Mixed Layer Research Articles

Impact of Saharan Dust Intrusions on Atmospheric Boundary Layer Height over Madrid

Atmospheric pollution caused by aerosols deteriorates air quality, increasing public health risks. Anthropogenic aerosols are usually located within the atmospheric boundary layer (ABL), which presents a daytime evolution that determines the air pollutants’ vertical mixing of those produced near the surface and, therefore, their ground-level concentration from local sources. Precise and complete characterization of the mixing layer is of crucial importance for numerical weather forecasting and climate models, but traditional methods such as radiosounding present some spatial and temporal limitations. Better resolutions have been obtained using lidar, which provides the aerosol vertical distribution. A particular type of lidar, the ceilometer, has demonstrated continuous measurement capabilities, providing vertical profiles with sub-minute time resolution and several-meter spatial resolution. Advanced methods, such as the recently developed STRATfinder algorithm, are required to estimate the ABL height in the presence of residual layers. More complex situations occur due to the advection of aerosols (e.g., due to long-range transport of desert dust, volcanic eruptions, or pyrocloud convection), producing a lofted layer in the free troposphere that may remain decoupled from the local ABL but can also be mixed. Aerosol-based methods for determination of the ABL height are challenging in those situations. The main objective of this research is the assessment of the impact of Saharan dust intrusions on the ABL using ceilometer signals, over a period of four years, 2020–2023. The ABL height database, obtained from ceilometer measurements every hour, is analyzed based on the most frequent synoptic patterns. A reduction in the ABL height was obtained from high dust load days (1576 ± 876 m) with respect to low dust load days (1857 ± 914 m), although it was still higher than clean days (1423 ± 772 m). This behavior is further studied discriminating by season and synoptic patterns. These results are relevant for health advice during Saharan dust intrusion days.

A revised ocean mixed layer model for better simulating the diurnal variation in ocean skin temperature

Abstract. Sea surface temperature (SST) is a crucial parameter in climate, weather, and ocean sciences due to its decisive role in ocean–atmosphere interactions. Identifying errors in the prognostic scheme used by the current European Centre for Medium-range Weather Forecasts (ECMWF) model for predicting the diurnal variation in ocean skin temperature led to a revisit and revision of the ocean mixed layer (OML) model. Validation of the revised model was conducted by comparing simulated temperatures at the sub-skin level and 1 m depth with observations from shipborne infrared measurements and buoys. These comparisons revealed a strong correlation, with an absolute mean deviation of less than 0.1 K and a standard deviation under 0.5 K, which are found to be comparable to errors in satellite observations of SST. Given that these results are derived from the same model simulations, the error statistics for the simulated skin temperature and its diurnal variation should have the same degree of accuracy. Furthermore, the simulation results closely align with anticipated solar radiation distributions, whereas ERA5 ocean skin temperature shows a significant lack of alignment with solar radiation. Consequently, the revised OML model shows promising potential for improving the simulation of diurnal SST variations in weather and climate models.

Effects of Mesoscale Eddies on Southern Ocean Biogeochemistry.

The Southern Ocean is rich in highly dynamic mesoscale eddies and substantially modulates global biogeochemical cycles. However, the overall surface and subsurface effects of eddies on the Southern Ocean biogeochemistry have not been quantified observationally at a large scale. Here, we co-locate eddies, identified in the Meta3.2DT satellite altimeter-based product, with biogeochemical Argo floats to determine the effects of eddies on the dissolved inorganic carbon (DIC), nitrate, and dissolved oxygen concentrations in the upper 1,500m of the ice-free Southern Ocean, as well as the eddy effects on the carbon fluxes in this region. DIC and nitrate concentrations are lower in anticyclonic eddies (AEs) and increased in cyclonic eddies (CEs), while dissolved oxygen anomalies switch signs above (CEs: positive, AEs: negative) and below the mixed layer (CEs: negative, AEs: positive). We attribute these anomalies primarily to eddy pumping (isopycnal heave), as well as eddy trapping for oxygen. Maximum anomalies in all tracers occur at greater depths in the subduction zone north of the Antarctic Circumpolar Current (ACC) compared to the upwelling region in the ACC, reflecting differences in background vertical structures. Eddy effects on air-sea exchange have significant seasonal variability, with additional outgassing in CEs in fall (physical process) and additional oceanic uptake in AEs and CEs in spring (biological and physical process). Integrated over the Southern Ocean, AEs contribute 0.01 Pg C (7 ) to the Southern Ocean carbon uptake, and CEs offset this by 0.01 Pg C (2 ). These findings underscore the importance of considering eddy impacts in observing networks and climate models.

Tribo-oxidation mechanism of gradient nanostructured Inconel 625 alloy during high-temperature wear

The tribo-oxidation layer is typically formed at the contact interface of high temperature wear, which exhibits a significant effect on the friction behavior of gradient nanostructured (GNS) materials. This study systematically investigated the wear resistance, near-surface microstructure, and compositional changes of ultra-thick GNS Inconel 625 alloy subjected to surface mechanical rolling treatment (SMRT) under high-temperature sliding wear conditions. The experimental results indicated that as the temperature increased to 500 °C, a tribo-oxidation layer was formed on the surface of the GNS sample, thereby resulting in an abnormal increase in the coefficient of friction (COF) and a rapid decrease in the wear rate. The gradient nanostructures facilitated oxidation diffusion channels, promoting the formation of a protective Cr2O3 film and spinel oxides, reducing the wear rate. At lower temperatures, a rapidly formed Cr2O3 film shielded the matrix, forming a tribo-oxidation layer composed of Cr2O3 and nickel. At 800 °C, the tribo-oxidation layer exhibited complex structures, including glaze, spinel oxide, Cr2O3, and Cr2O3/Ni mixed layers. This complexity was attributable to the oxidation diffusion rate of the gradient nanostructures and tribo-oxide layers. The findings not only elucidated the tribo-oxidation mechanism of GNS nickel-based superalloys but also offered valuable insights for designing wear-resistant materials.

Simulations on perturbation growth and mixing of a shocked light fluid layer with two different interfaces

The Richtmyer–Meshkov instability of a light fluid layer with two different interface modes is studied numerically. By fixing the wavelength of the second interface (I2) while varying that of the first interface (I1), we examine distinct cases with identical wavelengths at both interfaces, as well as smaller or larger wavelengths at I1, to explore the effects of initial layer configurations on instability development. The larger wavelength interface significantly transmits modes to the smaller wavelength interface, whereas mode transmission in the reverse direction is limited. This results in two primary consequences: (i) the smaller wavelength interface and the overall mixing layer evolve periodically with the larger wavelength; (ii) compared to the identical wavelength case, the linear amplitude growth duration of I2 is slightly extended for the smaller I1 wavelength case, but significantly prolonged for the larger I1 wavelength case. The linear amplitude growth rate of I2 for all cases can be predicted by the model of Jacobs et al. [J. Fluid Mech., vol. 195, 23–42 (1995)]. For cases with identical wavelengths and larger I1 wavelengths, the collisions of finger structures at both interfaces occur earlier, suppressing the growth of mixing width at early times while enhancing the mixed mass. In the later stages, the overall mixing efficiency in these cases significantly declines, despite continuous increases in both mixing width and mixed mass. This decline is attributed to severe deformation of the mixing layer due to interactions between finger structures, confining intense mixing to localized regions.

Multiple effects of high efficiency solid inertants on fire hazard of the accumulated Mg dust layer

Due to low melting and boiling points and extreme reactivity in the chemical reaction of Mg powder, inert powders that have a significant inerting effect on Mg dust clouds can cause significant combustion enhancement of the accumulated Mg dust layer. To circumvent this unforeseen fire hazard, this research selects five types of inertants that have been demonstrated to exert an inerting effect on metal dust clouds and possess a potential flame-retardant effect on Mg dust layers. This research aims to investigate the effect of inert powders on Mg dust layers to identify an efficient inerting mechanism for Mg dust layers. The results indicate that the selection of inertants for Mg dust must be based on a comprehensive evaluation of their physical and chemical properties. The presence of substances with strong decomposition and decomposition products that readily produce gases will destroy the oxide crust on the surface of the accumulated Mg dust layer, thereby causing violent gas-phase combustion. In the case of highly chemically stable substances, the melting point is of primary importance. The formation of cracks in the oxide crust is also a consequence of the higher melting point of inertants, resulting in a combustion enhancement of the mixed dust layer. Inertants with a low melting point and a high boiling point demonstrate a high degree of inerting efficiency for Mg dust layers. The melting of the inert substances forms a liquid film, which prevents the Mg powder from coming into contact with the air surrounding and within the combustion zone. The results of this research are both instructive and valuable for preventing explosions in the process industry involving metal dust materials.

Structural and functional parameters of the Black Sea phytoplankton during the summer bloom of the coccolithophore Emiliania huxleyi

The aim of the study was to examine the main primary production indicators, describe the controlling factors and identify the conditions for the weak bloom of Emiliania huxleyi in the Crimea coast of the Black Sea during June – July 2022. The surface chlorophyll a (Chl a) varied between 0.3 to 1.5mgm-3 and primary production (PP) within 12–174mgC m-3 day-1. The integrated concentration of Chl a in the euphotic layer was 4–29mgm-2, and that of PP - 240–835mgC m-3 day-1. On average, 49% of Chl a was located bellow the photosynthetic zone. The relationship between integral PP and the total Chl a, nitrogen (nitrates and ammonium), phosphates and silicates in the euphotic layer, analyzed by a multiple regression, showed that 70% of the PP variability was accounted for by the first three variables. While the significance of total Chl a was the highest, followed by phosphates, nitrogen had a negligible effect and that of silicates was not detected. In the surface layer (0–1m), the total phytoplankton biomass was co-dominated by dinoflagellates, the large cell diatom Pseudosolenia calcar-avis and the coccolithophore E. huxleyi. A weak bloom of E. huxleyi (cell abundance 1.0–1.8·106 cells L-1) was detected at 11 out of the 23 sampling stations. The relatively large thickness of the upper mixed layer (about 10m on average) and phosphorus deficiency were the main factors limiting the bloom of this coccolithophore.

Contribution of High-mode Near-inertial Waves to Enhanced Typhoon-induced Sea Surface Temperature Cooling in the South China Sea

Sea surface temperature cooling (SSTC) is an important indicator of the ocean response to typhoons and is a factor in the evolution of typhoons. Understanding the intricate mechanisms underlying the SSTC induced by different typhoons is important. Based on the numerical simulation, we investigated the SSTC induced by typhoons Megi (2010), Linfa (2015), and Sarika (2011), which had relatively similar tracks in the South China Sea. As the strongest (weakest) typhoon, Megi (Sarika) induced the largest (smallest) SSTC, which is consistent with the traditional understanding that stronger typhoons usually induce larger SSTC than weaker typhoons. However, the SSTC induced by the moderate typhoon Linfa was nearly comparable to that induced by Megi, while Linfa had a wind power input an order of magnitude smaller. A comparison of near-inertial waves (NIWs) induced by Linfa and Megi showed that the former contained a larger proportion of high modes, substantially contributing to vertical shear. Consequently, the vertical mixing coefficient during Linfa reached one third of that during Megi. Because the SSTC is primarily influenced by vertical mixing, which is dominated by vertical diffusion at the mixed layer depth, the relatively strong vertical mixing coefficient and large temperature gradient during Linfa ultimately resulted in the SSTC nearly comparable to that induced by Megi. The results of this study enhance the understanding of typhoon-induced SSTC.

High-temperature abrasive wear behaviour of strengthened iron-aluminide laser claddings

Strengthened iron-aluminides (Fe3Al-based) show notable mechanical properties alongside good scratch hardness up to 600 °C. To investigate the influence of strengthening mechanisms for alternative high temperature wear resistant materials, laser metal deposited alloys based on Fe with 30 at.% Al were studied in detail. After cladding the Fe30Al base material and its alloys – with either 5 at.% Si, 5 at.% C or 3 at.% Ti combined with 6 at.% B – thorough investigations by scanning electron microscopy, electron backscatter diffraction, nanoindentation, hot hardness measurements, and high temperature scratch tests were performed.All alloyed Fe3Al-based claddings show increased strength. The highest overall hardness of ~405 HV10 exhibits the carbon-alloyed one containing a high fraction of Fe3AlC0.6 carbides. Contrary, the Ti + B alloyed as well as the Si-alloyed claddings are superior with their scratch hardness (especially at elevated temperatures), through the formation of TiB2 precipitates and pronounced solid solution strengthening, respectively. Wear tests reveal decreasing wear rates with increasing test temperatures (from 20 to 500 to 700 °C) for all alloyed Fe3Al-based claddings due to the formation of abrasive-containing mechanically mixed layers. Contrary, the reference cladding, cobalt-based Stellite 21 exhibits not only a higher wear rate but also increased ones upon increasing the test temperature. Detailed investigations show that the scratch hardness correlates with the wear resistance and that the incorporation of abrasive material into the wear-induced formation of mechanically mixed layers is highly beneficial. Due to this self-protection effect, the promising overall high temperature behaviour, combined with the alloying concept (no Co, Ni, or Cr), these alloyed Fe3Al-based claddings are promising candidates for sustainable wear protection outperforming currently used wear protection solutions.

Modelling global mesozooplankton biomass using machine learning

Mesozooplankton are a crucial link between primary producers and higher trophic levels and play a vital role in marine food webs, biological carbon pumps, and sustaining fishery resources. However, the global distribution of mesozooplankton biomass and the relevant controlling mechanisms remain elusive. We compared four machine learning algorithms (Boosted Regression Trees, Random Forest, Artificial Neural Network, and Support Vector Machine) to model the spatiotemporal distributions of global mesozooplankton biomass. These algorithms were trained on a compiled dataset of published mesozooplankton biomass observations with corresponding environmental predictors from contemporaneous satellite observations (temperature, chlorophyll, salinity, and mixed layer depth). We found that Random Forest achieved the best predictive accuracy with R2 and RMSE (Root Mean Standard Error) of 0.57 and 0.39, respectively. Also, the global distribution of mesozooplankton biomass predicted by the Random Forest model was more consistent with the observational data than other models. We used the Random Forest model to create a global map of mesozooplankton biomass which serves as a reference for validating process-based ecosystem models. The model outputs confirm that environmental factors, especially surface Chl a, a proxy for prey availability, significantly correlate with the spatiotemporal distribution of mesozooplankton biomass. The scaling relationship between the mesozooplankton biomass and Chl a can be used as an emergent constraint for model validation and development. Moreover, our model predicts that the global mesozooplankton biomass will decrease by 3% by the end of this century under the “business-as-usual” scenarios, potentially reducing fishery production and carbon sequestration. Our study contributes to predicting global mesozooplankton biomass and provides deep insights into the underlying environmental impacts on the distribution of mesozooplankton biomass.

Evidence for a Sharp CO Snow Line Transition in a Protoplanetary Disk and Implications for Millimeter-wave Observations of CO Isotopologues

Observations of CO isotopologue emission from protoplanetary disks at millimeter wavelengths are a powerful tool for probing the CO snow line, an important marker for disk chemistry, and also for estimating total disk gas mass, a key quantity for planet formation. We use simple models to demonstrate that the vertical thickness of an isothermal layer around the disk midplane has important effects on the CO column density radial profile, with a thick layer producing a sharp CO snow line transition. We simulate next-generation Very Large Array (ngVLA) and Atacama Large Millimeter/submillimeter Array (ALMA) images to show that this sharp change in the CO column density can be detected in the derivative of the radial profile of emission from optically thin CO isotopologue lines. We apply this method to archival ALMA observations of the disk around the Herbig Ae star HD 163296 in the C17O and C18O J = 1–0 and J = 2–1 lines to identify a sharp CO snow line transition near ∼80 au (0.″8 at 101 pc), and show the CO column density decreases by more than a factor of 20. This finding is consistent with previous inferences from the steep rise of N2H+ emission, which marks the location where CO depletes. We also demonstrate that the disk’s thermal structure introduces significant systematic uncertainty to estimates of total disk gas mass derived from these lines. The substantial improvement in sensitivity envisioned for the ngVLA over ALMA for observations of ground-state lines of CO isotopologues has the potential to extend this approach to a much larger population of disks.

Optimizing Stretchability and Electrical Stability in Bilayer-Structured Flexible Liquid Metal Composite Electrodes

Gallium-based liquid metals remain in a liquid state at room temperature and exhibit excellent electrical and thermal conductivities, low viscosity, and low toxicity, making them ideal for creating highly stretchable and conductive composites suitable for flexible electronic devices. Despite these benefits, conventional single-layer liquid metal composites face challenges, such as liquid metal leakage during deformation (e.g., stretching or bending) and limited elongation due to incomplete integration of the liquid metal within the elastomer matrix. To address these limitations, we introduced a bilayer structure into liquid metal composites, comprising a lower polydimethylsiloxane (PDMS) layer and an upper PDMS-liquid metal mixed layer. In the mixed layer, the liquid metal precipitates, forming a conductive network spanning both layers. This bilayer composite structure demonstrated significantly improved stretchability and elongation compared to pure PDMS or single-layer composites. Additionally, by adjusting the size and content of the liquid metal particles, we optimized the composite’s mechanical and electrical properties. Under optimal conditions, spherical liquid metal particles deform into elliptical shapes under tensile stress, increasing conductive pathways and reducing electrical resistance. The combined effects of the bilayer structure and particle shape deformation enhanced the composite’s stretchability and elongation, supporting its potential for flexible electronics applications.

Momentum Transport in Heterogeneous Forest Canopies

This study investigates the impact of spatial heterogeneity on momentum transport within forest canopies through wind tunnel experiments using 1:200 scale forest models. The models, crafted from 10 Pores Per Inch reticulated foam, emulate a leaf area index of 5.3 and include alternating patches and gaps of various sizes. Statistical results of the mean velocity profiles and velocity standard deviations show that the canopies develop a mixing layer. By employing lacunarity analysis to quantify spatial heterogeneity, we establish that the heterogeneity scale effectively represents variations in canopy height. The success of the lacunarity analysis as a metric is particularly noteworthy, providing a robust and practical measure of heterogeneity that can be easily applied in future research. Control volume analysis reveals that horizontal and vertical momentum advection terms rise as canopy heterogeneity increases, emphasizing its critical role in heterogeneous canopies and the possibility of describing this role using the lacunarity scale. The gaps also give rise to pressure terms through the local pressure gradient at each pattern. The study highlights the higher influence of gap size over heterogeneity scale on momentum flux. These insights contribute to improved parameterization of heterogeneous canopies in numerical weather prediction models, aiding in better representation of sub-grid scale processes and enhancing our understanding of canopy-atmosphere interactions.

On the importance of species immiscibility in mixing-layer dynamics at supercritical pressures

The mixing dynamics of injected propellants is a key factor in determining the ignition performance and combustion-instability response of rocket engines, internal combustion engines, and gas turbines. A key source of uncertainty in the prediction of phase-exchange dynamics is the immiscibility of the injected propellants at supercritical pressure conditions, which induces liquid/vapor phase separation and surface-tension dynamics. While experimental observations indicate the presence of liquid/vapor interfacial structures, this interfacial dynamics is typically neglected in numerical analyses. To address this issue, the objective of the present study is to systematically evaluate the importance of species immiscibility on the phase-exchange dynamics of cryogenic LOX/GH2 mixing layers at typical rocket engine injection conditions. This is accomplished by comparing simulations of (i) a recently developed interface-capturing Regularized-Interface Method (RIM) formulation, and (ii) the commonly employed Diffuse-Interface Method (DIM) formulation. Analysis shows that the interfacial dynamics significantly impact the atomization and mixing of the propellants in the near-injector region, which is not captured by the DIM formulation. The findings of this study extend to other immiscible injection systems, such as LOX/kerosene and hydrocarbon-fuel/air, thereby highlighting the importance of resolving species immiscibility in simulating high-pressure combustion engines.

INVESTIGATING LARGE-SCALE STRUCTURES IN TURBULENT MIXING LAYERS USING TWO-POINT CORRELATION

The formation and development of large-scale structures are primary research subjects in the study of turbulent mixing layers. Visualizing these structures based on published experimental data enhances the understanding of complex flow behaviors, which is the main objective of this article. The authors employed a two-point statistical correlation method to evaluate the size of large vortex structures along the interaction region. Additionally, the article provides a guide for analyzing the turbulent energy spectrum at selected fixed points. The calculations were performed using MATLAB software. The results indicate that at the beginning of the mixing layer, the vortices are small and highly anisotropic, with large-scale structures stretching in irregular directions. Further downstream, the vortices increase in size in all directions, and the degree of anisotropy decreases. In the self-similar region, isotropic states are almost achieved. The energy spectrum analysis findings align with Kolmogorov's theory of energy cascade in turbulent flow. The two-point statistical correlation method proves to be highly effective for analyzing structures within turbulent flows.

Microstructures along the Indian west-coast continental shelf: layering and vertical mixing

During the month of October, the West Indian Coastal Current (WICC) is in a stage of transition from equatorward to poleward flow. The sea surface salinity near the Indian Coast is lower in the south compared to the north. Whereas the sea surface temperature is higher in the north than in the south. A salinity maximum (SM, Salinity ≥ 35.7 psu) exists in the sub-surface between depth ranges of 50–80 m. In situ vertical microstructure profiles collected along the continental shelf off the West Coast of India (WCI) for the first time, are used in this study to characterize vertical mixing under these complex thermodynamic regimes. Estimated sectional mean (median) values of the dissipation rates of turbulent kinetic energy (ɛ) and thermal variance (χ) are in the range 10−9−10−8 (10−9−10−8) W kg−1 and 10−8−10−7 (10−9−10−8) °C2 s−1 respectively. Sectional mean (median) values of the diapycnal diffusivity (Kρ) and eddy thermal diffusivity (KT) are in the range 10−6−10−5 (10−6−10−5) m2 s−1 and 10−4−10−2 (10−6−10−4) m2 s−1, respectively. The barrier layer (BL) was observed at most of the measurement locations. The layering structures in the salinity profiles observed within BL indicate the phase of transition of halocline reformation. Experiments using a one-dimensional model suggest that this layering is caused by the mixing of surface freshwater (surface freshening caused by heavy rains) with mixed-layer water. Double diffusion with weak staircase structures in temperature and salinity is observed predominantly in the interior layer of the ocean in this region. The presence of SM at most stations, with its thickness decreasing from north to south, created conditions favorable for double-diffusive mixing. Signatures of salt fingering (SF) and diffusive convection (DC) were observed in 40% and 8% of the water column, respectively. Turbulent mixing in the column below the mixed layer (ML) is weak (KT≤10−6 m2 s−1) to moderate (KT∼10−4 m2 s−1), with some highly turbulent intermittent regions (KT∼10−2 m2 s−1) conducive to DC. The data presented here show the prevalence of two mixing regimes in the vertical: (1) vertical mixing of freshwater (due to rain) with the ambient mixed layer water, and (2) small-scale double-diffusive mixing due to contrasting temperature–salinity gradients predominantly in the ocean’s interior layer (below the isothermal layer).

Warming of newly-subducted subtropical mode water in the North Pacific was suppressed from 1999 to 2017

Abstract Subtropical mode waters are important water masses influencing the regional and global climate. By tracing water masses from the mixed layer into the deeper ocean in late winter, we identified the newly-subducted North Pacific Subtropical Mode Water (NPSTMW) and therefore investigated its temperature changes. The temperature of newly-subducted NPSTMW showed significant warming during 1981-1999, but the warming was suppressed during 1999-2017. The newly-subducted NPSTMW temperature generally agreed with the March-April mixed layer temperature in the subduction region, but was half a degree lower. A mixed layer heat budget analysis indicates that the suppressed warming was caused by the combination of reduced warming effects of shortwave radiation due to the deepened mixed layer, strengthening of sea surface latent heat loss due to the warmer sea surface and enhanced cooling effects of vertical entrainment due to the strengthened subsurface stratification in the subduction region. Our results imply that the oceanic response to global warming can exert a cooling effect on the newly-subducted NPSTMW through these three mechanisms. The shift in trends of the newly-subducted NPSTMW temperature has important implications for the climate variabilities and the marine ecosystem in the North Pacific.

A distributed and process-based model coupling water-sediment-antibiotic interactions to simulate dynamic source-transport-fate of antibiotics at catchment scale

A lack of hydro-biogeochemical models for catchment-scale antibiotic dynamics limits our mechanistic understanding of the transport and fate of antibiotics. This study addresses this gap by developing a distributed and process-based model that focuses on the complex water-sediment-antibiotic interactions. We applied the model to a typical agricultural catchment and selected tetracyclines (TCs) as the target antibiotics. Parameter sensitivity analysis demonstrated that source distribution, groundwater discharge, and water-soil/sediment partitioning were crucial processes. The multi-site performance evaluation generally proved the model's validity, though some overestimation of riverine concentration dynamics was observed. The grid-based distribution of the annual source inputs of the summation of the four TCs (∑4TCs) highly varied in space (μ = 3494.92 mg·ha−1·yr−1, σ = 4761.20 mg·ha−1·yr−1). About 99 % of the source inputs were retained in soil, with mixing layer as the largest reservoir and degradation as the primary loss pathway. Daily terrestrial discharged loading of ∑4TCs peaked with rainfall events. Surface runoff contributed more than 50 % of the terrestrial load of ∑4TCs in summer, while groundwater discharge dominated in other seasons. These results imply that the catchment-scale TCs dynamics are transport-limited rather than source-limited. Our model offers new insights into the high-resolution sources-transport-fate of antibiotics, aiding in developing strategies to mitigate antibiotic contamination.

Diverse impacts of sea ice and ice shelf melting on phytoplankton communities in the Cosmonaut Sea, East Antarctica

Abstract Antarctic sea ice and glacier melt profoundly impacts marine ecosystems. Our study in the Cosmonaut Sea summer measures seawater oxygen isotopes, size-fractionated chlorophyll-a, and phytoplankton communities. We quantify sea ice meltwater, meteoric water, and winter water contents using a Bayesian isotope-mixing model. Contrary to common belief, our findings suggest that the reduced net export of sea ice to the north and the basal melting of ice shelves have deepened the mixed layer in coastal waters, altering the survival depth of phytoplankton. Freshwater primarily stimulates phytoplankton growth by supplying dissolved iron rather than by increasing water stability, which influences the size distribution and species composition of the phytoplankton community. These insights highlight the complex interplay between freshwater inputs, nutrient dynamics, and phytoplankton communities, and are crucial for understanding the dynamics of Antarctic ecosystem and its vulnerability to climate change.

A three-axis regime diagram for quantitative analyses of the mixing field structure in laminar and turbulent combustion

The combustion characteristics and stability are affected primarily by the mixing field structure. The goal of many practical systems is to achieve higher stability by creating Inhomogeneous, Partially Premixed, and Stratified (IPPS) environments. A three-axis regime diagram is proposed in this work to describe the mixing field structure of the IPPS, the non-premixed, and the premixed environments. The proposed axes of the diagram are the mean, the fluctuations, and the 2-D gradients of the conserved scalar mixture fraction.Highly resolved two-dimensional measurements of the mixture fraction in highly stabilized burners with well-controlled mixture inhomogeneity using advanced Rayleigh scattering measurements are used in this study to investigate the abilities of the proposed diagram. The effects of the mixing level, equivalence ratio, and Reynolds number on the mixing field structure were investigated using this diagram adequately. The three-axis diagram provided quantitative detailed information on the mixing field structure at different operating conditions. In addition, the local mixing layer thickness data are extracted from the diagram based on the mixture fraction profiles and the corresponding mixture fraction gradients profiles in the mixture fraction space.The level of mixture inhomogeneity and equivalence ratio significantly affect the mixing field structure, while the effect of the Reynolds number in turbulent conditions is weak. The correlations between the local mixing layer thickness and the main operating parameters are observed using its PDFs. Reducing the level of mixture inhomogeneity reduces the maximum mixture fraction gradients at zero fluctuations of the mean mixture fraction. The correlations are clear for further analytical investigation. This study shows that the proposed three-axis diagram is a useful tool to investigate and analyze the mixing field structure of the IPPS regimes.