{"id":284,"date":"2023-10-25T08:45:33","date_gmt":"2023-10-25T08:45:33","guid":{"rendered":"https:\/\/moutinpress.yadlapomme.com\/?page_id=7"},"modified":"2023-10-25T08:45:33","modified_gmt":"2023-10-25T08:45:33","slug":"contexte-scientifique","status":"publish","type":"page","link":"https:\/\/thierry-moutin.fr\/en\/research\/scientific-context\/","title":{"rendered":"Scientific context"},"content":{"rendered":"

The concentration of carbon dioxide in the atmosphere is increasing due to the activities of industrialized countries (anthropogenic CO2<\/sub>), and is the main cause of current global warming. It is particularly important to be able to quantify anthropogenic carbon sinks (terrestrial biosphere and ocean) because they determine the fraction of CO2<\/sub> that will remain in the atmosphere and thus warm the planet. The role that the ocean can play in fixing this additional CO2<\/sub> is therefore a central issue in contemporary oceanography.<\/p>\n

A good understanding of the marine carbon cycle is a prerequisite for studying the oceanic storage capacity of anthropogenic CO2<\/sub>. CO2<\/sub> fluxes exchanged at the atmosphere-ocean interface depend essentially on the partial pressure difference between the atmosphere and the ocean. Oceanic pCO2<\/sub> is highly variable and depends on both physical and chemical processes (physical or solubility pumps), and physical and biological processes (biological pumps). Two main biological pumps are distinguished: the \u201csoft\u201d biological pump associated with the photosynthetic capture of CO2<\/sub> (primary production) and its export to the deep ocean (figure above), and the \u201chard\u201d biological pump linked to the formation of calcium carbonate in the surface ocean. The \u201csoft\u201d biological pump is responsible for most of the dissolved mineral carbon gradient between the surface and deep oceans. It therefore accounts for the bulk of carbon transfer within the ocean. This pump is assumed to have functioned at equilibrium for a few thousand years before our era (Holocene) and to have continued to do so since the beginning of the industrial era (Anthropocene). It\u2019s only since the 2000s that climate disturbance seems to be beginning to modify the functioning of this pump (Sarmiento & Gr\u00fcber, 2006). It therefore seems crucial to study all the processes that characterize the ocean\u2019s main carbon pump, as well as its likely evolution in the face of climate change (decadal scale).<\/p>\n

The driving force behind the \u201csoft\u201d biological pump, oceanic primary production, depends on both light and nutrient availability (figure above). Most of the photosynthesized organic matter is recycled within the illuminated layer, and the CO2<\/sub> formed is returned to the atmosphere on a relatively short timescale, ranging from a few days to a few months. A fraction leaves the surface layer in particle form and is exported to deeper waters. Another fraction, the quantity of which is still poorly understood, is directly exported in dissolved organic form. The sum of these two flows corresponds to exportable production. The temporal evolution of exportable production needs to be quantified in order to assess the importance of the ocean as a sink for atmospheric CO2<\/sub>. Carbon export, associated with biological processes, is not (or only slightly) conditioned by the presence of CO2<\/sub>. CO2<\/sub> is not a limiting factor for phytoplankton growth, instead of the availabilities of other biogenic elements (nitrogen, phosphate, silicon, iron), which are essential for the synthesis of organic matter and which will control (limit or, on the contrary, enable) the functionning of the biological carbon pump.<\/p>\n

Most of my works concerns the study of the \u201csoft\u201d biological pump. They are described in the various articles accessible here, and range from descriptions of the main stocks and fluxes of carbon and nutrients in the ocean, to modeling studies. They have of course been obtained in collaboration with numerous French and foreign colleagues, and thesis students. If I had to highlight one result, it would be the control by phosphate availability of nitrogen input by nitrogen fixation in the iron-rich waters of the tropical southwest Pacific (Moutin et al., 2018). This region appears central to the natural fertilization of the ocean.<\/p>\n

Moutin, T., Wagener, T., Caffin, M., Fumenia, A., Gimenez, A., Baklouti, M., Bouruet-Aubertot, P., Pujo-Pay, M., Leblanc, K., Lefevre, D., Helias Nunige, S., Leblond, N., Grosso, O., and de Verneil, A.: Nutrient availability and the ultimate control of the biological carbon pump in the western tropical South Pacific Ocean, Biogeosciences, 15, 2961-2989, https:\/\/doi.org\/10.5194\/bg-15-2961-2018<\/a>, 2018<\/p>\n

Sarmiento J.L. & N. Gruber. 2006. Ocean Biogeochemical Dynamics<\/a>. Princeton University Press\/ Princeton and Oxford. ISBN-13: 978-0-691-01707-5<\/p>\n","protected":false},"excerpt":{"rendered":"

The concentration of carbon dioxide in the atmosphere is increasing due to the activities of industrialized countries (anthropogenic CO2), and is the main cause of current global warming. It is particularly important to be able to quantify anthropogenic carbon sinks (terrestrial biosphere and ocean) because they determine the fraction of CO2 that will remain in … <\/p>\n

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