I.  INTRODUCTION

1.1  Introduction

The DeSoto Canyon Eddy Intrusion Study will provide the Minerals 
Management Service (MMS) with information and analyses which expands the 
understanding of physical oceanographic conditions and processes in the 
northeastern Gulf of Mexico.  In turn, these insights will support an 
enhanced basis for developing sound, rationally based environmental 
assessments.  The threat of a spill contacting land in the northeastern 
Gulf of Mexico is of great concern to the MMS.  To estimate the 
potential for such a spill coming into contact with resources in the 
region, a robust “climatological” circulation, which includes the means 
and dominant oceanographic phenomena is needed.  On the northeastern 
Gulf slope, Loop Current (LC) and eddy intrusions are two important 
processes to be included in any climatological circulation 
characterization of the area (see Figure 1.1-1 as an example).

To gather the data needed to assemble the oceanographic climatological 
database for oil spill trajectory analysis, the MMS funded the present 
DeSoto Canyon Eddy Intrusion Study.  Knowledge acquired through this 
study will facilitate MMS’s understanding of the outer shelf 
circulation, e.g., how the LC and associated eddies exchange momentum 
and mass with the shelf.  The role of the DeSoto Canyon as a route that 
facilitates these intrusions and as a conduit of mass exchange between 
the deep Gulf and the shelf will be further elucidated by characterizing 
processes and conditions over the adjacent slope.  As described below, 
results and data from this study will also be useful to other concurrent 
oceanographic studies that the MMS and others are sponsoring in the 
northeastern Gulf.

1.2  Project Objectives

The general objectives of this study are:
*	Use in-situ current measurements, hydrographic data, and satellite 
images to document and characterize LC intrusions and interactions 
with the northeastern Gulf slope (Figure 1.2-1, for illustration).  
This study shall examine the frequency and horizontal and vertical 
extent of these interactions and intrusions.  Through the use of 
dynamical principles, a conceptual model will be used to help 
explain the character and evolution of LC-slope interactions 
observed in the course of the study.
*	Document and examine the dynamical processes of momentum, mass and 
vertical vorticity exchanges occurring during LC-slope 
interactions.  These analyses shall be based on the in-situ 
current measurements and hydrographic data. 
*	Estimate the frequency of LC, LC rings and secondary eddies’ 
interactions with the northeastern slope, and conduct an 
assessment of the vertical and horizontal shears, exchanges of 
vorticity, momentum, and mass fields associated with the eddy-s 
lope interactions.
*	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.

The overall program was to last 4 years with two complete years of field 
observations in the general study area (enclosed by solid lines in 
Figure 1.1-1).  The general location and configuration of moorings were 
specified in the Scope of Work provided by the MMS.  The general area 
for the hydrographic sampling scheme was also specified.  SAIC proposed 
some limited modifications that were incorporated into the overall 
design that produced the observational database used for this report.  
It is important to note that several concurrent and complementary 
programs involving physical oceanographic measurements were conducted in 
this general study area.  The MMS is funding Texas A&M University to 
conduct a study titled “ Northeastern Gulf of Mexico Chemical 
Oceanography and Hydrography Study” (Contract No. 1435-01-97-CT-30851).  
Additionally, selected physical oceanographic measurements are being 
made in the pinnacle area near and at the shelf break offshore of 
Alabama as part of an NBR/USGS-funded study being conducted by 
Continental Shelf Associates.