microbial cities – A new study in PNAS points to dense communities of microbes living inside “marine snow” as a driver of faster calcite dissolution and greater carbon dioxide release—processes that could weaken the ocean’s ability to store carbon long term.
When “marine snow” drifts downward—part dead plankton shells. fish poop. dust. and other debris—it is supposed to carry carbon away from the atmosphere.. But researchers have now identified a hidden population living inside those sinking particles: dense microbe “cities” that can dissolve the shells they inhabit and help turn stored carbon back into carbon dioxide.
The findings. published in the Proceedings of the National Academy of Sciences (PNAS). trace how those microscopic neighborhoods may reduce the ocean’s carbon-trapping capacity.. The ocean already relies on this slow descent to move atmospheric carbon into long-term storage.. Yet scientists have long noted that something was dissolving calcite shells and releasing carbon dioxide instead.
The new work says the culprit is not just chemical conditions in the water column. It’s the way microbes reshape the tiny chemistry around themselves—inside what looks like floating debris to the naked eye.
To understand how these microbe communities work. lead author Benedict Borer. a biogeochemist at Rutgers University. and his team “brought the ocean into the laboratory.” They used a microfluidic chip designed to mimic marine-snow particles.. Into that chip, they introduced microbes and fluorescent molecules that changed glow depending on oxygen levels and acidity.
The setup was so sensitive that even routine human breathing in the lab interfered with the measurements at first, according to the study’s description.
The microbial “cities” didn’t just coexist with the calcite shells.. Their chemical microenvironments increased calcite dissolution.. The pathway starts with oxygen-breathing microbes that feed on carbon and then release carbon dioxide.. Once the carbon dioxide enters seawater, it can become carbonic acid.
In the tight quarters around marine-snow particles. the researchers say the sheer number of microbes breathing locally creates concentrated pockets of carbonic acid in and around the debris.. That acid then helps dissolve the calcite, reducing the shell structure that would otherwise help bury the carbon.
There’s another catch: as the particles dissolve and become lighter, they sink more slowly. In the researchers’ account, this extra time in the water column could give the carbon more opportunity to escape before it reaches deep-ocean storage.
How much this all shifts ocean acidity on a global scale remains unknown. The team says more research is needed to calculate microbial cities’ full influence because dissolved calcite can counteract carbonic acid to an extent.
The scale of the microbial problem is enormous.. Co-author Andrew Babbin. an oceanographer at the Massachusetts Institute of Technology. points to how dense microbial life is in the sea: a shot glass of seawater can contain millions of bacterial cells.. He adds that if every bacterial cell in the ocean were lined up end to end. the chain would stretch 50 times around the Milky Way.
For outside experts, the work fits a broader message: major ocean chemistry changes may hinge on microscopic interactions.. “Large-scale biogeochemical processes often depend on very small-scale interactions. ” said Hongjie Wang. an oceanographer at the University of Rhode Island who was not involved in the study.
Babbin agrees, framing the stakes in planetary terms: “Ultimately everything that’s happening at these microscales—that’s really what’s terraforming our planet.”
marine snow microbial cities ocean carbon storage calcite dissolution carbonic acid biogeochemistry PNAS microfluidic chip