Excerpt from "Microbes in underground aquifers beneath deep-sea Mid-Atlantic Ridge 'chow down' on carbon," posted on NSF News, April 23, 2018.
All life on Earth -- from blue whales to microbes -- uses carbon in one form or another. But all carbon is not created equal.
In the oceans, some carbon-containing compounds, such as sugars and proteins, are quickly gobbled up by microorganisms, while others -- such as the chitin found in fish scales -- are much harder to consume.
Scientists have long believed that relatively little of the latter, called "refractory carbon," is degraded in the ocean. Much of it falls to the ocean floor and helps make up deep-water sediment, or so the thinking has been.
Deep-sea underground aquifers change the picture
Now a research team led by ecologists Sunita Shah Walter of the University of Delaware and Peter Girguis of Harvard University has shown that underground aquifers near the undersea Mid-Atlantic Ridge act like natural biological reactors, pulling in cold, oxygenated seawater, and allowing microbes to consume more -- perhaps much more -- refractory carbon than scientists believed.
"This work shows that the vast sub-seafloor community of microbes can be fed by seawater circulating through deep ocean crust," said Michael Sieracki, a program director in the National Science Foundation's Division of Ocean Sciences, which funded the research through its Center for Dark Energy Biosphere Investigations and International Ocean Discovery Program. "In turn, these microbes change the composition of the seawater that circulates back to the ocean." The results are published this week in the journal Nature Geoscience.
"This has the prospect of reshaping the way we think about carbon cycling in the deep ocean," Girguis said. "We know that carbon is produced at the surface by photosynthetic algae. We know fish eat some of it. We know some of it sinks. We can account for that, but we've had some giant questions in our 'carbon budget.'"
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