The purpose of this cruise was to map the sea floor between approximately the shelf edge and the seaward limit of the EEZ using the GLORIA system owned and operated by IOS. Leg 1 focused on the western half of the Gulf of Mexico seaward of Texas and Louisiana abutting GLORIA coverage from a 1982 survey. This portion of the Gulf is dominated by salt tectonics. The area mapped with GLORIA during this leg was 45,000 sq nautical miles.
Location
western Gulf of Mexico, Texas, Louisiana, United States, North America, North Atlantic;
Summary
Hurricane Denny resulted in a loss of 13 hours of operation on August 14, 1985, and Hurricane Elena delayed arrival in New Orleans one day, from September 2 to September 3, 1985. The impact that the warm surface water and strong thermocline present in the Gulf of Mexico in the summer would have on the range of the GLORIA system was not realized. Although GLORIA was run at a 30 sec. repetition rate, 45 km swath width, the maximum swath width actually obtained was 8 km in approximately 1000 m of water. This required reducing the trackline spacing and adding additional tracklines and limited the effort in water depths shallower than 1000 m. Initially much time was spent getting all equipment operational. The GLORIA system suffered from logging problems resulting in a loss of approximately 24 hours of data during the cruise. The longest continuous down time period was 12 hours. Dirt particles in the air being pulled across the recording heads by the air conditioning system appears to have been the major problem. The air gun system was down a total of approximately 24 hours due to compressor, streamer and gun problems. The longest continuous period of down time was 7 hours. The magnetometer required 3 days to get operational initially but this was partly a result of its lower priority. A new computer system was installed for this cruise. Most of the leg was required to get the system operating properly. Navigation has to be plotted by hand for the duration of the cruise. Summary data plots for the cruise, however, were completed with the computer system at the end of the cruise. The data in the western Gulf are very interesting geologically. The Sigsbee Escarpment can be identified on the sonographs with piles of debris in places at its base. A continuous channel can be traced from the shelf edge through the diapir province of the slope, forming a reentrant in the Sigsbee Escarpment, and then meandering seaward across the rise into the deep water of the Gulf. The fan of the Rio Grande has a braided channel system and features which are interpreted to be bedforms on it. Similar bedforms are present seaward of the Sigsbee Escarpment suggesting that strong bottom currents are present in the region.
Info derived
As part of a cooperative program between the U.S. Geological Survey
and the Institute of Oceanographic Sciences (IOS), U.K., a survey of the
Exclusive Economic Zone (EEZ) in the Gulf of Mexico was conducted aboard the
M/V FARNELLA. The purpose of the cruise was to map the sea floor between
approximately the shelf edge and the seaward limit of the EEZ, using the
GLORIA (Geologic LOng-Range Inclined Asdic) system owned and operated by
IOS.
Additional geophysical data collected simultaneously with the
sidescan data include: 10 kHz, 3.5 kHz, air gun (160 cubic-inch chamber)
with two-channel hydrophone, and magnetometer. Navigation was principally
based on Loran-C, although transit satellite and Global Positioning System
(GPS) data were also logged for comparison. All geophysical data were
recorded digitally on magnetic tape and the airgun data were recorded on
analog magnetic tape. A preliminary mosaic of the sidescan data was
constructed at sea at a scale of 1:375,000, using an anamorphic camera to
adjust the images to the ship's track. Post-cruise image processing and
enhancement of the data are planned before construction of the final mosaic.
Comments
Data holdings also at PCMSC; added FACS ID to AKA
Bonnie McGreggor and Guy Rothwell; PIs
Platform; Farnella
Original Center People field contained: Dann Blackwood - photographer, Woods Hole.
Project = GLORIA Gulf of Mexico survey 1985, GLORIA Gulf of Mexico survey 1985
Chief Scientist's cruise report includes personnel and a summary for each leg of the operation (covers 2 cruises - 85027 and 85028) as well as trackmaps.
Contractor's report
Contract Report (pdf file) Institute of Oceanographic Sciences contract report. Includes personnel, program description, cruise narrative, scientific results and trackmaps. The report specified 4 legs of operation.
