Vertical gradient

H. Weimann, J. Amon, T. Jung, G. Mueller. Numerical simulation of the growth of 2" diameter GaAs crystals by the vertical gradient freeze technique. J Crys Growth 180 560, 1997. 

Predictions no abundance gradients the thick disk thin disk stars will all have [Fe/H] larger than found in the thick disk period of star formation in thick disk was short < 1 billion years thin disk always younger than thick disk Observations no vertical gradients metallicity distributions for the disks overlap star formation in thick disk includes SNela and AGB star formation in thick disk probably > 1 billion years... 

Observations no vertical gradients abundance trends differ star formation in thick disk includes SNela and AGB... 

Conclusion. Thanks to our large sample, the statistic is improved and the separation between the two disks is quantified. It is now clear that the thin and the thick disks are chemically well separated. We found a transition in the age distribution of the thin disk and the thick disk stars at 10 Gyr but no clear vertical gradient in the thick disk. These results constrain the formation scenarii of the Milky Way s disks. 

Turbulence and advection can lead to the mixing of adjacent water masses (or types). These water motions create horizontal and vertical gradients in temperature and salinity. As illustrated in Figures 4.17a and 4.17b, vertical mixing at the boundary between two water types produces waters of intermediate temperature and salinity. Since mixing does not alter the ratios of the conservative ions, the water in the mixing zone acquires a salinity intermediate between that of the two water types. The salinity of... 

The nutrient profiles are characterized by much higher concentrations in the deep-waters than in the surface. In some locations, such as shown in Figure 9.1, mid-water concentration maxima are present. The depth region over which concentrations exhibit the largest vertical gradients is usually defined by the thermocline. All biolimiting elements have similar depth profiles, having surfece-water depletions and deep-water enrichments. 

The influence of river water inputs on trace metal distributions is illustrated in Figure 11.17c, which shows that the surface-water concentration of dissolved Mn in the Pacific Ocean decreases with increasing distance from the California coast. The vertical profile measured in the coastal zone (Figme 11.17b) exhibits a strong surface enrichment characteristic of scavenged trace elements. A similar vertical gradient is seen in the... 

Particulate matter that reaches the seafloor becomes part of the blanket of sediments that lie atop the crust. If bottom currents are strong, some of these particles can become resuspended and transported laterally until the currents weaken and the particles settle back out onto the seafloor. The sedimentary blanket ranges in thickness from 500 m at the foot of the continental rise to 0 m at the top of the mid-ocean ridges and rises. Marine scientists refer to this blanket as the sedimentary column. Like the water column, the sediments contain vertical gradients in their physical and chemical characteristics. Similar to the vertical profile convention used in the water column, depth in the sediments is expressed as an increasing distance beneath the seafloor. 

Reaction rates of nonconservative chemicals in marine sediments can be estimated from porewater concentration profiles using a mathematical model similar to the onedimensional advection-diffusion model for the water column presented in Section 4.3.4. As with the water column, horizontal concentration gradients are assumed to be negligible as compared to the vertical gradients. In contrast to the water column, solute transport in the pore waters is controlled by molecular diffusion and advection, with the effects of turbulent mixing being negligible. 

Vertical segregation The vertical gradient in biogenic materials, such as nutrients and O2, that is established by the interaction between the biogeochemical cycling of particulate organic matter and the vertical density stratification of the water column. Strongest at mid and low latitudes. 

Within the framework of the AsiaFlux program, Saigusa et al. (2005) measured the C02 fluxes since 1993 in the forest ecosystem of Takayama using an aerodynamic method to estimate the vertical gradient of C02 concentration and a vortex divergence method to calculate the coefficient of diffusion over the forest canopy. Also, measurements were made of vortex fluxes of sensible heat, water vapor, and C02. 

An interesting relationship has been observed between MAA concentration and water flow.143 When exposed to higher water velocities but the same radiation environment, corals accumulate larger amounts of MAAs. This positive correlation has been attributed to the stimulatory effect of increased water velocity on photosynthesis that, in turn, supplies the necessary substrates for MAA synthesis. If this is true, then the observed vertical gradient of MAAs may also be a function of photosynthetic rate relative to the attenuation of PAR and not only a direct signaling of MAA synthesis by radiation intensity. Alternatively, there could be a mechanical stimulatory mechanism related to a damage-induction response for MAA synthesis in the zooxanthellae. 

The mixing zone usually includes an area of the most intense interaction and mixing of river and sea water, where horizontal and vertical gradients of hydrological and hydrochemical characteristic, and primarily water salinity, are maximum. This area is called frontal zone. 

In the vertical distribution of the modules of mean current vectors (Fig. 3a), the highest vertical gradient (shear) is observed between 10 and 25 m (total mean values of 0.215 and 0.165 m s-1, respectively). This is probably related to the effect of the wind drift. In the layer 25-50 m, mean velocities are homogeneous and the main shear in their values takes place deeper down... 

The principal features of the vertical T,S structure of the Black Sea waters are shown in Fig. 3. The upper mixed layer (UML) of the Black Sea in the warm period of the year has a thickness less than 10 m (see Fig. 3a). At this time, it is underlain by the layer of the seasonal pycnocline (ther-mocline) this layer is also thin (10-20 m) but features high vertical gradients of temperature (0.2-0.3 °Cm 1) and, correspondingly, of water density... 

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