In turn, these chemical variations can have a profound impact on rates of biological processes. The distributions of dissolved elements in the ocean are generally controlled by the interplay of three processes. The major flow of ocean currents, called the conveyor , transports ocean waters horizontally from the major sources of deep water in the Atlantic Ocean to the deep waters of the Pacific Ocean. Finally, the distributions of some elements may reflect external sources that act as a source of elements to the ocean or a sink that removes elements.
Elemental distributions fall into five major categories.
The only process that create detectable changes in their concentrations are the addition or removal of water by precipitation or evaporation. Conservative elements typically have residence times greater than several hundred thousand years. Sources or sinks of these elements are so small, relative to the amount in the ocean, that they do not produce appreciable impacts on the concentration. As an example, look at the distribution of sodium. The euphotic zone may range from a few meters deep in particle rich coastal waters to 150 m in the clearest ocean waters.