A Most Unusual Lake

4 min read

Lake Unter-See in Antarctica, sealed beneath thick ice, contains unusually high levels of dissolved oxygen and cone-shaped microbial reefs resembling some of Earth’s oldest fossils.

NASA Earth Observatory

• Landsat 9 — OLI

• Glaciers & Ice Sheets
• Surface Water

Scientists estimate that Earth is home to more than 100 million lakes. Among the most unusual is Lake Unter-See, one of Antarctica’s largest and deepest surface lakes, known for its distinctive water chemistry. Its ice-covered waters have exceptionally high levels of dissolved oxygen, low dissolved carbon dioxide, and a strongly alkaline (basic) pH.

The OLI (Operational Land Imager) on Landsat 9 captured this image on February 16, 2026, during the Antarctic summer. Most of the lake's water comes from seasonal meltwater draining from the margins of the nearby Anuchin Glacier, which flows south from the Gruber Mountains in Queen Maud Land.

With mean annual temperatures of about minus 10 degrees Celsius (14 degrees Fahrenheit), Lake Unter-See remains frozen year-round, its waters sealed beneath several meters of ice. Sunlight penetrates the ice and warms the water below, but the cold surface and strong winds drive evaporation and sublimation, preventing significant surface melting. The lake's maximum depth is thought to reach nearly 170 meters (558 feet).

The lake’s water chemistry is unusual partly because it is one of the only perennially frozen lakes with a community of large, conical stromatolites. The layered microbial reef structures grow slowly upward as photosynthetic microbes—primarily cyanobacteria—trap sediment on their sticky surfaces and form calcium carbonate mineral crusts. These conical stromatolites—as well as pinnacle and flat forms of the microbial communities—release oxygen that becomes trapped under the ice, increasing its concentration in the lake.

Lake Unter-See's stromatolites, southwestern Greenland and western Australia.

The scientists noted that similar periodic flooding may provide "biological stimuli to other carbon dioxide-depleted Antarctic ecosystems and perhaps even icy lakes on early Mars.”

Some Antarctic lakes, such as Lake Joyce in the McMurdo Dry Valleys, contain conical stromatolites, but they reach only a few centimeters tall. By contrast, the formations in Lake Unter-See tower up to half a meter. Scientists think Unter-See's stromatolites grow unusually tall because they are sheltered from tides and waves beneath permanent ice, live in exceptionally clear waters with little sediment, grow toward limited light, and face little grazing. The lake’s largest creatures are tardigrades—microscopic "water bear" invertebrates known for their ability to survive in extreme environments.

Astrobiologists also point to the lake as a possible analog for the type of environment where life might have formed or survived on icy moons with oceans such as Europa and Enceladus, or perhaps on Mars, which has ice caps and glaciers.  

Yet despite its seemingly stable conditions, Lake Unter-See occasionally experiences abrupt changes. During fieldwork in 2019, researchers observed an increase in the lake’s water levels. The team, led by scientists at the University of Ottawa, later analyzed elevation data from NASA’s ICESat-2 (Ice, Cloud, and Land Elevation Satellite-2) and confirmed a 2-meter rise was caused by a glacial lake outburst flood from nearby Lake Ober-See.

The University of Ottawa team also showed that the outburst flood had released 17.5 million cubic meters of meltwater, altering Unter-See’s pH and replenishing it with carbon dioxide-rich waters that likely enhanced the productivity of the lake's microbial life. The scientists noted that similar periodic flooding may provide "biological stimuli to other carbon dioxide-depleted Antarctic ecosystems and perhaps even icy lakes on early Mars.”

NASA Earth Observatory image by Michala Garrison, using Landsat data from the U.S. Geological Survey.Story by Adam Voiland.

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February 16, 2026

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References & Resources

• Andersen, D.T., et al. (2011) Discovery of large conical stromatolites in Lake Untersee, Antarctica. Geobiology, 9(3), 280-293.
• Astrobiology (2026) Dale Andersen's Field Reports. Accessed March 10, 2026.
• Austrian Polar Research Institute (2023, May 22) Glacier shapes unique Antarctic lake ecosystem. Accessed March 10, 2026.
• Extinct (2025, June 1) From Stromatolites to Martian Leopard Spots: Circumstantial Traces and the Reconstruction of Early Life. Accessed March 10, 2026.
• Faucher, B., et al. (2021) Glacial lake outburst floods enhance benthic microbial productivity in perennially ice-covered Lake Untersee (East Antarctica).Communications Earth & Environment, 2, 211.
• Greco, C. et al. (2020) Microbial Diversity of Pinnacle and Conical Microbial Mats in the Perennially Ice-Covered Lake Untersee, East Antarctica. Frontiers in Microbiology, 11(607251).
• NASA Earth Observatory (2006, June 18) Strelley Pool Chert and Early Life. Accessed March 10, 2026.
• SETI (2026, February 26) Dale Andersen’s Antarctic Field Season 18-19 February. Accessed March 10, 2026.
• Verpoorter, C., et al. (2014) A global inventory of lakes based on high-resolution satellite imagery. Geophysical Research Letters, 41(18), 6396-6402.
• Vimercati, L. Lake Untersee, Queen Maud Land, Antarctica. Accessed March 10, 2026.

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