bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rapid variations in fluid chemistry constrain hydrothermal phase separation at the Main Endeavour Field
Authors: Love Brooke , Lilley Marvin , Butterfield David , Olson Eric , Larson Benjamin 
Published: December 2016

AbstractPrevious work at the Main Endeavour Field (MEF) has shown that chloride concentration in high‐temperature vent fluids has not exceeded 510 mmol/kg (94% of seawater), which is consistent with brine condensation and loss at depth, followed by upward flow of a vapor phase toward the seafloor. Magmatic and seismic events have been shown to affect fluid temperature and composition and these effects help narrow the possibilities for sub‐surface processes. However, chloride‐temperature data alone are insufficient to determine details of phase separation in the upflow zone. Here we use variation in chloride and gas content in a set of fluid samples collected over several days from one sulfide chimney structure in the MEF to constrain processes of mixing and phase separation. The combination of gas (primarily magmatic CO2 and seawater‐derived Ar) and chloride data, indicate that neither variation in the amount of brine lost, nor mixing of the vapor phase produced at depth with variable quantities of (i) brine or (ii) altered gas rich seawater that has not undergone phase separation, can explain the co‐variation of gas and chloride content. The gas‐chloride data require additional phase separation of the ascending vapor‐like fluid. Mixing and gas partitioning calculations show that near‐critical temperature and pressure conditions can produce the fluid compositions observed at Sully vent as a vapor‐liquid conjugate pair or as vapor‐liquid pair with some remixing, and that the gas partition coefficients implied agree with theoretically predicted values.
Geochemical and microstructural evidence for interseismic changes in fault zone permeability and strength, Alpine Fault, New Zealand
Authors: Boulton Carolyn , Menzies Catriona D. , Toy Virginia G. , Townend John , Sutherland Rupert 
Published: December 2016

AbstractOblique dextral motion on the central Alpine Fault in the last circa 5 Ma has exhumed garnet‐oligoclase facies mylonitic fault rocks from ∼35 km depth. During exhumation, deformation, accompanied by fluid infiltration, has generated complex lithological variations in fault‐related rocks retrieved during Deep Fault Drilling Project (DFDP‐1) drilling at Gaunt Creek, South Island, New Zealand. Lithological, geochemical, and mineralogical results reveal that the fault comprises a core of highly comminuted cataclasites and fault gouges bounded by a damage zone containing cataclasites, protocataclasites, and fractured mylonites. The fault core‐alteration zone extends ∼20–30 m from the principal slip zone (PSZ) and is characterized by alteration of primary phases to phyllosilicate minerals. Alteration associated with distinct mineral phases occurred proximal the brittle‐to‐plastic transition (T ≤ 300–400°C, 6–10 km depth) and at shallow depths (T = 20–150°C, 0–3 km depth). Within the fault core‐alteration zone, fractures have been sealed by precipitation of calcite and phyllosilicates. This sealing has decreased fault normal permeability and increased rock mass competency, potentially promoting interseismic strain buildup.
Formation of hydrothermal pits and the role of seamounts in the Guatemala Basin (Equatorial East Pacific) from heat flow, seismic, and core studies
Authors: Villinger H. W. , Pichler T. , Kaul N. , Stephan S. , Pälike H. , Stephan F. 
Published: December 2016

AbstractWe acquired seismic and heat flow data and collected sediment cores in three areas in the Guatemala Basin (Cocos Plate, Eastern Pacific) to investigate the process by which depressions (pits) in the sedimentary cover on young oceanic crust were formed. Median heat flow of 55 mW/m2 for the three areas is about half of the expected conductive cooling value. The heat deficit is caused by massive recharge of cold seawater into the upper crust through seamounts which is inferred from depressed heat flow in the vicinity of seamounts. Heat flow inside of pits is always elevated, in some cases up to three times (max. 300 mW/m2) relative to background. None of the geochemical pore water profiles from cores inside and outside of the pits show any evidence of active fluid flow inside the pits. All three areas originated within the high productivity equatorial zone and moved northwest over the past 15 to 18 Ma. Pits found in the working areas are likely relict dissolution structures formed by diffuse hydrothermal venting in a zone of high biogenic carbonate production which were sealed when they moved north. It is likely that these pits were discharge sites of “hydrothermal siphons” where recharging seamounts could feed cold seawater via the upper crust to several discharging pits. Probably pit density on the whole Cocos Plate is similar to the three working areas and which may explain the huge heat deficit of the Cocos Plate.
An experimental model of episodic gas release through fracture of fluid confined within a pressurized elastic reservoir
Authors: Rocco Stefano , Woods Andrew W. , Harrington Jon , Norris Simon 
Published: December 2016

AbstractWe present new experiments that identify a mechanism for episodic release of gas from a pressurized, deformable reservoir confined by a clay seal, as a result of the transition from bulk deformation to channel growth through the clay. Air is injected into the center of a thin cylindrical cell initially filled with a mixture of bentonite clay and water. For sufficiently dry mixtures, the pressure initially increases with little volume change. On reaching the yield stress of the clay‐water mixture, the lid of the cell then deforms elastically and an air‐filled void forms in the center of the cell as the clay is driven radially outward. With continued supply of air, the pressure continues to increase until reaching the fracture strength of the clay. A fracture‐like channel then forms and migrates to the outer edge of the cell, enabling the air to escape. The pressure then falls, and the clay flows back toward the center of the cell and seals the channel so the cycle can repeat. The phenomena may be relevant at mud volcanoes.
Automated force‐free flux rope identification
Authors: Smith A. W. , Slavin J. A. , Jackman C. M. , Fear R. C. , Poh G.‐K. , DiBraccio G. A. , Jasinski J. M. , Trenchi L. 
Published: December 2016

AbstractWe describe a method developed to automatically identify quasi force‐free magnetotail flux ropes from in situ spacecraft magnetometer data. The method locates significant (greater than 1σ) deflections of the north‐south component of the magnetic field coincident with enhancements in other field components. The magnetic field data around the deflections are then processed using Minimum Variance Analysis (MVA) to narrow the selection down to those that exhibit the characteristics of flux ropes. The subset of candidates that fulfills the requirements are then compared to a cylindrical, linear (constant‐α) force‐free model. Those that can be well approximated as force free are then accepted. The model fit also provides a measure of the physical parameters that describe the flux rope (i.e., core field and radius). This process allows for the creation of a repeatable, consistent catalog of flux ropes. Automation allows a greater volume of data to be covered, saving time and allowing the exploration of potential selection biases. The technique is applied to MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) magnetometer data in the Hermean magnetotail and successfully locates flux ropes, some of which match previously known encounters. Assumptions of the method and potential future applications are discussed.
Whistler mode waves upstream of Saturn
Authors: Sulaiman A. H. , Gurnett D. A. , Halekas J. S. , Yates J. N. , Kurth W. S. , Dougherty M. K. 
Published: December 2016

AbstractWhistler mode waves are generated within and can propagate upstream of collisionless shocks. They are known to play a role in electron thermodynamics/acceleration and, under certain conditions, are markedly observed as wave trains preceding the shock ramp. In this paper, we take advantage of Cassini's presence at ~10 AU to explore the importance of whistler mode waves in a parameter regime typically characterized by higher Mach number (median of ~14) shocks, as well as a significantly different interplanetary magnetic field structure, compared to near Earth. We identify electromagnetic precursors preceding a small subset of bow shock crossings with properties which are consistent with whistler mode waves. We find these monochromatic, low‐frequency, and circularly polarized waves to have a typical frequency range of 0.2–0.4 Hz in the spacecraft frame. This is due to the lower ion and electron cyclotron frequencies near Saturn, between which whistler waves can develop. The waves are also observed as predominantly right handed in the spacecraft frame, the opposite sense to what is typically observed near Earth. This is attributed to the weaker Doppler shift, owing to the large angle between the solar wind velocity and magnetic field vectors at 10 AU. Our results on the low occurrence of whistler waves upstream of Saturn also underpin the predominantly supercritical bow shock of Saturn.
Comparison between low‐pressure laboratory discharges and atmospheric sprites
Authors: Robledo‐Martinez A. , Garcia‐Villarreal A. , Sobral H. 
Published: December 2016

AbstractThe discharge of a charged dielectric in low‐pressure air has characteristics that resemble some of the features of mesospheric discharges. The dielectric discharges in steps when the pressure of the surrounding air is gradually reduced from nearly atmospheric to ~0.01 torr. The setup employed here decouples the discharge from the power supply, and, thanks to that, unique properties of the discharge manifest themselves. For example, in the pressure interval ~10–100 torr streamers are emitted from the surface of the dielectric but when the pressure decreases to 2–16 torr these are replaced by spherically symmetrical discharges that we call peonies. These have interesting properties, like (a) they do not produce electrical field, (b) they remain static, and (c) their size increases with decreasing pressure. The peonies are a type of discharge that has not been reported before. They resemble sprite beads and are assumed to consist of large avalanches that do not lead to the formation of a streamer. At further lower pressures, in the interval 0.01–0.1 torr, diffuse volume discharges were observed that have some morphological similarities with sprite halos and the top of columnar sprites. The spectrographic measurements carried out show that the discharges have bands from the first and second positive systems in N2 as well as lines of N2+. Quenching of the first negative system of N2 was observed at 3 torr. In this work it was also observed how a cosmic ray can go on to trigger a discharge inside the experimentation chamber.
Tsunamis generated by long and thin granular landslides in a large flume
Authors: Miller Garrett S. , Andy Take W. , Mulligan Ryan P. , McDougall Scott 
Published: December 2016

AbstractIn this experimental study, granular material is released down slope to investigate landslide‐generated waves. Starting with a known volume and initial position of the landslide source, detailed data are obtained on the velocity and thickness of the granular flow, the shape and location of the submarine landslide deposit, the amplitude and shape of the near‐field wave, the far‐field wave evolution, and the wave runup elevation on a smooth impermeable slope. The experiments are performed on a 6.7 m long 30° slope on which gravity accelerates the landslides into a 2.1 m wide and 33.0 m long wave flume that terminates with a 27° runup ramp. For a fixed landslide volume of 0.34 m3, tests are conducted in a range of still water depths from 0.05 to 0.50 m. Observations from high‐speed cameras and measurements from wave probes indicate that the granular landslide moves as a long and thin train of material, and that only a portion of the landslide (termed the “effective mass”) is engaged in activating the leading wave. The wave behavior is highly dependent on the water depth relative to the size of the landslide. In deeper water, the near‐field wave behaves as a stable solitary‐like wave, while in shallower water, the wave behaves as a breaking dissipative bore. Overall, the physical model observations are in good agreement with the results of existing empirical equations when the effective mass is used to predict the maximum near‐field wave amplitude, the far‐field amplitude, and the runup of tsunamis generated by granular landslides.
Mixing efficiency in the thermocline of lakes observed from eddy correlation flux measurements
Authors: Weck Julika , Lorke Andreas 
Published: December 2016

AbstractVertical mixing in the thermocline of lakes is poorly understood and most of the current knowledge is based on ex situ methods like laboratory measurements and simulations. Here we used the eddy correlation technique (EC) to directly measure oxygen and buoyancy fluxes in the thermocline of two lakes (Lake Scharmützelsee and Lake Arendsee in 2012 and 2013, respectively). Additionally, sets of temperature microstructure profiles (SCAMP) were measured during the EC deployments. We used these data to quantify the mixing efficiency as well as the turbulent diffusivity. The derived turbulent diffusivities from EC for the Prandtl number of DO were one order of magnitude higher than predicted by commonly applied parameterization, while the diffusivities for the Prandtl number of heat confirmed the parameterization. The results from EC and SCAMP showed strong differences which we attribute to the fact that SCAMP measurements reflect snapshots of the instantaneous turbulence field while EC provides a temporal average of the prevailing turbulence. Finally, we discuss problems of the EC and the inertial dissipation method in a strongly stratified environment and propose how they could be improved to resolve the full temporal variability of mixing in thermoclines.
The importance of deep, basinwide measurements in optimized Atlantic Meridional Overturning Circulation observing arrays
Authors: McCarthy G. D. , Menary M. B. , Mecking J. V. , Moat B. I. , Johns W. E. , Andrews M. B. , Rayner D. , Smeed D. A. 
Published: December 2016

AbstractThe Atlantic Meridional Overturning Circulation (AMOC) is a key process in the global redistribution of heat. The AMOC is defined as the maximum of the overturning stream function, which typically occurs near 30°N in the North Atlantic. The RAPID mooring array has provided full‐depth, basinwide, continuous estimates of this quantity since 2004. Motivated by both the need to deliver near real‐time data and optimization of the array to reduce costs, we consider alternative configurations of the mooring array. Results suggest that the variability observed since 2004 could be reproduced by a single tall mooring on the western boundary and a mooring to 1500 m on the eastern boundary. We consider the potential future evolution of the AMOC in two generations of the Hadley Centre climate models and a suite of additional CMIP5 models. The modeling studies show that deep, basinwide measurements are essential to capture correctly the future decline of the AMOC. We conclude that, while a reduced array could be useful for estimates of the AMOC on subseasonal to decadal time scales as part of a near real‐time data delivery system, extreme caution must be applied to avoid the potential misinterpretation or absence of a climate time scale AMOC decline that is a key motivation for the maintenance of these observations.
Satellite observation of particulate organic carbon dynamics on the Louisiana continental shelf
Authors: Le Chengfeng , Lehrter John C. , Hu Chuanmin , MacIntyre Hugh , Beck Marcus W. 
Published: December 2016

AbstractParticulate organic carbon (POC) plays an important role in coastal carbon cycling and the formation of hypoxia. Yet, coastal POC dynamics are often poorly understood due to a lack of long‐term POC observations and the complexity of coastal hydrodynamic and biogeochemical processes that influence POC sources and sinks. Using field observations and satellite ocean color products, we developed a new multiple regression algorithm to estimate POC on the Louisiana Continental Shelf (LCS) from satellite observations. The algorithm had reliable performance with mean relative error (MRE) of ∼40% and root mean square error (RMSE) of ∼50% for MODIS and SeaWiFS images for POC ranging between ∼80 and ∼1200 mg m−3, and showed similar performance for a large estuary (Mobile Bay). Substantial spatiotemporal variability in the satellite‐derived POC was observed on the LCS, with high POC found on the inner shelf (<10 m depth) and lower POC on the middle (10–50 m depth) and outer shelf (50–200 m depth), and with high POC found in winter (January–March) and lower POC in summer to fall (August–October). Correlation analysis between long‐term POC time series and several potential influencing factors indicated that river discharge played a dominant role in POC dynamics on the LCS, while wind and surface currents also affected POC spatial patterns on short time scales. This study adds another example where satellite data with carefully developed algorithms can greatly increase the spatial and temporal observations of important biogeochemical variables on continental shelf and estuaries.
Low‐CCN concentration air masses over the eastern North Atlantic: Seasonality, meteorology, and drivers
Authors: Wood Robert , Stemmler Jayson D. , Rémillard Jasmine , Jefferson Anne 
Published: December 2016

AbstractA 20 month cloud condensation nucleus concentration (NCCN) data set from Graciosa Island (39°N, 28°W) in the remote North Atlantic is used to characterize air masses with low cloud condensation nuclei (CCN) concentrations. Low‐CCN events are defined as 6 h periods with mean NCCN<20 cm−3 (0.1% supersaturation). A total of 47 low‐CCN events are identified. Surface, satellite, and reanalysis data are used to explore the meteorological and cloud context for low‐CCN air masses. Low‐CCN events occur in all seasons, but their frequency was 3 times higher in December–May than during June–November. Composites show that many of the low‐CCN events had a common meteorological basis that involves southerly low‐level flow and rather low wind speeds at Graciosa. Anomalously low pressure is situated to the west of Graciosa during these events, but back trajectories and lagged SLP composites indicate that low‐CCN air masses often originate as cold air outbreaks to the north and west of Graciosa. Low‐CCN events were associated with low cloud droplet concentrations (Nd) at Graciosa, but liquid water path (LWP) during low‐CCN events was not systematically different from that at other times. Satellite Nd and LWP estimates from MODIS collocated with Lagrangian back trajectories show systematically lower Nd and higher LWP several days prior to arrival at Graciosa, consistent with the hypothesis that observed low‐CCN air masses are often formed by coalescence scavenging in thick warm clouds, often in cold air outbreaks.
Contributions of volatile and nonvolatile compounds (at 300°C) to condensational growth of atmospheric nanoparticles: An assessment based on 8.5 years of observations at the Central Europe background site Melpitz
Authors: Wang Zhibin , Birmili Wolfram , Hamed Amar , Wehner Birgit , Spindler Gerald , Pei Xiangyu , Wu Zhijun , Cheng Yafang , Su Hang , Wiedensohler Alfred 
Published: December 2016

AbstractLong‐term measurements of particle number size distributions in combination with thermodenuder analysis have been performed since July 2003 at the Central European station of Melpitz, Germany. Up to the end of 2011, 20% of all investigated days during the 8.5 years of measurements showed new particle formation and subsequent growth. To investigate the role of various chemical compound candidates for condensational nanoparticle growth, we focused on nucleation events in which the measured size distributions with and without thermodesorption both showed growth patterns (accounting for up to ~85% of all nucleation events). In this study, particulate compounds that volatilize at 300°C were specifically defined as “volatile,” in contrast to “nonvolatile” compounds, which remain in the particulate phase after being heated to 300°C. A strong correlation between ambient temperature and growth rate associated with volatile substances (except gaseous sulfuric acid) was found, which implies the importance of organics (possibly oxidized biogenic organic compounds) in particle growth at Melpitz. The contributions of the volatile compounds to the growth rate due to condensation of gaseous sulfuric acid and organics were found to be about 19% and 47%, respectively. The remaining ~25% was attributed to nonvolatile residuals, which appear to form gradually during the particle growth process and are characterized as extremely low‐volatility compounds. The growth rate associated with volatile components exhibited significant seasonal variation, with the highest value during summertime, whereas the growth rate associated with the nonvolatile fraction showed less fluctuation.
Sources and composition of PM2.5 in the Colorado Front Range during the DISCOVER‐AQ study
Authors: Valerino M. J. , Johnson J. J. , Izumi J. , Orozco D. , Hoff R. M. , Delgado R. , Hennigan C. J. 
Published: December 2016

AbstractMeasurements of particulate matter (PM2.5) chemical composition were carried out in Golden, CO, during the Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER‐AQ) field study. Chemical composition was dominated by organic compounds, which comprised an average of 75% of the PM2.5 mass throughout the study. Most of the organic matter was secondary (i.e., secondary organic aerosol) and appears to derive predominantly from regional sources, rather than the Denver metropolitan area. The concentration and composition of PM2.5 in Golden were strongly influenced by highly regular wind patterns and the site's close proximity to the mountains (~5 km). This second factor may be the cause of distinct differences between observations in Golden and those in downtown Denver, despite a distance between the sites of only ~15 km. Concentrations of aerosol nitrate, ammonium, and elemental carbon increased significantly during the daytime when the winds were from the northeast, indicating a strong local source for these compounds. Local sources of dust appeared to minimally impact the Golden site, although this was not likely representative of other conditions in the Colorado Front Range. Conversely, dust that had undergone long‐range transport from the southwestern U.S. likely impacted the entire Colorado Front Range, including Golden. During this event, water‐soluble Ca2+ concentrations exceeded 1 µg m−3, and the PM2.5/PM10 ratio reached its lowest level throughout the study. The long‐range transport of wildfire emissions also impacted the Colorado Front Range for 1–2 days during DISCOVER‐AQ. The smoke event was characterized by high concentrations of organics and water‐soluble K+. The results show a complex array of sources, and atmospheric processes influence summertime PM in the Colorado Front Range.