · m−2 · day−1 for the CAA during the summer and autumn seasons, but caution that a more rigorous budgeting approach is required to fully account for biases in dates and locations of our measurements.
Simulating the Weekly Cycle of NOx‐VOC‐HOx‐O3 Photochemical System in the South Coast of California During CalNex‐2010 Campaign
Authors: Cai Chenxia , Avise Jeremy , Kaduwela Ajith , DaMassa John , Warneke Carsten , Gilman Jessica B. , Kuster William , de Gouw Joost , Volkamer Rainer , Stevens Philip , Lefer Barry , Holloway John S. , Pollack Ilana B. , Ryerson Thomas , Atlas Elliot , Blake Donald , Rappenglueck Bernhard , Brown Steven S. , Dube William P. 
Published: February 2019

AbstractUnited States Environmental Protection Agency guidance on the use of photochemical models for assessing the efficacy of an emissions control strategy for ozone requires that modeling be used in a relative sense. Consequently, testing a modeling system's ability to predict changes in ozone resulting from emission changes is critical. We evaluate model simulations for precursor species (NOx, CO, and volatile organic compounds [VOCs]), radicals (OH and HO2), a secondary pollutant (O3), and the model response of these compounds to weekend/weekday emission changes during California Nexus study in 2010. The modeling system correctly simulated the broad spatial and temporal variation of NOx and O3 in California South Coast. Although the model generally underpredicted the daytime mixing ratios of NO2 at the surface and overpredicted the NO2 column, the simulated weekend to weekday ratios are consistent with each other and match the observed ratios well. The modeling system exhibited reasonable performance in simulating the VOC compounds with fossil fuel origins but has larger bias in simulating certain species associated with noncombustion sources. The modeling system successfully captured the weekend changes of the enhancement ratios for various VOC species to CO and the relative changes of HOx, which are indicators of faster chemical processing on weekends. This work demonstrates satisfactory model performances for O3 and most relevant chemical compounds with more robust performance in simulating weekend versus weekday changes. Improved planetary boundary layer height simulations, a better understanding of OH‐HO2 cycling, continued improvement of emissions, especially urban biogenic emissions and emissions of oxygenated VOCs, are important for future model improvement.
Parameter Analysis and Estimates for the MODIS Evapotranspiration Algorithm and Multiscale Verification
Authors: Zhang Kun , Zhu Gaofeng , Ma Jinzhu , Yang Yuting , Shang Shasha , Gu Chunjie 
Published: February 2019

AbstractAccurate estimation of terrestrial evapotranspiration (E) is critical to understand the world's energy and water cycles. MOD16 is the core algorithm of the widely used global E data set (the Moderate Resolution Imaging Spectroradiometer [MODIS] E product). However, it exhibits considerable uncertainties in some regions. Based on the data from 175 flux towers, we identified the key parameters of the MOD16 algorithm using the Sobol’ sensitivity analysis method across biomes. The output of the MOD16 algorithm was sensitive to eight parameters. Among them, β, which is treated as a constant (0.2 kPa) across biomes in the original MOD16 algorithm, was identified as the parameter to which the algorithm was most sensitive. We used the differential‐evolution Markov chain method to obtain the proper posterior distributions for each key parameter across a range of biomes. The values of the key parameters for the different biomes were accurately estimated by differential‐evolution Markov chain in comparison with data from the flux towers. We then evaluated the performances of the original MOD16 and the optimized MOD16 and compared them at multiple spatial scales (i.e., site, catchment, and global). We obtained relatively consistent and more reliable E simulations using the optimized MOD16 at all three scales. In the future, more attention should be paid to uncertainties in the algorithm's structure and its parameterizations of soil moisture constraint, canopy resistance, and energy partitioning.
A CFD‐Based Mixing Model for Vegetated Flows
Authors: Sonnenwald F. , Guymer I. , Stovin V. 
Published: February 2019

AbstractThis paper provides a computational fluid dynamics (CFD)‐based modeling framework for predicting flow field, turbulence, and mixing characteristics within vegetated environments such as ponds and wetlands. The framework has been implemented within a commercial CFD code—ANSYS Fluent 19—via a set of user‐defined functions. Following the approach outlined by King et al. (2012, https://doi.org/10.1017/jfm.2012.113), the standard k‐ε turbulence closure model has been modified to capture the energy transfer at the vegetation/clear flow shear interface and within the vegetation. The implementation assumes that vegetation is vertical, but nonorthogonal flow in the horizontal plane is accounted for. Values for the drag coefficient and the mixing coefficients are estimated based on the vegetation stem diameter and density. Following Tanino and Nepf (2008, https://doi.org/10.1017/S0022112008000505), a switch has been incorporated to account for the fact that the relevant length scale changes from stem diameter to stem spacing as stem density increases. A set of model parameters is proposed, based on a reevaluation of previously published laboratory data and theoretical analysis. Five different experimental data sets are used to demonstrate that the model is able to predict mixing within fully vegetated systems and due to both vertical and horizontal shear layers. The framework was developed to provide a practical prediction tool for engineering purposes, in particular for the estimation of residence time distributions in real partially vegetated stormwater management ponds. Its implementation here within a commercial CFD package potentially facilitates application to complex pond geometries, including patches of different types of vegetation with different bulk stem diameter and density characteristics.
Taming chlorophylls by early eukaryotes underpinned algal interactions and the diversification of the eukaryotes on the oxygenated Earth
Authors: Kashiyama Yuichiro , Yokoyama Akiko , Shiratori Takashi , Hess Sebastian , Not Fabrice , Bachy Charles , Gutierrez-Rodriguez Andres , Kawahara Jun , Suzaki Toshinobu , Nakazawa Masami , Ishikawa Takahiro , Maruyama Moe , Wang Mengyun , Chen Man , Gong Yingchun , Seto Kensuke , Kagami Maiko , Hamamoto Yoko , Honda Daiske , Umetani Takahiro , Shihongi Akira , Kayama Motoki , Matsuda Toshiki , Taira Junya , Yabuki Akinori , Tsuchiya Masashi , Hirakawa Yoshihisa , Kawaguchi Akane , Nomura Mami , Nakamura Atsushi , Namba Noriaki , Matsumoto Mitsufumi , Tanaka Tsuyoshi , Yoshino Tomoko , Higuchi Rina , Yamamoto Akihiro , Maruyama Tadanobu , Yamaguchi Aika , Uzuka Akihiro , Miyagishima Shinya , Tanifuji Goro , Kawachi Masanobu , Kinoshita Yusuke , Tamiaki Hitoshi 
Published: February 2019

Abstract
Extant eukaryote ecology is primarily sustained by oxygenic photosynthesis, in which chlorophylls play essential roles. The exceptional photosensitivity of chlorophylls allows them to harvest solar energy for photosynthesis, but on the other hand, they also generate cytotoxic reactive oxygen species. A risk of such phototoxicity of the chlorophyll must become particularly prominent upon dynamic cellular interactions that potentially disrupt the mechanisms that are designed to quench photoexcited chlorophylls in the phototrophic cells. Extensive examination of a wide variety of phagotrophic, parasitic, and phototrophic microeukaryotes demonstrates that a catabolic process that converts chlorophylls into nonphotosensitive 132,173-cyclopheophorbide enols (CPEs) is phylogenetically ubiquitous among extant eukaryotes. The accumulation of CPEs is identified in phagotrophic algivores belonging to virtually all major eukaryotic assemblages with the exception of Archaeplastida, in which no algivorous species have been reported. In addition, accumulation of CPEs is revealed to be common among phototrophic microeukaryotes (i.e., microalgae) along with dismantling of their secondary chloroplasts. Thus, we infer that CPE-accumulating chlorophyll catabolism (CACC) primarily evolved among algivorous microeukaryotes to detoxify chlorophylls in an early stage of their evolution. Subsequently, it also underpinned photosynthetic endosymbiosis by securing close interactions with photosynthetic machinery containing abundant chlorophylls, which led to the acquisition of secondary chloroplasts. Our results strongly suggest that CACC, which allowed the consumption of oxygenic primary producers, ultimately permitted the successful radiation of the eukaryotes throughout and after the late Proterozoic global oxygenation.