Nina Pullano / 6 August 2020

Annual summer hypoxia points to global trends.

GIVEN A CLIMATE’S CURRENT (AND ACCELERATING) STATE, it has become unremarkable to see environmental reports peppered with superlatives: the hottest decade in the books, a record-setting ice melt.

What we don’t see as frequently are temperate reports like the one National Oceanic and Atmospheric Administration (NOAA) released this week. The agency confirmed that this year’s Gulf of Mexico dead zone — a massive spot of low oxygen that returns to the water every summer — turned out to be “smaller than expected.”

It sounds like good news at first blush. But between a hurricane mixing up this year’s data and global dead zone patterns, scientists say that the state of our seas continues to demand our attention — and our action.

Since at least 1950, when shrimpers first noticed it, a mass of low-oxygen water has formed every year in the Gulf. Warmer temperatures and excess nutrients from farms and cities feed algae — a lot of algae. The aquatic plants flourish, die, and sink in the ocean. There, they decompose, with the help of bacteria that soak up oxygen.

The result is an oxygen-depleted, also called hypoxic, zone that has a difficult time supporting life.

When NOAA predicted in June what this year’s dead zone would look like, they forecasted it to be larger than usual. Instead, the opposite occurred: The 2020 dead zone is the third-smallest recorded in the past 34 years, NOAA announced on Tuesday.

That’s due, in large part, to a tropical storm-turned hurricane. In the days before researchers set out to measure the dead zone in July, Hurricane Hanna swept through the central and western Gulf before making landfall in Texas. The storm mixed up the water column which temporarily disrupted the dead zone, making its distribution patchy.

Louisiana State University researcher Nancy Rabalais is the principal investigator on the NOAA-supported team. During a press call, Rabalais explained that events like this are the reason it’s important to look at a five-year average.

The small size is “directly related to the tropical storm,” she says. “This contributes to the variability that we see every year.”

BIGGER PATTERNS — This year’s dead zone was only slightly larger than the target set by the Hypoxia Task Force, a group that includes federal and state agencies, and the tribes within the Mississippi/Atchafalaya River Basin, which works to reduce and control hypoxia in the Gulf. But the five-year average tells a different story.

The 2020 dead zone is one of the smallest from the past three decades.

Over the past five years, the dead zone average is 5,408 square miles — or 2.8 times larger than the goal set for the year 2035. There’s a long way to go to decrease the zone’s size in the long run.

Dead zones are an increasing issue outside of the Gulf of Mexico. Algal blooms continue to plague the Great Lakes, Chesapeake Bay watershed, and coastal areas like Cape Cod. NOAA recently developed a plan to tackle Great Lakes acidification, citing algal blooms as a top concern.

“These are global situations — they occur around the globe,” Rabalais says. “Most of them in coastal waters are related to increased and excess nutrient loads.”

Those excess nutrients come from agriculture, wastewater, and fossil fuels, the US Environmental Protection Agency reports. Those tend to fall under local and state government regulations. But most of the efforts to reduce excess nutrients from those industries remain voluntary.


Iowa agricultural secretary Mike Naig is co-chair of the Hypoxia Task Force. He joined the NOAA press call to discuss how states like Iowa, 85 percent of which is farmland, are reducing the nutrients they put into the ground, and eventually, the watershed.

Naig said states should come up with different voluntary solutions to nutrient excess, tailoring them to individual states’ needs. “Waving a regulatory wand will not solve this issue,” he said during the call.

But experts have warned that voluntary efforts fall short of the sweeping changes needed to seriously reduce dead zones. Former NOAA scientist Donald Scavia wrote in 2017 that “taming nutrient pollution will require a broad national approach” — which would include changing America diet, agricultural supply chains, and fuel production.

“We also need to find the will to set legally binding limits,” Scavia wrote, “when voluntary steps aren’t enough.”