Total salinity in the open ocean averages 33-37 ppt, but it can vary significantly in different locations. But since the major ion proportions are constant, the regional salinity differences must be due more to water input and removal rather than the addition or removal of ions. Although the amount of salt in the ocean is relatively constant on time scales of years to decades, sea surface salinity (SSS) varies because freshwater input & output - part of the global hydrologic or water cycle - varies from place-to-place. • An algorithm will account for the variation of seawater composition from the standard composition – using either measured parameters (e.g., total alkalinity, silicate and nitrate) or simply the spatial location (longitude, latitude and pressure) When we talk about salinity, it’s not just sodium and chloride, we’re talking about everything. The beauty of this whole idea is the concept of salinity involves all of these ions, and the salinity varies from place to place. Quantitative analysis of the salt content in different oceans shows that although the total amount of dissolved salt varies from place to place, the major elements are always present in the same relative proportions. This amazing fact is called the principle of constancy of composition. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has approximately 35 grams (1.2 oz) of dissolved salts (predominantly sodium (Na+) and chloride (Cl−) ions). For practical reasons salinity is usually related to the sum of masses of a subset of these dissolved chemical constituents (so-called solution salinity), rather than to the unknown mass of salts that gave rise to this composition (an exception is when artificial seawater is created). Total salinity in the open ocean averages 33-37 ppt, but it can vary significantly in different locations. But since the major ion proportions are constant, the regional salinity differences must be due more to water input and removal rather than the addition or removal of ions. Variations occur in ocean salinity due to several factors. The most common factor is the relative amount of evaporation or precipitation in an area. If there is more evaporation than precipitation then the salinity increases (since salt is not evaporated into the atmosphere). These salts have different chemical compositions and properties. If seawater evaporates from a surface with a slight curve, the different types of salt appear as distinct rings due to their different solubilities.