Depth-averaged rate

Assuming that the water column is mixed more rapidly than photoreaction occurs, it can be shown (22, 23) that v. x, the depth-averaged rate for a photoreaction at depth z, is expressed approximately by ... 

In a study of sediment trap samples collected at a depth of 3,200 m in the Sargasso Sea, Bacon et al. (1985) found that the fluxes of several radionuclides exhibited a seasonal cycle in phase with the total mass flux of particles. Mass flux, in turn, was found to be closely coupled to the seasonal cycle of primary production in surface waters of this region (Deuser et al., 1981). Seasonally varying fluxes of radionuclides produced in the deep sea (e.g., Th, Pa, and °Pb) are inconsistent with the view that these nuclides are removed by scavenging to small particles which constitute the bulk of particle mass in the deep sea and which are inferred to sink at an average rate of several hundred meters per year (Section 6.09.3). A seasonal cycle in the flux of these nuclides implies that scavenging in the deep sea responds rapidly to changes in the export of particles from surface waters. 

The °Th and Pa methods are not used directly for absolute dating of individual sedimentary horizons, because the assumption that No is constant over time does not hold exactly but can be upset by fluctuations due to changes in sediment-deposition rate and other factors. Instead, the common practice is to use the decreasing activity with depth to derive an average rate of sediment accumulation over the length of a core or some other long interval. If t is the age (time since deposition) of a sediment horizon at depth z, and if S is the average sediment accumulation rate (thickness per unit time), then from Equation (1)... 

Two parameters are useful in the design of a machined microchannel. The first parameter is z0, the channel depth at time zero. This value is obtained by extrapolating the channel profile curves, such as the one in Fig. 6.16, to time t = 0. The second parameter is md, the average channel depth increase rate over time. The depth z(t) of the channel over time is then given by ... 

Incorporated to a depth of 6-10 cm in the soil immediately prior to sowing, butylate, is used at an average rate of 4 kg/ha for the control of the grass and broad-leaved weeds of maize. The effective rate is about half of that of EPTC, but butylate also depresses yield in maize. To prevent this effect, as in the case of EPTC, an antidotal formulation has been put on the market. The product, with the trade name Sutan Plus 6 EC contains 6 lb of Sutan and 1/4 lb of R-25788 (N,N-dialIyI-2,2-dichloroacetamide), and is used for weed control in field maize, sweet corn and silage maize. 

The purpose of the injection subassembly is to inject the sample at an average rate of about IpL/s and an instantaneous rate that never exceeds that which would starve the thermal oxidation process of oxygen and so cause incomplete combustion. Also, any carbonization of the sample within the injector must be avoided. The sample is driven by a flow of inert carrier gas (argon) that is controlled by a combination of a flow restricter (MMVl) and a pressure regulator (LPRl). The injector, which is a stainless steel tube, penetrates the pyrolysis tube to a depth where the temperature is high enough to ensure sample volatilization within the injector while avoiding... 

Figure 4. Computed depth dependence for the direct photolysis of trifluralln and pentachlorophenol In different water types (average rate constants parenthesized).

The and 5D values of snow collected at increasing depth below the surface identify layers of snow deposited during successive summers and winters (Epstein et al. 1965). The layers of summer snow in Fig. 17.23 are less depleted in and D than the layers of winter snow. The resulting stratigraphic profile can be used to date snow layers by counting backward from the present. Epstein et al. (1965) concluded that the average rate of snow accumulation at the South Pole in the 6-year period between 1958 and 1963 was 7 cm of water per year. 

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