Depth profiling history

Uncertainty in the depth history of a sample is a primary source of uncertainty for the cosmogenic-nuclide paleoaltimeter. Because of the >2000-fold difference in rock density versus atmospheric density, a 0.5-m uncertainty in depth is equivalent to >l-km uncertainty in altitude. Uncertainty in the depth of a sample during exposure is particularly problematic in regions where loess deposits may episodically bury a surface. For example, Hancock et al. (1999) find cosmogenic evidence of an ephemeral 0.5-1.5 m silt cap on currently uncapped, 600-ka terraces in the Wind River basin, Wyoming. The duration of time required to deposit a sedimentary layer may also result in a complex exposure history that can only be deduced with depth profiles and multiple nuclides (Riihimaki et al. 2006). However, Dunai et al. (2005) suggest that some deposits in the hyperarid Atacama Desert, Chile, have remained at the same depth without erosion or deposition for >20 Ma. 

Sediment depth profiles as records of intertidal pollution history... 

CFCs, and Kr were studied in a sandy, unconfined aquifer on the Delmarva Peninsula in the eastern USA by Ekwurzel et al. (1994). H and H+ He depth-profiles show peak-shaped curves that correspond to the time series of H concentration precipitation, smoothed by dispersion (Fig. 18a). The peak occuring at a depth of about 8m below the water table therefore most likely reflects the H peak in precipitation that occurred in 1963 (Fig. 6). The H- He ages show a linear increase with depth, reaching a maximum of about 32 years. The H- He ages are also supported by CFC-11, CFC-12, and Kr tracer data (Fig. 18b). The latter tracers are used here as dyes and their concentrations are converted into residence times by using the known history of the atmospheric concentrations and their solubility in water. From the vertical H- He age profile at well nest 4 at the Delmarva site, the vertical flow velocity can be... 

Complex exposure histories may also show up as a disturbed pattern of cosmogenic nuclide concentration versus depth. Particular care must be taken when dating soil or alluvial deposits, which often experience varying sedimentation rates, sudden burial, or bioturbation (i.e., soil mixing by living organisms) of the uppermost layers (e.g., Phillips et al. 1998 Braucher et al. 2000). In such studies it is extremely important that depth profiles are taken. 

Electrocatalytic reactions occur on catalyst surfaces. The catalyst surface structure and chemically bonded or physically absorbed substances on the catalyst surface exert strong influences on catalyst activity and efficiency. X-ray photoelectron spectroscopy (XPS) (also known as electron spectroscopy for chemical analysis (ESCA), auger emission spectroscopy (AES), or auger analysis) is a failure analysis technique used to identify elements present on the surface of the sample. For instance, this can be used to identify Pt and carbon surface chemical species that may present histories of chemical reactions or contamination in the catalyst layer. AES and XPS can also provide depth profiles of element analysis. Wang et al. [41] studied XPS spectra of carbon and Pt before and after fuel cell operation. They observed a significant increase in O Is peak value for each oxidized carbon support, the result of a higher surface oxide content in the support surface due to electrochemical oxidation. However, sample preparation in AES and XPS analysis is critical because these methods are very sensitive to a trace amount of contaminants on sample surfaces, and detect as little as 2-10 atoms on the sample surface. 

Fig. 18-8 Characteristic temperature-depth distributions at an ice divide. For a climatic temperature history as shown in (a) the temperature-depth distribution changes as shown in (b). Following the step increase in surface temperature, the initial steady temperature profile (fi in (b)) is altered by a warming wave (e.g., at time fa) but eventually reaches a new steady profile by time t. (c) Temperature data from Greenland measured by Gary Clow of the US Geological Survey, showing wiggles due to climate variations (Cuffey et ah, 1995).

At site A in Table 16, concentrations of all metals in the second soil-core depth were higher than those in the first soil-core depth. Bismuth and antimony concentrations in the soil core under the second core depth were less than those of natural concentrations, 0.34 and 0.37 /rgg , respectively. At sites B and C, the profiles of metal concentrations were somewhat different from those in site A The difference is probably due to dissimilarities in pollution history, surrounding circumstances and properties of soil. 

The effective P may be determined with the electron beam apparatus. When the sample (slab geometry) is thick enough to absorb all of the incident electrons, a compressive stress wave propagates from the irradiated region into the sample bulk. A transducer, located just beyond the deposition depth, may be used to record the stress pulse. Alternatively, the displacement or velocity of the rear surface of sample may be observed optically and used to infer the initial pressure distribution from the experimentally measured stress history. Knowledge of the energy-deposition profile then permits the determination of the Gruneisen coefficient. 

Grove and Harrison (1999) investigated the feasibility of obtaining Th-Pb age profiles in the surface regions of natural monazites and found that ion intensities were adequate to resolve age differences of <1 Myr with better than 500 A depth resolution in late Tertiary monazites. These age gradients were then used to extract continuous thermal history information from which they constrained the displacement history of a Himalayan thrust. The sputtering of natural surfaces was found to yield inter-element calibration plots of similar reproducibility to that of polished surfaces. 

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