The chemical composition of sea water is practically constant in all parts of the ocean except for elements that are present in small quantity and which are needed for the growth of organisms. Life in the sea depends mainly upon the development of the microscopic plants, or the phytoplankton, as they are called. The phytoplankton develops in the upper 100 meters of water where sun-light is effective, as long as certain mineral nutrients, such as nitrates, phosphates, silicates, and iron compounds, are present above certain minimum quantities. If the amount of any of one of the inorganic requisite foods for the phytoplankton drops below the particular minimum, the growth of phytoplankton ceases and no more phytoplankton develops until the essential nutrients have been repl nished. Organisms when they die are decomposed by bacteria and the mineral substances that they contain and which are essential for plant life are returned to the sea again, mostly below the zone of photosynthesis. If this subsurface water rich in nutrients is raised to the surface by turbulence, convection, or currents the phytoplankton begins to grow again. The phytoplankton removes carbon dioxide from the surface layers of water, thus tending to make them over-saturated with respect to calcium carbonate. Below the zone of photosynthesis, decomposing organic matter gives off carbon dioxide to the water, which tends to make the deep water undersaturated with calcium carbonate. Organisms in the sea contain a larger percentage of metals, such as copper, zinc, arsenic, and even gold and si ver, than does the water itself. Some of these metals are needed for the metabolic process of the organisms, others are adsorbed on the surface of the organisms. (Editor's abstract.)