Mixing Event Research Articles

Analyzing the Mineralogy and Space Weathering Characteristics of the Finest Fraction in Apollo Core Sample 73002

AbstractApollo 17 core sample 73001/2 was recently made available to researchers for analysis using state‐of‐the‐art techniques in the framework of a modern understanding of lunar surface processes. In this work, we employ transmission electron microscopic analysis to observe the mineralogy, microstructural, and chemical characteristics of space weathering and solar energetic particle (SEP) track distribution in soil grains in the <20 μm size fraction in core sample 73002. The modal mineralogy and stratigraphic space weathered grain abundance suggests that a geologically recent mixing event affected the top 3 cm of 73002. Surface exposure age distributions derived from SEP tracks demonstrate that individual regolith grains rarely reside on the surface for longer than ∼4 million years. The abundance of surface exposed monomineralic fragments with respect to depth correlates well with bulk measurements of space weathered soils using other techniques, such as ferromagnetic resonance. Exposure age distributions suggest the presence of two unique in situ reworking zones spanning the top 8 cm of the core and median exposure ages decrease with increasing depth for both reworking zones, albeit at different rates. These rates were compared to reworking models and suggest a relationship between median exposure age and reworking rate with respect to depth. Applications of modern transmission electron microscopy to core sample 73001/2 have proven useful in understanding lunar regolith evolution both within the context of the Apollo 17 field site and more broadly via in situ reworking.

The Foraminifera Fossil Record of the Sedimentary Rock at Kotadjawa, Lampung, Indonesia: The Significance of Marine Paleontological Insight

Kotadjawa, located on the west coast of Lampung, directly faces the Indian Ocean. Lithified calcareous sedimentary beds are prevalently outcropped along this coastline. These beds likely belong to the Simpangaur Formation, which may be associated with the paleocoastal depositional environment and tectonic uplift of the Indian Ocean. Therefore, we investigated the paleontological record, focusing on foraminifera as potential indicators of the paleoenvironment. This study aimed to identify, record, and calculate the relative abundance of benthic foraminifera in the sedimentary beds of Kotadjawa, Lampung. The samples were prepared via chemical treatment of 10% H2O2 for 48 hours. Our results revealed a diversity of benthic foraminiferal fossils within the sedimentary rock. Notably, 11 benthic foraminifera genera were fossilized in the observed outcrop: Textularia (18.4%), Sigmoilopsis (16.5%), Rectobolivina (15.4%), Uvigerina (15.5%), Nodosaria (14.5%), Elphidium (11.5%), Lenticulina (7.7%), Hormosina (6.8%), Bolivina (6.8%), and Globobulimina (5.8%). These results suggested that the sedimentary beds exposed in our study area ranging from the foreshore to the deep ocean floor ecosystem. This suggests that a sediment mixing event, possibly triggered by a paleocatastrophic event, influenced the deposition of these beds. This study provides new insights into marine paleoenvironmental conditions and paleocatastrophic events along the west coast of Lampung, Sumatra.

Early Thermal Histories of IAB Main Group Irons: Insights From Ca‐Phosphates in Campo del Cielo and Nantan

AbstractCa‐phosphates in Campo del Cielo (CdC) and Nantan were comprehensively studied to provide insights into the thermal histories of the IAB main group (MG) and related irons. In CdC, apatite grains are characterized by (a) close intergrowth with troilite/graphite in border area between silicate and metal in most cases and (b) near‐flat rare earth elemental patterns (LaN/YbN = 0.6–0.7). This indicates they were formed during a metal‐silicate mixing event at a relatively high temperature. Combining with petrographic textures, we suggest that the replacement of high‐Ca pyroxene by low‐Ca pyroxene at ∼950–1,000°C could release Ca and facilitate the formation of apatite grains. In the Nantan nodule, Ca‐phosphates do not share a similar origin with those in CdC, as indicated by their different mineral chemistries and mineral associations. Ca‐phosphates and associated silicates could crystallize from a P‐C‐S‐rich metallic melt with the oxidation of lithophile elements. Combining all analyses from CdC and Nantan yielded a SIMS Pb‐Pb isochron age of 4,558 ± 56 Ma. Considering that all the IAB‐MG irons experienced a rapid high‐temperature cooling process, the age of 4,558 ± 56 Ma provides another line of evidence that the parent body of IAB‐MG and related irons experienced metal‐silicate mixing in first 50 Myr of solar system. The previously reported Ar‐Ar ages of ≤4.47 Ga could be related to the late reheating process(es). The degrees of late shock heating may vary from specimen to specimen.

Lithium-rich Cepheid V470 Cas

In this Letter, we report the discovery of a new lithium-rich yellow supergiant star -- the Cepheid V470 Cas -- that has a high lithium abundance, $ A(Li)$ = 3.29. This is highly unusual for supergiant stars. V470 Cas is joining a very select group of lithium-rich Cepheids, with only nine members known to date in our Galaxy. For the analysis of our high-resolution echelle spectrum obtained at the Canada-France-Hawaii Telescope, methods based on both local thermodynamic equilibrium (LTE) and non-local thermodynamic equilibrium (NLTE) assumptions were applied. In particular, the lithium abundance was derived by analysing the equivalent width of the 6707 line. Most lithium-rich Cepheids are located near the blue edge of the instability strip near the bottom of the Hertzsprung--Russell diagram. Their main sequence progenitors are distributed over a mass range of three to five solar masses. Of the nine lithium-rich Cepheids known, six are double-mode pulsators, including our programme Cepheid. It is very likely that the stars of this small group are entering the instability strip for the first time and have not yet passed the red giant phase. Therefore, they have not experienced the large-scale mixing event that could destroy lithium in their convective zones.

Influence of rapid vertical mixing on bacterial community assembly in stratified water columns

Water column mixing homogenizes thermal and chemical gradients which are known to define distribution of microbial communities and influence the prevailing biogeochemical processes. Little is however known about the effects of rapid water column mixing on the vertical distribution of microbial communities in stratified reservoirs. To address this knowledge gap, physicochemical properties and microbial community composition from 16 S rRNA amplicon sequencing were analyzed before and after mixing of vertically stratified water-column bioreactors. Our results showed that α-diversity of bacterial communities decreased from bottom to surface during periods of thermal stratification. After an experimental mixing event, bacterial community diversity experienced a significant decrease throughout the water column and network connectivity was disrupted, followed by slow recovery. Significant differences in composition were seen for both total (DNA) and active (RNA) bacterial communities when comparing surface and bottom layer during periods of stratification, and when comparing samples collected before mixing and after re-stratification. The dominant predicted community assembly processes for stratified conditions were deterministic while such processes were less important during recovery from episodic mixing. Water quality characteristics of stratified water were significantly correlated with bacterial community diversity and structure. Furthermore, structural equation modeling analyses showed that changes in sulfur may have the greatest direct effect on bacterial community composition. Our results imply that rapid vertical mixing caused by episodic weather extremes and hydrological operations may have a long-term effect on microbial communities and biogeochemical processes.

Insight Into Geological Evolution of the Mesosiderite Parent Body From Olivine Alteration and Merrillite Pb‐Pb Age in Dong Ujimqin Qi

AbstractMesosiderites are thought to be created by a catastrophic impact that mixes the silicate crust with the metallic core of a differentiated asteroid(s). The metal‐silicate mixing event greatly affects the subsequent geological evolution of the mesosiderite parent body. To gain a better understanding of this mixing event, we carried out studies on olivine alteration and merrillite Pb‐Pb thermochronology in the Dong Ujimqin Qi mesosiderite. The primary olivine in this meteorite has been altered through sulfidation reactions, leading to the formation of troilite‐orthopyroxene intergrowths. This alteration likely took place during metal‐silicate mixing, as the mixing environment can provide favorable chemical and thermal conditions for this reaction. Phosphate‐chromite veins crosscutting the troilite‐orthopyroxene intergrowths indicate a secondary alteration process likely induced by subsequent impacts. Additionally, the metal‐silicate mixing event likely contributed to the occurrence of abundant merrillites at the boundary between silicates and Fe‐Ni metals, as supported by the distinctly depleted incompatible elements resulting from the redox reaction between metals and adjacent silicates. The ion microprobe analyses for these merrillites yielded a Pb‐Pb age of 4,064 ± 120 Ma, which is interpreted as the record of the Pb isotopic closure of merrillite during prolonged cooling associated with the deep burial. Our two‐stage cooling model suggests that the mesosiderite parent body's burial potentially started around 4.52 Ga, which is consistent with the Sm‐Nd, Ar‐Ar, and Pb‐Pb thermochronological records in mesosiderites.

Monazite and titanite U[sbnd]Pb ages of granitoids from the North Qinling Terrane: Implications for the subduction of the Shangdan Ocean and accretionary processes

The early Paleozoic granitoids of the North Qinling Terrane have been widely viewed as the products of an Andean-type margin related to the long-lasting subduction of the Proto-Tethys (Shangdan) ocean. However, the spatial and temporal distributions of the arc granitoids coupled with subduction-accretion processes are still a subject of debate. Here, we report LA-ICP-MS UPb monazite and titanite ages and trace element concentrations for granites and a paragneiss from the North Qinling Terrane. The results, together with data in the literatures, are used to reconstruct the magmatic evolution related to the subduction of the Shangdan ocean during the early Paleozoic. As revealed by UPb geochronology, subduction-related magmatism in the southern belt of the North Qinling magmatic arc (NQMA) was most active between 423 and 404 Ma, and therefore younger and shorter than previously speculated. The ages are in agreement with a metamorphic monazite UPb age (415 Ma) obtained from the paragneiss, suggesting that crustal anatexis of the NQMA was contemporaneous with the magmatism. Overall, magmatism in the NQMA moved progressively from north to south. This southward propagation is consistent with roll-back of the Shangdan oceanic slab and transition from an oceanic arc into a back-arc basin setting. The timing of magmatism and migmatization as well as high-temperature granulite metamorphism in the NQMA signifies that the Shangdan ocean retreated to the North Qinling Unit before c. 423 Ma. Monazites from NQMA generally show HREE depletion and negative Eu anomalies, and some display the REE tetrad effect. These geochemical features indicated that the NQMA granites were highly fractionated. In addition, the abrupt changes in REE compositions displayed by titanites probably record a mixing event with a mafic magma along the Shangdan suture zone.

Consider the Source: The Impact of Social Mixing on Drylot Housed Steer Behavior and Productivity.

Cattle are a social species in which social mixing can induce physical and psychosocial stress; however, the impact of social mixing on cattle welfare is unknown. Two different sources of genetically similar Angus crossbred steers were transported to the same feedlot and assigned to a pen where they were either socially mixed or housed with individuals from their source herds. Social mixing did not impact average daily gains in pens, feed intake, or feed efficiency; pens of socially mixed steers were more active. Sources differed in their responses to social mixing. One source was unaffected, whereas social mixing negatively impacted productivity for the other source. Irrespective of social mixing, the sources differed in the amount of time per day they spent ruminating and drinking. Group analyses indicated that socially mixing two sources of feedlot steers did not negatively impact group productivity, yet the impacts that were observed at the individual level suggest that prior experiences may influence their ability to cope with social stress, emphasizing the importance of early-life experiences to long-term welfare and productivity. Social mixing was not universally detrimental to cattle welfare, and the source of cattle may have the greatest affect on their performance regardless of whether a social mixing event has occurred.

Response of microbial community of surface and deep chlorophyll maximum to nutrients and light in South China Sea

In oligotrophic seas such as South China Sea, the subsurface or deep chlorophyll maximum (DCM) is always present. The surface planktonic community receives sufficient light, but is short of nutrients. The DCM layer is under light limitation, but frequent supply of nutrients. Therefore, vertical mixing becomes critical in determining their community composition and drives their changes by responding to light and nutrients. In this study, we conducted an onboard experiment by collecting seawater samples at surface and the DCM layer and adding nutrients, and incubated them under full sunlight and 10% light, and examined the diversity of bacterial and eukaryotic communities and their cell abundance using 16/18S high throughput sequencing and FCM approaches. Our study found large differences in bacterial and eukaryotic community structure and cell abundance between the surface and DCM. After 72 hours of culture, taxonomically the incubated surface water was dominated by pico-eukaryotic phytoplankton, while the incubated DCM layer water is dominated by diatoms, which suggests diatoms are the main functional group of phytoplankton bloom after a vertical mixing event. These findings indicate that phytoplankton at the DCM respond to enhanced light and frequent supplied nutrients due to vertical mixing and thus maintain primary productivity in the otherwise oligotrophic oceans.

Taxonomic Composition of Protist Communities in the Coastal Stratified Lake Kislo-Sladkoe (Kandalaksha Bay, White Sea) Revealed by Microscopy

Lake Kislo-Sladkoe is a stratified water body partly isolated from the White Sea. Perennial meromixis in the lake irregularly alternates with mixing events. Taking into account that the protists of Arctic coastal stratified water bodies are understudied, we evaluated for the first time the vertical structure, species richness, and diversity of protists assigned to different taxonomic groups in Lake Kislo-Sladkoe using light, luminescent, and scanning electron microscopy. To test the research hypothesis that a mixing event affects the vertical stratification and species composition of protists in a stratified lake, we compared the protist communities of Lake Kislo-Sladkoe in two extremely different states: strong meromixis vs. full vertical mixing. A total of 97 morphologically distinct phototrophic, heterotrophic, and mixotrophic protists were revealed with the most diverse supertaxa SAR (59), Obazoa (9), and Excavates (14). The hidden diversity of protists (43 species) was a bit less than the active diversity (54 species). A taxonomic list and micrographs of cells for the observed protists are provided. The majority of species revealed are cosmopolitan or widespread in the northern sea waters. The vertical patterns of protist communities were absolutely different in 2018 and 2021. In July 2018, clearly distinct protist communities inhabited different layers of the lake. Bloom of cryptophyte Rhodomonas cf. baltica was detected in chemocline, whereas the maximum density of its grazers was observed in adjacent layers, mainly dinoflagellates Gymnodinium sp. and Scrippsiella trochoidea, as well as a ciliate Prorodon sp. In 2021 due to the recent mixing of lake and seawater, there were no distinct communities in the water column except the superficial 0–1 m layer of fresh water.

Magnetite-manganoan ilmenite transformation and its implications for magma mixing and migmatization in the Assam-Meghalaya Gneissic Complex, Northeast India

The migmatites of Chandrapur area near Guwahati, which forms a part of the Assam-Meghalaya Gneissic Complex (AMGC) in Northeast India, have preserved magnetite ocelli. Petrographic observations have revealed that magnetite crystals occurring in the ocellar rock are surrounded by partial to complete thin rims of biotite. Moreover, mineral chemical analyses, backscattered electron images, and quantitative elemental mapping have revealed that magnetite crystals occurring in the ocellar rock have been extensively replaced by manganoan ilmenite at the periphery. From field observations, textural, and mineral chemical analyses, it has been inferred that invasion of hot, volatile-bearing pegmatitic magmas into thermally rejuvenated basement gneisses of the AMGC during the late Pan-African tectonothermal episode (ca. 530–450 Ma) induced very restricted partial melting in the gneissic rocks producing neosomes. The newly formed neosomes were then infiltrated by the nearby pegmatitic melts leading to mixing between the two melts. The mixing event facilitated transformation of magnetite to manganoan ilmenite owing to diffusion of elements like Mn and Ti from the neosome to the pegmatitic domains. Moreover, formation of ilmenite released surplus Fe hosted in the magnetite that combined with in situ K and Al, and diffusing Mg from the neosome to form biotite crystals around magnetite. From this study, it can be concluded that magnetite-manganoan ilmenite transformation may be considered as one of the petrogenetic indicators to decipher magma mixing events.

The Influence of Sea Ice Cover and Atlantic Water Advection on Annual Particle Export North of Svalbard

AbstractThe Arctic Ocean north of Svalbard has recently experienced large sea ice losses and the increasing prominence of Atlantic water (AW) advection. To investigate the impact of these ongoing changes on annual particle export, two moorings with sequential sediment traps were deployed in ice‐free and seasonally ice‐covered waters on the shelf north (NSv) and east (ESv) of Svalbard, collecting sinking particles nearly continuously from October 2017 to October 2018. Vertical export of particulate organic carbon (POC), total particulate matter (TPM), planktonic protists, chlorophyll a, and zooplankton fecal pellets were measured, and swimmers were quantified and identified. Combined with sensor data from the moorings, these time‐series measurements provided a first assessment of the factors influencing particle export in this region of the Arctic Ocean. Higher annual TPM and POC fluxes at the ice‐free NSv site were primarily driven by the advection of AW, higher grazing by large copepods, and a wind‐induced mixing event during winter. Higher diatom fluxes were observed during spring in the presence of sea ice at the ESv site. Along with sea ice cover, regional differences in AW advection and the seasonal presence of grazers played a prominent role in the biological carbon pump along the continental shelf off Svalbard.

Seasonality of water column methane oxidation and deoxygenation in a dynamic marine environment

Most of the methane input to the world’s oceans is intercepted by microorganisms in sediment and the overlying water column and oxidized before it has an opportunity to reach the atmosphere, where it acts as a greenhouse gas. The factors controlling methane consumption in the ocean are not well established and its biogeochemistry in dynamic marine environments is understudied in-part because of challenges in capturing spatial and temporal variability. Our study focused on the factors that structure methane’s biogeochemistry in a dynamic marine environment, the Santa Barbara Basin. The deep-water column of the Santa Barbara Basin experiences seasonal oxygen loss and episodic replenishment which we found to be major factors in structuring the accumulation of methane and the rate at which microorganisms consumed that methane. We found the gradual decline in oxygen that commonly occurs through the summer culminated with a pronounced accumulation of methane in the water column during the fall. Rates of methane oxidation remained low in summer, increased with the buildup of methane in fall, and remained elevated into spring, even after methane concentration had declined. However, results from methane oxidation kinetics experiments revealed a zero-order kinetic dependence on oxygen concentration, indicating that oxygen’s effect on methanotrophy at the ecosystem scale is likely indirect. We also captured an apparent mixing event during fall that drove spatial and temporal variability in oxygen, nitrate and methane concentrations in the Santa Barbara Basin, with stark variations at the investigated timescale of 8 days and along isobaths at a spatial scale of 7 km. Collectively, these results indicate the seasonal development and attenuation of a methanotrophic community associated with restricted circulation, but also of a spatiotemporal variability not previously appreciated for this environment.

Bacterioplankton response to physical stratification following deep convection

Dissolved organic carbon (DOC) produced by primary production in the sunlit ocean can be physically transported to the mesopelagic zone. The majority of DOC exported to this zone is remineralized by heterotrophic microbes over a range of timescales. Capturing a deep convective mixing event is rare, as is observing how microbes respond in situ to the exported DOC. Here, we report ship and Argo float observations from hydrostation North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) 2 Station 4 (N2S4; 47.46°N, 38.72°W), a retentive anticyclonic eddy in the subtropical region of the western North Atlantic. Changes in biogeochemistry and bacterioplankton responses were tracked as the water column mixed to approximately 230 m and restratified over the subsequent 3 days. Over this period, rapid changes in bacterioplankton production (BP) and cell abundance were observed throughout the water column. BP increased by 91% in the euphotic zone (0–100 m) and 55% in the upper mesopelagic zone (100–200 m), corresponding to 33% and 103% increases in cell abundance, respectively. Within the upper mesopelagic, BP upon the occupation of N2S4 (20 ± 4.7 nmol C L–1 d–1) was significantly greater than the average upper mesopelagic BP rate (2.0 ± 1.6 nmol C L–1 h–1) at other stations that had been stratified for longer periods of time. BP continued to increase to 31 ± 3.0 nmol C L–1 d–1 over the 3-day occupation of N2S4. The rapid changes in BP in the upper mesopelagic did not coincide with rapid changes in community composition, but the taxa that increased in their relative contribution included those typically observed in the epipelagic zone. We interpret the subtle but significant community structure dynamics at N2S4 to reflect how injection of labile organic matter into the upper mesopelagic zone by physical mixing supports continued growth of euphotic zone-associated bacterioplankton lineages on a timescale of days.

Copepod Diel Vertical Distribution in the Open Southern Adriatic Sea (NE Mediterranean) under Two Different Environmental Conditions

Diel vertical migration of the copepod the community was investigated in the open South Adriatic, in June 2020 and February 2021, under two very different hydrographical conditions. The influence of a winter wind-induced mixing event on copepod vertical migration at the species level was determined for the first time and compared to the situation in June when pronounced thermal stratification was observed. The samples were collected during a 24 h cycle in four depth layers from the surface down to 300 m depth, using a Nansen opening–closing net with 250-µm mesh size. In winter, the bulk of the copepod population remained in the epipelagic zone (0–100 m) over the entire 24 h cycle, with calanoids remaining the dominant group. An increasing trend of copepod standing stocks from midnight to early morning in the surface layer found in June is in agreement with previous records of copepod day–night variations in the Mediterranean Sea. Day–night differences in diversity and the number of taxa of the epipelagic area were more pronounced in June, confirming the higher intensity of diel vertical migration in summer. Although the epipelagic community was composed of numerous weak diel vertical migrant species, for the majority of investigated copepod taxa, migration patterns differed between the environmentally contrasting seasons. A multivariate non-metric analysis showed that the copepod community was strongly affected by temperature, thus exhibiting a clear seasonal structure.

Mica Types as Indication of Magma Nature, Central Anatolia, Turkey

AbstractThis study focuses on the nature of giant micas occurring at the contact between the Özvatan (foid‐bearing) syenites and the metamorphic basement in Central Anatolia. The studied micas are dark greenish‐black in color and crystallized within vein shape like bodies as a narrow lens. The origin and processes responsible for the formation of these independent crystals of the giant micas were investigated by mineralogical, petrographical and geochemical analyses with the use of Confocal Raman Spectroscopy (CRS), Fourier Transform Infrared (FTIR) Spectroscopy, X‐Ray Diffraction (XRD), Polarized Energy Dispersive X‐Ray Fluorescence Spectrometer (PED‐XRF) and Electron Probe Micro Analysis (EPMA). According to XRD, CRS, FTIR and EPMA data, the giant micas are phlogopite. EPMA results reveal that studied mica minerals represent the products of re‐equilibrated primary mica characterized by high MgO and FeO and low Al2O3 and TiO2 contents. The trace element concentrations of the giant micas display similar patterns with the upper crust. The giant micas are crystallized within small cubicles from an alkaline magma and their composition is possibly modified by a mixing event between the crust‐ and mantle‐derived magmas and contaminated at varying extent by the basement metamorphic rocks.

CAMPUR KODE PADA NOVEL RESIGN! (2018) KARYA ALMIRA BASTARI

The aims of this research are (1) to describe the form of code mixing in Resign! (2018) by Almira Bastari, (2) describes the function of code mixing in the novel Resign! (2018) by Almira Bastari.
 The approach used in this research is a qualitative approach. The qualitative approach in this study is to describe the form of code mixing and the function of code mixing. The data analysis technique used in this study is using library techniques and reading and note-taking techniques.
 The results of this study indicate that there is a code mixing event in the novel Resign! (2018) by Almira Bastari. First, the form of code mixing found in the novel Resign! (2018) by Almira Bastari totaling 251 data. The data specifically relates to the inclusion of elements of English into Indonesian. (1) mixed code in the form of words, there are 143 data, (2) mixed code in the form of phrases, there are 55 data, (3) mixed code in the form of clauses, there are 11 data, (4) mixed code in the form of repetition of words, there are 2 data, (5) mixed code in the form of expressions or idioms, there are 3 data, and (6) code mixing in the form of baster, there are 37 data. Second, the code mixing function contained in the novel Resign! (2018) Almira Bastari's work is (1) to respect the interlocutor there is 1 data, (2) to emphasize a certain intention there are 23 data, (3) to show self-identity there are 30 data, (4) as the influence of the subject matter there are 2 data, (5) as speech opponent specifications there are 192 data, (6) as quotations there are 3 data. As for the code mixing function, the inclusion of English elements into Indonesian as sentence inserts and as repetition was not found by the researchers.

Pre-Eruptive Conditions and Dynamics Recorded in Banded Pumices from the El Abrigo Caldera-Forming Eruption (Tenerife, Canary Islands)

Abstract The El Abrigo member of the Diego Hernández Formation (Tenerife, Canary Islands) represents the final (170 ka) and most voluminous eruption (>20-km3 DRE) of the last cycle of explosive activity of the Las Cañadas volcano. It is a dominantly phonolitic ignimbrite containing both mafic and banded pumices, suggesting that magma mixing played an important role in triggering the eruption and modulating eruptive dynamics. Here we use petrology, together with glass and mineral geochemistry of enclave-rich mafic scoriae, banded and phonolitic pumices from El Abrigo ignimbrite, to shed light on the pre-eruptive storage conditions and processes governing magma ascent and interaction dynamics and to provide a first-order assessment of the contribution of magma mixing and crystal mush melting to the dynamics of this eruptive event. The distribution of major elements in glasses is consistent with diffusive exchange between the interacting melts whereby Na transfers from the phonolite to the tephriphonolitic melt. However, V, Zr, Ba, and Eu suggest a complex scenario in which an intruding tephritic to phonotephritic magma interacted with two distinct zones of a phonolitic magma chamber, one occupied by a crystal-rich, low-Zr, and high-Ba phonolite, and the other by an evolved, crystal-poor, high-Zr phonolite. These results, coupled with mineral–melt thermobarometry, allow us to reconstruct the Las Cañadas plumbing system at the end of the Diego Hernández cycle and to evaluate the contribution of cumulate mush melting and magma mixing in as follows: (1) the parental tephritic magma was stored at or near the Moho (410–450 MPa) at 1050°C where it was periodically replenished by more primitive basanitic magma; (2) upon ascent, the tephrite intruded into a shallow and zoned phonolitic storage system, triggering the disruption of a crystal mush in its base; and (3) subsequently interacted with a crystal-poor zone within the reservoir. Energy balance evaluations suggest that relative mafic magma volume ratios ranged from 20 to 43 vol%, and the conservation of small-scale magma mingling structures and their geochemical distribution suggest that the mixing event took place very shortly before the eruption, on a timescale of hours.

Fast state detection in F1-ATPase rotation enhanced by theory of mixed states and external torque

During brief 120° transitions between long catalytic dwells, single F1-ATPase molecules exhibit angular jumps that vary with rotation angles. Using the angular jump profile enables the detection of fast states in the mechano-chemical scheme of the enzyme, states that are difficult to capture from single-molecule trajectories due to the fluctuations of the imaging nanoprobe. In a previous work, a short-lived, three occupancy state was postulated from a multi-state, probabilistic theory to explain the mean angular jump profile. An assumption in the theory was that the ‘mixing’ of chemical states is negligible during jumps. In a mixing event, two subsequent angular positions recorded by the imaging apparatus belong to two different chemical states of the motor enzyme due to fast reactions within a recording frame. In this paper, we provide an enhanced method for the detection of fast states. On one hand, we show using Langevin simulations that state mixing leads to faster mean angular jump, shifting up the profile. Consequently, the improved method provides a correction to the angular position and lifetime of the postulated three-occupancy metastable state. On the other hand, we show that when F1-ATPase is subject to torques opposing rotation in hydrolysis direction, the torques shift down the dwell angles without affecting the angle-dependent reaction rates. The torques improve detection capability for the fast state by increasing dwell times which is made evident by the flattening of the mean angular jump profile within 40°–60° from the catalytic dwell. In the three-occupancy state release of ADP occurs in concert with the binding of ATP to a different site in the F1-ATPase. Similarly, in the full ATP synthase when torques are created by the proton gradient in the FO region, the release of the product ATP is presumably accelerated by the binding of ADP to a different site in the F1 domain.

Observations of dissolved oxygen variability and physical drivers in a shallow highly stratified estuary

Evaluating the role of long-term anthropogenic changes on dissolved oxygen (DO) in coastal systems is often a challenge due to variability in a system and measurement sensitivity to spatial and temporal trends. Physical processes can significantly modify the DO variability and act as a major driver of uncertainty when it comes to quantifying the bio-chemical changes associated with the DO budget. Stratification has been observed to be a dominant factor in controlling the hypoxic conditions that can develop in Mobile Bay, AL, a shallow highly stratified estuary prone to episodic hypoxia. Using CTD transect data and long-term water quality monitoring stations the variability of DO was examined throughout Mobile Bay. This study examined the physical drivers of these trends and highlighted the role stratification, temperature, and advection play in driving the bay wide variability. Under stable conditions, the spatial trend in Mobile bay will reflect the along-estuary gradient. When stable conditions don't occur due to random episodic mixing events and cross estuary exchange, the Bay can be driven by a number of factors: the along-estuary gradients, time since the previous mixing event, level of stratification, and biochemical oxygen demand. The combination of these elements provides an increased understanding of the complex dynamics driving low DO in this system. Long-term trends show the DO is decreasing in Mobile Bay based on changes in DO in the shipping channel, northern region, and Bon Secour region.