ACCESS NUMBER: 30825

STUDY TITLE: DeSoto Canyon Eddy Intrusion Study 

REPORT TITLE: DeSoto Canyon Eddy Intrusion Study, Final Report, Volume I: 

Executive Summary and Volume II: Technical Report 

CONTRACT NUMBER: 1435-01-96-CT-30825 

SPONSORING OCS REGION: Gulf of Mexico 

APPLICABLE PLANNING AREA: Eastern Gulf of Mexico 

FISCAL YEARS OF PROJECT FUNDING: 1996,1997,1998,1999,2000 

COMPLETION DATE OF REPORT: November 2000 

COSTS: FY 1997: $747,459; FY 1998: $797,707; FY 1999: $799,774: FY 2000: 

$577,428: CUMULATIVE PROJECT COSTS: $2,924,368 

PROJECT MANAGER: E. Waddell 

AFFILIATION: Science Applications International Corporation 

ADDRESS: 615 Oberlin Rd., Suite 100; Raleigh, NC 27605 

PRINCIPAL INVESTIGATORS: J. Churchill, P. Hamilton, R. Leben, T. Lee, W. 

Sturges, J. Singer, T. Berger 

KEY WORDS: Gulf of Mexico, DeSoto Canyon, Loop Current, eddies, rings, currents, 

hydrography, sea surface height, sea surface temperature, circulation, field 

measurements, transport, slope, shelf break. 

BACKGROUND: The DeSoto Canyon region is of interest for possible development of 

oil and gas potential. The U.S. Department of the Interior requires an environmental 

characterization of potential lease areas for making appropriate management decisions. 

The present report presents the results of a field measurement and synthesis study for 

the DeSoto Canyon. The study was conducted by a team of scientists from several 

different institutions. 

OBJECTIVES: In-situ current measurements, hydrographic data, and satellite images 

were used to document and characterize LC intrusions and interactions with the 

northeastern Gulf. This study used these data to examine the dynamical processes of 

momentum, mass and vertical vorticity exchanges occurring during LC-slope 

interactions. An estimate was developed of the frequency of LC, LC rings, and 

secondary eddies’ interactions with the northeastern slope, and an assessment of the 

exchanges of vorticity, momentum, and mass fields associated with the eddy-slope 

interactions was conducted. It elucidate the role of the DeSoto Canyon in LC and eddy 

processes as a mechanism and as well as a route of mass and momentum exchange 

between the shelf and deep water of the northeastern Gulf. 

DESCRIPTION: The study area is generally located in the DeSoto Canyon over the 

slope in the northeastern Gulf of Mexico, extending from the shelf break (100m isobath) 

seaward to a nominal southerly limit of 28.5°N. However, to connect processes 
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occurring within this area, it was necessary to examine and detail dynamics and 

characteristics of the Loop Current and related eddies and rings that were outside that 

region. 

In March 1998 at the beginning of the two-year field measurement program, thirteen 

moorings were deployed along four transects in water depths of 100m, 500m and 

1300m. An additional mooring was placed in 200m on the axis of the DeSoto Canyon. 

Approximately 76 hydrographic stations were occupied every four months during 

mooring rotation and maintenance cruises. A variety of current measuring devices were 

used, with Acoustic Doppler Current Profilers at the top of each mooring to provide 

detailed information concerning currents in the surface layer. In addition to 

current/temperature sensors, a number of internally recording conductivity/temperature 

and temperature sensors were deployed on each mooring to provide more detailed 

information on the vertical and horizontal water mass structure. Two special studies 

were conducted, involving higher spatial resolution hydrographic sampling, with a goal 

of helping resolve some finer scaled or ephemeral features. Satellite-derived sea 

surface height and sea surface temperature data was available on a daily basis to 

supplement the above in-situ and survey data. A very high data return was maintained 

to produce a comprehensive program data set. 

Complete data sets (in-situ, hydrography and remotely sensed) were provided to the 

team of Principal Investigators to use in an integrated characterization of key physical 

oceanographic processes and patterns occurring in the study area. 

SIGNIFICANT CONCLUSIONS: Eddy-like (cyclonic and anticylonic) features and 

related flow patterns over the slope had a significant impact on the circulation in and 

adjacent to the DeSoto Canyon. Many eddies could be linked directly to the Loop 

Current and related features such as frontal eddies. The linkage of other eddies to the 

Loop Current was not well defined. The variable location, sense of rotation and strength 

of each eddy caused aperiodic patterns to be prevalent. Over the deeper slope regions, 

currents often appeared to be uncoupled from conditions nearer the surface. Wind 

stress on the ocean surface affected surface currents at the shelf break and over the 

slope, and had a substantial role in shelf break exchange. Severe storms such as 

hurricanes created substantial flux across the shelf break as well as establishing a 

strong pattern of inertial currents that varied both vertically and horizontal. 

STUDY RESULTS: This study region is affected simultaneously by diverse influences 

of wind driven currents and circulation associated with eddy-like features, some of 

which are related to the Loop Current. Because eddy-like features varied in location, 

strength and size, their impact on observed current patterns varied with time and 

location. Many of the features were linked to Loop Current rings that had detached, or 

migrating frontal boundary eddies that could be associated with both the Loop Current 

and detached Loop Current rings. Depending on the structure of these features, they 

were affected by interaction with the bathymetry that defines the DeSoto Canyon. 

Several modes of eddy-bathymetry interaction were identified. 

Meteorological processes had a significant role in near surface and deeper currents. 

Regular wind stress was strongly coherent with surface currents and contributed to shelf 
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break exchange as well as currents over the slope. During significant storms, such as 

hurricanes, meteorological forcing caused large shelf break flux as well as creating a 

pattern of strong inertial currents that propagated vertically and horizontally. 

Wind stress and eddies combined to produce a statistical pattern of currents within 

DeSoto Canyon. A surface/near surface current to the east occurred near the shelf 

break. Down slope and at mid-depth, a counter current (with a westerly component) 

was evident. Offshore, and extending from the surface to 7-800m depth, circulation 

seems to be controlled by the presence and location of eddies, in particular cyclonic 

eddies, and related current patterns. 

STUDY PRODUCTS: Hamilton, P., T.J. Berger, J.J. Singer, E. Waddell, J.H. Churchill, 

R.R. Leben, T.N. Lee, and W. Sturges. DeSoto Canyon Eddy Intrusion Study; Final 

Report Volume I: Executive Summary. OCS Study MMS 2000-079. U.S. Department 

of the Interior, Minerals Management Service, Gulf of Mexico OCS Region, New 

Orleans, LA. 47 pp. 

Hamilton, P., T.J. Berger, J.J. Singer, E. Waddell, J.H. Churchill, R.R. Leben, T.N. Lee, and 

W. Sturges. DeSoto Canyon Eddy Intrusion Study, Final Report Volume II: Technical 

Report. OCS Study MMS 2000-080. U.S. Department of the Interior, Minerals Management 

Service, Gulf of Mexico OCS Region, New Orleans, LA. 293 pp. 

Science Applications International Corporation, 1997. DeSoto Canyon Eddy Intrusion 

Study, Annual Report: Year 1. OCS Study MMS 97-0028. U.S. Department of the Interior, 

Minerals Management Service, Gulf of Mexico OCS Region, New Orleans, LA. 11 pp. 

Science Applications International Corporation, 1998. DeSoto Canyon Eddy Intrusion 

Study, Annual Report: Year 2. OCS Study MMS 98-0053. U.S. Department of the Interior, 

Minerals Management Service, Gulf of Mexico OCS Region, New Orleans, LA. 8 pp. 

Science Applications International Corporation, 1999. DeSoto Canyon Eddy Intrusion 

Study, Annual Report: Year 3. OCS Study MMS 99-0051. U.S. Department of the Interior, 

Minerals Management Service, Gulf of Mexico OCS Region, New Orleans, LA. 10 pp. 

Sturges, W. and R. Leben, 2000. Frequency of ring separations from the Loop Current in the 

Gulf of Mexico: A revised estimate. J. Phy. Oceangr., 30, 1814-1819 

*P.I.’s affiliation may be different than that listed for the Project Manager(s).