Below the surface of the sea, tiny clumps of material slowly sink toward the seafloor. They include plankton remains and other organic matter. Scientists call them “marine snow.” As they fall, these flakes transport carbon that can remain out of the atmosphere for a long time.
But they do not all reach the same depths. Bacteria feed on them during their descent. Some clumps break apart quickly, while others remain intact much longer. Why this difference?
Marine snow particles falling through the water column. They transport organic matter from the upper layers to the depths.
Source: Wikimedia Commons.
Californian researchers have discovered that their consistency plays an important role. Some flakes are quite fluid, while others form a very thick, jelly-like material. Using a microscope and fluorescent molecules, the team observed how bacteria colonize their surface and move inward.
Microbes easily penetrate the least viscous regions. By contrast, the stickier parts slow them down: they must first break down the material to move forward. These thick clumps therefore resist degradation more effectively, giving them more time to sink toward the deep ocean.
To understand the consequences of this phenomenon, the researchers combined their experiments with simulations. Their results indicate that highly viscous particles could transport more than six times as much carbon to the depths as less viscous ones.
This figure remains an estimate based on experiments and calculations. But it shows that a detail long overlooked could change our understanding of the carbon cycle.
The oceans naturally contribute to carbon storage. When it sinks very deep, some of it can remain there for centuries. To better estimate this amount, scientists will now need to consider not only the size and sinking speed of the flakes, but also their consistency.