Gulf of Mexico dead zone: Summer 2023 forecast

A boat with many arms and a net in wavy waters.
A shrimp boat trawls through the Gulf of Mexico. NOAA has released its 2023 forecast for the Gulf of Mexico dead zone, an area of low oxygen that occurs every summer. Marine life can’t live in these dead zones. Image via NOAA Fisheries.

Gulf of Mexico dead zone

Every year in June, NOAA scientists forecast the expected size of the dead zone in the Gulf of Mexico. Generally speaking, the dead zone occurs every summer as an area of hypoxia, where low oxygen levels can’t sustain life. Now, for the summer of 2023, NOAA is forecasting a below-average extent of about 4,155 square miles. The average dead zone is 5,364 square miles over the 36-year history of dead zone measurements in the region.

NOAA explained some of the factors leading to the low forecast:

In May 2023, discharge in the Mississippi and Atchafalaya rivers was about 33% below the long-term average between 1980 and 2022, and the nitrate and phosphorus loads were about 42% and 5% below the long-term averages, respectively.

A monitoring survey, scheduled for later this summer, will confirm the size of the 2023 dead zone. Also, it’s a key test of the accuracy of NOAA’s models. Those results will be available, accordingly, in early August.

What is a dead zone?

NOAA explained that:

The annual Gulf of Mexico dead zone is primarily caused by excess nutrient pollution from human activities in urban and agricultural areas throughout the Mississippi River watershed. When the excess nutrients reach the Gulf, they stimulate an overgrowth of algae, which eventually die and decompose, depleting oxygen as they sink to the bottom. The resulting low oxygen levels near the bottom of the Gulf cannot support most marine life. Fish, shrimp and crabs often swim out of the area, but animals that are unable to swim or move away are stressed or killed by the low oxygen.

Gulf of Mexico dead zone: Map of U.S. with large green area with yellow and red patches and many rivers in blue.
The Mississippi River watershed includes more than 40% of the continental U.S. and 22 states. Agricultural and urban contributions of nitrogen and phosphorus pollution cause the annual summer dead zone in the Gulf of Mexico. In this image, yellow is for agriculture, red for cities and green for natural, plus the gray is the dead zone. Image via NOAA.

A new type of forecast

Overall, this is just the 6th year that NOAA has produced a dead zone forecast. Nicole LeBoeuf of NOAA explained their usefulness:

NOAA hypoxia forecasts aim to provide coastal managers and stakeholders with the information they need to take proactive action to mitigate the impacts of hypoxic events. These forecasts also help managers set nutrient reduction targets necessary to reduce the frequency and magnitude of future dead zones.

Among the tools at their disposal, the USGS uses thousands of real-time stream gauges throughout the Mississippi-Atchafalaya watershed. The Interagency Mississippi River and Gulf of Mexico Hypoxia Task Force is working toward a goal of reducing the dead zone to 1,900 square miles by the year 2035.

Bottom line: NOAA’s summer 2023 forecast for the Gulf of Mexico dead zone calls for a below-average extent of about 4,155 square miles. These dead zones are areas where low oxygen doesn’t allow for marine life to survive.

Read more: Largest-ever Gulf of Mexico dead zone in 2017

June 8, 2023

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Kelly Kizer Whitt

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