Tracer budgets

A large value of F indicates that the simulated tracer concentrations differ much from the observations. Bringing the model close to the data, therefore, is equivalent to minimizing F, subject to satisfying the model equations (tracer budget equations) E, = 0 exactly. 

In fluid reservoirs like fhe afmosphere or the ocean, the turnover time of a tracer is also related to the spatial and temporal variability of ifs concentration within the reservoir a long turnover time corresponds to a small variability and vice versa (Junge, 1974 Hamrud, 1983). Figure 4-2 shows a plot of measured trace gas variability in the atmosphere versus turnover time estimated by applying budget considerations as indicated by Equation (1). An inverse relation is obvious, but the scatter in the data... 

Robbins JA (1988) A model for particle-selective transport of tracers in sediments with conveyor-belt deposit feeders. Journal of Geophysical Research 91 8542-8558 Robinson LF, Belshaw NS, Henderson GM (in press) U and Th isotopes in seawater and modem carbonates from the Bahamas. Geochim Cosmochim Acta Rosenthal Y, Boyle EA, Labeyrie L, Oppo D (1995a) Glacial enrichments of authigenic Cd and U in subantarctic sediments A climatic control on the elements oceanic budget Paleoceanography 10(3) 395-413... 

The role of radionuclides as tracer of the chemical transport in river is also reinforced by the fact that each of the U-Th-Ra elements has several isotopes of very different half-lives belonging to the U-Th radioactive series. Thus, these series permit comparison of the behavior of isotopes of the same element which are supposed to have the same chemical properties, but very different lifetimes. These comparisons should be very helpful in constraining time scales of transport in rivers. This was illustrated by Porcelli et al. (2001) who compared ( " Th/ U) and ( °Th/ U) ratios in Kalix river waters and estimated a transit time for Th of 15 10 days in this watershed. The development of such studies in the future should lead to an important progress in understanding and quantifying of transport parameters in surface waters. This information could be crucial for a correct use of U-series radioactive disequilibria measured in river waters to establish weathering budgets at the scale of a watershed. 

In the following section, we discuss three classes of tracers that have recently proved useful for assessing sources of DOC and in constructing both DOC and DON budgets for aquatic ecosystems. Measurements of these tracers could be combined with measurements of the established lignin and carbohydrate tracers in a field study. Our intent is to provide related examples rather than a thorough literature review of each class of tracer. 

Rowland, et al. (14) have used radiochemical tracer techniques to study reaction (1) and obtain equal yields of CO and COS. CS oxidation could account for a significant fraction of the atmospheric COS budget ( ) and definitive measurements of the mechanism of reaction (2), its primary products and the routes to, and yields of the ultimate stable products are needed. 

Because of greatly contrasting low tritium levels before thermonuclear tests and because of the distinct peak tritium levels that occurred in the atmosphere during 1962-1965, tritium has been used as an environmental tracer in the studies on surface water budgets, groundwater age and flow velocities, groundwater recharge, and dispersion and diffusion in aquifers. A 1989 study detailed the distribution of tritium... 

An alternative approach that has been used is to construct an atmospheric mass budget based on measurements of DMS in air and water olf Cape Grim, Australia in combination with an atmospheric model to estimate the air-sea flux of DMS (Gabric et al., 1995). Their results were consistent with a parametrization of with U based on deliberate tracers (Liss and Merlivat, 1986) but somewhat lower than the " C-derived values (see Section 6.03.2.4.1). 

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