Salinity describes the concentration of dissolved salts in a body of water, typically expressed as parts per thousand (ppt) or a percentage. The average global ocean salinity is approximately 3.5%. While the source of these salts comes from geological deposits and mineral leaching, the ultimate factor determining a water body’s extreme saltiness is the rate of water loss. When evaporation significantly exceeds the inflow of fresh water, the remaining water becomes hypersaline as the dissolved minerals are left behind and concentrated.
Identifying the World’s Saltiest Body of Water
The body of water holding the title for the highest sustained salinity concentration is Don Juan Pond, located in the McMurdo Dry Valleys of Antarctica. This small, shallow basin often registers a salinity level exceeding 40%, with some measurements reaching as high as 45.8%. This concentration makes the pond approximately 12 to 13 times saltier than the average ocean.
The pond’s brine has a unique chemical composition, dominated by calcium chloride (\(CaCl_2\)) rather than the sodium chloride found in ocean water. This high concentration of salt drastically lowers the water’s freezing point. Consequently, Don Juan Pond remains liquid even when air temperatures drop to -50 degrees Celsius.
Although called a “pond” due to its small size and extreme shallowness—its depth rarely exceeds 30 centimeters—its status as the saltiest natural body of water is consistently recognized.
The Geology of Hypersalinity
Extreme salinity requires a specific set of geological and climatic conditions to develop and persist over time. The fundamental requirement is that the water body must be part of an endorheic basin, meaning it is a closed system with no outlet. Inflow brings dissolved salts into the basin, but since water can only leave through evaporation, the mineral salts accumulate.
A high rate of evaporation is the mechanism that concentrates these salts, which typically occurs in arid environments. This process is evident in Don Juan Pond, situated in the extremely cold and dry McMurdo Dry Valleys, where moisture is rapidly lost to the atmosphere. The source of the salts often originates from the surrounding rock and soil, which are naturally rich in specific minerals that leach into the water.
The calcium chloride brine in Don Juan Pond is thought to be fed by deep groundwater that upwells into the basin. As the water evaporates, salts precipitate and form mineral deposits around the margins of the pond. This cycle of inflow, evaporation, and mineral deposition sustains the water body’s stable and extraordinary salt concentration.
Unique Life Forms in Extreme Salt Environments
The high salt concentrations in hypersaline environments create conditions hostile to most forms of life, forcing organisms to develop specialized biological adaptations for survival. Life forms that thrive here are known as extremophiles, specifically categorized as halophiles, or “salt-lovers.” These organisms must overcome the physiological challenge of osmotic pressure, where the surrounding salty water tends to draw water out of the cells.
Halophiles, which include certain types of bacteria, archaea, and algae, maintain their internal water balance by accumulating compatible solutes, such as potassium chloride, inside their cells. This process equalizes the osmotic pressure, preventing cellular dehydration. For instance, the algae Dunaliella salina synthesizes high concentrations of beta-carotene to protect itself from intense sunlight.
The presence of certain halophilic bacteria and archaea often gives the water or the surrounding salt flats a distinct coloration. In highly saline waters, these organisms produce pigments that result in striking red, pink, or purple hues.
Salinity Comparison with Other Famous Lakes
When comparing Don Juan Pond’s peak salinity of over 40% to other famous hypersaline bodies, the magnitude of its salt concentration becomes clear. The Dead Sea, often mistakenly cited as the world’s saltiest body of water, maintains a salinity of approximately 33.7% to 34.2%. This measurement is roughly 9.6 times saltier than the world’s oceans.
The Great Salt Lake in Utah, the largest salt lake in the Western Hemisphere, has a highly variable salinity, typically fluctuating between 5% and 27%. This variability depends heavily on the lake’s water level and the amount of freshwater inflow it receives. Its northern arm, separated by a causeway, often reaches the higher end of this range.
Even at its saltiest, the Great Salt Lake falls significantly below the Dead Sea, which in turn is less saline than Don Juan Pond. This comparison highlights how the unique conditions in the Antarctic Dry Valleys allow Don Juan Pond to achieve an unmatched salt concentration.