This year’s dead zone in the Gulf of Mexico turned out to be smaller than anticipated.

NOAA-funded scientists went on their yearly research cruise aboard the R/V Pelican in order to determine the size of the dead zone in the Gulf of Mexico. They discovered that not only is this summer’s size below average, but is the fourth smallest area mapped since 1985. Researchers approximated the zone as 2,720 square miles, which is much lower than NOAA’s June forecast of 5,780 square miles.

GCOOS Board Member, Dr. Nancy Rabalias, a professor at LSU and LUMCON who led the survey mission, attributes the low levels to persistent winds from the west and northwest in the few weeks preceding the cruise that “likely pushed the low oxygen water mass to the east and piled it toward the central shelf and toward Grand Isle. Additional winds and waves at the beginning of the cruise in the area of the immediate west of the Mississippi River delta to the area off Barataria Pass, likely mixed oxygen into these shallower waters.”

Original Post

The bottom area of low oxygen in Louisiana coastal waters west of the Mississippi River, commonly known as the ‘Dead Zone,’ was mapped at a smaller-than-average size this summer. The area was 2,720 square miles (7,040 square kilometers), slightly larger than the state of Delaware and well below the projected estimate of 6,570 square miles (17,000 square kilometers). This summer’s Dead Zone size is the fourth smallest area mapped since 1985. The average over 2014 to 2018 is 5,770 square miles (about three times the size of the Hypoxia Task Force five-year goal reduction of 1,930 square miles, 5,000 square kilometers)).

Distribution of bottom-water dissolved oxygen, July 23 – July 28, 2018. Data source: N. N. Rabalais, Louisiana State University & Louisiana Universities Marine Consortium; R. E. Turner, Louisiana State University. Funding: National Oceanic and Atmospheric Administration, National Centers for Coastal Ocean Science.

The university and government scientists mapping the 2018 summer area of the ‘Dead Zone’) returned to dock on July 28 after measuring bottom-water dissolved oxygen levels less than 2 milligrams per liter (equal to 2 ppm) at 25 of 80 stations from the Mississippi River west along the Louisiana coast to Lake Calcasieu near the Louisiana-Texas border. Many other water quality and physical oceanographic data were collected along with the bottom-water oxygen values. The small size this summer is a surprisingly low area based on factors, especially the May nitrogen load from the Mississippi River that normally strongly influences the size of bottom-water hypoxia (low oxygen) in mid-summer.