The figure to the right summarizes both inputs and outputs to ocean basins. Detrital solids carried by rivers 2. Chemical Sediments precipitated from sea water 3. Biological Sediments resulting from organic processes. Chemical Sediments Chemical sediments form from the precipitation of minerals from water when the solution becomes saturated or supersaturated in that particular mineral.
Rivers deliver to the oceans elements dissolved within the water.
There is good geological evidence that the oceans have not significantly changed their chemical composition for several hundreds of million years. This means that as new material is added to sea water, an equal amount of material is removed by precipitation. The average length of time a particular element remains dissolved in sea water is known as its r esidence time , and can be calculated from the total amount of the element in sea water divided by the rate of input to the oceans from rivers. The influx rate is calculated from the average concentration of Ca in river water times the influx of river water to the oceans per year. It is very important to be able to calculate or measure the residence times for elements and compounds in sea water.