Residence time oceanic

Because of its relatively long mean residence time, ocean water has a constant isotope composition. Corals are about l%c and foraminifera are about 4.5%o lighter than ocean water. Thus significant Mg isotope fractionations occur during biomineralization of carbonate secreting organisms which is larger than for Ca isotopes (see Section 2.11). 

Oceanic residence time, log yr Predominant species Cone, seawater, -log M... 

Residence times were computed hy r = M/Q where M for a particular constituent is equal to its concentration in seawater times the mass of the oceans, and is equal to the concentration of the constituent in average river water times the annual flux of river water to the ocean. 

Fig. 12. The relationship between the mean oceanic residence time, T, yr, and the seawater—cmstal rock partition ratio,, of the elements adapted from Ref. 29. , Pretransition metals I, transition metals , B-metals , nonmetals. Open symbols indicate T-values estimated from sedimentation rates. The sohd line indicates the linear regression fit, and the dashed curves show the Working-Hotelling confidence band at the 0.1% significance level. The horizontal broken line indicates the time required for one stirring revolution of the ocean, T. ...

If uranium is internally cycled in coastal environments or if the riverine delivery of U shows some variability, residence time estimates (regardless of their precision) cannot be sensitive indicators of oceanic uranium reactivity. Based on very precise measurements of dissolved uranium in the open ocean, Chen et alJ concluded that uranium may be somewhat more reactive in marine environments than previously inferred. Furthermore, recent studies in high-energy coastal environments " indicate that uranium may be actively cycled and repartitioned (non-conservative) from one phase to the next. 

Fluxes are linear functions of reservoir contents. Reservoir size and the residence time of the carbon in the reservoir are the parameters used in the functions. Between the ocean and the atmosphere and within the ocean, fluxes rates are calculated theoretically using size of the reservoir, surface area of contact between reservoirs, concentration of CO2, partial pressures of CO2, temperature, and solubility as factors. The flux of carbon into the vegetation reservoir is a function of the size of the carbon pool and a fertilization effect of increased CO2 concentration in the atmosphere. Flux from vegetation into the atmosphere is a function of respiration rates estimated by Whittaker and Likens (79) and the decomposition of short-lived organic matter which was assumed to be half of the gross assimilation or equal to the amount transferred to dead organic matter. Carbon in organic matter that decomposes slowly is transferred... 

The concept of average residence time, or turnover time, provides a simple macroscopic approach for relating the concentrations in ocean reservoirs and the fluxes between them. For the single box ocean in Fig. 10-17 the rate of change of the concentration of component n can be expressed as... 

Chemically reactive elements should have a short residence time in seawater and a low concentration. A positive correlation exists between the mean ocean residence time and the mean oceanic concentration however, the scatter is too great for the plot to be used for predictive purposes. Whitfield and Turner (1979) and Whitfield (1979) have shown that a more important correlation exists between residence time and a measure of the partitioning of the elements between the ocean and crustal rocks. The rationale behind this approach is that the oceanic concentrations have been roughly constant, while the elements in crustal rocks have cycled through the oceans. This partitioning of the elements may reflect the long-term chemical controls. The relationship can be summarized by an equation of the form... 

The present sources to the ocean are the weathering of old evaporites (75% of river flux) and CP carried by atmospherically cycled sea-salts (25% of river flux). Loss from the ocean occurs via aerosols (about 25%) and formation of new evaporites. This last process is sporadic and tectonically controlled by the closing of marginal seas where evaporation is greater than precipitation. The oceanic residence time is so long for CP ( 100Myr) that an imbalance between input and removal rates will have little influence on oceanic concentrations over periods of less than tens of millions of years. 

The product fg gives us the fraction of the elements that are permanently removed for each visit to the surface ocean. Conversely l//l/y) gives the number of times an element is recycled before it is permanently removed. For example, for a total ocean residence time of 1600 years, P goes through 105 cycles of 15 years each before being permanently removed. 

There is some debate about what controls the magnesium concentration in seawater. The main input is rivers. The main removal is by hydrothermal processes (the concentration of Mg in hot vent solutions is essentially zero). First, calculate the residence time of water in the ocean due to (1) river input and (2) hydro-thermal circulation. Second, calculate the residence time of magnesium in seawater with respect to these two processes. Third, draw a sketch to show this box model calculation schematically. You can assume that uncertainties in river input and hydrothermal circulation are 5% and 10%, respectively. What does this tell you about controls on the magnesium concentration Do these calculations support the input/removal balance proposed above Do any questions come to mind Volume of ocean = 1.4 x 10 L River input = 3.2 x lO L/yr Hydrothermal circulation = 1.0 x 10 L/yr Mg concentration in river water = 1.7 X 10 M Mg concentration in seawater = 0.053 M. 

Whitfield, M. (1979). The mean oceanic residence time (MORT) concept - a rationalization. Mar. Ghent. 8, 101-123. 

The definition of turnover time is total burden within a reservoir divided by the flux out of that reservoir - in symbols, t = M/S (see Chapter 4). A typical value for the flux of non-seasalt sulfate (nss-SOl"") to the ocean surface via rain is 0.11 g S/m per year (Galloway, 1985). Using this value, we may consider the residence time of nss-S04 itself and of total non-seasalt sulfur over the world oceans. Appropriate vertical column burdens (derived from the data review of Toon et ai, 1987) are 460 fxg S/m for nss-801 and 1700 jig S/m for the sum of DMS, SO2, and nss-S04. These numbers yield residence times of about 1.5 days for nss-S04 and 5.6 days for total non-seasalt sulfur. We might infer that the oxidation process is frequently... 

Figure 13-5 is the box model of the remote marine sulfur cycle that results from these assumptions. Many different data sets are displayed (and compared) as follows. Each box shows a measured concentration and an estimated residence time for a particular species. Fluxes adjoining a box are calculated from these two pieces of information using the simple formula, S-M/x. The flux of DMS out of the ocean surface and of nss-SOl back to the ocean surface are also quantities estimated from measurements. These are converted from surface to volume fluxes (i.e., from /ig S/(m h) to ng S/(m h)) by assuming the effective scale height of the atmosphere is 2.5 km (which corresponds to a reasonable thickness of the marine planetary boundary layer, within which most precipitation and sulfur cycling should take place). Finally, other data are used to estimate the factors for partitioning oxidized DMS between the MSA and SO2 boxes, for SO2 between dry deposition and oxidation to sulfate, and for nss-SO4 between wet and dry deposition. 

More informative is the comparison between the residence times of P in the land and ocean biota. Although there is 5.6 times more biological incorporation of P in the oceans, the standing stock is only 1.7-4.1% of that on land. The residence time of a P atom incorporated into... 

Ruttenberg, K. C. (1993). Reassessment of the oceanic residence time of phosphorus. Chem. Geol. 107,405-409. 

Fig. 15-5 Comparative adsorption of several metals onto amorphous iron oxyhydroxide systems containing 10 M Fej and 0.1 m NaNOs. (a) Effect of solution pH on sorption of uncomplexed metals, (b) Comparison of binding constants for formation of soluble Me-OH complexes and formation of surface Me-O-Si complexes i.e. sorption onto Si02 particles, (c) Effect of solution pH on sorption of oxyanionic metals. (Figures (a), (c) reprinted with permission from Manzione, M. A. and Merrill, D. T. (1989). "Trace Metal Removal by Iron Coprecipitation Field Evaluation," EPRI report GS-6438, Electric Power Research Institute, California. Figure (b) reprinted with permission from Balistrieri, L. et al. (1981). Scavenging residence times of trace metals and surface chemistry of sinking particles in the deep ocean, Deep-Sea Res. 28A 101-121, Pergamon Press.)...

The average residence times for mercury in the atmosphere, terrestrial soils, oceans, and oceanic sediments are approximately 1 yr, 1000 yr, 3200 yr, and 2.5 x 10 yr, respectively. (See Bergan et al. (1999) for more details on atmospheric residence times.)... 

Balistrieri, L., Brewer, P. G. and Murray, J. W. (1981). Scavenging residence times of trace metals and surface chemistry of sinking particles in the deep ocean. Deep-Sea Res. 28A, 101-121. 

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