7430 Overview

			SEAFLOOR SCIENCES (Code 7430) The Seafloor Sciences Branch provides the Navy with the understanding, description, modeling, and quantitative prediction of marine geological environments in terms that relate to Navy systems design, construction, and operations. The branch investigates biological, geological, geochemical, historical, and subsequent diagenetic processes that control distribution, range, and variability of sediment physical properties including bathymetry, roughness, and subseafloor morphology.

			GEOACOUSTICS/GEOTECHNICAL SECTION (Code 7431) The Geoacoustics/Geotechnical Section performs basic and applied research primarily associated with the coastal benthic boundary layer. Fundamental research topics include sediment geoacoustic and geotechnical behavior over varying stress-strain conditions, effects of biological and hydrodynamic processes on seafloor physical properties and morphology, effects of sediment microstructure on sediment properties and behavior, and early diagenetic processes in sediments. Applied research includes mine burial, sediment acoustic classification, high-frequency acoustic bottom interaction, characterization of sediment physical properties and biological remediation.

			ELECTRON MICROSCOPY FACILITY (Code 7431.1) Performs basic and applied research in the diverse areas of marine geosciences, geophysics, physics, materials science, space science, and microbiology using advanced microanalytical, electron-beam techniques. The relationships between formation/alteration mechanisms and resultant microstructures are studied at the atomic-scale by scanning and transmission electron microscopy. For example, natural microstructures represent direct fossil records of the mechanisms which produced them or caused subsequent alteration.

			MARINE BIOGEOCHEMISTRY The Marine Biogeochemistry Section conducts basic research in diverse areas of aquatic and sediment biogeochemistry. Aquatic sediments are the host to abundant microorganisms, which oxidize sedimentary organic matter using terminal electron donors such as dissolved oxygen, nitrate, metal oxides, and sulfate. Consequently, sediments can be considered as a dynamic redox reactor, where metals and nutrients are continuously cycled. The section also couples geochemistry with microbiological techniques (molecular biology, DNA technology, and traditional culturing) to investigate microbial communities and the processes by which microorganisms transform sediment materials to increase the understanding of microbial ecology and the ecophysiology of mineral cycling.

			SEAFLOOR SENSING The Seafloor Sensing Group is developing sensor technologies, signal processing algorithms, data inversion techniques, and data fusion methodologies for characterization of the seafloor as required by Naval tactical decision aids. A primary focus of the team is the exploitation of fleet tactical sonars for seafloor characterization (a “through the sensors” approach). Vertically integrated efforts span the gamut from basic research in acoustic interaction with seafloor sediments through demonstrations of mature technologies with near-term transitions to the Naval Oceanographic Office and fleet system. Current efforts include the demonstration of acoustic seafloor sediment classification, seafloor imaging, and seafloor bathymetry with sonars currently installed on fleet mine countermeasure ships, on nuclear attack submarines, and on helicopter-towed mine hunting sonars. The Seafloor Sensing Team crosses branch administrative boundaries and include elements of NRL Code 7440.4.

			GEOLOGY/GEOPHYSICS SECTION (Code 7432) The Geology and Geophysics Group performs fundamental research in seafloor and subseafloor processes using geophysical (primarily seismic and acoustic) techniques. Field measurements, many of which are made by the section's unique deep-towed multichannel seismic system, DTAGS, are supported by expertise in wave propagation and fluid flux modeling, particularly concerning studies of methane hydrates. More applied research is directed toward inverting the response from conventional acoustic transducers to obtain seafloor sediment properties, aiding the speedy geotechnical assessment of previously unknown, or very dynamic areas. These efforts are also supported through physical modeling, where exceedingly careful measurements can be made to corroborate numerical models.