Transfer Of Tracers Research Articles

Ventilation of the Southern Ocean Pycnocline.

Ocean ventilation is the transfer of tracers and young water from the surface down into the ocean interior. The tracers that can be transported to depth include anthropogenic heat and carbon, both of which are critical to understanding future climate trajectories. Ventilation occurs in both high- and midlatitude regions, but it is the southern midlatitudes that are responsible for the largest fraction of anthropogenic heat and carbon uptake; such Southern Ocean ventilation is the focus of this review. Southern Ocean ventilation occurs through a chain of interconnected mechanisms, including the zonally averaged meridional overturning circulation, localized subduction, eddy-driven mixing along isopycnals, and lateral transport by subtropical gyres. To unravel the complex pathways of ventilation and reconcile conflicting results, here we assess the relative contribution of each of thesemechanisms, emphasizing the three-dimensional and temporally varying nature of the ventilation of the Southern Ocean pycnocline. We conclude that Southern Ocean ventilation depends on multiple processes and that simplified frameworks that explain ventilation changes through a single process are insufficient.

Wall-induced anisotropy effects on turbulent mixing in channel flow: A network-based analysis.

Turbulent mixing is studied in the Lagrangian framework with an approach based on the complex network formalism. We consider the motion of passive, noninertial particles inside a turbulent channel simulated at Re_{τ}=950. The time-dependent network is built to evaluate the transfer of tracers between thin wall-parallel layers which partition the channel in the wall-normal direction. By doing so, we are able to assess the spatial and temporal complexities arising from turbulence dynamics and their influence on the mixing process. This approach highlights the effects of small-scale features of turbulent flow structures and also the larger scale effects determined by wall-induced anisotropy. Complex networks, coupled to the Lagrangian description of turbulence, are effective in providing novel insights into inhomogeneous turbulence and mixing.

Marine sources of bromoform in the global open ocean – global patterns and emissions

Abstract. Bromoform (CHBr3) is one important precursor of atmospheric reactive bromine species that are involved in ozone depletion in the troposphere and stratosphere. In the open ocean bromoform production is linked to phytoplankton that contains the enzyme bromoperoxidase. Coastal sources of bromoform are higher than open ocean sources. However, open ocean emissions are important because the transfer of tracers into higher altitude in the air, i.e. into the ozone layer, strongly depends on the location of emissions. For example, emissions in the tropics are more rapidly transported into the upper atmosphere than emissions from higher latitudes. Global spatio-temporal features of bromoform emissions are poorly constrained. Here, a global three-dimensional ocean biogeochemistry model (MPIOM-HAMOCC) is used to simulate bromoform cycling in the ocean and emissions into the atmosphere using recently published data of global atmospheric concentrations (Ziska et al., 2013) as upper boundary conditions. Our simulated surface concentrations of CHBr3 match the observations well. Simulated global annual emissions based on monthly mean model output are lower than previous estimates, including the estimate by Ziska et al. (2013), because the gas exchange reverses when less bromoform is produced in non-blooming seasons. This is the case for higher latitudes, i.e. the polar regions and northern North Atlantic. Further model experiments show that future model studies may need to distinguish different bromoform-producing phytoplankton species and reveal that the transport of CHBr3 from the coast considerably alters open ocean bromoform concentrations, in particular in the northern sub-polar and polar regions.

Novel approach for modeling kinetic interface-sensitive (KIS) tracers with respect to time-dependent interfacial area change for the optimization of supercritical carbon dioxide injection into deep saline aquifers

Tracer methods represent techniques commonly used for the characterization and for the monitoring of transport processes in geo-reservoirs (e.g., CO2 storage). The current short communication addresses the development of a conceptual, mathematical and numerical model for a new tracer class (KIS tracers, Schaffer et al., 2013) useful for the characterization of fluid–fluid interfacial areas during supercritical CO2 injection into deep saline aquifers. This tracer type has the potential to quantify the amount of fluid–fluid interfacial areas, important for the quantification of reactions at the fluid interface, which can implicitly lead to optimized injection strategies, a better assessment of the extent of the CO2 plume and of the storage efficiency.The presented modeling approach overcomes the drawback of the current standard multiphase multicomponent models, which ignore kinetics of mass transfer over the interfacial area between the CO2 and brine and consider only the volumetric fraction of the fluids or their mass and molar fractions, respectively. In this model, the concept of a specific interfacial area obtained from pore network modeling is used to complement the constitutive relationships between capillary pressure and saturation. It is a two-phase four component flow and transport model with a kinetic mass transfer of tracers between the two fluids and taking the dissolution of CO2 in brine into account. Two numerical simulation scenarios are shown as examples for the design of experimental work in laboratory and eventually in the field. The modeling approach follows the assumptions of previous experimental work (Schaffer et al., 2013). Their implications are investigated by sensitivity analyses to narrow the physical range of reaction rates for further experiments and molecular tracer design. Both examples indicate that the tracer concentration is sensitive with respect to the interfacial area and, therefore, KIS tracer utilization both in the lab and in the field appear to be feasible for implementation.

A Numerical Model of Tracer Transport in a Non-isothermal Two-Phase Flow System for $${\text{ CO}}_2$$ Geological Storage Characterization

For the purpose of characterizing geologically stored $$\text{ CO}_{2}$$ including its phase partitioning and migration in deep saline formations, different types of tracers are being developed. Such tracers can be injected with $$\text{ CO}_{2}$$ or water, and their partitioning and/or reactive transfer from one phase to another can give information on the interactions between the two fluid phases and the development of their interfacial area. Kinetic rock–water interactions and geochemical reactions during two-phase flow of $$\text{ CO}_{2}$$ and brine have been incorporated in numerical simulators (e.g., Xu et al., TOUGHREACT User’s Guide: A Simulation Program for Non-isothermal Multiphase Reactive Geochemical Transport in Variably Saturated Geologic Media. LBNL Report 55460, V.1.2., Berkeley, CA, 2004). However, chemical equilibrium between the fluid phases is typically assumed, and multi-component, multiphase, non-isothermal codes for $$\text{ CO}_{2}$$ –brine systems that incorporate kinetic mass transfer of tracers between the two fluid phases are not readily available. New models or further developments of existing models are therefore needed to provide the capability for interpreting the signals of novel tracers, including tracers with kinetic/time-dependent interface transfer. This paper presents such new numerical model of tracer transport in a non-isothermal two-phase flow system. The model consists of five different governing equations describing liquid phase (aqueous) flow, gas ( $$\text{ CO}_{2})$$ flow, heat transport and the movement of the tracers within the two phases, as well as allowing kinetic transport of the tracers between the two phases. A finite element method is adopted for the spatial discretization and a finite difference approach is used for temporal discretization. Some special technologies and solution strategies are adopted for increasing the convergence, ensuring the numerical stability and eliminating non-physical oscillations. The new numerical model is validated against the code TOUGH2/ECO2N as well as some analytical/semi-analytical solutions. Good agreement between the simulated and analytical results indicates that the model has capability to simulate two-phase flow and tracer transport in a non-isothermal two-phase flow system with high confidence. Finally, the capability to model transport and kinetic mass transfer of tracers between the two fluid phases is demonstrated through examples.

Mg and Ca root uptake and vertical transfer in soils assessed by an in situ ecosystem-scale multi-isotopic (26Mg & 44Ca) tracing experiment in a beech stand (Breuil-Chenue, France)

The sustainability of forest ecosystems may be at stake especially in forests on base-poor soils due to reduced nutrient deposition and intensified silvicultural practices. Understanding nutrient availability and cycling is therefore essential to manage forest soil fertility. This study aims to assess in a beech plot Mg and Ca vertical transfer in soil and root uptake using an isotopic tracing experiment. A simulated rainfall containing a small amount (960 g Mg.ha−1; 530 g Ca.ha−1) of highly enriched 26Mg and 44Ca was sprayed on the forest floor of a 35-yr-old beech plot. The isotopic composition of fine roots and of the soil exchangeable Mg and Ca pool was monitored during 1 year. A pool and flux model (IsoMod) was developed to predict the labeling of the soil and vertical transfer of tracers. Tracers (44Ca and 26Mg) were immediately retained in the thin litter layer. During the following year, Mg and to a lesser extent Ca were progressively released. After 1 year, the exchangeable Mg and Ca pools of the upper mineral layer (0–5 cm) were strongly labeled (~660 ‰, representing ~55 % of the tracer input and ~370 ‰, ~41 % of the tracer input respectively). A significant proportion (~8 % 26Mg, ~2 % 44Ca) of tracer was leached through the soil, below 10 cm. This amount was much larger than what was predicted using a simple mixing model. The Ca and Mg isotopic composition of fine roots at all depths was close or lower than that of exchangeable Ca and Mg respectively. An in situ ecosystem-scale 26Mg and 44Ca isotopic tracing experiment was successfully carried out. Tracers were at first strongly retained in the litter layer, then progressively transferred to soil horizons below. Nutrient cycling of Mg and Ca were proven to be very different. Mg had a higher mobility in the soil than Ca, and nutrient uptake sources were proven to be different.

Direct geoelectrical evidence of mass transfer at the laboratory scale

Previous field‐scale experimental data and numerical modeling suggest that the dual‐domain mass transfer (DDMT) of electrolytic tracers has an observable geoelectrical signature. Here we present controlled laboratory experiments confirming the electrical signature of DDMT and demonstrate the use of time‐lapse electrical measurements in conjunction with concentration measurements to estimate the parameters controlling DDMT, i.e., the mobile and immobile porosity and rate at which solute exchanges between mobile and immobile domains. We conducted column tracer tests on unconsolidated quartz sand and a material with a high secondary porosity: the zeolite clinoptilolite. During NaCl tracer tests we collected nearly colocated bulk direct‐current electrical conductivity (σb) and fluid conductivity (σf) measurements. Our results for the zeolite show (1) extensive tailing and (2) a hysteretic relation betweenσfandσb, thus providing evidence of mass transfer not observed within the quartz sand. To identify best‐fit parameters and evaluate parameter sensitivity, we performed over 2700 simulations ofσf, varying the immobile and mobile domain and mass transfer rate. We emphasized the fit to late‐time tailing by minimizing the Box‐Cox power transformed root‐mean square error between the observed and simulatedσf. Low‐field proton nuclear magnetic resonance (NMR) measurements provide an independent quantification of the volumes of the mobile and immobile domains. The best‐fit parameters based onσfmatch the NMR measurements of the immobile and mobile domain porosities and provide the first direct electrical evidence for DDMT. Our results underscore the potential of using electrical measurements for DDMT parameter inference.

Are mesoscale eddies in shelf seas formed by baroclinic instability of tidal fronts?

The formation of eddies along tidal fronts in the shelf seas is investigated through both the analysis of high‐resolution conductivity‐temperature‐depth (CTD) data and drifters for the North Sea as well as experiments with an eddy‐permitting model. Baroclinic eddies are difficult to observe in the shelf seas due to their small size, and their surface signals are dampened by air‐sea interaction and eroded by wind and tidal mixing. High‐resolution CTD profiles reveal possible eddy signals along the thermocline where there are intrusions of waters of reduced salinity on the eddy scale. These freshwater intrusions carry low potential vorticity, indicating their origin from the surface mixed layer. An instability analysis of these frontal systems suggests that these eddy signals can be formed by baroclinic instability. Numerical model integrations reveal that mesoscale eddy variability along the thermocline increases in strength in late summer, in accord with the increase in stratification. The stability analysis of the modeled fronts and the scaling of the eddy kinetic energy to the available potential energy are also consistent with baroclinic instability theory. While influencing the eddy variability through the passage of synoptic weather systems, wind energy input is too small to explain the high values of eddy kinetic energy during late summer. These eddy circulations provide localized regions of high vorticity and high stirring, which are important for the transfer of tracers at middepth, such as potential vorticity, salinity, and nutrients.

Comparing Surface Residue Transfer Efficiencies to Hands using Polar and Nonpolar Fluorescent Tracers

Transfer of chemicals from contaminated surfaces such as foliage, floors, and furniture is a potentially significant source of both occupational exposure and children's residential exposure. Increased understanding of relevant factors influencing transfers from contaminated surfaces to skin and resulting dermal-loading will reduce uncertainty in exposure assessment. In a previously reported study, a fluorescence imaging system was developed, tested, and used to measure transfer of riboflavin residues from surfaces to hands. Parameters evaluated included surface type, surface loading, contact motion, pressure, duration, and skin condition. Results of the initial study indicated that contact duration and pressure were not significant for the range of values tested, but that there are potentially significant differences in transfer efficiencies of different compounds. In the study reported here, experimental methods were refined and additional transfer data were collected. A second fluorescent tracer, Uvitex OB, with very different physicochemical properties than riboflavin, was also evaluated to better characterize the range of transfers that may be expected for a variety of compounds. Fluorescent tracers were applied individually to surfaces and transfers to skin were measured after repeated hand contacts with the surface. Additional trials were conducted to compare transfer of tracers and co-applied pesticide residues. Results of this study indicate that dermal loadings of both tracers increase through the seventh brief contact. Dermal loading of Uvitex tends to increase at a higher rate than dermal loadings of riboflavin. Measurement of co-applied tracer and pesticide suggest results for these two tracers may provide reasonable bounding estimates of pesticide transfer.

Submarine groundwater discharge: Effects of hydrogeology and of near shore surface water bodies

Submarine groundwater discharge is investigated numerically for a confined aquifer considering three types of permeability distribution (uniform, anisotropic and heterogeneous lognormal) as well as for an aquifer in which a surface water body is embedded. The latter case corresponds to aquifers with lagoons, flat lakes or wetlands near the coast. The numerical simulations are performed using the code FAST-C(2D), developed by Holzbecher (1998). For the confined aquifer, the portion of recirculated seawater in submarine groundwater discharge and the length of the recirculation zone are investigated. The parameters influencing these variables in the case of homogeneous aquifer (isotropic or anisotropic) are discussed. Further, the validity of a linear relationship between the submarine groundwater discharge and the flux of terrestrial groundwater toward the sea, proposed by Destouni and Prieto (2003), is investigated. As far as possible, our results are compared with results presented by Smith (2004), which were obtained using different codes. The investigation of a heterogeneous model aquifer concerns the influence of the variability of the permeability distribution on the portion of recirculated seawater and is performed by means of Monte Carlo analyses. Finally, for coastal aquifers in which surface water bodies are embedded, the main flow features are investigated. Particularly, the pathway of terrestrial groundwater to the sea, the flux of groundwater of marine origin to the surface water body, the recirculation of seawater and the flux from the surface water body to the sea have been considered. The parameters influencing these fluxes, which are important for the transfer of pollutants and tracers from the groundwater to the surface water and to the near shore seawater, are discussed.

The role of eddies in the isopycnic transfer of nutrients and their impact on biological production

Eddies provide a systematic, large-scale transfer of tracers and nutrients along isopycnals through a combination of eddy-induced diffusion and advection. The nutrient distribution is controlled by advection, rather than diffusion, when the nutrient lifetime exceeds a timescale given by k/V 2 where k is the lateral diffusivity and V is the characteristic transport velocity. Idealized, eddy-resolving experiments are conducted using an isopycnic model configured for a zonal channel. Whether the eddies act to enhance or inhibit biological production depends on the location of the nutrient source and the nutrient lifetime. For a subtropical gyre and the Southern Ocean, the eddy-induced diffusion and advection are likely to oppose each other over the euphotic zone but reinforce each other at depth. Over the euphotic zone, the combination of eddy diffusion and Ekman advection of nutrients should dominate the opposing eddy-induced advection. This lateral transfer becomes more important for long-lived nutrients, such as dissolved organic nitrogen, within the euphotic zone.

On the eddy transfer of tracers: Advective or diffusive?

Geostrophic eddies have traditionally been viewed within oceanography as diffusing water masses and tracers in a down-gradient manner. However, eddies also have an advective role that may lead to an up-gradient transfer of tracers, as has been recognized in atmospheric tracer studies and recent eddy parameterizations developed for the ocean. Eddies provide an advective transfer or “bolus” velocity through the secondary circulation formed by the slumping of density surfaces in baroclinic instability. Here we use an eddy-resolving isopycnal ocean model to investigate the meridional transfer across a zonal jet. The jet undergoes baroclinic instability, forming a vibrant eddy field and inducing a meridional bolus velocity. The bolus velocity is found to be correlated with gradients of potential

Linear gap and tight junctional assemblies between capillary endothelial cells in the eel rete mirabile.

Interendothelial tight junctions and gap junctions have been described in large blood vessels and in cultures of endothelium derived from large blood vessels. Transfer of microinjected small-molecular weight tracers between adjacent endothelial cells also has been demonstrated indicating the presence of gap junctional interendothelial communication. Similar transfer of tracers is evident between microvessel endothelial cells in culture and in microvessels in situ. However, gap junctions have not been detectable by electron microscopy of intact capillary systems. This may be due to limited sampling available in diffuse capillary systems and a small area of overlap between adjacent endothelial membranes. Thin slices of the parallel, tightly packed capillary bed of the eel rete mirabile were cryofixed and prepared for conventional TEM by freeze-substitution. Other samples were freeze-fractured and replicated for examination of endothelial junctional components. A novel tight-gap junctional complex between rete capillary endothelial cells is described. In freeze-fracture replicas of the membrane P face, rows of gap junction subunits are flanked on either side by linear depressions representing grooves previously occupied by tight junctional strands that partition to the E face. In thin sections, the junctions appear in profile as short lengths of closely apposed membranes characteristic of gap junctions. The tight junctional components imply a barrier to paracellular transport across the capillary wall between the endothelial cells. The gap junctional component may provide a mechanism for communication between endothelial cells along the length of the vessel wall.

Utility of intensely fluorescent cyanine dyes (CY3) for assay of gap junctional communication by dye-transfer

Utilization of a class of florescent cyanine dyes (Cy3 ™) for the assay of gap junctional communication by the dye transfer method was examined. When comp ed with Lucifer Yellow (LY), a commonly used tracer, microinjected Cy3 dye was found to yield similar degrees of cell coupling. Blockade of the transfer of both tracers by 12- O-tetradecanoylphorbol-13 acetate (TPA), which is known to cause closure of communicating channels, confirmed gap junctional mediation of dye movement. The fixability of a microinjected amine derivative of Cy3 dye demonstrated its compatibility with immunostaining protocols involving fluorescein isothiocyanate (FITC)-conjugated reagents. These results together with the brilliant fluorescence of Cy3 dyes suggest the potential of Cy3 reagents as additional tools to study gap junction function.

On calculating the transfer of carbon-13 in reservoir models of the carbon cycle

An approach to calculating the transfer of isotopic tracers in reservoir models is outlined that takes into account the effects of isotopic fractionation at phase boundaries without any significant approximations. Simultaneous variations in both the rare isotopic tracer and the total elemental (the sum of its isotopes) concentration are considered. The proposed procedure is applicable to most models of the carbon cycle and a four-box model example is discussed. Although the exact differential equations are non-linear, a simple linear approximation exists that gives insight into the nature of the solution. The treatment will be in terms of isotopic ratios which are the directly measured quantities.

On calculating the transfer of carbon-13 in reservoir models of the carbon cycle

An approach to calculating the transfer of isotopic tracers in reservoir models is outlined that takes into account the effects of isotopic fractionation at phase boundaries without any significant approximations. Simultaneous variations in both the rare isotopic tracer and the total elemental (the sum of its isotopes) concentration are considered. The proposed procedure is applicable to most models of the carbon cycle and a four-box model example is discussed. Although the exact differential equations are non-linear, a simple linear approximation exists that gives insight into the nature of the solution. The treatment will be in terms of isotopic ratios which are the directly measured quantities.

Studies of the Rate of Transfer of Rb 86 , K 39 , Na 24 , Na 23 . Cl 36 , and Cl 35 Across the Pericardium of Dogs

Studies of the simultaneous rates of transfer of various tracers and stable isotopes from the pericardium of normal dogs under pentobarbital anesthesia indicated that the rate of transfer of Rb 86 was greater than that of Na 24 and Cl 36 , which were approximately equal. These observations show the pericardium to be a very active serous membrane concerned with electrolyte transfer phenomena as well as an excellent experimental model for the study of the kinetics of exchange of electrolytes across a normal living membrane.