A permanently ice-covered lake with the highest pH (11.3) of any natural body of a water on Earth. Photosynthetic cyanobacteria thrive under thick ice, using diffuse light to build massive microbial pinnacles.
Wilfried Bauer, CC BY-SA 3.0, via Wikimedia Commons
An otherworldly chemical laboratory
In the Gruber Mountains of Queen Maud Land, Lake Untersee is a body of water sealed from the world. A permanent ice sheet, averaging 3 meters thick, caps the lake year-round. This freshwater lake is one of Antarctica's largest and deepest, measuring 6.5 kilometers long, 2.5 kilometers wide, and reaching a maximum depth of 169 meters. Its defining feature is its extreme water chemistry. The water is exceptionally alkaline, with pH values recorded between 9.8 and 12.1, and is supersaturated with oxygen.
The lake is meromictic, meaning its water layers do not mix. While the main basin is oxygen-rich, a distinct sub-basin in its southern end is anoxic, or completely without oxygen, below a depth of 80 meters. This anoxic zone contains one of the highest concentrations of methane found in any lake on Earth, with levels approaching 21.8 millimoles per liter. This unique chemical environment is a result of the lake's isolation by its thick ice cover, which prevents gas exchange with the atmosphere. Water enters the lake primarily from the melting of the adjacent Anuchin Glacier.
Towers of ancient life
Despite the extreme cold, low light, and chemistry, life persists. The lake floor hosts expansive microbial mats that form large, conical structures resembling stromatolites—some of the earliest fossilized forms of life on Earth. Discovered in 2008 by an expedition led by Dale Andersen of the SETI Institute, these living structures are the largest of their kind found in a modern environment.
The cones are built layer by layer by photosynthetic cyanobacteria, primarily of the genus Phormidium. They can reach heights of up to half a meter. These organisms grow slowly toward the faint sunlight that penetrates the ice, trapping sediment and forming mineral crusts that build the laminated cones over long periods. The lake's constant ice cover protects the fragile structures from wave action and grazing animals, which are absent except for microscopic tardigrades.
Because of its sealed, icy environment and its unique microbial life that thrives without oxygen, Lake Untersee is a significant analog for scientists studying how life might exist on other worlds. Researchers consider it a model for conditions found in the subsurface oceans of icy moons like Jupiter's Europa or Saturn's Enceladus, or in paleolacustrine basins on Mars.
💡Fun Facts
The name "Untersee" is German for "Lower Lake".
The sediment at the bottom of the lake's anoxic basin has the highest methane concentration ever recorded for a lake.
The only animals found in the lake are microscopic invertebrates known as tardigrades, or "water bears," known for their ability to survive extreme conditions.
Scientists first set foot on the lake's ice in 1969, thirty years after it was first spotted during a German aerial reconnaissance flight in 1939.
Not applicable. Access is restricted to scientific expeditions with national Antarctic program permits.
Admission
Not applicable.
Accessibility
The site is extremely remote, located deep within the interior of East Antarctica. Access is only possible via specialized aircraft and tracked vehicles as part of permitted scientific research expeditions.
