Hypoxia occurs when the amount of dissolved oxygen in the water becomes too low to support most marine life, including shrimp, crabs and fish. Through mid-July, scientists from the NOAA National Coastal Data Development Center and NOAA Fisheries at Stennis Space Center, Miss., will post online maps of dissolved oxygen near the sea floor, from Texas to Louisiana. (Click NOAA image for larger view of the ‘Dead Zone in the Gulf of Mexico being studied. Click here for high resolution version - Image Soruce: NOAA)

Mostly a summertime phenomenon, this low dissolved oxygen, or “dead zone” begins to form in June and extends from the mouth of the Mississippi River westward to Texas. Though hypoxia in the Gulf of Mexico has appeared naturally for thousands of years, its geographic area has increased significantly since NOAA began measuring it in the early 1980s.

NOAA scientists believe this increase, attributed in part to the growing use of nitrogen fertilizers in the Mississippi River watershed, has led to a demand for more information about the causes and effects of hypoxia. In 2001, NOAA scientists in Mississippi began the Hypoxia Watch Project, which provides near-real-time, Web-based maps of dissolved oxygen near the sea floor over the Texas-Louisiana continental shelf from mid-June to mid-July.

“The science community needs to stay on the leading edge of finding the causes and impacts of hypoxia to marine life in the Gulf. Hypoxia Watch, and all the resulting data from this project, will help scientists do just that,” said Gregory W. Withee, assistant administrator for the NOAA Satellites and Information Service, NCDDC’s parent agency.

Scientists aboard the NOAA research vessel, Oregon II, measure seawater temperature, salinity, chlorophyll and dissolved oxygen at more than 200 locations throughout the region as the ship makes its way from Brownsville, Texas, to the mouth of the Mississippi River. This environmental data complements the main objective of a four-week cruise, called the Southeast Area Monitoring and Assessment Program (SEAMAP) Summer Groundfish Survey, which examines stocks of commercially important fish in the Gulf.

"By pulling together resources from across NOAA, we gain a better understanding of how fish and other marine life are affected by their physical environment," said Bill Hogarth, assistant administrator for NOAA Fisheries. "This collaborative effort allows NOAA to provide the best scientific information for the benefit of the American public."

SEAMAP is a cooperative state, federal and university program that collects, manages and disseminates fishery-independent data and information in the southeastern United States. A scientist aboard the ship processes the measurements from electronic dissolved oxygen sensors, checks the measurements with chemical analyses of the seawater, then sends the data by e-mail to NCDDC at Stennis Space Center every three to four days.

Hypoxia Watch System for the Gulf of Mexico
Maps & Data can be accessed Here - Image above shows Bottom Dissolved Oxygen Contours

NOAA scientists transform the dissolved oxygen measurements into contour maps, which identify areas of low oxygen, or hypoxia. During the cruise, as the ship receives the data, NCDDC generates new maps and immediately publishes them on the Web. The first map will cover the continental shelf from Brownsville to Corpus Christi, with the final map covering the entire Texas-Louisiana coast. Dissolved oxygen contour maps, maps of actual sampling station locations, and corresponding sea surface temperature and chlorophyll-a maps from the NOAA CoastWatch program, will be available to the public. Maps are published every three to four days from June 22 through July 20.

Scientists use these environmental data to understand the effects of the physical environment on fish and other marine organisms. The dissolved oxygen maps generated during the SEAMAP cruise also help NOAA scientists plan the annual survey of the Gulf’s hypoxic zone, which is conducted by the Louisiana Universities Marine Consortium (LUMCON) in late July, when the hypoxic zone is typically at its peak. Cooling waters and storms in the fall mix up the water throughout the Gulf and restore normal oxygen levels to the sea floor.

The NOAA CoastWatch Gulf of Mexico Regional Node at Stennis Space Center developed the Hypoxia Watch process. CoastWatch provides satellite imagery and other environmental data to government decision makers and academic researchers.

The NOAA Satellites and Information Service is the nation’s primary source of space-based oceanographic, meteorological and climate data. It operates the nation’s environmental satellites, which are used for ocean and weather observation and forecasting, climate monitoring and other environmental applications. Some of the oceanographic applications include sea-surface temperature for hurricane and weather forecasting and sea-surface heights for El Niño prediction.

NOAA is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and providing environmental stewardship of the nation’s coastal and marine resources. NOAA is part of the U.S. Department of Commerce.

Relevant Web Sites

• NOAA National Coastal Data Development Center
• NOAA Hypoxia Watch System for the Gulf of Mexico
• NOAA Coastal Ecosystem Program
• Hypoxia Watch System for the Gulf of Mexico
  Maps & Data - SHP format data & JPGs