RECENTLY RESEARCHERS discovered a freakish submarine lake of liquid carbon dioxide trapped under a layer of sediment in the Okinawa Trough hydrothermal system. An accompanying commentary article reports that globules of liquid carbon dioxide have been found in the deep ocean before, but such lakes were not anticipated since liquid carbon dioxide is less dense than sea water until a depth of 3000-3800 meters (at deeper depths the density once again decreases). This lake was found at a depth of 1400 meters, and is only able to exist because it is capped with a sediment-overlain layer of sulfur-rich carbon dioxide hydrate. Even more amazingly, the carbon dioxide lake appears to contain bacteria.

A video included in the supporting information shows deep sea creatures including crabs and shrimp, black smokers, and transparent jets of carbon dioxide leaking out of cracks in the sea floor. In one scene the submersible drills a core from the lake’s cap and a streamer of liquid carbon dioxide sprays up into the ocean like water from a fireman’s hose.

Liquid carbon dioxide is of great interest to some chemists as a solvent because it is extremely nonpolar, but this makes it an unfriendly environment for life. In spite of this, these scientists found bacteria floating around in the lake. They were at a much lower density than those in the sediment cap, but testing revealed that live bacteria in the liquid carbon dioxide were oxidizing methane. Bacteria identified include several types of archaea and unidientified sulfur-reducing bacteria from several proteobacteria groups. However, it seems that these prokaryotes are insufficient to explain the methane consumption, and the authors theorize that the lake may contain unknown chemolithotrophs. It’s possible that the identified prokaryotes were set adrift in the lake and are accidental survivers from the sediment above. Perhaps unknown methane-consuming bacteria inhabit the lake or its shores, living in the carbon dioxide hydrate layer just below the sediment. In this less harsh environment these bacteria would find ample carbon sources below and mild seawater above.

“Microbial community in a sediment-hosted CO2 lake of the southern Okinawa Trough hydrothermal system.” Inagaki, F., et al. Proceedings of the National Academy of Sciences, USA. 2006, 103, 14164-14169.

“Lakes of liquid CO2 in the deep sea.” Nealson, K. Proceedings of the National Academy of Sciences, USA. 2006, 103, 13903-13904.