The ocean is the largest carbon sink on the planet and plankton plays a fundamental role in the Earth climate system. This is the main result of a research done by an interdisciplinary team of scientists from different institutions that includes the Institute of Marine Sciences. The results have been recently published in the journal Nature and they clearly describe the community of planktonic organisms involved in the removal of carbon from the upper layers of the ocean.
The ocean is the largest carbon sink on the planet and plankton plays a fundamental role in the Earth climate system. This is the main result of a research done by an interdisciplinary team of scientists from different institutions that includes the Institute of Marine Sciences. The results have been recently published in the journal Nature and they clearly describe the community of planktonic organisms involved in the removal of carbon from the upper layers of the ocean.
Silvia G. Acinas, researcher at the ICM and coordinator of the prokaryote consortium of Tara Oceans expedition, states: “The paper provides a first overview of the network of species linked to the oceanic biological pump and reveals some new players as well as the main bacterial functions participating in this process”. The results were obtained by analyzing samples collected by the Tara Oceans expedition (2009-2013) in the nutrient-poor regions that cover most of the oceans, more than 70% of their surface.
The research team, formed by oceanographers, biologists and computer scientists, showed that the presence of a small number of bacterial and viral genes predicts variation in carbon export from the upper layers of the ocean to the depths. These findings should enable researchers to better understand the sensitivity of this network to a changing ocean and to better predict the effects that climate change will have on the functioning of the biological carbon pump, which is a key process for sequestering carbon at global scale.
Two main processes drive the carbon capture storage in the ocean. One is the physical pump, which pulls surface waters rich in dissolved carbon dioxide down to deeper layers, where it becomes cut off from the atmosphere. The second process is the biological pump, which fixes carbon, either in the tissue of organisms via photosynthesis, or in the calcareous shells of certain microorganisms. Part of this fixed carbon in the form of marine particles then sinks to the deep ocean (a process called carbon export), finally reaching the ocean floor where it is stored (it is said to be sequestered). The biological pump is thus one of the major biological processes that can sequester carbon on geological timescales.
Double network
The researchers used computer analyses to describe the first 'planktonic social network' associated with carbon export in nutrient-poor regions. Many of the players involved, such as certain photosynthesizing algae (especially diatoms) and copepods (tiny shrimp-like organisms) were already known. However the role played by certain microorganisms (unicellular parasites, cyanobacteria and viruses) in carbon export was previously grossly underestimated.
Going further, the researchers then characterized a network of functions, based this time on the analysis of the genes of bacteria and viruses. The Tara Oceans database thus enabled them to establish that the relative abundance of a small number of bacterial and viral genes can predict a significant proportion of variations in carbon export from the upper layers of the ocean to the deep ocean.
Understanding the structure of these networks and the function of the genes linked to carbon export opens up a wide range of possibilities, especially for modelling the biological processes associated with the oceanic carbon cycle.
This work is a collaboration of several institutions such as the Centre National de la Recherche Scientifique (CNRS), Université Pierre et Marie Curie, Université de Nantes, VIB, European Molecular Biology Laboratory (EMBL), CEA / Institut de Génomique, and the Institut de Ciències del Mar-CSIC, among others.
Reference
Plankton networks driving carbon export in the oligotrophic ocean. Lionel Guidi, Samuel Chaffron, Lucie Bittner, Damien Eveillard, Abdelhalim Larhlimi, Simon Roux, Youssef Darzi, Stephane Audic, Léo Berline, Jennifer Brum, Luis Pedro Coelho, Julio Cesar Ignacio Espinoza, Shruti Malviya, Shinichi Sunagawa, Céline Dimier, Stefanie Kandels-Lewis, Marc Picheral, Julie Poulain, Sarah Searson, Tara Oceans coordinators, Lars Stemmann, Fabrice Not, Pascal Hingamp, Sabrina Speich, Mick Follows, Lee Karp-Boss, Emmanuel Boss, Hiroyuki Ogata, Stephane Pesant, Jean Weissenbach, Patrick Wincker, Silvia G. Acinas, Peer Bork, Colomban de Vargas, Daniele Iudicone, Matthew B. Sullivan, Jeroen Raes, Eric Karsenti, Chris Bowler, Gabriel Gorsky. DOI: 10.1038/nature16942.