NOAA Forecast Predicts Large Dead Zone for Gulf of Mexico this Summer

21 June 2009

A team of NOAA-supported scientists from the Louisiana Universities Marine Consortium, Louisiana State University, and the University of Michigan is forecasting that the “dead zone” off the coast of Louisiana and Texas in the Gulf of Mexico this summer could be one of the largest on record. The dead zone is an area in the Gulf of Mexico where seasonal oxygen levels drop too low to support most life in bottom and near-bottom waters.

Dead zone visualization. Credit: NOAA. Click to enlarge.

Scientists are predicting the area could measure between 7,450 and 8,456 square miles, or an area roughly the size of New Jersey. However, additional flooding of the Mississippi River since May may result in a larger dead zone. The largest one on record occurred in 2002, measuring 8,484 square miles.

Dead zones are caused by nutrient runoff, principally from agricultural activity, which stimulates an overgrowth of algae that sinks, decomposes, and consumes most of the life-giving oxygen supply in the water.

The dead zone size was predicted after researchers observed large amounts of nitrogen feeding into the Gulf from the Mississippi and Atchafalaya Rivers. The rivers experienced heavy water flows in April and May that were 11% above average.

The high water volume flows coupled with nearly triple the nitrogen concentrations in these rivers over the past 50 years from human activities has led to a dramatic increase in the size of the dead zone

—Gene Turner, Ph.D., a lead forecast modeler from Louisiana State University

This hypoxic, or low-to-no oxygen area, is of particular concern because it threatens valuable commercial and recreational Gulf fisheries by destroying critical habitat.

NOAA has been funding investigations and forecast development for the dead zone in the Gulf of Mexico since 1990 and currently oversees the two national hypoxia programs authorized by the Harmful Algal Bloom and Hypoxia Research and Control Act. Data from the US Geological Survey on river flow and nutrient concentrations this spring was critical information required by the models to produce the forecasts.

An announcement of the official size of the 2009 hypoxic zone, which is an annual requirement of the Gulf of Mexico Task Force Action Plan, will follow a NOAA-supported monitoring survey led by the Louisiana Universities Marine Consortium on 18-26 July.

In addition, NOAA’s Southeast Area Monitoring and Assessment Program currently is providing near real-time data on the hypoxic zone during a five-week NOAA Fisheries Service summer fish survey in the northern Gulf of Mexico between 8 June and 18 July.

The information is available on the NOAA’s Gulf of Mexico Hypoxia Watch Web page. The objective of Hypoxia Watch is to develop new near-real-time data and map products using shipboard measurements of bottom-dissolved oxygen and to disseminate them over the Internet. These products form the basis for summertime advisories to fishermen in the North-central Gulf of Mexico, indicating where fish and other living marine resources may not be found due to low or non-existent oxygen levels.