ACCESS NUMBER: M04PC00008 

(1435-01-04-CT-34239) 

STUDY TITLE: Study of Deepwater Currents in the Eastern Gulf of Mexico 

REPORT TITLE: Study of Deepwater Currents in the Eastern Gulf of Mexico 

CONTRACT NUMBERS: M04PC00008 (1435-01-04-CT-34239) 

SPONSORING OCS REGION: Gulf of Mexico 

APPLICABLE PLANNING AREA: Eastern 

FISCAL YEAR(S) OF PROJECT FUNDING: 2004; 2005; 2006; 2007; 2008; 2009 

COMPLETION DATE OF REPORT: December 2010 

COSTS: FY 2004: $843,752; FY 2005: $1,207,416; CUMULATIVE PROJECT COST: 

$2,051,168. 

PROJECT MANAGER: J. Cox 

AFFILIATION: Evans-Hamilton, Inc. 

ADDRESS: 4608 Union Bay Place NE, Seattle, Washington, 98105 

PRINCIPAL INVESTIGATORS*: J. Cox, C. Coomes, S. DiMarco, K. Donohue, G. 

Forristall, P. Hamilton, R. Leben, D. R. Watts 

KEY WORDS: Eastern Gulf of Mexico, Loop Current, Loop Current Eddy, deep water 

currents, PIES array, topographic Rossby waves, spectral energy, kinetic energy, 

altimetry, satellite imagery, hurricanes, vertical coupling, hydrography, remote sensing. 

BACKGROUND: The major source of energy forcing currents in the surface waters of 

the Gulf of Mexico is the Loop Current (LC) which flows northward through the Yucatan 

Channel into the Gulf of Mexico, and then turns eastward and exits through the Straits 

of Florida to join the Gulf Stream. The LC varies in its penetration into the Gulf of 

Mexico, sometimes constraining itself to the southern Gulf, and sometimes penetrating 

far northward into the northern Gulf. During most periods when the LC has penetrated 

northward, cold core eddies and warm water filaments can be found migrating around 

its periphery. Often when extended far northward, the LC pinches off, forming a Loop 

Current Eddy (LCE) that migrates through the northern Gulf, eventually moving 

westward to die within its western regions. LCEs detach from the LC at periods ranging 

from 3 to 17 months, with a mean frequency of separation near 10 months (Sturges and 

Leben 2000). Very energetic LCEs interact with one another, the LC, and bathymetry, 

forming cyclonic eddies with which they also interact; this activity imparts significant 

energy to the surface waters of the Gulf of Mexico. While the overall net circulation of 

the surface waters in the Gulf of Mexico is generally understood, the magnitude of the 

velocity and variance of the surface currents are known to be greatest in the vicinity of 

the Loop Current, where speeds often exceed 1.5 m s-1. 
ACCESS NUMBER: M04PC00008 

(1435-01-04-CT-34239) 

OBJECTIVES: (1) Conduct measurements of currents using moorings to increase the 

regional database of ocean currents in the Eastern GOM; (2) Improve the scientific 

community’s overall knowledge and understanding of circulation features in this 

deepwater area; (3) Collect hydrographic, remote sensing, and other relevant 

measurements useful to understanding what controls the region’s circulation; (4) Assess 

the key processes energizing the circulation; (5) Add to the database of LC and LCE 

characteristics, and how these features affect the study area; (6) Establish an improved 

base of knowledge to help design future circulation studies in this part of the GOM; (7) 

Provide measurements and knowledge which could assist with future calculations of 

horizontal and vertical trajectories of released oil and its dispersion. 

DESCRIPTION: The study called for a one-year measurement program to collect an 

integrated set of current, hydrography, remote sensing, and ancillary measurements 

that could provide an excellent understanding of the circulation processes in the area. 

As a result, from January 2005 to January 2006 one year of current measurements 

were collected from four moorings in water depths from ranging from 2500 to 2800 m. 

The moorings also contained measurements of water temperature and conductivity in 

the upper 500 m. The mooring measurements were supplemented with measurements 

from bottom-moored PIES, three hydrography (profiling CTD and XBT) cruises, and 

satellite imagery and altimetry. Eddy Watch, a proprietary operational oceanographic 

product that tracks, maps, and forecasts the LC and its eddies, along with drifting buoy 

data used in the Eddy Watch analysis, were obtained from Horizon Marine, Inc. for the 

period of the study’s measurements, and utilized under a limited license for additional 

analyses of the characteristics of the LC and LCE’s. Publicly available river discharge 

data, coastal and offshore wind data, and coastal water level data during the 

measurement period were also obtained as ancillary data. 

The current measurement moorings consisted of three tall (M1, M2, & M3) and one 

short (M4) moorings. The tall moorings were full water column moorings designed to 

reach within 70 m of the surface. The short mooring was 250 m tall, and was designed 

to provide additional near-bottom current measurements. The tall moorings contained 

upward-looking 75 kHz ADCPs at 500 m depth, with single point current meters spaced 

at intervals from 750 m to near bottom. PIES measurements were obtained from seven 

locations. The PIES moorings were deployed in December 2004, interrogated in 

August 2005 when additional PIES were added to the array, and recovered in January 

2006. 

Hydrographic measurements consisting of CTD casts and XBT profiles were collected 

in January and August 2005, and January 2006 during mooring deployment, servicing, 

and recovery cruises. The hydrographic measurements were targeted to capture 

interesting loop current, eddy, or other related features affecting the study area. The 

final hydrographic survey was targeted to capture small scale interactions between the 

edge of a Loop Current Eddy (LCE) and a Cold Core Eddy (CCE) that lay over a portion 

of the study area. 

SIGNIFICANT CONCLUSIONS: The primary conclusion from the study is that the 

eastern GOM is a very active region in terms of circulation, especially when the LC or 
ACCESS NUMBER: M04PC00008 

(1435-01-04-CT-34239) 

an LCE is present. The circulation characteristics of the region are very similar to those 

in the north-central GOM when similar processes are at work, whether they be the 

presence of the LC, and LCE, frontal features, or major storms. Deep circulation 

experiences TRW packets, though generations of TRWs that translate into the northcentral GOM do not appear to be generated in this region. TRW generated currents are 

also not affected significantly by steep bathymetry in this region. 

STUDY RESULTS: Prior to the study, the deep water portion of the eastern GOM was 

thought to be impacted less frequently by the LC and LCEs or their frontal features, 

resulting in less energetic circulation than is found in the north-central GOM where the 

LC and LCE’s often penetrate. On a quasi-annual basis, the northern edge of the Loop 

Current reaches between 24° and 28° N into the Gulf of Mexico (Sturges and Evans 

1983), yet for the majority of the field measurement period, the northern edge (as the 

LC or Eddy Vortex) remained between 27° and 28° N, and impacted the study area for 

much of the measurement period. 

During the study, the LC spawned Eddy Vortex. Eddy Vortex had the largest number of 

detachment/reattachment events observed during a single LC intrusion cycle within the 

historical altimeter record. During this period of detachment and reattachment, the 

extended intrusion of the LC and an associated eddy was one of the most northerly 

intrusions on record. It was only exceeded by the intrusion that generated Eddy 

Sargassum during the Exploratory Study. As a result of the detachment and 

reattachment process, Eddy Vortex resided in, and impacted the circulation of, the study 

area for much of the field measurement period. During the mooring deployments five 

hurricanes and one tropical storm traversed the gulf, the most severe being Hurricanes 

Katrina and Rita. The combination of the extended stay of the LC and Eddy Vortex in 

the northern GOM, and the number of severe storms passing near the study area, 

resulted in extensive periods of energetic currents within the study during the study. 

STUDY PRODUCTS: Cox, J., C. Coomes, S. DiMarco, K. Donohue, G. Z. Forristall, P. 

Hamilton, R. R. Leben, and D. R. Watts. 2010. Study of Deepwater Currents in the 

Eastern Gulf of Mexico. U. S. Department of the Interior, Bureau of Ocean Energy 

Management, Regulation and Enforcement, Gulf of Mexico OCS Region, New Orleans, 

LA. OCS Study BOEMRE 2010. 473 pp. 

Cole, K. L. and S. F. DiMarco. 2010. Low-frequency variability of currents in the 

deepwater eastern Gulf of Mexico. U.S. Dept. of the Interior, Minerals Management 

Service, Gulf of Mexico OCS Region, New Orleans, LA. OCS Study MMS 2010-015. 

136 pp. 

Cole, K. L. 2008. Low frequency variability of currents in the deepwater eastern Gulf of 

Mexico. MS Thesis, Dept. of Oceanography, Texas A&M University. 

Cole, K. L., S. F. DiMarco and R. R. Leben. Febuary 2008. Dynamic mode variability in 

the deep Gulf of Mexico. CORALS, Texas A&M Seminar Series. College Station, TX. 

Poster presentation. 
ACCESS NUMBER: M04PC00008 

(1435-01-04-CT-34239) 

 

Cole, K. L., S. F. DiMarco and R. R. Leben. March 2008. Dynamic mode variability in 

the deep Gulf of Mexico. OCEAN SCIENCES MEETING, Orlando, FL. Poster 

presentation. 

Coomes, C. January 2007. Gulf of Mexico Circulation Study: Intensive Hydrographic 

Survey of Loop Current Edge Fine Scale Features. PowerPoint presentation for: MMS 

24th Information Transfer Meeting. 

Cox, J. 2007. Eastern GOM Circulation Study: Overview of the Study Goals and 

Objectives, Measurements Obtained, and Features Measured. PowerPoint presentation 

for: MMS Information Transfer Meeting. 

Cox, J. 2006. Eastern GOM Circulation Data Meeting: Overview of Study Goals, 

Objectives, Measurements Obtained, and GOM Storms. PowerPoint presentation for: 

MMS Data Meeting. 

*

 P.I.’s affiliation may be different than that listed for Project Managers.