Salinity describes the concentration of dissolved salts in water. While sodium chloride is the most common salt, other dissolved minerals like magnesium, sulfate, and calcium also contribute to this measurement. Salinity is typically quantified in grams per liter or kilogram, often expressed as parts per thousand (ppt) or a percentage. The presence of these dissolved salts significantly influences water’s physical properties, such as increasing its electrical conductivity and density, and lowering its freezing point. Water bodies naturally contain varying levels of salts, ranging from very low concentrations in freshwater to an average of 35 ppt in oceans.
The World’s Saltiest Natural Water Body
The Dead Sea, a landlocked salt lake between Jordan, Israel, and the Israeli-occupied West Bank, is the world’s saltiest natural body of water. Its average salinity of approximately 34.2% makes it nearly 10 times saltier than the average ocean. This high salt concentration contributes to its density, allowing people to float effortlessly.
The Dead Sea lies within the Jordan Rift Valley, a geological depression that also makes its shores the lowest land-based elevation on Earth, currently recorded around 439.78 meters (1,443 feet) below sea level. Historically, it has been known by various names, including the “Sea of Salt” in Hebrew, reflecting its most prominent characteristic. Its name, ‘Dead Sea,’ reflects its high salinity, which prevents the survival of most fish and aquatic plants. Its unique mineral-rich waters have also been valued for therapeutic and cosmetic purposes for millennia.
Factors Contributing to Extreme Salinity
The Dead Sea’s extreme salinity results from a combination of geological, hydrological, and climatic factors. It is an endorheic basin, meaning it has no outflow to external bodies of water. Water entering the Dead Sea can only leave through evaporation, which concentrates dissolved salts over time.
The region’s hot, arid climate, characterized by high temperatures and minimal annual rainfall (often less than 50-100 millimeters), drives intense evaporation. Additionally, the Dead Sea’s location in the Jordan Rift Valley, a rift formed by tectonic plate movement, contributes to its unique composition. Rivers and streams, such as the Jordan River, carry dissolved minerals from surrounding rocks and geological deposits into the lake, where they accumulate without an exit point. Human activities, including the diversion of water from the Jordan River for irrigation, have exacerbated this process, reducing freshwater inflow and accelerating the concentration of salts and the decline of the lake’s water level.
Unique Characteristics of Hypersaline Environments
Hypersaline environments, like the Dead Sea, possess distinct physical and chemical properties due to their elevated salt content. One noticeable characteristic is their exceptional density. The Dead Sea’s water, for instance, has a density of approximately 1.24 kilograms per liter, which is why people can float so easily.
The mineral composition of these waters also differs notably from typical ocean water. While ocean water is predominantly sodium chloride (around 85%), the Dead Sea contains much higher concentrations of other salts, including magnesium chloride (about 53%), potassium chloride (around 37%), calcium chloride, and bromide. In fact, the Dead Sea holds the highest concentration of bromide ions found in any body of water on Earth. This extreme salinity creates a challenging environment where most macroscopic aquatic organisms, such as fish and plants, cannot survive. However, specialized microorganisms known as extremophiles, including certain bacteria, archaea, and algae like Dunaliella, have adapted to thrive in these harsh conditions. These organisms have developed unique biological mechanisms to cope with high salt concentrations, sometimes even imparting a reddish hue to the water.
Other Notable Hypersaline Lakes
While the Dead Sea is renowned for its extreme salinity, other notable hypersaline lakes exist around the world, each with unique characteristics. In the United States, the Great Salt Lake in Utah is a prominent example, with salinity levels that can range from 5% to 27% (50 to 270 ppt), depending on water levels and specific sections of the lake. Like the Dead Sea, it is a terminal lake, leading to salt accumulation. This lake supports an ecosystem of brine shrimp and brine flies, earning it the nickname “America’s Dead Sea”.
Lake Assal in Djibouti is another highly saline body of water and is the lowest point in Africa, lying 155 meters below sea level. Its average salt concentration is about 34.8%, reaching up to 40% at greater depths, making it saltier than the Dead Sea in some areas and often cited as the second or third saltiest lake globally. Further to the extreme, Don Juan Pond in Antarctica is often considered the saltiest body of water on Earth, with salinity measurements reaching as high as 45.8% to over 47%. Dominated by calcium chloride, this pond remains liquid even at temperatures as low as -50°C due to the salt’s interference with water’s freezing point. Gaet’ale Pond in Ethiopia is also a contender for the highest salinity, with some measurements exceeding Don Juan Pond’s.