“CO2 sequestration in the Ocean, an important criterion in current climate models.”

© C.Carre/Tara Expéditions

The 35,000 samples of plankton collected during the Tara Oceans expedition have not yet revealed all their secrets. After allowing scientists to decipher the interactions, distribution and diversity of planktonic organisms, the “Tara’s data” are now highlighting how plankton is of paramount importance in the great climate machine. A NEW SCIENTIFIC PUBLICATION EXPLAINS THE COMPLEX MECHANISMS CONTROLING THE LARGEST “CARBON PUMP” OF THE PLANET.

If Amazonia is the Earth’s green lung, the Ocean is undoubtedly its blue lung. Half of the oxygen we breathe comes from plankton, more specifically from the photosynthetic organisms that produce oxygen, as any land plant would do. Moreover, the impact of the global ocean on the climate system doesn’t end there. These organisms emit a huge amount of oxygen in the atmosphere, but they also consume carbon dioxide, the famous CO2. During the last decades, the ocean has thus slowed the pace of climate change by absorbing nearly 30% of anthropogenic emissions of carbon dioxide.

Several mechanisms participate in this gigantic carbon pump: 1) The oceans naturally trap through their physical and chemical properties a portion of the atmospheric CO2 that they carry into the  depths; 2) %Phytoplankton% – the “vegetal” plankton – captures carbon dioxide and transforms it into oxygen during photosynthesis; 3) Droppings and remains of planktonic organisms slowly sink to the bottom of the ocean. This shower of carbon-rich organic particles – external skeletons, shells and calcareous envelopes of microorganisms – will end up buried in the sediment on the ocean floor and gradually be transformed into hydrocarbons. This process, known as carbon sequestration, is in other words a huge carbon sink.

By observing this shower of organic fragments at various depths, a simple yet striking fact can be pointed out: the deeper the depth, the fewer particles there are. In the end, only a small proportion of fragments – in the range of 1 to 10% – will reach the ocean floor. In reality, a large part of these particles will be consumed on their way down by other planktonic organisms. Scientists speak of carbon remineralization, ie, the transformation of organic matter into inorganic matter – in this case, CO2. For instance, instead of ending up as oil, a fraction of algae will be eaten by a small crustacean. The carbon the algae contains will be assimilated by the crustacean and then be rejected as CO2 through breathing.

Schema of the biological carbon pump

Schema of the biological carbon pump 

 

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- Tara Oceans reveals a new world in the Ocean

- Ocean, Climate and Science: learn more about the Ocean & Climate Platform