In 1865, Johann Georg Forchhammer found that the ratio of major salts in samples of seawater from various locations was constant. This constant ratio is known as Forchhammer's Principle, or the Principle of Constant Proportions. The ocean appears in chemical equilibrium. This means the proportion and amounts of dissolved salts per unit volume of ocean are nearly constant. The theory that is used to suggest that ions are added to the ocean at the same rate they are removed is the concept of residence time.
Residence time is the average length of time an element spends in the ocean.
Plants and animals in the ocean depend on these dissolved gases to survive. Living organisms need nitrogen to build proteins and other important biochemicals, but they can not use the nitrogen directly. The nitrogen must first be fixed into a usable chemical form by specialized organisms. Most of the nitrogen compounds must be recycled among the organisms themselves. Most of the ocean's oxygen comes from photosynthetic plants.