The Great Salt Lake in Utah stands as the largest saline lake in the Western Hemisphere, defined by its lack of an outlet to the ocean. As a terminal lake, all water that enters the basin eventually leaves only through evaporation, a process that continuously concentrates the dissolved minerals within. This mechanism has created an environment with salt levels far exceeding those of the world’s oceans, resulting in a unique ecosystem and a highly variable chemical profile. The amount of salt in the lake is a dynamic measurement that reflects the balance between freshwater inflow and relentless evaporation.
Quantifying the Great Salt Lake’s Salinity
The concentration of salt in the Great Salt Lake is measured as a percentage of dissolved solids by weight, and it is highly variable depending on the lake’s volume. Historically, the overall salinity of the main body of water has ranged from approximately five percent to nearly 27 percent. This immense variability is a defining characteristic of the lake, directly tied to fluctuations in water level.
The average salinity of the global ocean is consistently around 3.5 percent. This means the Great Salt Lake can be anywhere from one-and-a-half to almost eight times saltier than seawater. The high concentration of dissolved solids increases the water’s density, a property measured as specific gravity.
Scientists use specific gravity to accurately determine the total amount of dissolved solids present. This density allows people to float easily in the lake’s brines. This extreme environment allows only specialized organisms, like brine shrimp and brine flies, to survive, while most other aquatic life cannot tolerate the high osmotic pressure.
Geological Origins of the Mineral Content
The immense quantity of salt currently in the Great Salt Lake is a legacy of a much larger, prehistoric body of water known as Lake Bonneville. This massive freshwater lake covered much of the Great Basin region during the Pleistocene epoch, but it began to recede and evaporate roughly 13,000 years ago. The modern Great Salt Lake is essentially the deepest, lowest remnant of that ancient lakebed.
Although Lake Bonneville was considered a freshwater lake, it contained dissolved minerals carried in by inflowing rivers and streams. As the lake shrank, the process of terminal drainage meant these minerals had nowhere to go. The water evaporated, leaving the dissolved salts behind to accumulate and concentrate.
The lake continues to receive dissolved minerals from its three major tributaries: the Bear, Weber, and Jordan Rivers. These waterways carry dissolved solids into the lake each year, leached from the surrounding soil and rock. Because there is no outflow, this continuous influx of minerals sustains the lake’s hypersaline condition.
Specific Chemical Makeup of the Dissolved Salts
The salts of the Great Salt Lake are not composed solely of sodium chloride. Instead, the water is a complex brine containing a variety of dissolved ions, similar to seawater but with distinct differences. The major dissolved components are Sodium and Chloride, but there are also high concentrations of Sulfate, Magnesium, and Potassium.
Compared to the ocean, the lake’s brine is notably enriched in potassium and slightly lower in calcium. When the lake level drops and the salinity rises, the relative proportions of these minerals change because sodium chloride is the first to precipitate out of the solution. This chemical complexity is leveraged by industries that extract valuable compounds from the lake, including common salt, potassium sulfate (potash), and magnesium chloride.
The specific ionic composition allows for the commercial production of various mineral salts through solar evaporation ponds adjacent to the lake. The brine’s unique chemical fingerprint, including a high concentration of lithium, further differentiates the lake’s composition from standard ocean water.
Water Level Dynamics and Concentration Changes
The amount of salt dissolved in the water constantly changes based on the balance between water inflow and evaporation, a condition exaggerated by the lake’s shallow depth. When the lake’s water level drops during drought, the existing salt mass is dissolved in a smaller volume of water, causing the concentration to spike. Conversely, during wet years, the influx of freshwater dilutes the brine, lowering the salinity.
A major factor influencing the lake’s salinity profile is the solid railroad causeway that was built across the lake in 1959, effectively dividing it into two distinct arms. The causeway significantly restricts water circulation, creating two chemically different environments. The South Arm, or Gilbert Bay, receives almost all the freshwater inflow from the major rivers and maintains a lower salinity, typically ranging from eight to fifteen percent.
The North Arm, or Gunnison Bay, is cut off from this freshwater source and relies only on evaporation. This isolation causes the North Arm to become hypersaline, with concentrations often reaching 24 to 28 percent, near the saturation point. This extreme difference in salt concentration is highly visible, as the hyper-saline North Arm often appears pink due to the proliferation of specific salt-tolerant microbes.