Volume of ocean

Table 10-1 Area, mean depth, and volume of oceans and seas...

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. 

The whole volume of oceanic water is considered as a single biocenosis in which the flux of organic matter produced in surface layers then descending to the bottom of the ocean is the main connecting factor. All model parameters are assumed to be able to change as functions of place and time, and their parametric description is made by average characteristics (i.e., deterministic models). 

If this continued over geologic time, the ocean would consist of nothing but sulphate. You must have some sink in the ocean. There is a possible sink that is the hydrothermal circulation in the bottom of the ocean. The entire volume of ocean water apparently passes through the top one or two kilometers of the crust every ten million years, and the sulphate is probably taken out at that time. 

When one considers the size of the ocean— its 10 1. of water covers 71% of the earth s surface—and its importance as the climatic mediator, as the source of food and materials, and as the ultimate sink for many of our pollutants, it is surprising how little is actually known about it. Only in very recent years has the volume of ocean research, chemical and otherwise, started increasing rapidly. With this increase has come an awareness of the inadequacy of our methodology. 

Recovery of Plutonium, Americium, Uranium and Polonium from Large Volumes of Ocean Water, Anal, Chem, (1974) 46, 1334. 

Present-day spreading rates allow us to estimate the volume of oceanic crust, which is subducted annually. Estimates are between 18 and 20 km3/ yr, the differences being in part due to different assumptions about the average thickness of the oceanic crust. If this rate of subduction has been constant over geological time, then the Earth s mantle should contain 5 % recycled oceanic crust (Helffrich Wood, 2001), although if this were concentrated in the upper part of the mantle then, of course, the proportion would be considerably greater. 

It can be seen that the shape of the ocean basins and the distribution of continental masses have an important effect on currents and the location of high productivity zones. The degree of flooding of continental margins, which is controlled by the relative volumes of ocean basins and seawater, is also important in terms of the area of productive coastal waters. Nutrient supply from land, via rivers, can contribute to the productivity of shelf seas. 

The total volume of ocean water is about 1 X 10 L. Thus, the ocean contains an almost inexhaustible supply of hydrogen. 

A l.O-mL volume of seawater contains about Ams 4.0 X 10 g of gold. The total volume of ocean... 

As we have seen in Chapter 7.2, its capacity for diluting trace elements added to it from industrial sources appears more than adequate. Such problems as arise from the discharge of metals into the hydrosphere appear to be entirely due to inadequate dispersion in the total volume of ocean water, and if it were possible to disperse all metal-containing industrial wastes immediately and completely in the ocean, this would be the ideal part of the hydrosphere for their reception. 

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