Iron isotope contribution to the study of ocean biogeochemical cycles in contrasting regions, Equatorial Pacific, North Atlantic and Southern Ocean

See the subject on the ADUM website

Start date : October 1, 2021

Deadline : June 9, 2021

Supervisor : François Lacan

Funding: Competition for a doctoral contract

General scientific context

In the ocean, primary production (phytoplankton growth) takes up carbon. The sedimentation of part of this organic matter into the deep ocean thus constitutes a carbon sink for the atmosphere. This is called the biological carbon pump. In vast regions of the ocean, primary production is limited by the lack of iron (algae are anemic). This element plays a key role in the ocean biogeochemical cycles and climate. Despite its importance, its cycle remains poorly understood, in particular its sources (eolian, fluvial, sedimentary and hydrothermal) as well as its cycle within the ocean (including interactions between the different phases of iron, dissolved and particulate). While intense research has been conducted on these topics over the last decades based on the study of iron concentrations, it is now possible to focus on the cycle of iron ISOTOPES in the ocean. These isotopes provide new information, inaccessible by concentration measurements, on the nature or intensity of biogeochemical processes. This theme is very innovative, since, at present, only a handful of laboratories in the world are capable of making this type of measurement. It is a highly multidisciplinary subject. Centered on the ocean, it also concerns its interfaces, the continents, the atmosphere and the seafloor. Within these different disciplines, this project, although focused on isotope geochemistry, will also involve physics, biology, geology and chemistry. This subject is part of the very dynamic and stimulating framework of the international program GEOTRACES.

Implementation plan

Natural samples, mainly oceanic (dissolved iron in water, suspended particles, phytoplankton), but also from the different sources of iron to the ocean (aerosols, rivers, sediments) were collected during the BONUS-GoodHope cruise in the Southern Ocean along the Greenwich meridian, the PANDORA cruise between New Caledonia and Papua New Guinea, and the GEOVIDE cruise in the North Atlantic, between Portugal, Greenland and Newfoundland. For some of these samples, the iron isotopic compositions have already been measured, for others the measurements remain to be done. Depending on the candidate’s profile, the work could consist in the interpretation of already available data, within the multidisciplinary scientific framework described above, or in the production of new data and the interpretation of these new data and the available data. The production of new data of iron isotopic compositions is obtained by mass spectrometry (MC-ICPMS), after ultra clean chemical purification in clean room.

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