Far below the waves, a constant drizzle of organic debris drifts toward the seabed. Scientists call it marine snow: clumps of dead plankton, faecal pellets, mucus and mineral grit. A new study suggests that how sticky these clumps are goes a long way toward explaining how much carbon the ocean can hide away.
The numbers behind the question are huge. Each year, sinking particles haul more than ten gigatonnes of carbon downward from the sunlit layer, yet only somewhere between one and three billion tonnes ends up deep enough to stay locked away for centuries. Most of it is eaten by bacteria on the journey down and released again as carbon dioxide.
A team from Lincoln in England and the Scripps oceanography institute in California set out to watch that feeding process up close. Combining 3D confocal imaging with fluorescent probes that respond to viscosity, they mapped the internal texture of single flakes and tracked live microbes moving across them. Their results, published in Science, show bacteria colonise runny patches easily but struggle to break into the thicker regions.
That resistance buys time. Laboratory tests showed viscous particles degrade and fragment more slowly, and simulations indicate they sink further as a result. By the team’s estimate, the thickest flakes can transport over six times more carbon into the abyss than thin, watery ones. Lead author Bryce Inman compares the microbes to a worm burrowing through fruit: easy going in the soft outer part, hard work once it reaches the centre.
The imaging method could prove useful well beyond oceanography. Microbes live in slimy habitats everywhere, whether on reefs, among seaweed, around roots in the soil or inside our own intestines. Inman says mucus turned out to have bulges and crevices nobody had seen before, opening a new way to study how bacteria behave in the places they call home.
