The “dead zone” in the Gulf of Mexico spreads out in the ocean each summer, with oxygen levels in the water so low that it suffocates and kills marine life, according to federal researchers.
Scientists forecast the size of the dead area, also known as the hypoxic zone, each year. The forecast for this summer was for the zone to cover about 7,829 square miles, researchers say. But researchers say the dead zone will be about 1,000 square miles smaller than forecast, according to the National Oceanic and Atmospheric Administration.
Nancy Rabalais, with Louisiana State University, said the zone is actually about 6,952 square miles, during a NOAA press conference Thursday.
She said she just returned from a research trip on the Gulf to measure the hypoxic zone and it was “not as large as we expected.”
Rabalais said Tropical Storm Barry, which was briefly a hurricane, helped keep the hypoxia zone smaller. She explained that the storm’s wind created waves, and those waves mix up the ocean down the water column and get more oxygen in the water.
The measurements researchers brought back from their research cruise may not be the maximum size for the summer, NOAA’s Steve Thur said Thursday.
“Past research indicates that hypoxia can take a week to reform in the summer after major wind events such as the recent passage of Hurricane Barry. We didn’t know what we would find when we went out to map the zone,” Rabalais said.
The largest Gulf of Mexico dead zone was in 2017, when it spread over 8,776 square miles of sea, NOAA reports. The five-year average is about 5,770 square miles.
Researchers have been measuring the dead zone for 33 years, according to NOAA. The measurements from Rabalais’ team make this the eighth largest since researchers started monitoring the Gulf dead zone.
Dead zones have less dissolved oxygen in the water, according to NOAA. They earned the name dead zone “because most marine life either dies, or, if they are mobile such as fish, leave the area. Habitats that would normally be teeming with life become, essentially, biological deserts,” NOAA said.
“The annually recurring Gulf of Mexico hypoxic zone is primarily caused by excess nutrient pollution from human activities, such as urbanization and agriculture, occurring throughout the Mississippi River watershed,” according to NOAA.
Those nutrients all flow down to the Gulf of Mexico and set off a chain reaction where algae overgrows the area, then dies and sinks into the water to decompose. “The resulting low oxygen levels near the bottom are insufficient to support most marine life and have long-term impacts to living marine resources that are unable to leave the area,” NOAA said.
“A major factor contributing to the large dead zone this year is the abnormally high amount of spring rainfall in many parts of the Mississippi River watershed, which led to record high river flows and much larger nutrient loading to the Gulf of Mexico,” NOAA said.