Research axis 4: sediment transfer from the coast to the abyss
Coordinators: Marina RABINEAU (LDO/IUEM) and Stéphan JORRY (GM/Ifremer)
LDO (Laboratoire Domaines Océaniques), UBO, CNRS/INSU
Laboratoire de Géosciences Marines, Ifremer
DYNECO (Département dynamiques de l’environnement côtier), Ifremer
LEMAR (Laboratoire des sciences de l'environnement marin), UBO, CNRS, IRD
LM2E (Laboratoire Microbiologie des Environnements Extrêmes), Ifremer, UBO, CNRS/INEE
Sedimentary processes occurring along continental margins are complex and result from the interaction between deep processes (Tectonics with Subsidence/Uplift) and surficial processes (Climate, Sea level and Hydrodynamic). Such processes, their origins and consequences are only partially known so that global models remain extremely limited and simplistic. Major questions remain unanswered as far as quantifying sedimentary fluxes are concerned as well as modeling precisely both solid matter transport from source to sink zones and their consequences on building margin architecture. Conditions of erosion, timing and processes of sedimentary bodies deposition and preservation as a function of paleoenvironmental and paleoclimatic conditions are still a challenge in earth science.
The main objective is to understand and quantify, using marine sediment archives, all changes related to natural parameters (climate, sea level, hydrodynamic and paleoceanographic, tectonics) and decipher their relative impact and timing on sedimentary fluxes. Among essential questions:
- Fluxes at the terrestrial-coastal interface are still, in fact, very poorly known. The relative role of extreme events (storms, floods, cyclones for example) compared to more continuous record (annual, pluriannual or millenial) is still undetermined. We will therefore concentrate on the reconstruction of these events at present and in the past. Those paleoenvironmental and paleoclimatic reconstruction will be useful to test models used for predictions.
- Another important question concerns transfer of sediment towards the deep domain during phases of erosion/transport/deposition on the shelf, by gravity processes via submarine canyons but also more generally through open-slope. Scientific questions in this topic concern at the same time the characterization of the processes at the origin of the fluxes and their role in the formation and evolution of canyons through time, the biogeochemical composition of these fluxes (C and associated biogenic elements) and their evolution through time and impact on global biogeochemical cycles.
These questions are related to different time scales: from an event-scale (hours, day to weeks with possible direct measurements and instrumentation) to years, thousands years and million years for which internal earth processes (e.g. thinning of the crust) that govern subsidence plays a fundamental role in preservation of sediments and ought to be further understood.
Scientific objectives will contribute to a better knowledge of the dynamics of sedimentary transfers between the coast to the abyss domains, integrated over the entire sedimentary continuum, and their consequences at geological time-scale. This understanding needs a 4D characterization of sedimentary architecture and paleoenvironments from drainage basins and continental shelves towards the foot of the slopes with a land to sea approach using multiples proxies, but also through a modelling approach dealing with the complete system, which has not yet been achieved within the scientific community. Answering these questions will enable to better understand and better anticipate evolutions that have important consequences such as natural hazards (e.g. tsunamis, storms), coastal areas sensibilities (sea-level rise), climate change but also natural resources (gravels, hydrocarbons, economic zones) in many regions of the world.