Sand ripple volume generator for underwater acoustic models, a cellular automaton Monte-Carlo approach

Cellular automata have been successfully used to model the sand dynamics of aeolian dunes and ripples. The cellular automata Monte-Carlo model proposed in this paper expands the capabilities of cellular automata models to under water ripple formation introducing not a two dimensional matrix but two three dimensional volumes, being a sand volume and a water volume. The proposed model has the capability to generate optimal environmental data to input in other mathematical models in need of environmental data. The following enhancements were implemented: optional abstraction levels of the hydrodynamic behavior, morphological formation of underwater ripples under unilateral currents in any direction as well as morphological formation of underwater ripples under wave current interaction, grain size distribution of the sand in every time step in the entire volume and compaction distribution in every time step in the entire sediment volume. The proposed cellular automata model is a closed toroidal system. The toroidal approach of the model enables to build up infinite rippled surfaces by using the generated sediment volumes as tiles; this solves boundary problems in for example acoustic models. Using the fractal properties of the sand ripples, infinite surfaces containing rippled dunes can be generated

The giant cold-water coral mound as a nested microbial/metazoan system: physical, chemical, biological and geological picture (ESF EuroDiversity MiCROSYSTEMS)

The MiCROSYSTEMS project under the ESF EUROCORES EuroDiversity scheme is a holistic and multi-scale approach in studying microbial diversity and functionality in a nested microbial/metazoan system, which thrives in deep waters: the giant cold-water coral mound. Studies on prolific cold-water coral sites have been carried out from the canyons of the Bay of Biscay to the fjords of the Norwegian margin, while the Pen Duick carbonate mound province off Morocco developed into a joint natural lab for studying in particular the impact of biogeochemical and microbial processes on modern sedimentary diagenesis within the reef sediments, in complement to the studies on I0DP Exp. 307 cores (Challenger Mound, off Ireland).Major outcomes of this research can be summarized as follows.IODP Exp. 307 on Challenger Mound had revealed a significant prokaryotic community both within and beneath the carbonate mound. MiCROSYSTEMS unveils a remarkable degree of compartmentalization in such community from the seawater, the coral skeleton surface and mucus to the reef sediments. The occurrence of such multiple and distinct microbial compartments associated with cold-water coral ecosystems promotes opportunities for microbial diversity in the deep ocean.New cases of co-habitation of cold-water corals and giant deep-water oysters were discovered in the Bay of Biscay, which add a new facet of macrofaunal diversity to cold-water coral reef systems.The discovery of giant, ancient coral graveyards on the Moroccan mounds not only fuels the debate about natural versus anthropogenic mass extinction, but these open frameworks simultaneously invite for the study of bio-erosion and early diagenesis, in particular organo-mineralization, and of the possible role and significance of these thick, solid rubble patches in 3D mound-building and consolidation.The assessment of the carbonate budget of a modern cold-water coral mound (Challenger Mound) reveals that only 33 to 40 wt % of carbonate is derived from corals and suggests a selective enrichment of the hemipelagic carbonate fraction, compared to adjacent sediment drift deposits.The detection of allochthonous fluids, in particular brines, in the pore space of the surficial mound sediments on the Pen Duick Escarpment hints towards the presence of salt deposits deep underneath, and simultaneously provides the first direct evidence of advective fluid transfer from the deep, throughout the mound substrate and the full mound height. Potential stratigraphic pathways leading from the deeper basinal realms directly to the mound setting have been imaged in a spectacular way through high-resolution pseudo-3D seismic imaging. Geophysical signatures of free gas accumulations have been detected a few hundreds of meters below the mound base, but low concentrations of methane and the absence of lipid biomarkers from methane-dependent prokaryotes suggest low fluxes of methane-derived carbon and thus very small rates of anaerobic oxidation of methane (AOM) in the immediate mound subsurface. Local changes in the sediment biogeochemistry are most likely dictated by slow diffusive fluid transfer, operating in a heterogeneous way in the subsurface.Cultivation experiments with sediments from microbially active mound zones have allowed to study microbially induced carbonate precipitation and provide a tool for the interpretation of carbonate mineralogy. The development and operation of a continuous high-pressure bioreactor (100 bars) allows to simulate in an ex situ mode the impact of environmental parameter changes onto the functioning of relevant microbial communities.The detected influx of sulfate in mound sediments implies that bacterial sulfate reduction can be the dominant anaerobic carbon mineralization process. Groundwater flow modeling suggests that currents impinging on the escarpment and the flanks of an exposed mound can account for a significant influx and transport of sulfate through convective fluid transfer within the mound sediments. Oceanic currents consequently provide not only a major control on the external flux of nutrients to the mound-building communities, but they also potentially drive internal flow in the mound. The extant hydrodynamic climate of the mound setting is documented through long-term lander deployments and CTD stations: the current records reveal a significant tidal and seasonal variability. The past environmental record over the last 400 ka is documented in a most comprehensive sedimentary archive, sampled with long cores at the foot of the Pen Duick Escarpment during the MD169 ‘MiCROSYSTEMS’ cruise in July 2008.MiCROSYSTEMS has significantly contributed to the successful submission of IODP proposal 673-Full, which should (i) document the whole-mound architecture and the mound setting on Pen Duick Escarpment as well as a most comprehensive stratigraphic record on a reference site at the foot of the escarpment, (ii) reveal the full spatial pattern in microbial diversity, activity and functionality throughout the mound and underneath, and (iii) unravel the plumbing system of a mound and the dynamic interaction between advective, convective and diffusive transfers of organic and inorganic compounds, which impact on biogeochemical equilibria, microbial activity and early diagenetic processes

Drilling Challenger Mound (Porcupine Basin,W of Ireland): a contribution to European research on the microbial mediation in carbonate formation at low temperatures?

In his monumental master work ‘The Face of the Earth’, the eminent Vienna geologist Eduard Suess has formulated visionary thoughts on fundamental topics ranging from the tectonic nature of Europe’s margins to the role of the ‘Biosphere’, a word that he had coined in 1875. This word turned into a concept of Life as a Geological Force through the vision of Vladimir I. Vernadksy (Biosfera, 1920). Recent studies (Vasconselos et al. 1995) have unveiled the possible role of microbial mediation in the formation of natural dolomite, a mineral named after Déodat de Dolomieu (1750-1801).But some of the most spectacular geological bodies, built by Life as a Geological Force, are the carbonate mounds. Carbonate mounds from the fossil record provide evidence of microbial mediation in the mound build-up and stabilization (Henriet et al. 2002). The study of carbonate mounds and associated cold-water coral reefs forms one of the first priorities of IOC/UNESCO’s new programme “Geosphere-Biosphere Coupling Processes” (GBCP).IODP Expedition 307 (Modern Carbonate Mounds: Porcupine Drilling) sets sail end of April, 2005 to the Porcupine Seabight, West of Ireland, to investigate the possible role of geofluids, microbial consortia and cold-water corals in the genesis and growth of Challenger mound, a giant carbonate mound towering over 170m above an enigmatic erosional surface, in water depths close to 1000m

Integrated geophysical and petrological study of fluid expulsion features along the Moroccan Atlantic margin

In this study we integrate a geophysical – carbonate petrological data set, collected during the TTR-14 cruise (summer 2004) along the Moroccan Atlantic margin in Gulf of Cadiz (Southern area, 400m – 1000m and El Arraiche mud volcano field). This allows us to investigate the deeper structure and its control on fluid venting, to address the nature of seafloor topographical features, fluid geochemistry and venting processes. The deeper structure of the Southern area is dominated by two NW trending anticlinal acoustic basement ridges. Their northern flank and top is cut by major present-day active, normal faults, along which four dome structures and the Meknes mud volcano (mv), are concentrated. These ridges correspond to rotated, faultbounded blocks breaking up the top of the accretionary wedge. This indicates the southward prolongation of extensional tectonics and its structural control on mud volcanism, south of the El Arraiche field, which is also evidenced by the typical sandstone mud breccias recovered at the Meknes mv. Carbonate cemented mud breccia from the Meknes (type M) and the Kidd (type K) mv, and cemented sediment portions from Pen Duick Escarpment (type PD), all possess similar carbon isotopic (-19 to -29%¸ VPDB) and carbonate geochemical signatures, indicating seepage of a geochemical similar thermogenic hydrocarbon-bearing fluid source. Slightly elevated d18O values of HMC-cemented type M crusts suggest the former presence and dissociation of gas hydrates. The brecciated fabric, intraclasts and aragonite cement morphology, typical of type K crusts testify of a relative vigorous fluid ascent. HMC-calcian dolomite cemented PD crusts were likely formed under conditions of slower fluid ascent. Their actual near-seafloor occurrence, well above the base of the SRZ, is hypothesized to relate to erosion and migration of the SRZ by variations in upward hydrocarbon fluxes