Apparent age

These are the most basic equations needed in order to utilize U-Th series radionuclides as time-dependent tracers. In turn, they can provide an apparent age of a process or a geochronological framework. 

In addition to the assumptions of initial conditions, the validity of U-Pb methodology relies on closed system behavior of U, Pb and intermediate nuclides in the decay chain. Concordance between the two U-series decay chains is most likely to be compromised by Rn loss because Rn is the only gas in the decay chains and has a high diffusivity. Radon-222 in the decay chain has a half life of 3.8 days. This is much longer than the half-life of Rn (3.96 s) in the decay chain. Therefore, partial loss of Rn will give rise to an apparent age younger than the true age, whereas the 207p /235p ... 

Figure 4. Graphical representation of detrital-isotope correction for °Th/U dating. Apparent ages (in parentheses) age shown for both the measured and detritus-corrected isotope ratios.

Figure 6. Rosholt (A) and Osmond (B) isochron diagrams for the same, synthetic AS data, shown as their lo error ellipses. Apparent age is 115.7 9.7 ka (MSWD = 1.7), calculated from either the slopes of the Rosholt isochrons or the intercepts of the Osmond isochrons.

Presenting excess-scatter isochrons without discussion of the cause and significance to the validity of the apparent age. 

Little is known about the effect of leaching on distribution of SOM with depth, which is unfavorable for evaluating the potential capacity of soil to sequester carbon. Sporopollen (pollen and spores) are abundant in upper soils, and their vertical distributions are controlled substantially by leaching (Zheng et al. 2002). The distribution of sporopollen with depth may be a useful index of leaching potential. We intended to evaluate the effect of leaching on SOM vertical distribution, based on variations in SOC concentration and SOM 14C apparent age with depth. The distribution of sporopollen with depth can serve as a reference for our evaluation. 

SOM turnover rate (m) (year ) was then calculated based on the methods in Chen et al. (2002b), and SOM apparent age (7) was obtained as llm (year). Due to the less magnitude of m values, variations of T values with depth are often evaluated to show the variations of SOM turnover rates with depth in subsequent analyses. 

Table 3. SOM 513C of topsoil (513Ct0psoii), the maximum SOM 513C value (533Cmaximum) and SOM 4C apparent ages of the bottom of soil profiles with different elevations at the Dinghushan Biosphere Reserve, South China...

Profile Vegetation type s13r O - topsoil (%o) s13r O - maximum (%o) s13r O - maximum s13r O -topsoil (%o) SOM 14C apparent ages of the bottom (yr B.P.)... 

The SOM 14C apparent age of soil section (0-0.05 m) is 80 yr B.R for WKS profile and 140 yr B.R for QYS profile, suggesting that the upper soil layers had been contaminated by some old carbons with negative A14C values. Contaminations from old carbon and bomb 14C can result in obvious alterations in SOM A14C values. However, SOM 513C value is relatively less susceptible to such contaminations, because the abundance of 13C is much greater than that of 14C in nature system. This indicates that 14C analysis alone is not adequate for studying SOM dynamics. 

Shen CD, Yi WX, Sun YM, Xing CP, Yang Y, Peng SL, Li ZA (2000) 14C apparent ages and 513C distribution of forest soils in Dinghushan Natural Reserve. Quaternary Sciences 20 335-344 (in Chinese with English abstract)... 

Figure 3. Relationship between actual age and apparent age for samples to which varying percentage of modern C has been added (31).

The concept of closure temperature is particularly important in geochronology. According to Dodson (1973), closure temperature f can be defined as the temperature of the system at the time corresponding to its apparent age. ... 

Elderly Dose proportionality was observed in nalmefene AUC following 0.5 to 2 mg IV administration to elderly male subjects. There was an apparent age-related decrease in the central volume of distribution that resulted in a greater initial nalmefene concentration in the elderly group. While initial plasma concentrations were transiently higher in the elderly, it would not be anticipated that this population would reguire dosing adjustment. 

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