Model Experiments Research Articles

Distinct Modulations of Northwest Pacific Tropical Cyclone Precipitation by Atlantic Multidecadal Oscillation and Interdecadal Pacific Oscillation

AbstractThe interdecadal variability of tropical cyclone precipitation (TCP) over the western North Pacific (WNP) has not been thoroughly explored in previous studies. Here, we show that the TCP variations are modulated by both the Atlantic Multidecadal Oscillation (AMO) and Interdecadal Pacific Oscillation (IPO) as evidenced by reanalysis data and model experiments. A clustering analysis of tropical cyclone tracks shows that the AMO dominates a dipole pattern of TCP anomalies in the South China Sea and along the coastal eastern China. Meanwhile, the IPO dominates TCP over the southeastern WNP. Further analyses show that the AMO, particularly its extratropical component, affects TCP over the WNP by triggering an eastward‐propagating Rossby‐wave train, resulting in a pair of anomalous gyres over the WNP. Contrastly, the IPO modulates TCP by stimulating tropical circulation anomalies via the tropical pathway. These findings shed light on improving near‐term TCP forecast and its regional influence on East Asia.

Mesoscale eddy modulation of winter convective mixing in the northern Arabian Sea

The formation of Arabian Sea High Salinity Water (ASHSW) during the winter monsoon in the northern Arabian Sea is driven by surface buoyancy loss, which increases surface density and triggers convective mixing. The depth of convective mixing is influenced by the interplay between surface cooling (buoyancy loss) and upper-ocean stratification. Mesoscale eddies present during winter can alter this stratification and modulate convective mixing. We investigated the impact of these eddies on convective mixing and ASHSW formation utilizing a combination of observations, data assimilative model results, and 1-D and 3-D model experiments. Our analyses consistently demonstrate that the depth of winter convective mixing is influenced by the stratification imposed by mesoscale features, resulting in distinct mixing characteristics. When subjected to identical buoyancy forcing, convective mixing associated with cyclonic eddies occurs at shallower depths compared to anticyclonic eddies. This difference is particularly pronounced during the peak period of convective mixing (January–February), exceeding 50 m, compared to the early stages (November–December). The combined effect of cyclonic and anticyclonic eddies generates spatially inhomogeneous convective mixing, which cannot be solely explained by buoyancy flux. These conclusions are supported by Argo observations and analyses of 1-D and 3-D model experiments. Overall, our study highlights the significant role of mesoscale eddies in modulating convective mixing and ASHSW formation in the northern Arabian Sea.

High-precision Lamb wave evaluation for corrosion damage with model-based Bayesian Optimization and Gaussian meta-modeling strategy

The presence of corrosion damage in metallic structures is a critical problem affecting system safety, which poses challenges for structural maintenance. Ultrasonic Lamb wave testing has shown many benefits, including high sensitivity and a large coverage area. However, multiple external factors are causing a mismatch between the imaging result and the actual damage. This study proposes a Bayesian Optimization-based model calibration framework, incorporating a Gaussian process (GP) measurement model, for accurate corrosion damage quantification. In this method, one critical problem is obtaining the high-fidelity Finite Element Method (FEM) model. The initial FEM model usually has inevitable modeling errors due to necessary simplifications and idealized constraints. Here we introduced Bayesian Optimization by which the numerical model could be calibrated. The calibrated FEM model, which had fewer discrepancies with actual experiments, could generate high-fidelity signals corresponding to various damage severity. Then, the GP measurement model outputted the mean and variance of the corrosion width and depth corresponding to the differences between experiment signals and model outputs. The inversion of damage information from the established GP model was accomplished by the genetic algorithm. Hence, both the damage size and depth could be evaluated with high accuracy. Once the corrosion information along different propagation paths was obtained, it can be combined with the location of the corrosion damage center for locating the edge points of the corrosion damage. In the end, the edge points were fitted using the least square algorithm. Validations were experimentally performed, and the detection result showed good consistency with the actual damage.

Research on Resistance Characteristics of Fire Zone of Mine Tunnel Fire and Construction of Calculation Model

To investigate resistance change in the fire area of a roadway caused by roadway fires, a mathematical calculation model for thermal resistance is developed. Theoretical research is conducted to analyze the factors influencing resistance change through theoretical derivation, revealing that temperature is a key factor contributing to the change in thermal resistance. By leveraging the correlation between changes in CO concentration and temperature on the downwind side of the roadway within the fire zone, researchers developed mathematical models to predict temperature increases at various points downwind of the fire source. These models were then used to determine the mathematical relationship governing the change in thermal resistance. The accuracy of the numerical simulation software was validated using Fluent numerical simulation software and scaled-down model experiments. Full-scale numerical simulation experiments were conducted to investigate the fire characteristics of roadway fires and validate the thermal resistance mathematical model. The results indicate that the thermal resistance in the numerical simulation is 7.55 Pa at 20m from the fire source and 5.54 Pa at the end of the roadway. The decrease in resistance is linear. The minimum error between the thermal resistance calculated by the mathematical model and the gradient of the pressure drop in the numerical simulation is 0.03 Pa, approximately 2.3%. Furthermore, the fitting degree of the pressure drop in each section is as high as 97.7%. The calculation model demonstrates high accuracy and offers a theoretical foundation for investigating fire resistance in tunnel fire.

Cavity shape measurement on propeller blade surface by combination line CCD camera measurement method

ABSTRACT A new combination-line-CCD camera method has been developed to accurately measure three-dimensional propeller blade cavitation shapes and volumes, which strongly correlate with pressure fluctuations. The effectiveness of this system was validated through model experiments conducted in NMRI's large cavitation tunnel using a propeller for a 749GT coastal vessel. The accuracy was verified by comparing the estimated pressure fluctuation, derived from the cavity volume, with the pressure sensor measurements. In the estimation, the unsteady cavity is replaced by a moving spherical bubble with a varying radius, and the pressure fluctuation induced by the sphere is calculated. Applying the proposed method to the experimental cavity shape data yielded pressure fluctuation estimates that closely matched the pressure sensor measurements. This result demonstrates the strong correlation between the time variability of the cavity volume and the pressure fluctuation induced by cavitation in the model tests.

Scour at the rear side of rubble mound revetments due to random wave overtopping: Laboratory experiments

This study presents the physical model experiments on the wave overtopping induced bed level changes at an unprotected rear side of a rubble mound revetment with a crown wall. In the experiments, the wave conditions, the backfill material size, and the backfill depth (vertical distance from the crest level to the rear side bed level) are varied. Two mobility parameters, namely the densimetric overtopping discharge and the relative fall velocity, are introduced to represent the initiation of motion and suspension of the backfill material, respectively. The temporal evolution of scour depth at the rear side is related to the mobility parameter, the number of waves and the backfill depth utilizing regression analyses. The effect of the backfill depth on the scour is found very limited for the available data set. However, the time scale of the scour is found to be related with the backfill depth only. For the present data set, it varied within a range of 1500–16000 number of waves approximately, with an average of 5600 waves. An equilibrium scour profile is reached 3 to 4 times the time scale. The geometry of the scour profile is expressed in terms of the scour depth, based on the equilibrium scour profile data.

Consolidation behaviour of marine clay improvement by combined vacuum preloading with geotextile

ABSTRACT The traditional vacuum preloading method of prefabricated vertical drain (PVDs) has been widely used in practical engineering. However, the serious clogging effect around PVDs in the process of vacuum-preloading reinforcement can easily lead to a series of problems such as uneven settlement and large lateral displacement of soil after reinforcement, which seriously affects the application of PVDs in marine clay foundation treatment. In this paper, the effect of combined treatment of marine clay by geotextiles and PVDs on reducing the clogging effect around PVDs was studied by laboratory model experiment. The effects of geotextiles with different diameters and spacings on the surface settlement, excess pore water pressure and lateral displacement of the reinforced soil were analysed. The experimental results show that this method has obvious help on alleviating the above problems, thus providing a reference for the application of geotextile combined with vacuum preloading method to treat marine clay foundation in engineering practice.

Experimental verification about treatment of Bu-Shen-Yi-Jing-Fang in Alzheimer’s disease by the analysis of the feasible signaling pathway of network pharmacology

ContextBu-shen-yi-jing-fang (BSYJF) has been reported to reduce amyloid-β (Aβ)1–42 deposition in the brain of APP/PS1 mice and ameliorate cognitive function. However, its neuroprotective mechanism remains unclear.ObjectiveThis study aims to investigate whether BSYJF exerts a protective effect on Aβ1–42-induced oxidative stress injury and explore its possible mechanism.Materials and methodsThe platform databases TCMSP, Swiss, TTD, DrugBank, and GeneCards were used to mine the targets of Alzheimer’s disease (AD) and BSYJF. The platform databases STRING and Metascape were used to build the interaction network of the target protein, and Cytoscape software was used to analyze this network and screen out the key pathways. Aβ1–42-treated SKNMC cells were established to verify the mechanism of BSYJF and the key proteins. The downstream proteins and antioxidants as well as apoptosis and ferroptosis of the PI3K/AKT/Nrf2 signaling pathway were validated using an in vitro SKNMC cell model experiment. The expression levels of related proteins were detected using Western blotting. Flow cytometry and immunofluorescence staining were used to analyze apoptosis and ferroptosis.ResultsKyoto encyclopedia of genes and genomes (KEGG) pathway enrichment analysis considered the key signal pathways, mainly involving the PI3K/AKT signaling pathway. Experimental validation demonstrated that BSYJF treatment markedly increased the activity of the PI3K/AKT pathway, which could exert anti-AD effects.ConclusionsOur data provided compelling evidence that the protective effects of BSYJF might be associated with their regulation of the PI3K/AKT/Nrf2 signaling pathway. These studies offered a potential therapy for natural herbal medicine treatment of AD.

An experimental mystery and a model experiment on ocean acidification – implemented in the KOALa student lab

An experimental mystery and a model experiment on ocean acidification – implemented in the KOALa student lab

Research on Response Characteristics of GPR Method for Detecting Phreatic Lines in Embankments

The excessive elevation of the phreatic lines under continuous high-water levels is the cause of many dangerous situations in embankments. Therefore, accurately understanding the dynamic changes in the infiltration characteristics of embankments is of great significance for judging and evaluating the stability of engineering. This study conducted indoor model experiments and used ground penetrating radar to detect the phreatic lines of soil. By comparing the radar detection results with the measured position of the phreatic lines, it was determined that the phreatic lines appeared as a continuous strong reflection surface with similar shapes in the radargram, and the reflection below the reflection surface became weaker. Through time-domain analysis of the single waveform at different time points, it was found that the amplitude of the reflected wave at the saturation line was larger, and the energy attenuation below the saturation line was faster, resulting in a rapid decrease in amplitude; perform Fourier transform on a single channel signal to obtain a spectrogram, and perform frequency domain analysis on it. The main frequency is around 600MHz, and the second main frequency is around 900MHz. As the saturation line rises, the main frequency gradually shifts towards lower frequencies.

An effective LC-MS method for the simultaneous determination of a potential anti-rheumatoid arthritis drug, carboxyamidotriazole, and its major metabolite in rat plasma.

Carboxyamidotriazole (CAI) was previously recognized as a well-tolerated anticancer drug. It has also demonstrated significant anti-inflammatory effects in various cell and animal model experiments, prompting its investigation as a potential treatment for rheumatoid arthritis. In this study, the potential biotransformation metabolites of CAI were identified both in vitro and in vivo. A sensitive, specific, and accurate LC-MS method was developed for the quantitative analysis of CAI and its major metabolite, CAI-OH, in rat plasma. CAI, CAI-OH, and telmisartan (used as an internal standard) were separated using a Zorbax SB C18 column. The mobile phase consisted of water (phase A, containing 0.1% formic acid) and acetonitrile (phase B, containing 0.1% formic acid) at a flow rate of 0.2 mL/min. The analytes were examined using a high-resolution mass spectrometer, with detected mass-to-charge ratios of m/z 424.01293 for CAI, m/z 440.00785 for CAI-OH, and m/z 515.24415 for telmisartan. Good linearity was observed within the range of 10-5000 ng/mL. Both inter- and intra-batch precision (relative standard deviation, %) were below 6%, and the accuracy ranged from 94.9% to 106.1%. The analytes remained stable throughout the entire experimental period. This method was successfully applied in a pharmacokinetic study of CAI following oral administration in rats.

Efficient two-way fluid–structure interaction simulation for performance prediction of pressure-compensating emitter

Drip irrigation using a high-performance pressure-compensating (PC) emitter is one of the essential components for precision agriculture, and it is necessary to accurately predict its performance prior to design. In this study, an efficient two-way fluid–structure interaction (FSI) simulation model was developed and verified through an enlarged model experiment. The computational fluid dynamics (CFD) and computational solid mechanics (CSM) models of the FSI simulation were systematically verified, and a calibration method for the overestimated flow rate in the re-rising range was applied. The CFD model was determined to be the shear stress transport turbulence model, and the CSM model was determined to be the Ogden hyperelastic model for the PC emitter. The minimum prediction error for the flow rate was 7.93%, which was within 10% for all cases. The simulation model demonstrated its efficiency by analysing the performance of a single PC emitter with an average total analysis time of 18.6 h. In addition, by comparing various cases according to the design parameters, it is considered that the hardness of the diaphragm has a significant impact on the design of low-pressure PC emitters. The simulation model of this study can accurately predict the performance of PC emitter under specific conditions, yet improvement of simulation model is required to be applied in design optimisation. Future studies may benefit from combining an improved FSI simulation with a surrogate model to further enhance optimisation efforts.

Higher Education 4.0: The Digital Transformation of Classroom Lectures to Blended Learning

Published by the Springer Nature Singapore Pte Ltd. in 2021, the book entitled “Higher Education 4.0 : The Digital Transformation of Classroom Lectures to Blended Learning” by Kevin Anthony Jones and Ravi S. Sharma presents an enlightening research for seeking out the impact of changing the instructional design from traditional lecturing to blended learning on the students’ academic achievements. As professional teacher and researchers of English in education, we read this book with particular interests, believing that it is a well-timed international publication under the global effects of the Covid-19 pandemic on teaching forms. The book under review exhibits a well-organized research project based on scientific experiment model, indicating the objectives, scope, methodology and findings of the research through 7 chapters. It provides readers with a thrilling opportunity to dig out the influencing factors in academic performances of students due to the teaching design transition. Besides, the significant findings can help improve the blended learning model. We believe this book is an essential guidance for future digital teaching and would appeal to educators and researchers.

Therapeutic effect and mechanisms of traditional Chinese medicine compound (Qilong capsule) in the treatment of ischemic stroke

Background Qilong capsule (QLC) is a well-known traditional Chinese medicine compound extensively used in clinical practice. It has been approved by the China's FDA for the treatment of ischemic stroke (IS). In our clinical trial involving QLC (ClinicalTrials.gov identifier: NCT03174535), we observed the potential of QLC to improve neurological function in IS patients at the 24th week, while ensuring their safety. However, the effectiveness of QLC beyond the initial 12-week period remains uncertain, and the precise mechanisms underlying its action in IS have not been fully elucidated.Purpose In order to further explore the clinical efficacy of QLC in treating IS beyond the initial 12-week period and systematically elucidate its underlying mechanisms.Study Design This study employed an interdisciplinary integration strategy that combines post hoc analysis of clinical trials, transcriptome sequencing, integrated bioinformatics analysis, and animal experiments.Methods In this study, we conducted a post-hoc analysis with 2302 participants to evaluate the effectiveness of QLC at the 12th week. The primary outcome was the proportion of patients achieving functional independence at the 12th week, defined as a score of 0–2 on the modified Rankin Scale (mRS), which ranges from 0 (no symptoms) to 6 (death). Subsequently, we employed RNA sequencing (RNA-Seq) and quantitative reverse transcription polymerase chain reaction (RT-qPCR) techniques in the QLC trial to investigate the potential molecular mechanisms underlying the therapeutic effect of QLC in IS. Simultaneously, we utilized integrated bioinformatics analyses driven by external multi-source data and algorithms to further supplement the exploration and validation of QLC's therapeutic mechanism in treating IS. This encompassed network pharmacology analysis and analyses at the mRNA, cellular, and pathway levels focusing on core targets. Additionally, we developed a disease risk prediction model using machine learning. By identifying differentially expressed core genes (DECGs) between the normal and IS groups, we quantitatively predicted IS occurrence. Furthermore, to assess its protective effects and determine the key regulated pathway, we conducted experiments using a middle cerebral artery occlusion and reperfusion (MACO/R) rat model.Results Our findings demonstrated that the combination of QLC and conventional treatment (CT) significantly improved the proportion of patients achieving functional independence (mRS score 0–2) at the 12th week compared to CT alone (n = 2,302, 88.65 % vs 87.33 %, p = 0.3337; n = 600, 91.33 % vs 84.67 %, p = 0.0165). Transcriptome data revealed that the potential underlying mechanism of QLC for IS is related to the regulation of the NF-κB inflammatory pathway. The RT-qPCR results demonstrated that the regulatory trends of key genes, such as MD-2, were consistent with those observed in the RNA-Seq analysis. Integrated bioinformatics analysis elucidated that QLC regulates the NF-κB signaling pathway by identifying core targets, and machine learning was utilized to forecast the risk of IS onset. The MACO/R rat model experiment confirmed that QLC exerts its anti-CIRI effects by inhibiting the MD-2/TLR-4/NF-κB signaling axis.Conclusion: Our interdisciplinary integration study has demonstrated that the combination of QLC with CT exhibits significant superiority over CT alone in improving functional independence in patients at the 12th week. The potential mechanism underlying QLC's therapeutic effect in IS involves the inhibition of the MD-2/TLR4/NF-κB inflammatory signaling pathway, thereby attenuating cerebral ischemia/reperfusion inflammatory injury and facilitating neurofunctional recovery. The novelty and innovative potential of this study primarily lie in the novel finding that QLC significantly enhances the proportion of patients achieving functional independence (mRS score 0–2) at the 12th week. Furthermore, employing a "multilevel-multimethod" integrated research approach, we elucidated the potential mechanism underlying QLC's therapeutic effect in IS.

Wetting of the retinal surface by perfluorocarbon liquid: implications for its use as an endotamponade agent and intraoperative tool in retinal detachment surgery

Perfluorocarbon liquids (PFCLs) are essential in ophthalmology due to their unique properties, such as higher density than water, inert chemical nature, and optical transparency. They serve as crucial tools in retinal detachment surgery, acting as both intraoperative aids and short-term tamponade agents. However, the interactions between PFCLs and the retinal surface are not fully understood, limiting insights into potential complications. This study investigates the interfacial interaction between perfluorodecalin (PFCL) and the retinal surface. Wetting behavior of animal retinas by water and PFCL was analyzed, revealing water droplets’ floating phenomenon in PFCL and calculating the critical radius for this effect. Dynamics of water spreading over the retina were examined. A model experiment demonstrated that water’s tendency to float over PFCL, interacting with a hydrophilic surface like the retina, could create traction and damage the retinal surface. These findings enhance our comprehension of physical processes at the PFCL/retina interface and offer practical insights for improving ophthalmic surgical procedures.

Model experimental study on special frequency of hydraulic pump working condition headcover for ultra-high head pump-turbine

Abstract With the accelerated construction of pumped-storage power stations, high-head and high-capacity pumped-storage units are gradually becoming the mainstream of development. When operated on-site, the high-head and high-capacity pumped-storage units reflect the phenomenon of special frequency of the head cover vibration of the water pump, which has attracted widespread attention from the industry. In order to deeply reveal the flow mechanism of pumped-storage units, model experiments on the head cover were conducted through the similarity conversion principle between the model and the prototype. The experiment results show that the occurrence of specific frequency in the Head cover of the water pump during operation is due to the rotating flow separation in the vaneless area.

Experimental investigation of dynamic characteristics of leaching tubing for solution mining of salt cavern carbon and energy storage

Salt caverns are extensively utilized for storing various substances such as fossil energy, hydrogen, compressed air, nuclear waste, and industrial solid waste. In China, when the salt cavern is leached through single-well water solution mining with oil as a cushion, engineering challenges arise with the leaching tubing, leading to issues like damage and instability. These problems significantly hinder the progress of cavern construction and the control of cavern shape. The primary cause of this is the flow-induced vibration instability of leaching tubing within a confined space, which results in severe bending or damage to the tubing. This study presents a model experimental investigation on the dynamic characteristics of leaching tubing using a self-developed liquid-solid coupling physical model experiment apparatus. The experiment utilizes a silicone-rubber pipe (SRP) and a polycarbonate pipe (PCP) to examine the effects of various factors on the dynamic stability of cantilevered pipes conveying fluid. These factors include external space constraint, flexural rigidity, medium outside the pipe, overhanging length, and end conditions. The experiments reveal four dynamic response phenomena: water hammer, static buckling, chaotic motion, and flutter instability. The study further demonstrates that the length of the external space constraint has a direct impact on the flutter critical flow velocity of the cantilevered pipe conveying fluid. Additionally, the flutter critical flow velocity is influenced by the end conditions and different external media.

Impact of injection pressure and polyaxial stress on hydraulic fracture propagation and permeability evolution in graywacke: Insights from discrete element models of a laboratory test

Understanding the hydromechanical behavior and permeability stress sensitivity of hydraulic fractures is fundamental for geotechnical applications associated with fluid injection. This paper presents a three-dimensional (3D) benchmark model of a laboratory experiment on graywacke to examine the dynamic hydraulic fracturing process under a polyaxial stress state. In the numerical model, injection pressures after breakdown (postbreakdown) are varied to study the impact on fracture growth. The fluid pressure front and crack front are identified in the numerical model to analyze the dynamic relationship between fluid diffusion and fracture propagation. Following the hydraulic fracturing test, the polyaxial stresses are rotated to investigate the influence of the stress field rotation on the fracture slip behavior and permeability. The results show that fracture propagation guides fluid diffusion under a high postbreakdown injection pressure. The crack front runs ahead of the fluid pressure front. Under a low postbreakdown injection pressure, the fluid pressure front gradually reaches the crack front, and fluid diffusion is the main driving factor of fracture propagation. Under polyaxial stress conditions, fluid injection not only opens tensile fractures but also induces hydroshearing. When the polyaxial stress is rotated, the fracture slip direction of a fully extended fracture is consistent with the shear stress direction. The fracture slip direction of a partly extended fracture is influenced by the increase in shear stress. Normal stress affects the permeability evolution by changing the average mechanical aperture. Shear stress can induce shearing and sliding on the fracture plane, thereby increasing permeability.

Laboratory Earthquakes Simulations—Emergence, Structure, and Evolution of Fault Heterogeneity

AbstractSeismic faults are known to exhibit a high level of spatial and temporal complexity, and the causes and consequences of this complexity have been the topic of numerous research works in the past decade. In this paper, we investigate the origins and the structure of this complexity by considering a numerical model of laboratory earthquake experiment, where we introduce a fault with homogeneous mechanical properties but allow it to evolve spontaneously to its natural level of complexity. This is achieved by coupling the elastic deformability of the off‐fault medium (and therefore allowing for heterogeneous stress fields to develop) and the discrete degradation and gouge formation at the fault plane (and therefore allowing for structural heterogeneity to develop). Numerical results show the development of persistent stress, damage, and gouge thickness heterogeneities, with a much larger variability in space than in time. Strong positive correlations are found between these quantities, which suggest a positive feedback between local normal stress and damage rate, only mildly mitigated by the mobility of the granular gouge in the interface. For a wide range of confining stresses, after a sufficient number of seismic cycles, the fault reaches a state of established disorder with a constant roughness, a certain amount of periodicity at the millimetric scale, and a power law decay of the Power Spectral Density at smaller spatial scales. The typical height‐to‐wavelength ratio of geometrical asperities and the correlations between stress and damage profiles are in good agreement with previous field or lab estimates.

Nitrification in a Subterranean Estuary: An Ex Situ and In Situ Method Comparison Determines Nitrate Is Available for Discharge

AbstractSubterranean estuaries (STEs) form in the subsurface where fresh groundwater and seawater meet and mix. Subterranean estuaries support a variety of biogeochemical processes including those transforming nitrogen (N). Groundwater is often enriched with dissolved inorganic nitrogen (DIN), and transformations in the STE determine the fate of that DIN, which may be discharged to coastal waters. Nitrification oxidizes ammonium (NH4+) to nitrate, making DIN available for N removal via denitrification. We measured nitrification at an STE, in Virginia, USA using in situ and ex situ methods including conservative mixing models informed by in situ geochemical profiles, an in situ experiment with 15NH4+ tracer injection, and ex situ sediment slurry incubations with 15NH4+ tracer addition. All methods indicated nitrification in the STE, but the ex situ sediment slurries revealed higher rates than both the in situ tracr experiment and mixing model estimations. Nitrification rates ranged 55.0–183.16 μmol N m−2 d−1 based on mixing models, 94.2–225 μmol N m−2 d−1 in the in situ tracer experiment, and 36.6–109 μmol N m−2 d−1 slurry incubations. The in situ tracer experiment revealed higher rates and spatial variation not captured by the other methods. The geochemical complexity of the STE makes it difficult to replicate in situ conditions with incubations and calculations based on chemical profiles integrate over longer timescales, therefore, in situ approaches may best quantify transformation rates. Our data suggest that STE nitrification produces NO3−, altering the DIN pool discharged to overlying water via submarine groundwater discharge.