Tropical Storm Bertha drops ‘dead zone’ ahead of survey
Gale-force winds, high waves stir oxygen-rich water in the Gulf and leave Aggie researchers with more questions to explore.
Scientists retrieve a package of ocean sensors used to check conductivity, temperature, depth during a survey of the hypoxic zone in the Gulf. (CREDIT: From NOAA Courtesy Cassandra Glaspie/LSU)
Named weather events typically get remembered for damage dealt on land, but Tropical Storm Bertha is earning notice for benefits discovered beneath the waves.
Scientists are crediting the second tropical storm of the Atlantic Hurricane Season with a massive reduction in the Gulf’s hypoxic zone, an area lacking the oxygen that fish, shellfish, corals, and aquatic plants need to thrive.
“While storms can be bad for the people living in coastal areas, they can be good for nature.”
– Dr. Jessica Labonté, associate professor of marine biology at Texas A&M University at Galveston
“Tropical storm-force winds and high waves churned the water across the (annual hypoxic zone survey) cruise area and mixed oxygen-rich surface waters down to the seabed,” the National Oceanic and Atmospheric Administration (NOAA) announced.
The result: the second smallest Gulf “dead zone” on record in 40 years of measurement – news that is getting the attention of researchers such as Dr. Jessica Labonté of Texas A&M University at Galveston (TAMUG).
“As in most studies, there are two sides to a story,” said the associate professor of marine biology in TAMUG’s College of Marine Sciences & Maritime Studies. “While storms can be bad for the people living in coastal areas, they can be good for nature.”
In late July, NOAA-supported scientists from Louisiana State University and the Louisiana Universities Marine Consortium found a zone of only about 1,332 square miles, instead of the 7,027 square miles predicted in June.
The forecast, based primarily on Mississippi River discharge and nutrient runoff data from the U.S. Geological Survey, hadn’t been able to account for a major storm like Bertha.
In separate research in the Gulf, Labonté and two doctoral students spent part of July onboard the R/V Pelican, sampling sediment cores on the continental shelf. They are researching how viruses influence sulfate-reducing bacteria.
“We had to come back a day early because of the storm,” Labonté said, noting how the same research vessel sailed again July 24 to 30 for NOAA’s hypoxic zone survey, immediately after Bertha dissipated.
“We all thought it was not the greatest timing for the dead zone cruise since the dead zones were going to shrink during the storm,” Labonté said. “The conditions of the Gulf, with the Mississippi Delta being so rich in nutrients, are conducive to the formation of a dead zone, so it will come back.”
Nutrients, when degraded by microbes, create dead zones as these microbes use up the oxygen through respiration, the Galveston researcher explained.
Nevertheless, Bertha may have offered a clue to how environmental changes could impact the zone over time.
“Storms may help in controlling its magnitude,” Labonté said. “The Gulf dead zone doesn’t always reach out to Galveston. As dead zones are expanding worldwide, storms like Bertha in the Gulf may help prevent it from reaching Galveston.”
Also, the latest incident leaves researchers with more to explore. For example, how long might the improved conditions brought by Bertha last?
“That’s a good question that can only be answered through time-series monitoring,” said the virus-focused researcher who can imagine other avenues of study. “As a microbial ecologist, I would be interested in following the impact of the storm on dead zone microbial communities and how microbes are helping in recovery or exacerbating the dead zones.”
