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WP4 Sediment dynamics & geohazards

WP leader: Miquel Canals, University of Barcelona, Spain
Vasilis Lykousis HCMR Athens, Greece Marine geohazards

Sedimentary processes transfer matter and energy from the atmosphere and the continent to ocean margins and basins. The study of sedimentary processes has profound implications for the deep-sea ecosystem, the climatic evolution of our planet, natural resources and geohazards. Therefore, their study represents a centerpiece within the frame of this Coordination Action as also shown by the close relation between WP4 and all the other science WPs (most importantly WPs 2, 3, 5 and 6).

(1) Sedimentary processes involve water column, near-bottom, seabed and subseafloor processes that occur at variable time scales, from minutes to millennia. Sedimentary processes have the ability to shape the seafloor as illustrated by the development of submarine canyons, valleys, gullies, mounds or deltas and deep-sea fans. Sedimentary processes synthesise the physical abiotic factors controlling the deep-sea ecosystems and, therefore, are key to understand their current status and future evolution (link to WP1-3). Sediments are porous and permeable, so that prokaryotes and, at shallow burial depth, eukaryotes become habitants and exchanges genetic information within and along them.

(2) The climatic evolution of Earth is closely related to specific sedimentary processes, to sediment volumes and accumulation sites as determined by climatically controlled sediment erosion and transport, and sea level changes. Recent findings on the capability of cascading sediment-laden dense shelf waters to capture large amounts of C and transfer it rapidly to the deep ocean where it could be stored in the sediment and therefore removed from the CO2 ocean-atmosphere exchange. On a longer time perspective, marine sedimentary archives contain the best, longest and most continuous record of past global environmental changes. Understanding the present day sedimentary processes is essential to better assess the significance of the past climatic and paleo-environmental signals preserved in the sediment and how the climatic evolution of Earth has determined modern deep-sea ecosystems (see details in WP6).

(3) Sedimentary processes in the ocean determine the formation of mineral and energy resources. Oil and gas resources result from the maturation of organic matter trapped in ancient marine sedimentary rocks leading to the formation of hydrocarbons that, after migration, accumulated in porous sediment layers and structures from where they are currently exploited. Furthermore, the last two decades have seen the move of the hydrocarbon industry to the deep ocean where energy resources are being increasingly exploited. The deep ocean is, also for the hydrocarbon industry, one of the very last frontiers on Earth targeted to ensure future energy supplies to our society. Exploiting deep ocean resources has various environmental implications concerning the deep-sea ecosystems that so far have been poorly investigated by independent research consortia. Gas hydrates trapped in marine sediments constitute the largest fossil C accumulation on Earth, are a potential future energy source and could lead to the catastrophic landsliding of ocean margins would the on-going near-bottom water temperature rising trend trespass the hydrate destabilization threshold.

Submarine landslides could behave as tsunamigenic sources or could add to tsunamigenic potential if combined with earthquakes best illustrate the contribution of sedimentary processes to geohazards. Several studies have shown that tsunamigenic submarine and coastal earthquakes often have a contribution by landslides triggered by the earthquake. Amongst many others, this was the case for the destructive Lisbon tsunami of 1755, the Amorgos 1956 and Gulf of Corinth 1963 tsunamis in the Mediterranean Sea, and also for the most recent Boumerdes earthquake of May 2003 that not only generated a tsunami impacting the Baleares where hundreds of boats sank, but also numerous submarine cables offshore Algeria were cut by landsliding sediment masses. Such catastrophic events are often harmful to marine ecosystems on the continental slopes and shelves, however, their immediate consequences are rarely assessed. Geohazards are notoriously difficult to predict because of their episodicity and wealth of potential triggers, so that viable risk assessment and hazard mitigation depend on a clearer understanding of the causes, distributions, and consequences of such natural events.

List of WP4 participants (Level 3)
R. Wynn, NOCS, UK (Marine geohazards); N. Sultan, IFREMER Brest, France (Marine geotechnics); M. Sacchi, IAMS, Naples, Italy (Volcanogenic geohazards); A. Camerlenghi, Univ. Barcelona, Spain (Submarine slides); M. Vanneste, ICG/NGI, Norway (Marine geohazards); T. Mulder, Univ. Bordeaux, France (Sedimentary processes); S. Heussner, CNRS-CEFREM, France (Particle fluxes); J.S. Laberg, Univ. Tromsø, Norway (Slope failure); P. Puig, ICM-CSIC Barcelona, Spain (Particle fluxes); M. White, NUI, Galway, Ireland (Physical oceanography); D. Masson, NOCS, UK (Sedimentary processes); J. Vitorino, Inst. Hidrografico, Portugal (Physical oceanography); M. Rebesco, OGS, Trieste, Italy (Sedimentary processes); A. Kopf, MARUM, Germany (Subduction zone hazards & landslides); L. Pratson, Duke Univ., USA (Seafloor shaping and marine geohazards); J.K. Morgan, Rice University, USA (Marine Geohazards); H.J. Lee, USGS, Menlo Park, USA (Submarine landslides).