The lake's existence seems to confirm a study published in PNAS earlier this month by Kurt Zenz House, a graduate student at Harvard University in Cambridge, Massachusetts.
In that study House postulates that a hydrate cap could be created deliberately as a way to sequester CO2 beneath the seas.
"It's an interesting paper," House says of the latest find.
Kenneth Nealson, a geobiologist at the University of Southern California in Los Angeles, agrees.
In a soon-to-be-published commentary, Nealson notes that while liquid CO2 has been found at other undersea volcanoes, few had expected it to accumulate in the manner seen by Inagaki's team.
"How many such lakes are there?" he writes. "How stable are they, and are they potential players in the global carbon cycle?"
Inagaki's team also looked at the impact of the lake on microbes living in its vicinity.
They found high numbers of bacteria above the hydrate cap, but only one percent as many adjacent to the liquid CO2 layer.
"That suggests that the presence of the liquid carbon dioxide is having a negative effect on the microbial communities," House said. "They still exist, but are much more sparse."
That's important to know, he adds, because if humans seriously attempt to dispose of large amounts of CO2 in the seafloor, it will create much larger artificial lakes.
Study co-author Inagaki adds that it's startling that any microbes exist within the liquid CO2 layer.
They probably survive in "microhabitats" within the complex mixture of carbon dioxide, hydrates, and seawater found in the sediments, he says.
"If we can find a similar environmental setting at the subsurface of polar Mars we may find a similar habitat for life," he said by email.
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