A hypoxic zone is an area where oxygen concentration is so low it chokes out marine life. The Gulf of Mexico's dead zone is primarily human-caused, a result of nutrient pollution, including nitrogen and phosphorus from urban environments and farms, traveling through the Mississippi River watershed and into the gulf.
The nutrients feed an explosion of algae, which then die, sink and decompose. This creates the dead zone.
A rush of spring rain feeding into the Mississippi is what's expected to push 2019's zone to a near-record size. NOAA calculated the record-setting 2017 dead zone reached an area of 8,776 square miles, while the five-year average is 5,770 square miles.
NOAA's forecast assumes normal weather conditions, but large storms could impact the ultimate area of the dead zone. NOAA will help launch a monitoring survey in August to confirm the size and see if it matches the forecast.
"Low oxygen conditions started to appear 50 years ago when agricultural practices intensified in the Midwest," LSU reported. "No reductions in the nitrate loading from the Mississippi River to the Gulf of Mexico have occurred in the last few decades." That's grim news for the gulf.
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