Gary W. Hill

Burrows of the ghost crab Ocypode quadrata (Fabricius) on the barrier islands, south-central Texas coast

ABSTRACT Burrows of the grapsoid crab Ocypode quadrata (Fabricius) are important biogenic sedimentary structures on Texas barrier islands. Variation in the shape, diameter, length, orientation, and areal density of the burrows can be used to define subenvironments of the beach and foredune ridge. An increase in diameter, length, and morphological complexity of the burrows together with a decrease in burrow abundance from the upper foreshore to the back edge of the beach differentiate beach subzones. Greater burrow size and abundance and a simpler shape distinguish O. quadrata burrows in the dune mounds from burrows in the interdune flats of the foredune ridge. A preferred burrow orientation descending to the northwest in the backshore contrasts with a random orientation of burrow in the foredune ridge. Although the preferred orientation is away from the shoreline, factors not directly related to shoreline trend may be responsible.

Nearshore current pattern off south Texas: an interpretation from aerial photographs.

Abstract Current patterns in a 4-km-wide zone along the south Texas coast were interpreted from patterns of water turbidity visible in aerial photographs taken during a winter day of moderate northerly winds. Features of the turbidity pattern remained recognizable on photographs taken 25 min apart. Currents measured from the movements of these features were southward and nearly parallel to shore, increasing from about 17 cm/sec in an offshore zone to about 40 cm/sec at the line of breaking waves. The shoreward increase in velocity was probably a manifestation of wave-driven longshore currents. Rip-current plumes were drifting with this longshore current and during their drift were deformed by the horizontal shear of the current. As a result of the shear, the plume axes trended seaward in an obliquely updrift direction. Much of the turbidity visible in the photographs was caused by suspended sediment apparently supplied to the Gulf of Mexico through Aransas Pass, a tidal inlet from which a large ebb-tidal plume of turbid water was issuing at the time of the photography. Another discrete mass of turbid water along the coast to the south was probably the preceding ebb-tidal plume, which had become separated from the inlet and was drifting with the shore-parallel shelf current. Still farther south, a linear pattern of turbid and less turbid bands in the offshore zone suggested the development of Langmoir circulation having cell axes parallel to the shelf current. The turbid bands probably marked the zones of surface divergence and upwelling of the Langmuir circulation. The spacing between the turbid bands averaged about ten times the water depth, and thus the cells were much flatter than Langmuir cells that have been observed in deeper water.

Small‐scale mapping of the exclusive economic zone using wide‐swath side‐scan sonar

Abstract The U.S. Geological Survey (USGS) started a program in April 1984 to map the deep‐water (greater than 200 m) areas of the U.S. Exclusive Economic Zone (EEZ) at a reconnaissance scale as a first effort to develop a geologic understanding of the new national offshore territory. This effort was in response to President Reagans EEZ proclamation in March 1983, which extended U.S. jurisdiction over an area extending 200 nautical miles offshore of the United States and U.S. trust territories. This USGS mapping effort is a cooperative effort with the Institute of Oceanographic Sciences (IOS) of the United Kingdom and uses a unique side‐scan sonar system named GLORIA (Geological Long‐Range Inclined Asdic) developed by IOS. To date, over 3,500,000 km2 have been mapped off the west coast, the east coast, the Island of Hawaii, Puerto Rico, and the U.S. Virgin Islands and in the Gulf of Mexico and the Bering Sea. All of these surveys have been highlighted by discoveries of major geologic features that contri...

Seafloor Exploration and Characterization: Prerequisite to Ocean Space Utilization

In 1983, the President proclaimed the establishment of an Exclusive Economic Zone (EEZ), 200 nautical miles seaward of the United States. This proclamation extended the Nations sovereign rights for the purposes of exploring, exploiting, conserving, and managing natural resources in the coastal ocean. This new area is approximately 3.4 million square nautical miles (sq. n.mi.) or about 1.3 times the Nations total land area. Information is needed to characterize the resources within it. It is essential to have the proper data to identify and recover the resources in an environmentally sound manner. The Departments of Interior and Commerce have established major programs to meet the national goal of determining the characteristics and resources of the EEZ. In order to meet this responsibility, the National Oceanic and Atmospheric Administration (NOAA) and the U.S, Geological Survey (USGS), are undertaking systematic mapping programs of the EEZ. NOAAs effort includes detailed bathymetric mapping of the seabed. The USGS is using a wide-swath side-scan sonar system to map the EEZ seafloor on a reconaissance scale. These programs are a prerequisite and are essential for planning and carrying out resource exploration, exploitation, and management activities. Existing maps do not provide adequate feature definition to meet academic, industrial, and government user needs. The NOAA and USGS programs are essential to resource development and needed by the Nations scientific community to understand the processes that form the continental margins and the mineral deposits in and on the seafloor. Advances in computer technology, the development of multi-beam sonar systems, and improved methods of obtaining navigational positions make it possible to respond to these needs. In 1984, NOAA and the USGS entered into a Memorandum of Understanding (MOU) to begin a coordinated National effort to map specific areas of the EEZ. These areas were identified on the basis of scientific interest and resource potential (e.g., hard mineral and oil and gas). Priorities for bathymetric mapping of specific sites by NOAA are being set to compliment the broad reconnaissance scale USGS Geological LOng-Range Inclined Asdic (GLORIA) surveys. Three NOAA ships are currently surveying the west coast, Alaska, and the Hawaiian Islands of the United States. East coast and Gulf of Mexico surveying will begin in the latter part of 1987 or 1988. USGS GLORIA surveys have been completed for the west coast, east coast, Gulf of Mexico, Puerto Rico, and U.S. Virgin Islands; surveys off Alaska and Hawaii were started in 1986.

A radiographic scanning technique for cores

Abstract A radiographic scanning technique (RST) can produce single continuous radiographs of cores or core sections up to 1.5 m long and up to 30 cm wide. Changing a portable industrial X-ray unit from the normal still-shot mode to a scanning mode requires simple, inexpensive, easily constructed, and highly durable equipment. Additional components include a conveyor system, antiscatter cylinder-diaphragm, adjustable sample platform, developing tanks, and a contact printer. Complete cores, half cores, sample slabs or peels may be scanned. Converting the X-ray unit from one mode to another is easy and can be accomplished without the use of special tools. RST provides the investigator with a convenient, continuous, high quality radiograph, saves time and money, and decreases the number of times cores have to be handled.

The US EEZ Program: Information and Technology Needs

In 1983 the US Geological Survey (USGS) and the National Oceanic & Atmospheric Administration (NOAA) initiated a program to characterize the seafloor of the US Exclusive Economic Zone. In the first 5 years of the program over 1,500,000 square nautical miles of the EEZ have been mapped with the GLORIA sidescan sonar system to identify major seafloor features. Results of these surveys are available as atlases and in digital form for advanced image processing.

Positioning in Marine Mapping and Charting

The workshop on “Positioning in Marine Mapping and Charting” (INSMAP 86 Workshop #5) was attended by 32 participants from several defense, governmental, and academic institutions. For mapping and charting at different scales, several specific topics were discussed. The different scales were defined as: (1) local - point sampling such as coring, dredging, photography, etc; (2) area - local studies restricted to areas smaller than several hundred to a few thousand square nautical miles; (3) regional - areas of substantial size such as the Exclusive Economic Zone off the west coast of the United States (approximately 250,000 square nautical miles) or the Gulf of Mexico; (4) global - areas equivalent to ocean basins or mapping programs associated with global tectonic problems. Topics for discussion at the various scales included: (1) what are the greatest demands (e.g., accuracy, range, lifespan) and limitations (e.g., cost, political boundaries) for the positioning system; (2) what are the unique demands asked of a positional system such as positioning of secondary systems (e.g., streamers, camera sleds, side-scan sonar fish, etc; (3) what are the real world factors limiting successful positioning; (4) what can be done to overcome particular factors; and (5) what recommendations can be made to INSMAP 86 regarding research and developmental activities which will meet future mapping and charting positional requirements.