MMS Releases Study on the Chemical Oceanography and Hydrography of the Northeastern Gulf of Mexico

U.S. Department of the Interior
Minerals Management Service
Gulf of Mexico OCS Region

NEWS RELEASE
November 14, 2002 Contact: Barney Congdon
(504) 736-2595

Caryl Fagot
(504) 736-2590

Debra Winbush
(504) 736-2597

MMS Releases Study on the Chemical Oceanography and Hydrography of the Northeastern Gulf of Mexico

The Minerals Management Service (MMS) today announces the release of a comprehensive field study of the northeastern Gulf of Mexico. Titled Northeastern Gulf of Mexico Physical Oceanography Program: Chemical Oceanography and Hydrography, Synthesis Report, the study focuses on water depths between 10 and 1,000 m from Tampa, Florida, to eastern Louisiana, (MMS 2002-055). The study was completed by Texas A&M for the MMS. The main objectives of the study were to conduct nine cruises and make measurements at 883 locations over the northeastern Gulf of Mexico to describe distributions of water properties such as salinity, oxygen content, and nutrients like nitrate and phosphate; to identify seasonal variations in these water properties; and to explain the processes that control the observations.

The study area is bounded by 89° W on the west, the 10-m water depth to the north, 27.5° N on the southeast, and the 1,000-m water depth offshore. Nine oceanographic research cruises were conducted from November 1997 to August 2000. During each field year, one cruise was conducted in spring (April/May), summer (July/August), and fall (November) seasons. Measurements of temperature, salinity, light transmission, and other parameters were made at 883 locations. Water samples were analyzed for oxygen, nitrate, phosphate, suspended sediment, and many other properties. The water movement or currents were measured for the entire cruise track. Additional information was gathered, such as river discharge, wind speed and direction, and sea surface height. This study was a direct consequence of a workshop held April 5-7, 1994, in Tallahassee, Florida.

Some conclusions of this study include:

Year to year variability is greater than seasonal changes even though the wind patterns were similar every year;
The dominant river is the Mississippi River and its discharge is often carried eastward along the Outer Continental Shelf, where it mixes with the saltier Gulf of Mexico water. The effects from the river are very complicated.
The currents along the shelf are primarily affected by water movement from far offshore rather than wind and river input.
Variability in both water movement and property distributions is judged considerably greater in the western region, near the Mississippi River, when compared with the eastern region.
The effect of river discharge, with its lower salinity, was to increase the oxygen concentrations in the surface waters. Plants living in the surface waters also contribute to the amount of oxygen.
Bottom dissolved oxygen concentrations were greatest in fall and lowest in summer. No hypoxic conditions, such are observed on the western side of the Mississippi, were observed during the cruises. However, very low concentrations were observed at a few locations near the Mississippi River during two spring and two summer cruises.
Regardless of season, nutrients such as nitrate and phosphate were elevated in areas where river water was present. Some forms of water movement also bring water from the deep parts of the Gulf to near the surface. The deeper water has more nutrients than surface water.
Four types of algae were identified as most abundant in the NEGOM area, although locally high abundances of other groups were detected.

Copies of the report (MMS 2002-055) are available at $25 from the Public Information Office, Minerals Management Service, 1200 Elmwood Park Boulevard, New Orleans, LA 70123, Telephone 1-800-200-GULF.

MMS is the federal agency in the U.S. Department of the Interior that manages the nation's oil, natural gas and other mineral resources on the outer continental shelf in federal offshore waters. The agency also collects, accounts for and disburses mineral revenues from federal and Indian leases. These revenues totaled nearly $10 billion in 2001 and more than $120 billion since the agency was created in 1982. Annually, nearly $1 billion from those revenues go into the Land and Water Conservation Fund for the acquisition and development of state and federal park and recreation lands.

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MMS's Website Address: http://www.mms.gov