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Observation-model approach to untangle carbon transfer mechanisms in the ocean (COSMIC)

Applicant Castrillejo Iridoy Maxi
Number 199289
Funding scheme Postdoc.Mobility
Research institution Department of Physics Imperial College London
Institution of higher education Institution abroad - IACH
Main discipline Oceanography
Start/End 01.01.2022 - 31.12.2023
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All Disciplines (2)

Other disciplines of Environmental Sciences

Keywords (5)

carbon cycle; ocean circulation; radiocarbon; observation-model interactions; water mass transformation framework

Lay Summary (French)

L'océan absorbe jusqu'à un tiers du dioxyde de carbone émis par les activités humaines. En diminuant l'accumulation de ce gaz à effet de serre dans l'atmosphère, l'océan contribue à moduler le changement climatique anthropique. En conséquence de l'absorption de dioxyde de carbone, l'eau de mer subit un changement dans la teneur en carbone ainsi que dans l'abondance relative de ses isotopes. Plus particulièrement, ce changement est observable dans le rapport océanique entre le 12C stable et le radio-isotope à la durée de vie la plus longue, le 14C ou le radiocarbone. Après l'échange air-mer de dioxyde de carbone, le gaz se dissocie en différents composés formant le pool de carbone inorganique dissous, qui est ensuite transporté par la circulation océanique et stocké dans les océans pendant des décennies ou plus.
Lay summary

Contenu et objectifs du travail de recherche
Bien que les échanges air-mer et la circulation océanique soient d'une grande importance pour le climat, il est nécessaire de mieux comprendre, d'un point de vue mécanistique, comment ces processus affectent le cycle du carbone marin. Notre objectif est de mieux comprendre les mécanismes physiques qui contrôlent l'absorption, le stockage et la distribution du carbone dans l'océan. Plus particulièrement, nous voulons quantifier le rôle des échanges air-mer, de l'advection, du mélange et de la diffusion sur le cycle du carbone en observant le contenu en radiocarbone inorganique dissous de différentes couches d'eau. À cette fin, nous utiliserons une nouvelle combinaison d'observations du radiocarbone et de simulations de modèles, ainsi que le water mass transformation framework. 

Contexte scientifique et social du projet de recherche
Ce projet apportera de nouvelles connaissances sur le cycle du (radio)carbone marin et l'océanographie physique. Le travail fournira également des capacités de prédiction pour mieux comprendre les rétroactions entre l'océan et l'atmosphère et pour aider à la prise de décision dans le domaine du changement climatique.
Direct link to Lay Summary Last update: 05.11.2021

Responsible applicant and co-applicants


The ocean plays a key role in modulating climate by taking up, storing and redistributing 90% of the heat and 30% of the anthropogenic CO2 that is added to the atmosphere as a consequence of human activities. Although the principal processes modulating the ocean uptake and redistribution have been studied for decades, many questions remain unresolved about the air-sea gas exchange and ocean circulation. While the traditional view in oceanography focused on the transport along isopycnals (along lines of equal density), recent studies have shown that diapycnal processes (across isopycnals) are relevant in setting the properties in upper waters and in their subsequent downward transport to the deep ocean. Our aim is to gain a better understanding of the physical mechanisms of circulation in the North Atlantic that govern the uptake and fate of radiocarbon (14C) by conducting new measurements of 14C and by applying model-data analysis, including a novel water mass transformation (WMT) framework to interpret the new and existing 14C data. The first goal is quantifying the separate contribution of each physical process: air-sea gas exchange, diapycnal mixing, diffusion and overturning. The second goal is to assess the shallow and deep overturning circulation of the North Atlantic in current models by comparison between model simulations and observations of ocean 14C. We have developed a fully automated method allowing the rapid and precise analyses of 14C in seawater that is far superior to other existing techniques. Using this new method, we have already produced hundreds of new 14C observations in the Atlantic Ocean. More samples have been collected by the host Dr. Heather Graven from Imperial College London. And, I have secured further samples from a forthcoming oceanographic expedition in the subpolar North Atlantic to ensure an adequate coverage of tracer observations. We have been granted full access to novel sample processing and measurement capabilities thanks to the collaboration that I established with the Laboratory of Ion Beam Physics, ETH-Zurich. Dr. Graven is leading the modelling of ocean geochemical tracers, including 14C, and we will use her connections with D. George Nurser from the National Oceanography Centre of Southampton who is an expert in WMT and specific models. Further, she has produced simulations of ocean 14C that are suitable for this project making the proposed research timely. The PI and the host cover the expertise that is required, respectively, in ocean observation and modelling. And, access to modelling and analytical infrastructures is granted by Imperial and LIP to ensure the feasibility of the project. On one hand, the success of the project will lead to transformative insights in ocean circulation by separating and quantifying each physical process involved in the uptake and transfer of 14C. The novel analysis will allow the evaluation of recent hypothesis about the large-scale ocean circulation that restrains the diapycnal transport. Because recent changes in 14C are governed by the same mechanisms that control anthropogenic carbon, the results will have a major impact on our understanding of how carbon is sequestered from the atmosphere and redistributed in the ocean. On the other hand, we will identify biases in modelled overturning circulation that have a major impact on the simulated uptake of anthropogenic CO2 and heat into the ocean. Thus, results will provide a more accurate view on how models project the future climate change. I will learn the new tools (modelling and WMT) and will extend my network to modelers, physical oceanographers and experts in the carbon cycle. After the fellowship, I will have a very unique skillset that combined with my expertise in tracer observations will facilitate a leading academic position in Switzerland. If I am successful with the Postdoc Mobility, I intend to apply for the return phase to expand to the global scale investigation of the overturning circulation and the carbon cycle.