ACCESS NUMBER: 31027 

STUDY TITLE: Analysis and Validation of a Mechanism that Generates Strong MidDepth Currents and a Deep cyclonic Gyre in the Gulf of Mexico 

REPORT TITLE: Strong Mid-Depth currents and a Deep Cyclonic Gyre in the Gulf of 

Mexico 

CONTRACT NUMBER: 1437-01-99-CT-31027 

SPONSORING OCS REGION: Gulf of Mexico 

APPLICABLE PLANNING AREA: Gulfwide 

FISCAL YEARS OF PROJECT FUNDING: 1999 - 2002 

COMPLETION DATE OF REPORT: June 2004 

COSTS: FY 1999, $158,047; FY 2000, $158,057; FY 2001, $169,017; FY 2002, 

$169,671 

CUMULATIVE PROJECT COST: $653,092 

PROJECT MANAGER: Prof. Wilton Sturges 

AFFILIATION: Florida State University 

ADDRESS: Dept. of Oceanography, Tallahassee FL 32306-4032 

PRINCIPAL INVESTIGATORS: Wilton Sturges, Tal Ezer, and Eric Chassignet 

KEY WORDS: Gulf of Mexico, ocean currents, deep circulation, topographic Rossby 

waves, Loop Current, eddies, Loop Current Rings, numerical modeling, Princeton 

Ocean Model, MICOM 

BACKGROUND: It has long been observed that strong but puzzling currents are found 

at depths of ~ 1000m and deeper along the steep topography beyond the edge of the 

west Florida continental shelf. These currents have been documented primarily in 

technical reports of MMS programs in the early 1980s, in NOAA reports (by Molinari), 

and others. Strong sporadic currents at shallower depths are often reported by the 

drilling operators. Our desire in this study was to understand the cause(s) of the deep 

flows as well as the sporadic strong shallower jets. We intended to use three 

approaches: an analysis of all available current meter and hydrographic data, 

simultaneous analyses of 3 operational numerical models, and the working hypothesis 

that the strong deep flows were the result of topographic rectification of topographic 

Rossby waves. Note that this study was initiated and carried out almost in its entirety 

before we knew the results of the Deep Star Joint Industry – Mexican mooring program 

in Yucatan Channel. 
ACCESS NUMBER: 31027 

OBJECTIVES: (1) To coordinate the analyses of the MICOM and Princeton Ocean 

Model, carried out by their usual principal scientists, as to the behavior of the deep flow 

in Yucatan Channel and the full Gulf of Mexico; (2) To analyze the existing (nonproprietary) long-duration 

current meter mooring data on the basis of topographic rectification; (3) To search the 

numerical modeling output data for bursts of strong shallow-to intermediate depth flows, 

and correlate any such flows with the motion of the Loop Current (or other available 

large-scale features). 

DESCRIPTION: This project did not involve the collecting of data, but the analysis of 

many data sets and comparisons with numerical model results. The work, involving 

major commitments of time by the principal investigators, one PhD student and a postdoc, resulted in over half a dozen published papers in refereed journals (see list below). 

SIGNIFICANT CONCLUSIONS: One major result was that all the historical mooring 

data, as well as the data that were taken (or discovered) as the project took place, can 

be fit into the framework of the original hypothesis: the mean currents around the edge 

of the deep Gulf of Mexico appear to flow in the counter-clockwise (or cyclonic) 

direction. The flows are observed to be in both directions (along topography) but the 

means, over many months, are consistently in the direction expected from topographic 

rectification. This mechanism is the most obvious candidate, but there is no firm 

evidence that this is the only mechanism involved. The Princeton Ocean Model 

contains this flow direction in its output, the MICOM does not; the Principal Investigators 

are now working together in an effort to explain or resolve this (previously unknown) 

discrepancy. High-speed flows are found at the “appropriate” depths in both models 

that resemble the high-speed flows reported by the drilling operators, but of lesser 

speeds. This may be a problem with model resolution, but the primary difficulty is that 

the observations are scarce and poorly (if at all) documented. During the course of our 

work the results of the moorings across the Yucatan Channel (by the Ensenada group) 

began to emerge; these results have changed our knowledge and understanding of this 

important region of the flow enormously but have not changed our results or 

interpretations in the open Gulf. 

STUDY RESULTS: The results, other than as contained in the Conclusions section, 

are described in full in the publications described below. 

STUDY PRODUCTS: Sturges, Chassignet, and Ezer, Strong Mid-Depth currents and a 

Deep Cyclonic Gyre in the Gulf of Mexico. Final Report OCS Study, MMS 2004-040. 

Cherubin, L.M, W. Sturges, and E. Chassignet, 2004. Deep flow variability in the 

vicinity of the Yucatan Straits from a high resolution MICOM simulation. J. Geophys 

Res., submitted. 

Cherubin, L.M., Y. Morel and E. Chassignet, 2004. Loop Current ring formation: a new 

mechanism. Submitted to J. Phys Oceanogr.
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DeHaan, Christopher J., 2002. Determining the Deep Current Structure in the Gulf of 

Mexico and the Yucatan Strait from Multiple Data Types. Doctoral Dissertation, Dept. of 

Oceanography, Florida State University, Tallahassee. October, 2002. 

DeHaan, C.J., and W. Sturges, 2004. Deep cyclonic circulation in the Gulf of Mexico. 

J. Phys Oceanogr. in press. 

Ezer, T., L.-Y. Oey. and H.-C. Lee, 2002. Simulation of velocities in the Yucatan 

Channel, In: Proc., Oceans 2002, MTS/IEEE Publ., 1467-1471. 

Ezer, T., L.-Y. Oey, H.-C. Lee, and W. Sturges, 2003. The variability of currents in the 

Yucatan Channel: Analysis of results from a numerical ocean model, J. Geophys. Res., 

108, 3012, 10.1029/2002JC001509. 

Romanou, Anastasia, Eric P. Chassignet, and Wilton Sturges, 2004. The Gulf of 

Mexico circulation within a high-resolution numerical simulation of the North Atlantic. J. 

Geophys. Res., 109, C01003, doi:10.1029/2003JC001770. 

Wang, D.-P., L.-Y. Oey, T. Ezer, and P. Hamilton, 2003. Near-surface currents in 

DeSoto Canyon (1997-99): Comparison of current meters, satellite observation and 

model simulation, J. Phys. Oceanogr., 33(1), 313-326. 
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The figure above shows the “deep” Gulf of Mexico, the focus of the study, as well as the 

mean temperature from all historical hydrographic observations at a depth of 1,500 m, 

averaged into one-degree bins. One of the remarkable features is that there is a warm 

region at the base of the mean Loop Current, although we know that this flow has to 

pass through the 800-m deep restriction off Miami. 

The figure below shows a 3-D view of the Gulf bottom topography.