Hydro and... Science

Habitat Suitability for Juvenile Common Sole (Solea solea, L.) in the Vilaine Estuary (Bay of Biscay, France) Nursery Ground
Nicolas, D., Le Loc’h, F., Desaunay, Y., Hamon, D., Blanchet, A. and Le Pape, O. 2007. ?
Estuarine, Coastal and Shelf Science, 73: pp. 639-650.

Coastal and estuarine systems are among the most threatened by human activities which damage their ecological function and, in particular, their nursery role for many marine species. In this context, the protection of these vital ecosystems is a critical issue for the management of fisheries resources. To that aim, functional approaches have to be developed that make it possible to assess habitat suitability and quality.

The purpose of this paper is to develop a Habitat Suitability Index (HIS) based on benthic macrofauna communities to describe the abundance and spatial distribution of juvenile sole, in order to determine essential nursery habitats.

Previous studies have shown that Young-Of-the-Year (YOY) sole are strongly dependent on various abiotic factors, especially bathymetry, sediment cover and the extent of river plumes. This paper investigated whether taking into account biological variables, based on benthic macrofauna biomasses aggregated into trophic groups, may improve the description of the juvenile sole distribution in the Vilaine estuary nursery. Results from generalised linear models demonstrated the importance of integrating these biological variables in the determin­ation of juvenile habitats at a local scale. The abundance of YOY sole was correlated with an index of the benthic invertebrate biomass and, more specifically, with the biomass of suspension feeders. This result was reinforced by a one-dimensional spatial statistical analysis, which pointed out the similar distribution of invertebrate macrobenthos and juvenile sole along the upstream/downstream gradient of the estuary.

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Methane Hydrate Exploration on the mid Chilean Coast: A Geochemical and Geophysical Survey
Coffin, R., Pohlman, J., Gardner, J., Downer, R., Wood, W., Hamdan, L., Walker, S., Plummer, R., Gettrust, J. and Diaz, J. 2007.
Journal of Petroleum Science and Engineering, Natural Gas Hydrate / Clathrate, 56: pp. 32-41.

Conditions in deep ocean sediment below water depths of approximately 400m and in high latitude permafrost provide the temperature and pressure requirements for gas hydrate stability. Methane hydrates are recognised as a potential source of future energy, influence offshore platform stability, are a major factor in climate change and provide a significant contribution to the ocean carbon cycle.

Although seismic surveys are a common approach for evaluation of marine hydrate distribution, the target phase (solid hydrate) is not sensed directly, but is inferred by the presence of a ‘bottom-simulating reflector’ at the expected base of hydrate stability. Complementary analysis of biogeochemical and seismic data is being evaluated to assist in the survey of sediment gas hydrate deposits. This study compares seismic data from a deep towed acoustic/geophysics system and geochemical data from shallow piston cores along the mid-Chilean Margin. The goal of this study was to integrate data from seismic surveys, which provide an outline of possible hydrate regions, with geochemical analysis of porewater samples and heat-flow probe data.?The results show that the seismic data set does not provide a definite survey of the hydrate distribution but, when coupled with geochemical and heat-flow profiles, a more thorough description for the potential location of deep methane hydrate deposits is available.

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Quantitative Study of the Deformation at Southern Explorer Ridge Using High-resolution Bathymetric Data
Deschamps, A., Tivey, M., Embley, R.W. and Chadwick, W.W. 2007.
Earth and Planetary Science Letters, 259: pp. 1-17.

This paper presents preliminary results of a morphological study of the summit of the Southern Explorer Ridge (SER). The SER is an inflated intermediate-rate spreading centre located in the north-east Pacific off the west coast of Canada, which hosts a large hydrothermal vent complex known as ‘Magic Mountain’. A quantitative assessment of faulting on the axial summit graben floor close to the ridge summit is accomplished through the analysis of high-resolution, near-bottom, bathymetric data.

These data were acquired using a multi-beam system mounted on an autonomous underwater vehicle operated a few tens of metres above the sea floor. The data from the high-resolution, near-bottom multi-beam (pixel size <1m) were combined with regional swath mapping using a hull-mounted multi-beam system (EM300) (pixel size, 30m). This data set provides an unparalleled view of the fracture evolution of young oceanic crust as it is accreted and moved away from the spreading axis.

This paper shows how quantitative measurements of the faulting patterns, and their distributions and statistics can be related to the brittle failure of newly formed oceanic crust.

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Relationships Between Benthic Macrofauna and Natural Radionuclides and 137Cs Distributions and Their Relationship with Sedimentological Processes in Patras Harbour, Greece
Papaefthymiou, H., Papatheodorou, G., Moustakli, A., Christodoulou, D. and Geraga, M. 2007.
Journal of Environmental Radioactivity, 94: pp. 55-74.

For several decades, the occurrence of natural and anthropogenic radionuclides in the marine environment has been studied in order to better understand the natural processes both in the sea floor and the water column, as well as the protection of the marine envir­onment. The study presented in this paper combines information from hydrographic, sedimentological and physical measurements to determine the sedimentological processes that affect the distrib­ution of radionuclides in an environment that is influenced by human activities.

Surficial and subsurface sediment samples derived from gravity cores were analysed for grain size, water content, bulk density, specific gravity, organic carbon content and specific activities of natural radionuclides and137Cs. The sediment cores were selected from a detailed bathymetric and marine seismic survey. This multidisciplinary approach has provided new insights into sedimentological processes that affected the distribution of radionuclides in a marine environment highly influenced by human activities.

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