Salinity is the concentration of dissolved salt content in a body of water, primarily consisting of sodium chloride (common table salt), magnesium, and calcium ions. The world’s oceans maintain a stable salinity level, typically hovering around 35 parts per thousand (ppt), or 3.5%. This consistent chemical balance is due to the ocean’s immense volume and constant circulation. Some landlocked bodies of water, however, defy this oceanic norm, reaching concentrations far beyond what any marine environment can sustain.
The World’s Saltiest Body of Water
The saltiest large body of water is the Dead Sea, a hypersaline lake bordering Jordan, Israel, and the West Bank. This natural feature lies in the Jordan Rift Valley, with its surface being the lowest land elevation on Earth. The Dead Sea’s average salinity is approximately 340 parts per thousand, nearly ten times saltier than the open ocean.
This extreme salt concentration creates a unique environment where the water density is so high that human bodies are naturally buoyant. Visitors can float effortlessly on the surface, a phenomenon resulting from the high mass of dissolved salts increasing the water’s specific gravity. The name “Dead Sea” reflects this hostile environment, as the high salinity prevents the survival of fish or other macroscopic aquatic life.
Measuring Saltiness
Salinity is quantified using the standard unit Parts Per Thousand (ppt). This measurement represents the mass of dissolved salt in grams found within one kilogram of water. For oceanographic studies, the Practical Salinity Unit (PSU) is also used, which is based on the water’s electrical conductivity and is numerically very close to ppt.
Standard ocean water contains about 35 grams of dissolved salt for every 1,000 grams of water, equating to 35 ppt. In contrast, the Dead Sea’s measurement of 340 ppt means that 340 grams of salt are present in the same volume. Scientists determine this concentration by measuring the water’s electrical conductivity, as salt ions significantly increase how well the water conducts electricity.
Factors Creating Hypersalinity
Hypersaline bodies of water require a specific combination of geological and climatic circumstances. One significant factor is a consistently high rate of water evaporation. These lakes are typically located in hot, arid desert climates where the rate of water turning into vapor far exceeds the rate of water replacement from precipitation.
The other necessary condition is the presence of an endorheic basin, a drainage system that retains water and does not allow for outflow to the ocean. Rivers and streams flow into these basins, bringing a continuous supply of dissolved minerals and salts leached from the surrounding rocks and soil. Since water can only exit the basin through evaporation, the salts are left behind to accumulate in concentration over millennia.
This constant cycle of inflow and evaporation acts as a massive natural concentration mechanism. The surrounding geology provides a rich source of mineral deposits carried into the lake by tributary rivers. Over time, this process results in the water becoming saturated with salts, turning it into the dense brine characteristic of hypersaline lakes.
Other Noteworthy Hypersaline Lakes and Seas
While the Dead Sea is the most famous example, several other landlocked lakes reach remarkable salt levels. Lake Assal in Djibouti, located in the Afar Depression, often surpasses the Dead Sea in salinity, reaching concentrations of approximately 34.8%. This lake is also an endorheic basin and is the lowest point in Africa.
Another recognized hypersaline water body is the Great Salt Lake in Utah, USA, a remnant of the ancient Lake Bonneville. Its salinity fluctuates, ranging from about 5% to 27% in different sections, which is still several times saltier than the ocean. The northern arm of the lake, separated by a causeway, can reach levels near 320 ppt, rivaling the Dead Sea.
For the most extreme concentration, a smaller, hot spring-fed pool named Gaet’ale Pond in Ethiopia holds the record with a salinity measured at 43.3%. This isolated pool demonstrates that the highest salt concentrations occur in the most restricted environments where evaporation is maximized and mineral input is intense.