Mixing Events Research Articles

Multistage fluid mixing events induced Sn polymetallic super-enrichment at Dulong in Yunnan Province, South China

Dulong Sn polymetallic deposit is a world-class skarn tin deposit situated at the Youjiang basin with a reserve of 0.4 Mt Sn at 0.56 %, 5.0 Mt Zn at 5.12 %, together with 7 kt In. The deposit predominantly occurs within the Neoproterozoic Xinzhaiyan Formation and is controlled by NS-trending faults. Based on elaborate field and petrographic observations, the Dulong Sn polymetallic deposit was divided into four mineralization stages: stage 1 (prograde stage), stage 2 (retrograde stage), stage 3 (quartz-sulfide stage) and stage 4 (carbonate stage). Tin mineralization primarily occurs as cassiterite during stage 2, with additional cassiterite-stannite formation noted in stage 3. Analysis of fluid inclusions across these stages reveals the evolutionary history of the mineralizing fluids and the precipitation mechanisms at Dulong. During stage 1, diopside hosts both daughter-bearing multiphase inclusions and vapor-rich inclusions. The daughter-bearing multiphase inclusions exhibit homogenization temperatures ranging from 510 to 574 °C and salinities between 44.7 and 49.6 wt% NaCl equiv., whereas the vapor-rich inclusions display homogenization temperatures of 573–586 °C and salinities from 2.9 to 4.0 wt% NaCl equiv., indicating a boiling fluid process. Cassiterite (stage 2) features primarily liquid-rich two-phase inclusions, with homogenization temperatures of 351–410 °C and salinities of 6.3–9.6 wt% NaCl equiv. These inclusions document the mixing of magmatic fluid with meteoric water, which is likely the principal mechanism driving initial tin mineralization. Similarly, the same type of inclusions is also recorded in cassiterite of stage 3. The homogenization temperature of the inclusions in cassiterite is 290–334 °C and the salinities of the inclusions is 3.4–8.4 wt% NaCl equiv. Comparatively, the temperature continued to decrease in stage 3, indicating that fluid mixing may have persisted during this stage which could also explain the occurrence of cassiterite and stannite in this stage. In addition, redox reaction where CO2 and/or As (III) serve as oxidants may also be another mechanism to exact cassiterite from ore-forming fluid. Our Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) data suggests that cassiterite of the Dulong deposit involves a variety of complex substitutional mechanism. Due to the differing geochemical properties of the elements and variations in their concentrations, there is an indication that two phases distinct mineralizing fluids may have been present. The varying geochemical properties and concentrations of elements such as Nb, Ta, Zr, Fe, In, and Ga align with microthermometric results, indicating a reduction in magmatic hydrothermal fluid contribution and/or a transition from high to low temperatures in the hydrothermal system. This variation is also likely attributable to fluid mixing processes.

Depth-dependent warming of the Gulf of Eilat (Aqaba)

The Gulf of Eilat (Gulf of Aqaba) is a semi-enclosed basin situated at the northern end of the Red Sea, renowned for its exceptional marine ecosystem. To evaluate the response of the Gulf to climate variations, we analyzed various factors including temperature down to 700 m, surface air temperature, and heat fluxes. We find that the sea temperature is rising at all depths despite inconclusive trends in local atmospheric variables, including the surface air temperature. The Gulf’s sea surface temperature (SST) warms at a rate of a few hundredths of a degree Celsius per year, which is comparable to the warming of the global SST and the Mediterranean Sea. The increase in sea warming is linked to fewer winter deep mixing events that used to occur more frequently in the past. Based on the analysis of the ocean-atmosphere heat fluxes, we conclude that the lateral advection of heat from the southern part of the Gulf likely leads to an increase in water temperature in the northern part of the Gulf. Our findings suggest that local ocean warming is not necessarily associated with local processes, but rather with the warming of other remote locations.

Community coalescence under variable hydrochemical conditions of the Chesapeake Bay shaped bacterial diversity and functional traits

Community coalescence related to bacterial mixing events regulates community characteristics and affects the health of estuary ecosystems. At present, bacterial coalescence and its driving factors are still unclear. The present study used a dataset from the Chesapeake Bay (2017) to address how bacterial community coalescence in response to variable hydrochemistry in estuarine ecosystems. We determined that variable hydrochemistry promoted the deterioration of water quality. Temperature, orthophosphate, dissolved oxygen, chlorophyll a, Secchi disk depth, and dissolved organic phosphorus were the key environmental factors driving community coalescence. Bacteria with high tolerance to environmental change were the primary taxa accumulated in community coalescence, and the significance of deterministic processes to communities was revealed. Community coalescence was significantly correlated with the pathways of metabolism and organismal systems, and promoted the co-occurrence of antibiotic resistance and virulence factor genes. Briefly, community coalescence under variable hydrochemical conditions shaped bacterial diversity and functional traits, to optimise strategies for energy acquisition and lay the foundation for alleviating environmental pressures. However, potential pathogenic bacteria in community coalescence may be harmful to human health and environmental safety. The present study provides a scientific reference for ecological management of estuaries.

42 Group sow housing considerations for improved survival and productivity

Abstract Group sow housing considerations for improved survival and productivity. The Australian pork industry decided in 2010 to voluntarily phase out stall housing for pregnant sows by 2017. The change was supported by extensive R&D by the Pork CRC for High Integrity Australian Pork and the time line was brought forward by two major retailers in Australia. For 85 to 90% of producers the transition was complete by 2019-2020 and sows were grouped at weaning or straight after mating. I reviewed the pertinent literature, interviewed many producers on what is required to make group housing successful for the sow and the producer and looked at trend from an Australian bench making project in some aspects of reproduction and sow mortality from 2006 to 2020. The research showed sows adapt to grouping and exhibit reduced aggressive behaviors, injuries and plasma indicators of stress within 4 to 5 d after mixing. During this period, it was all about space at mixing, grouping sows based on size/parity, ensuring they all receive adequate feed and familiarization with group housing by the sow and staff. Producers said it is all about ensuring sows are grouped on size/parity, feeding with many using ad libitum feeding for the week after mixing, space with a preference between 1.8 and 2.2 m2, flooring (slats preferred) and minimizing mixing events. Producers were split on the use of drop feeding and electronic sow feeders with opinions very divided. For drop feeding the preferred housing system comprised full length feeding stalls without a back gate. All producers said they would not go back to stalls. Most producers experienced a decline in farrowing rate and increased lameness during the transition. However, reproduction improved over time and sow mortality decreased. If the top 4 to 5 factors affecting aggressiveness and overall welfare are followed, group housing sows improves their welfare and does not reduce their reproductive performance or longevity. Detection of estrus can be more difficult in groups and a number of Australian producers have implemented the use of satiety blocks during the first 2 and last 2 wk of gestation to further improve welfare and meet retailer requirements. Mating in groups (not stalls) has also been reported to improve reproduction.

Evaluation of water quality and trophic status in relation to seasonal water mixing in a highland Lake Ardibo, Ethiopia.

The aim of the present study was to evaluate the spatio-temporal variability of various physical and chemical parameters of water quality and to determine the trophic state of Lake Ardibo. Water samples were collected from October 2020 to September 2021 at three sampling stations in four different seasons. A total of 14 physico-chemical parameters, such as water temperature, pH, dissolved oxygen (DO), electrical conductivity, turbidity, alkalinity, Secchi-depth, nitrate, ammonia, silicon dioxide, soluble reactive phosphorus, total phosphorus, chloride, and fluoride were measured using standard methods. The results demonstrated that temporal variation existed throughout the study period. Except for turbidity, the water quality of the lake varied significantly within the four seasons (ANOVA, p < 0.05). DO levels decreased significantly during the dry season following water mixing events. Chlorophyll-a measurements showed significant seasonal differences ranging from 0.58 μg L-1 in the main-rainy season to 8.44 μg L-1 in the post-rainy period, indicating moderate algal biomass production. The overall category of Lake Ardibo was found to be under a mesotrophic state with medium biological productivity. A holistic lake basin approach management is suggested to maintain water quality and ecological processes and to improve the lake ecosystem services.

Campur Kode dalam Lirik Lagu-Lagu Bagus Wirata: Kajian Sosiolinguistik

In recent years, the practice of code mixing in public communication in Bali has increased. Code mixing events can occur anytime and anywhere. One form of code mixing that has attracted attention is code mixing in pop song lyrics, especially Balinese pop songs. This is a concern in itself regarding the character of Balinese Pop songs, which were initially aimed at preserving Balinese art and culture, especially in terms of language, but have become something that seems to be forced solely for the sake of market demands. The formulation of the problem in this research is: 1) What is the form of code mixing in the lyrics of songs sung by Bagus Wirata 2) What factors encourage code mixing in the lyrics of songs sung by Bagus Wirata. The research approach used is an empirical method because the use of Balinese in the lyrics of Bagus Wirata's songs already exists naturally. The object of research in this research is the songs sung by singer Bagus Wirata. The data collection methods used were document study, observation and interviews.The research results are; 1. The form of code mixing in the lyrics of songs sung by Bagus Wirata is: The use of code mixing in the form of words is most often used in the lyrics of songs sung by Bagus Wirata with a total usage percentage of 63%. Code mixing in the form of clauses ranks second with a usage percentage of 19%. The remainder is code mixing in the form of phrases amounting to 13%, code mixing in the form of basters 3% and code mixing in the form of repeated words 2%. 2. Factors that encourage code mixing in the lyrics of songs sung by Bagus Wirata are; 1) language dominance, 2) language attitudes, 3) psycholinguistic motivation, 4) lack of equivalent words in Balinese, 5) commercial target market. 3. The impact of using code mixing on the Balinese language, namely; 1) destruction of the Balinese language system, 2) extinction of the Balinese language.

Intensification and shutdown of deep convection in the Labrador Sea were caused by changes in atmospheric and freshwater dynamics

Labrador Sea winter convection forms a cold, fresh and dense water mass, Labrador Sea Water, that sinks to the intermediate and deep layers and spreads across the ocean. Convective mixing undergoes multi-year cycles of intensification (deepening) and relaxation (shoaling), which have been also shown to modulate long-term changes in the atmospheric gas uptake by the sea. Here I analyze Argo float and ship-based observations to document the 2012-2023 convective cycle. I find that the highest winter cooling for the 1994-2023 period was in 2015, while the deepest convection for the 1996-2023 period was in 2018. Convective mixing continued to deepen after 2015 because the 2012-2015 winter mixing events preconditioned the water column to be susceptible to deep convection in three more years. The progressively intensified 2012-2018 winter convections generated the largest and densest class of Labrador Sea Water since 1995. Convection weakened afterwards, rapidly shoaling by 800 m per year in the winters of 2021 and 2023. Distinct processes were responsible for these two convective shutdowns. In 2021, a collapse and an eastward shift of the stratospheric polar vortex, and a weakening and a southwestward shift of the Icelandic Low resulted in extremely low surface cooling and convection depth. In 2023, by contrast, convective shutdown was caused by extensive upper layer freshening originated from extreme Arctic sea-ice melt due to Arctic Amplification of Global Warming.

Thermal stratification and meromixis in four dilute temperate zone lakes

Abstract. Four adjacent lakes (Arco, Budd, Deming, and Josephine) within Itasca State Park in Minnesota, USA, are reported to be meromictic in the scientific literature. However, seasonally persistent chemoclines have never been documented. We collected seasonal profiles of temperature and specific conductance and placed temperature sensor chains in two lakes for ∼1 year to explore whether these lakes remain stratified through seasonal mixing events and what factors contribute to their stability. The results indicate that all lakes are predominantly thermally stratified and are prone to mixing in isothermal periods during spring and fall. Despite brief, semi-annual erosion of thermal stratification, Deming Lake showed no signs of complete mixing from 2006–2009 and 2019–2022 and is likely meromictic. However, the other lakes are not convincingly meromictic. Geochemical data indicate that water in Budd Lake, which contains the most water, is predominantly sourced from precipitation. The water in the other three lakes is of the calcium–magnesium–bicarbonate type, reflecting a source of water that has interacted with the deglaciated landscape. δ18OH2O and δ2HH2O measurements indicate the lakes are supplied by precipitation modified by evaporation. Josephine, Arco, and Deming lakes sit in a valley with likely permeable sediments and may be hydrologically connected through wetlands and recharged with shallow groundwater, as no streams are present. The water residence time in meromictic Deming Lake is short (100 d), yet it maintains a large reservoir of dissolved iron, indicating that shallow groundwater may be an additional source of water and dissolved ions. All four lakes develop subsurface chlorophyll maxima layers during the summer. All lakes also develop subsurface oxygen maxima that may result from oxygen trapping in the spring by rapidly developed summer thermoclines. Documenting the mixing status and general chemistry of these lakes enhances their utility and accessibility for future biogeochemical studies, which is important as lake stratification and anoxia are becoming more prevalent due to changes in climate and land use.

Prandtl number effects on extreme mixing events in forced stratified turbulence

Relatively strongly stratified turbulent flows tend to self-organise into a ‘layered anisotropic stratified turbulence’ (LAST) regime, characterised by relatively deep and well-mixed density ‘layers’ separated by relatively thin ‘interfaces’ of enhanced density gradient. Understanding the associated mixing dynamics is a central problem in geophysical fluid dynamics. It is challenging to study LAST mixing, as it is associated with Reynolds numbers $Re := UL/\nu \gg 1$ and Froude numbers $Fr :=(2{\rm \pi} U)/(L N) \ll 1$ ( $U$ and $L$ being characteristic velocity and length scales, $\nu$ the kinematic viscosity and $N$ the buoyancy frequency). Since a sufficiently large dynamic range (largely) unaffected by stratification and viscosity is required, it is also necessary for the buoyancy Reynolds number $Re_{b} := \epsilon /(\nu N^{2}) \gg 1$ , where $\epsilon$ is the (appropriately volume-averaged) turbulent kinetic energy dissipation rate. This requirement is exacerbated for oceanically relevant flows, as the Prandtl number $Pr := \nu /\kappa = {O}(10)$ in thermally stratified water (where $\kappa$ is the thermal diffusivity), thus leading (potentially) to even finer density field structures. We report here on four forced fully resolved direct numerical simulations of stratified turbulence at various Froude ( $Fr=0.5, 2$ ) and Prandtl ( $Pr=1, 7$ ) numbers forced so that $Re_{b}=50$ , with resolutions up to $30\,240 \times 30\,240 \times 3780$ . We find that, as $Pr$ increases, emergent ‘interfaces’ become finer and their contribution to bulk mixing characteristics decreases at the expense of the small-scale density structures populating the well-mixed ‘layers’. However, extreme mixing events (as quantified by significantly elevated local destruction rates of buoyancy variance $\chi _0$ ) are always preferentially found in the (statically stable) interfaces, irrespective of the value of $Pr$ .

Insights into carbonate environmental conditions in the Chukchi Sea

Abstract. Healthy Arctic marine ecosystems are essential to the food security and sovereignty, culture, and wellbeing of Indigenous Peoples in the Arctic. At the same time, Arctic marine ecosystems are highly susceptible to impacts of climate change and ocean acidification. While increasing ocean and air temperatures and melting sea ice act as direct stressors on the ecosystem, they also indirectly enhance ocean acidification, accelerating the associated changes in the inorganic carbon system. Yet, much is to be learned about the current state and variability of the inorganic carbon system in remote, high-latitude oceans. Here, we present time series (2016–2020) of pH and the partial pressure of carbon dioxide (pCO2) from the northeast Chukchi Sea continental shelf. The Chukchi Ecosystem Observatory includes a suite of subsurface year-round moorings sited amid a biological hotspot that is characterized by high primary productivity and a rich benthic food web that in turn supports coastal Iñupiat, whales, ice seals, walrus (Odobenus rosmarus), and Arctic cod (Boreogadus saida). Our observations suggest that near-bottom waters (33 m depth, 13 m above the seafloor) are a high carbon dioxide and low pH and aragonite saturation state (Ωarag) environment in summer and fall, when organic material from the highly productive summer remineralizes. During this time, Ωarag can be as low as 0.4. In winter, when the site was covered by sea ice, pH was &lt;8 and Ωarag remained undersaturated under the sea ice. There were only two short seasonal periods with relatively higher pH and Ωarag, which we term ocean acidification relaxation events. In spring, high primary production from sea ice algae and phytoplankton blooms led to spikes in pH (pH &gt; 8) and aragonite oversaturation. In late fall, strong wind-driven mixing events that delivered low-CO2 surface water to the shelf also led to events with elevated pH and Ωarag. Given the recent observations of high rates of ocean acidification and a sudden and dramatic shift of the physical, biogeochemical, and ecosystem conditions in the Chukchi Sea, it is possible that the observed extreme conditions at the Chukchi Ecosystem Observatory are deviating from the carbonate conditions to which many species are adapted.

Magma Differentiation in Dynamic Mush Domains From the Perspective of Multivariate Statistics: Open‐ Versus Closed‐System Evolution

AbstractOpen‐conduit conditions characterize several of the most hazardous and active volcanic systems of basaltic composition worldwide, persistently refilled by magmatic inputs. Eruptive products with similar bulk compositions, chemically buffered by continual mafic inputs, nevertheless exhibit heterogeneous glass compositions in response to variable magma mixing, crystallization, and differentiation processes within different parts of the plumbing system. Here, we document how multivariate statistics and magma differentiation modeling based on a large data set of glass compositions can be combined to constrain magma differentiation and plumbing system dynamics. Major and trace elements of matrix glasses erupted at Stromboli volcano (Italy) over the last 20 years provide a benchmark against which to test our integrated petrological approach. Principal component analysis, K‐means cluster analysis, and kernel density estimation reveal that trace elements define a multivariate space whose eigenvectors are more readily interpretable in terms of petrological processes than major elements, leading to improved clustering solutions. Comparison between open‐ and closed‐system differentiation models outlines that steady state magma compositions at constantly replenished and erupting magmatic systems approximate simple fractional crystallization trends, due to short magma residence times. Open‐system magma evolution is associated with magma storage crystallinities that are lower than those associated with closed‐system scenarios. Accordingly, open‐system dynamics determine the efficient crystal‐melt separation toward the top of the reservoir, where eruptible melts continuously supply the ordinary activity. Conversely, a mush‐like environment constitutes the bottom of the reservoir, where poorly evolved magmas result from mixing events between mush residual melts and primitive magmas injected from deeper crustal levels.

Irreversible Mixing Induced by Geostrophic Turbulence over the Global Ocean

Abstract Two recently proposed mixing diagnostics are employed to estimate the global surface irreversible mixing based on particle and tracer simulation driven by satellite-derived geostrophic velocities. These two novel diagnostics, similar to the traditional dispersion diffusivity and Nakamura’s effective diffusivity but defined in a localized and instantaneous sense, have the following advantages: 1) they reconcile the theoretical discrepancies between Eulerian-, particle-, and contour-based diffusivities and 2) they do not rely on the stationary and homogeneous assumptions of the turbulent ocean and are free from traditional average operators (e.g., Eulerian time–space or along-contour mean). Our results show that evident discrepancies among these three types of diffusivities do emerge when employing traditional estimates. However, these discrepancies could be significantly mitigated with the adoption of new diagnostic methods, implying that the three types of diffusivities can be effectively reconciled within a global framework. Moreover, finescale mixing structures and transient elevated mixing events due to geostrophic stirring can be clearly identified by the two new diagnostics, in contrast to previous estimates that are spatially and/or temporally smoothed. In particular, it is interesting to note that large values of the new diagnostics usually occur along narrow filaments/fronts associated with mesoscale eddies, and elevated mixing is observed to be located at the periphery of eddies. Our study presents a novel revisit of the global surface mixing induced by geostrophic eddies with an emphasis on irreversibility and provides new insights into previous questions regarding different mixing diagnostics in the community. Significance Statement Previous estimates of eddy mixing over the global ocean, using particle-based, tracer-based, and Eulerian-based diffusivities, have shown evident discrepancies. By using recently proposed novel mixing diagnostics, this study demonstrates that the three types of diffusivity estimates agree well with each other, indicating a practical unification of the three types of diffusivities. Also, since the new mixing diagnostics do not involve any traditional average operator, the local and instantaneous mixing maps over the global ocean are presented here, in contrast to previous spatial- or temporal-averaged ones. These new insights can address several unresolved issues in the mixing community.

Ocean Mixing in a Shelf Sea Driven by Energetic Internal Waves

AbstractInternal waves drive ocean mixing and enhance the transport of heat, momentum and other tracers in shelf seas. We collected observations of mixing over a 30‐day period from three cross‐shore moorings placed on the 330, 200 and 150 m isobaths on the offshore side of a pelagic ridge on the Australian North West Shelf. The region is forced by energetic surface and internal tides, exhibits non‐linear internal waves, experiences flow‐topography interactions, and is subject to episodic intense wind events. This complex forcing drove energetic diapycnal mixing at all sites. We identified five dominant internal wave forcing categories: mode‐1 waves at low‐frequency (time scales from double the buoyancy period to 4 hr), mode‐1 waves at high‐frequency (HF) (time scales between the buoyancy period and double the buoyancy period), mode‐2 waves, internal bores, and internal hydraulic jumps. Overall, just 15% of mixing events accounted for 90% of the total observed heat flux over the record. Mixing during internal wave events accounted for as much as 50% of the total heat flux in some locations. Of the internal wave categories, HF mode‐1 waves were the most significant contributors to the total heat flux at all sites (∼20%). On the other hand, internal bores made significant contributions to mixing only at the 200 and 150 m moorings; they made no contribution to mixing at the 330 m mooring. At the shallowest mooring, the different internal wave categories all made similar contributions to the total flux, indicating an increasingly complicated relationship between the evolving internal wavefield and the mixing.

A volatile sulfur sink aids in reconciling the sulfur isotope mass balance of closed basin lakes

Sedimentary rocks from the early Eocene Green River Formation comprise the largest known lacustrine oil shale deposits, contain remarkably well-preserved fossils, and provide a unique record of climate evolution across the Early Eocene Climate Optimum, a period of high atmospheric CO2. The depositional environment of these intermountain lakes spanned from relatively fresh and fluvially influenced to expanded and stratified saline closed basin lakes under the influence of the Laramide orogeny and alternating humid and arid climatic conditions. As the surface area of the lakes expanded, alkalinity and salinity increased, with depositional cycles that linked to evaporative cycles and marked by an increasing abundance of organic matter-rich shales (TOC > 10 wt%). Simultaneously, an intriguing 20 ‰ positive shift in the sulfur isotope composition of sulfide minerals and organic sulfur is observed. Given that this trend cannot be simply explained by a change in the source of sulfate delivered to the basin, the evolution of biogeochemical sulfur cycling and the balance of fluxes in response to basin evolution remain unresolved. Here, we combine the sulfur isotope compositions of pyrite, organic sulfur, and carbonate-associated sulfate and molecular proxies of euxinia in samples from the Uinta basin's depocenter. We find that organic matter-rich sediments reflect deposition in a stratified water column with enhanced burial of pyrite and sulfurized organic matter, while organic-lean facies present evidence of, at least transiently, euxinic conditions reaching the photic zone during arid conditions presumably because of evaporation. As the lake became both saline-stratified and euxinic, we observe that δ34S values of all measured sulfur-bearing sedimentary proxies increase and evolve along a 1:1 line, a trend independent of facies that we interpret as reflecting a sulfate-limited system despite saline conditions. The isotopic mass balance of sulfur fluxes implies the existence of a sink of sulfur depleted in 34S that is spatially decoupled from burial in the depocenter. Modeling sulfur biogeochemical processes in a saline stratified lake system allows us to estimate that at least 50 % of the sulfur entering the lake could have been lost from the upper part of the euxinic water column where the fractionation factor imparted by microbial sulfate reduction is expressed. We propose that the overall isotopic enrichment of the system was caused by H2S degassing during arid climate intervals, presumably enhanced by transient water column mixing events. Further, episodic intrusion of euxinic bottom waters into the upper part of the water column might have triggered mass fish and plankton mortality, consequently facilitating the formation of these exceptionally fossiliferous and organic matter-rich rocks. Our study finds that volatile outgassing may be an underappreciated mechanism for the sulfur mass balance of stratified lacustrine systems.

Chronological and Mineralogical Records of the Langqi Pluton, Fuzhou: Constraints on the Magma Mixing Process

The mafic microgranular enclaves (MMEs) from Mesozoic intermediate-acid magmatic rocks, widely developed along the Fujian coast, are considered to be the results of large-scale crust–mantle interaction by magma mixing. This paper is based on zircon U-Pb chronology, along with zircon Hf isotope and mineral analyses for the host granite and MMEs from Langqi Island, in order to investigate the magma mixing mechanism of the Langqi pluton in Fuzhou, Southeast China. The results indicate that the MMEs were emplaced during the late Early Cretaceous (98.9 ± 2.2 Ma), identical to the age of the granite (100.1 ± 1.1 Ma) within the error range. The zircon εHf(t) values for the granite and MMEs are in the ranges of −2.1~0.0 and −1.7~+1.1. The zircon Hf isotope data indicate that both the granite and MMEs were predominantly derived from the ancient crustal basement of Cathaysia, with a partial mantle-derived contribution. The An values of plagioclase phenocrysts with oscillatory zoning patterns in the MMEs show oscillatory changes from the core to the rim, indicating multiple mixing events between the two magmas with different compositions. Amphiboles in the MMEs show characteristics of crust–mantle contamination, and the Ti migrated from the mafic magma with high concentration to the felsic magma with low concentration during the magma mixing process. Biotites in the host rock and MMEs belong to primary biotite, and they have relatively high MgO contents (ave. 12.78 wt.%) and relatively low FeOT/(MgO + FeOT) ratios (ave. 0.56), showing characteristics of crust–mantle contamination. The crust–mantle magma interaction in a crystal, mushy state played a significant role in controlling the formation and evolution of the Langqi pluton. The magmatism was predominantly sourced from mixing between the mantle-derived mafic magma and the crust-derived felsic magma during the subduction of the Paleo-Pacific Plate, resulting in the formation of the Langqi doleritic veins, granites, and MMEs.

Overlap between the Mid-Atlantic Bight Cold Pool and offshore wind lease areas

AbstractThe Mid-Atlantic Cold Pool is a seasonal mass of cold bottom water that extends throughout the Mid-Atlantic Bight (MAB). Formed from rapid vernal surface warming, the Cold Pool dissipates in the fall due to mixing events such as storms. The Cold Pool supports a myriad of MAB coastal ecosystems and economically valuable commercial and recreational fisheries. Offshore wind energy has been rapidly developing within the MAB in recent years. Studies in Europe demonstrate that offshore wind farms can impact ocean mixing and hence seasonal stratification; there is, however, limited information on how MAB wind development will affect the Cold Pool. Seasonal overlap between the Cold Pool and pre-construction wind lease areas at varying distances from shore in the MAB was evaluated using output from a data-assimilative ocean model. Results highlight overlap periods as well as a thermal gradient that persists after bottom temperatures warm above the threshold typically used to identify the Cold Pool. These results also demonstrate cross-shelf variability in Cold Pool evolution. This work highlights the need for more focused ocean modeling studies and observations of wind farm effects on the MAB coastal environment.

Instabilities Across the Agulhas Current Enhance Upward Nitrate Supply in the Southwest Subtropical Indian Ocean

AbstractThe Agulhas Current, like other western boundary currents (WBCs), transports nutrients laterally from the tropics to the subtropics in a subsurface “nutrient stream.” These nutrients are predominantly supplied to surface waters by seasonal convective mixing, to fuel a brief period of productivity before phytoplankton become nutrient‐limited. Episodic mixing events characteristic of WBC systems can temporarily alleviate nutrient scarcity by vertically entraining deep nutrients into surface waters. However, our understanding of these nutrient fluxes is lacking because they are spatio‐temporally limited, and once they enter the sunlit layer, the nutrients are rapidly consumed by phytoplankton. Here, we use a novel application of nitrate Δ(15–18), the difference between the nitrogen and oxygen isotope ratios of nitrate, to characterize three (sub)mesoscale events of upward nitrate supply across the Agulhas Current in winter: (1) mixing at the edges of an anticyclonic eddy, (2) inshore upwelling associated with a submesoscale meander of the Agulhas Current, and (3) overturning at the edge of the current core driven by submesoscale instabilities. All three events manifest as upward injections of high‐Δ(15–18) nitrate into the thermocline and surface where nitrate Δ(15–18) is otherwise low; these entrainment events are not always apparent in the other co‐collected data. The dynamics driving the nitrate supply events are common to all WBCs, implying that nutrient entrainment facilitated by WBCs is quantitatively significant and supports productivity in otherwise oligotrophic subtropical surface waters. A future rise in energy across WBC systems may increase these nutrient fluxes, partly offsetting the predicted stratification‐induced decrease in subtropical ocean fertility.

Heat content and temperature trends in the Mediterranean Sea as derived from Argo float data

The Mediterranean Sea is very sensitive to climatic changes due to its semi-enclosed nature and is therefore defined as one of the hotspots in future climate change projections. In this study, we use Argo float data to assess climatologies and trends in temperature and Ocean Heat Content (OHC) throughout the Mediterranean Sea and for specific sub-basins (e.g. Western and Eastern Mediterranean, Gulf of Lion, South Adriatic). The amount of the OHC, spatially averaged in bins of 1°x1° over the period from 2001 to 2020, increases from west to east in the Mediterranean Sea. Time series of temperature and OHC from 2005 to 2020, estimated in the surface and intermediate layers (5-700 m) and deeper layer (700-2000 m), reveal significant warming trends and an increase of OHC. The upper 700 m of the Mediterranean Sea show a temperature trend of 0.041 ± 0.012°C·yr-1, corresponding to an annual increase in OHC of 3.59 ± 1.02 W·m-2. The Western Mediterranean Sea (5-700 m) is warming fastest with an increase in temperature at a rate of 0.070 ± 0.015°C·yr-1, corresponding to a yearly increase in OHC of 5.72 ± 1.28 W·m-2. Mixing and convection events within convection sites and along boundary currents transport and disperse the temperature and OHC changes. Significant warming trends are evident in the deeper layers (700-2000 m) of the two deep convection sites in the Mediterranean Sea (Gulf of Lion, South Adriatic), with an exceptionally strong warming trend in the South Adriatic from 2013 to 2020 of 0.058 ± 0.005°C·yr-1, corresponding to a yearly increase in OHC of 9.43 ± 0.85 W·m-2. The warming of the different water masses will show its feedback on ocean dynamics and air-sea fluxes in the next years, decades, and even centuries as these warming waters spread or re-emerge. This will provide more energy to the atmosphere, resulting in more extreme weather events and will also stress ecosystems and accelerate the extinction of several marine species. This study contributes to a better understanding of climate change in the Mediterranean region, and should act as another wake-up call for policy makers and society.

Environmental controls on macrozooplankton and fish distributions over diurnal to seasonal time scales in the northern Barents Sea

We present acoustic observations obtained by bottom mounted echosounders at two locations in the northern Barents Sea and a third on the northern continental slope of the Barents Sea. Data collected over a period of approximately two years reveal significant variability in the density and depth distribution of pelagic macrozooplankton and fish. Variability over diurnal to seasonal timescales is related to light conditions, prevailing currents, water column characteristics (temperature, stability, and pycnocline depth) and to sea ice conditions. Of particular importance is the relative volume of Polar Water and Atlantic influenced water present at the mooring sites. On the northern continental shelf, above average concentrations of macrozooplankton and fish were observed during late summer and early autumn following ice melt, and during winter. Minimum densities of macrozooplankton and fish were observed during spring and early summer. These data demonstrate the persistent presence of a macrozooplankton community throughout the winter months in the northern Barents Sea. On the Great Bank full depth diel vertical migrations were observed throughout the Polar Night and under sea ice. At the two more northerly stations the density of the sound scattering layers performing diel vertical migrations and the vertical range of the migrations was greatest during the transition period between the polar night and mid-night sun periods. Superimposed on the seasonal variability in density distribution was significant shorter-term variability driven by hydrographic processes occurring over synoptic time scales. Significant mixing events, or changes in the prevailing current direction that lead to a change in water mass characteristics, forced changes in the concentration and depth distribution of macrozooplankton over periods of hours that were on occasion of similar magnitude to the seasonal variability. On the northern continental slope, a mesopelagic sound scattering layer more than 300 m thick at its seasonal maximum, was located for most of the year within the warm core of the Atlantic Water Boundary Current, ascending into the epipelagic zone for 5–6 weeks during summer. The density and thickness of this sound scattering layer were greatest during the late summer/early autumn and lowest during early spring. Fish-like scatterers were present, concentrated within the deeper regions of the sound scattering layer, during the winter months and during July.

Tracking Grade Heterogeneity in a Panel Cave Mine: A Reconciliation Study Investigating the Impact of Mixing from an Ore Sorting Perspective

Bulk ore sorting is a preconcentration method applied to bulk streams or batches of material. The effectiveness of bulk ore sorting relies on the degree of the naturally occurring in situ grade heterogeneity of an ore deposit. The blending of ore during mining and material handling degrades the in situ grade heterogeneity initially present in an orebody and reduces the potential to apply bulk ore sorting. Block and panel cave mines experience mixing from the establishment of caves to the delivery of the caved ore to concentrators. This study focused on tracking the grade heterogeneity and quantifying the impact of mixing on the sorting potential of the Cadia East panel cave mine via the reconciliation of the grade measurements performed at different locations. The results showed that the copper and gold grades were almost fully homogenized via various mixing events identified for the mine. The tracked grade heterogeneity values revealed that the mixing during material handling, which included ore blending according to mine planning, reduced the grade variability more drastically than the mixing within the caves. As the ore travelled from its original in situ location, the grade distributions gradually transformed, and the grades eventually normalized around the mean values. Only insignificant amounts of low-grade material that could have potentially been discarded were reported to the on-belt sensor located at the surface. The results of this study are significant for cave mines exploring sorting systems for preconcentration as they highlight how mixing can impact the variability in ore grades.