33 



2.1.6 



LOUISIANA/TEXAS SHELF PHYSICAL 

 OCEANOGRAPHY PROGRAM: A STATUS REPORT 



Dr. Murray Brown 



Environmental Studies Staff 



Minerals Management Service 



Gulf of Mexico OCS Region 



INTRODUCTION 



The Minerals Management Service (MMS), Gulf of Mexico OCS Region, sponsored a Symposium on the 

 Physical Oceanography of the Texas/Louisiana (TEXLA*) Shelf in Galveston, Texas, on May 24-26, 1988. The 

 symposium brought together a number of physical oceanographers, meteorologists, and ecologists to discuss the 

 state of knowledge and to begin the planning process for a long-term study of shelf circulation covering the 

 region from the mouth of the Mississippi River to approximately 24 degrees latitude along the Mexican coast and 

 from the shore out to a depth of approximately 500 meters. The proposed study is expected to take place during 

 the period 1990-1993. It is anticipated that the work will be done principally through contracts after a 

 competitive procurement process. Specific charges to the participants were as follows: 



To assess the current state of knowledge concerning the circulation on the TEXLA shelf; 



To identify significant gaps in that knowledge, 



To recommend a field measurement program to address these gaps, 



To recommend a circulation modeling program for the TEXLA shelf that will improve MMS' oil spill 

 risk assessments, and 



To identify and initiate coordination mechanisms and data-sharing arrangements with other proposed 

 research efforts. 



SUMMARY OF TOPICS 



The forcing mechanisms important to shelf circulation in the TEXLA domain include wind stress, buoyancy flux, 

 and mass flux (evaporation-precipitation) across the air-sea interface; influx of momentum/energy across the 

 open seaward boundary; and influx of freshwater at the eastern lateral boundary. Loop current eddies (LCE's) 

 are recognized as an important mechanism by which energy is transferred from the eastern Gulf toward the west 

 and from deep water onto the shelf, with significant impacts on circulation and watermass characteristics. 

 Transient storm systems can create shelf wave energy, which is effectively trapped by the TEXLA shelf. 



The combined plume of the Mississippi and Atchafalaya Rivers has a significant density contrast with the 

 surrounding shelf water and is traceable to the Texas/Mexico border. The plume front could serve as a barrier 

 to onshore movement of pollutants and as a "fast lane" for pollutant transport down the Texas coast. Some of 

 the boundary current appears to recirculate eastward along the outer shelf during summer, resulting in significant 

 amounts of relatively freshwater over the middle and outer shelves. Satellite images have revealed highly complex 

 frontal structures over and beyond the shelf. River fronts, turbidity fronts, the coastal boundary current front, 

 remnant LCE's, and "squirts" and "jets" along the shelf break have all been observed, contributing to the 

 complexity of measuring and modeling the circulation of this area. 



Throughout this document, the Texas-Louisiana Continental Shelf is referred to as TEXLA. In the Physical 

 Oceanography Programs and other documents, the Continental Shelf is referred to as LATEX. 



