Large 2019 dead zone in Gulf of Mexico | 8/16/2019 | Deanna Conners
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The R/V Pelican. Image appears courtesy of Arne Diercks, University of Southern Mississippi, via NOAA.

A dead zone of oxygen-depleted waters forms every summer in the Gulf of Mexico in response to nutrient runoff from the Mississippi River watershed. Scientists have been tracking the summer dead zone for 33 years now, and have found that this year’s area of low oxygen waters extends for 6,952 square miles (18,006 square km). It is the eighth largest dead zone ever recorded.

Runoff - Nitrogen - Phosphorus - Lands - Sewage

Nutrient-rich runoff containing nitrogen and phosphorus from agricultural lands and sewage causes the summer dead zone in the Gulf of Mexico. These nutrients, in combination with sunlight and warm waters in the Gulf, trigger algal blooms. Then, as the algae die off and are decomposed by bacteria, oxygen in the bottom waters drops to levels that can be deadly for many marine organisms.

Extent of the summer dead zone in the Gulf of Mexico according to sampling data collected by Louisiana scientists in July 2019. Image via LUMCON.

Scientists - Measurements - Extent - Year - Zone

Scientists took measurements of the extent of this year’s dead zone from onboard the R/V Pelican over July 23–29, 2019. The area of the dead zone was estimated at 6,952 square miles (18,006 square km). This is the 8th largest dead zone recorded in the 33 year historical record of such events.

The dead zone was actually smaller in size than that predicted back in spring based on the amount of rainfall and runoff generated this year. Scientists suspect that Hurricane Barry, which made landfall along the Louisiana coast on July 13 as a Category 1 storm, stirred up the waters and disrupted the growth of the dead zone. The dead zone is expected to continue its rapid growth if future conditions remain calm. The dead zone will eventually dissipate in the autumn as water temperatures cool and...
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