Seabed

About: Seabed is a research topic. Over the lifetime, 3655 publications have been published within this topic receiving 62544 citations. The topic is also known as: sea floor & seafloor.

Geoacoustic modeling of the sea floor

Abstract: Geoacoustic models of the sea floor are basic to underwater acoustics and to marine geological and geophysical studies of the earth’s crust, including stratigraphy, sedimentology, geomorphology, structural and gravity studies, geologic history, and many others A ’’geoacoustic model’’ is defined as a model of the real sea floor with emphasis on measured, extrapolated, and predicted values of those properties important in underwater acoustics and those aspects of geophysics involving sound transmission In general, a geoacoustic model details the true thicknesses and properties of sediment and rock layers in the sea floor A complete model includes water‐mass data, a detailed bathymetric chart, and profiles of the sea floor (to obtain relief and slopes) At higher sound frequencies, the investigator may be interested in only the first few meters or tens of meters of sediments At lower frequencies information must be provided on the whole sediment column and on properties of the underlying rocks Complete geoacoustic models are especially important to the acoustician studying sound interactions with the sea floor in several critical aspects: they guide theoretical studies, help reconcile experiments at sea with theory, and aid in predicting the effects of the sea floor on sound propagation The information required for a complete geoacoustic model should include the following for each sediment and rock layer In some cases, the state‐of‐the‐art allows only rough estimates, in others information may be nonexistent (1) Identification of sediment and rock types at the sea floor and in the underlying layers (2) True thicknesses and shapes of layers, and locations of significant reflectors (which may vary with sound frequencies) For the following properties, information is required in the surface of the sea floor, in the surface of the acoustic basement, and values of the property as a function of depth in the sea floor (3) Compressional wave (sound) velocity (4) Shear wave velocity (5) Attenuation of compressional waves (6) Attenuation of shear waves (7) Density (8) Additional elastic properties (eg, dynamic rigidity and Lame’s constant); given compressional and shear wave velocities and density, these and other elastic properties can be computed There is an almost infinite variety of geoacoustic models; consequently, the floor of the world’s ocean cannot be defined by any single model or even a small number of models; therefore, it is important that acoustic and geophysical experiments at sea be supported by a particular model, or models, of the area However, it is possible to use geological and geophysical judgement to extrapolate models over wider areas within geomorphic provinces To extrapolate models requires water‐mass data (such as from Nansen casts and velocimeter lowerings), good bathymetric charts, sediment and rock information from charts, cores, and the Deep Sea Drilling Project, echo‐sounder profiles, reflection and refraction records (which show detailed and general layering and the location of the acoustic basement), sound velocities in the layers, and geological and geophysical judgement Recent studies have provided much new information which, with older data, yield general values and restrictive parameters for many properties of marine sediments and rocks These general values and parameters, and methods for their derivation, are the main subjects of this paper

Seabed Fluid Flow: The Impact on Geology, Biology and the Marine Environment

Abstract: Acknowledgements 1 Seabed fluid flow introduction 2 Pockmarks, shallow gas and seeps: an initial appraisal 3 Seabed fluid flow around the world 4 The contexts of seabed fluid flow 5 The nature and origins of flowing fluids 6 Shallow gas and gas hydrates 7 Migration and seabed features 8 Seabed fluid flow and biology 9 Seabed fluid flow and mineral precipitation 10 Impacts on the hydrosphere and atmosphere 11 Implications for man References Index

Multiscale Terrain Analysis of Multibeam Bathymetry Data for Habitat Mapping on the Continental Slope

Abstract: Multibeam surveys can provide detailed bathymetry data for the continental slope from which quantitative descriptors of the seabed terrain (e.g., slope) may be obtained. We illustrate the value of these descriptors for benthic habitat mapping, and highlight the advantages of multiscale analysis. We examine the application of these descriptors as predictor variables for species distribution models, which are particularly valuable in the deep sea where opportunities to directly survey the benthic fauna remain limited. Our initial models are encouraging and suggest that wider adoption of these methods may assist the delivery of ecologically relevant information to marine resource managers.

East Pacific Rise: Hot Springs and Geophysical Experiments

Abstract: Hydrothermal vents jetting out water at 380° ± 30°C have been discovered on the axis of the East Pacific Rise. The hottest waters issue from mineralized chimneys and are blackened by sulfide precipitates. These hydrothermal springs are the sites of actively forming massive sulfide mineral deposits. Cooler springs are clear to milky and support exotic benthic communities of giant tube worms, clams, and crabs similar to those found at the Galapagos spreading center. Four prototype geophysical experiments were successfully conducted in and near the vent area: seismic refraction measurements with both source (thumper) and receivers on the sea floor, on-bottom gravity measurements, in situ magnetic gradiometer measurements from the submersible Alvin over a sea-floor magnetic reversal boundary, and an active electrical sounding experiment. These high-resolution determinations of crustal properties along the spreading center were made to gain knowledge of the source of new oceanic crust and marine magnetic anomalies, the nature of the axial magma chamber, and the depth of hydrothermal circulation.