PhD studentships 2018

PhD studentships contracts for this year. You can apply for to scientific persons in charge.

1) Stratigraphic modeling of the tide and marine currents forcing. Application to the Bay of Brest

Supervisor: : Marina Rabineau (Marina.Rabineau@univ-brest.fr)
Co-supervisor: Estelle Leroux (Estelle.Leroux@ifremer.fr) et Didier Granjeon (Didier.Granjeon@ifpen.fr)

Stratigraphic numerical modeling (DionisosFlow) simulates sediment processes to predict geometry, bathymetry and facies within sedimentary basins. Today the challenge in stratigraphic modeling is to obtain a more detailed description and understanding of these sediment processes, by including, in particular, the hydrodynamic control (tidal- and swell- currents, waves, littoral drift ...). Whilst present oceanographic processes, studied for decades, are nowadays rather well constrained, their impact on the regional sediment transport, architecture and properties (petro-acoustic and mechanical) remains poorly understood. This thesis aims thus to understand, and predict this hydrodynamic forcing. This work will rely on the study of semi-coupled processes on different time and spacescales in order to assess the impact of daily processes (tidal currents) to annual (currents in marine platform domain) on the regional (distance> 10 km) and geological distribution (duration> 1000 years) sediments. To achieve this temporal upscaling, the student will work in strong collaboration with IFREMER and UBO (hydrosedimentary modeling with MARS3D-MUSTANG, interpretation of datasets using bathymetric, seismic, cores and logs data…) and IFPEN (stratigraphic modeling with DIONISOSFLOW). A main study-case is defined: the Holocene geological evolution in the Bay of Brest (the last 10 kyr).

Keywords : Numerical stratigraphic modeling, hydro-dynamism, tide-currents, macroscopic law of sediment transport, Bay of Brest.

2) Contribution of mineralogical and geochemical studies of Fe-Mn crusts to palaeogeographic and paleoceanographic reconstructions of the Mozambique Channel

Supervisor: Jean-Alix Barrat (jean-alix.barrat@univ-brest.fr)
Co-supervisor: Ewan Pelleter (ewan.pelleter@ifremer.fr)

The Mozambique Channel is a key sector for understanding the global thermohaline circulation as it corresponds to a mixing zone between the water masses of the Indian and Atlantic Oceans. Recent hydrographic studies have shown that the North Atlantic Deep Water (NADW) flows to the Comoran Basin leading to the conclusion that the Davie Ridge does not constitutes a topographic barrier to deep circulation. However, the Cenozoic geodynamic history and its consequences on the topography of the Mozambique Channel probably induced a strong modification of the hydrodynamic conditions during the last 50 million years. Ferromanganese deposits are an archive of the chemistry of water masses. Isotopic studies show that Fe-Mn hydrogeneous crusts can be used to reconstruct major modifications of the deep currents in connection with paleogeographic changes. During the PAMELA-MOZ1 and PAMELA-MOZ5 cruises, many ferromanganese crusts were sampled along a NE-SW profile (2000km) from the glorious islands (Comoros Basin) to the Mozambican margin. With growth rates estimated at less than 5 mm/Ma and thicknesses up to 14 cm, these samples could therefore be used to reconstruct the paleoceanographic and paleogeographic history of the Mozambique Channel during the last 15 to 30 Ma.

Keywords : Geochemistry, radiogenic isotopes, paleoceanography, paleogeography, mineralogy, ferromanganese crusts, Mozambique Channel.

3) Isotopic constraints on the biogeochemical cycling of copper in seafloor hydrothermal systems

Supervisor: Olivier Rouxel (Olivier.Rouxel@ifremer.fr)
Co-supervisor: Cécile Cathalot (Cecile.Cathalot@ifremer.fr)

This PhD work focuses on the Copper (Cu) cycle in hydrothermal systems at the oceanic ridges, from its input from hot springs, export in the water column (through hydrothermal plume dispersal), to precipitation in metalliferous sediments. The originality of the approach will be based on the use of stable isotopes of copper, coupled with a study of the chemical and physical speciation of this element in the water column, and a mineralogical and geochemical study of the different minerals carrying this element in hydrothermal sediments. In hydrothermal systems, copper is a metal of economic interest with unique physicochemical properties, which is both indispensable and potentially toxic to biological organisms. The main scientific and technological objective of this project is to develop a new tracer of the biogeochemical cycles of metals in deep sea environments. The thesis work will state-of-the-art analytical equipments available at Ifremer (e.g. Pôle Spectromérie Océan) and will rely on high quality samples from recent and future Ifremer-led research cruises carried out along the mid-Atlantic ridge (TAG and Snake Pit hydrothermal sites), located in the exploration license area recently obtained by France from the International Seabed Authority.

Keywords : Geochemistry, mineralogy, chemical speciation, stable isotopes, copper, sulfides, sediments, hydrothermal systems.