The purpose of the cruise was to map the sea floor between the shelf edge and the seaward limit of the EEZ, using the GLORIA system owned and operated by IOS. Leg 2 focused in the central Gulf of Mexico on the Mississippi Fan seaward of Louisiana, Mississippi, Alabama, and Florida.
Location
central Gulf of Mexico, Mississippi fan area, Louisiana, Mississippi, Alabama, Florida, United States, North America, North Atlantic;
Summary
This cruise was very successful. Equipment down time was minimal. The warm surface water temperature continued to limit the GLORIA range necessitating closer line spacing than planned. The presence of the loop current for the last half of the cruise not only provided warm surface water temperatures but also a strong current often approaching 4 knots. The current shear prevented the GLORIA fish from towing parallel to the ship's track, introducing some distortion in the mosaic. In the northeast portion of the Gulf near Desoto Canyon fishing boats with lines set across our proposed track caused a problem requiring several lines to be terminated early. Leg 3A will collect data to cover these data gaps. An additional 8 days will be necessary on Leg 3 to complete the coverage of the Mississippi Fan. The objective of this leg was to map the surface features in the Mississippi Fan area. Although the channel of the Mississippi could be identified on the mid-fan, over much of the fan the channel was obscured by a major submarine slide or slides. Flow patterns were well displayed on the surface and the slide could be mapped to the base of the West Florida Escarpment. Another submarine slide was also present in the Desoto Canyon area. The meandering channel from Desoto Canyon was traced from this slide seaward parallel to the escarpment. Mass wasting appears to be an important process in distributing sediments in the deep water of the central Gulf. The Sigsbee Escarpment was mapped to the east as far as the Mississippi Canyon. Isolated salt diapirs were present to the east of the Mississippi Canyon.
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
image2segy data at PCMSC on FAD
PI's Bonnie McGregor, Neil Kenyon
Platform Farnella
Original Center People field contained: Ronald Circe; John Schlee - geologist; Dave Twichell - Data curator.
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.
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.
