Lake Unter-See in Antarctica is one of Earth's most unusual lakes. It is known for its unique water chemistry. The lake has very high levels of dissolved oxygen and low carbon dioxide. It also has a strongly alkaline pH.
A Frozen Lake with Ancient Life
The Operational Land Imager (OLI) on Landsat 9 captured an image of the lake on February 16, 2026. Most of its water comes from meltwater from the Anuchin Glacier. This glacier flows from the Gruber Mountains in Queen Maud Land.
Lake Unter-See stays frozen all year. Its waters are sealed beneath several meters of ice. Sunlight can get through the ice and warm the water. However, the cold surface and strong winds cause evaporation and sublimation. This prevents significant surface melting. The lake is thought to be almost 170 meters (558 feet) deep.
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SETI geobiologist Dale Andersen and his team discovered Lake Unter-See's stromatolites in 2011. They offer a look back more than 3 billion years ago. At that time, microbes were the only life on Earth. These formations are thought to be living examples of organisms that created some of Earth's oldest fossils. These ancient stromatolites are found in places like southwestern Greenland and western Australia.
Other Antarctic lakes, like Lake Joyce, have conical stromatolites. But they are only a few centimeters tall. The formations in Lake Unter-See, however, can reach up to half a meter. Scientists believe these stromatolites grow so tall because they are protected from tides and waves by permanent ice. They also live in very clear waters with little sediment. They grow towards limited light and face little grazing. The largest creatures in the lake are tardigrades, also known as "water bears." These microscopic invertebrates can survive in extreme environments.
Astrobiologists also see Lake Unter-See as a possible example of where life might have formed or survived on icy moons. Moons like Europa and Enceladus have oceans. Mars also has ice caps and glaciers, making it another potential analog.
Unexpected Changes and Solutions
Despite its stable conditions, Lake Unter-See can change suddenly. In 2019, researchers saw the lake's water levels rise. A team from the University of Ottawa used data from NASA’s ICESat-2 satellite. They confirmed a 2-meter rise. This was caused by a glacial lake outburst flood from nearby Lake Ober-See.
The University of Ottawa team found that the flood released 17.5 million cubic meters of meltwater. This changed Unter-See’s pH and added carbon dioxide-rich waters. This likely boosted the microbial life in the lake. Scientists noted that similar floods might provide "biological stimuli to other carbon dioxide-depleted Antarctic ecosystems and perhaps even icy lakes on early Mars.”
Deep Dive & References
- Discovery of large conical stromatolites in Lake Untersee, Antarctica - Geobiology, 2011
- Glacial lake outburst floods enhance benthic microbial productivity in perennially ice-covered Lake Untersee (East Antarctica) - Communications Earth & Environment, 2021
- Microbial Diversity of Pinnacle and Conical Microbial Mats in the Perennially Ice-Covered Lake Untersee, East Antarctica - Frontiers in Microbiology, 2020
- A global inventory of lakes based on high-resolution satellite imagery - Geophysical Research Letters, 2014
