TINY ORGANISMS HAVE A BIG IMPACT ON THE EARTH’S CARBON CYCLE

Researchers from Florida State University have discovered that single-celled organisms called phaeodarians, which inhabit the the area 100 to 1,000 metres below the ocean’s surface, consume sinking carbon-rich particles before they settle on the seabed. These particles would otherwise be stored and sequestered from the atmosphere for millennia.

This is significant as it suggests that microorganisms around the world could be playing a much bigger role in the carbon cycle than scientists previously believed.

Carbon dioxide is constantly diffused into the ocean from the atmosphere and back into the atmosphere from the ocean. In the surface ocean, during the photosynthesis process of phytoplankton, carbon dioxide is absorbed. However, phytoplankton have short lifespans, between days and weeks, and are consumed by small organisms like krill. Krill in turn release carbon dioxide when they breathe, eventually adding to the carbon dioxide in the atmosphere. In this sense, the carbon dioxide in the surface ocean and atmosphere remains balanced at a near equilibrium. Thus, the only way the ocean sees an uptake in carbon dioxide from the atmosphere is when organic carbon from the surface is transported to the deep ocean in the form of sinking particles.

These sinking particles consist of anything from dead organisms to faecal matter. In addition, diatoms, which are an abundant type of phytoplankton, produce glass-like silica shells that also sink. If all of these particles sink unobstructed, the carbon can be kept out of the atmosphere for millennia. However, the study revealed that as much as 20 percent of the particles are being consumed, meaning that a lot less carbon reaches the seabed. In addition, the presence of the phaeodarians vary from place to place, from being abundant enough to consume

30 percent of sinking particles to barely being present at all. Given this, scientists have yet to determine the impact of phaeodarians on the global carbon cycle, but believe that the discovery has significant implications.

ABOVE Phytoplankton are microscopic marine algae that require sunlight to live and grow