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Press release | Scientific result | Genomics | Environment
The ocean is the largest carbon sink on the planet.
The network of planktonic organisms of this carbon sink has been described as a
social network by an interdisciplinary team comprising oceanographers,
biologists and computer experts mainly from the CNRS, UPMC, University of
Nantes, VIB, EMBL and CEA. This first overview of the network of species
associated with the oceanic biological pump has highlighted new elements and
the main bacterial functions involved in this process. It was obtained by
analysing samples that were collected during the Tara Oceans expedition
in the nutrient-poor regions that cover most part of the oceans. Scientists
have also shown that the presence of a small number of bacterial and viral
genes predicts variation in the carbon export to the depths of the ocean. These
discoveries should help researchers in testing the strength of this network in
the face of climatic disturbances and the consequences on the biological carbon
pump. This work, published on 10 February, 2016 on the website of the Nature
journal, emphasizes the importance of plankton in the climate system.
The ocean is our planet’s main carbon sink owing to
two main mechanisms: the physical pump and the biological pump. The physical
pump pulls surface water, rich in dissolved carbon dioxide, down to the deep
ocean where it is isolated from the atmosphere. The biological pump fixes the
carbon, either in the tissues of organisms through photosynthesis or in the
calcareous shells of certain microorganisms. A part of the carbon thus fixed in
the form of marine particles then sinks to the depths of the ocean (this is
called carbon export), before reaching the ocean floor where it will be stored
(this is called sequestration). The biological pump is thus one of the major
biological processes that help to sequester carbon on geological timescales.
This process, which has been widely studied since the
80s, involves the ocean's plankton. These extraordinarily varied microscopic
beings (plankton constitutes unicellular and multicellular eukaryotes,
bacteria, viruses )
produce half of the Earth’s oxygen and are at the base of the oceanic food
chain that feeds fish and marine mammals. Numerous studies have shown that the
strength of the biological pump is directly correlated with the abundance of
certain planktonic species. However, the structure of the communities involved
in the carbon sink remains largely misunderstood.
By analysing samples collected during the Tara
Oceans expedition (2009-2013), an interdisciplinary team comprising
biologists, computer experts and oceanographers has shed light on these
planktonic species, their interactions and the main functions associated with
the biological pump in the oceanic regions that are particularly “poor” in
nutrients. These regions occupy the most part of the oceans (more than 70%).
Researchers, mainly from the CNRS, UPMC, University of Nantes, VIB, EMBL and
CEA (refer to the list of laboratories below), referred to earlier articles
published in Science on 22 May, 2015, especially the first mapping of
the interactions between planktonic organisms .
Using computer analyses, they described the first “planktonic social network”
associated with carbon export in the regions “poor” in nutrients. Numerous
recorded elements like certain photosynthetic algae (particularly diatoms) or
copepods (these are microscopic shrimps) were already known. However, the
involvement of certain micro-organisms (unicellular parasites, cyanobacteria
and virus) in the export of carbon was largely underestimated until then.
Moving further, the researchers then characterised a
network of functions which was based on the analysis of the genes of bacteria
and viruses. The Tara Oceans database thus helped to establish that the
relative abundance of a small number of bacterial and viral genes predicts a
significant proportion of the variability of carbon export to the depths of the
ocean. A part of these genes is involved in photosynthesis and membrane
transport, encouraging, among other things, the breakdown and sedimentation of
organic matter. However, the role of a majority of these genes is still
Understanding the structure of these networks and the
function of the genes involved in the carbon cycle provides numerous
perspectives, mainly the possibility of modelling the biological processes
involved in the oceanic carbon cycle. It should therefore be possible to test
the strength of these networks under various climatic conditions and to better
understand how the different planktonic species affect the carbon cycle and
climate regulation. One of the future goals is to repeat this work for the
nutrient-rich oceanic regions in order to complete the revealed planktonic
networks and better understand their dynamics at the global level.
These are the unicellular or multicellular organisms
whose genetic material is contained in a nucleus (contrary to bacteria and
Lima-Mendez G, Faust K, Henry N, Decelle J, Colin S,
Carcillo F, et al. Top-down determinants of community structure in the global
plankton interactome. Science. 2015;
348: 1262073-1262073. doi: 10.1126/science.1262073
Plankton networks driving carbon export in the oligotrophic ocean, Publié le 10 février 2016 sur le site de Nature. DOI: 10.1038/nature16942
CEA is a French government-funded technological research organisation in four main areas: low-carbon energies, defense and security, information technologies and health technologies. A prominent player in the European Research Area, it is involved in setting up collaborative projects with many partners around the world.