On Friday, Texas A&M Professor Steve DiMarco and other researchers will depart Galveston in the research vessel “Trident,” to measure and record oxygen levels in the Gulf of Mexico. DiMarco, a Texas A&M oceanographer and researcher explains that rivers carrying record amounts of fresh water into the Gulf act to “cap” the heavier saltier water underneath it, creating a zone of hypoxia, or oxygen-depleted “dead zone.”
“Dead zones” are formed when freshwater empties into the salty waters of the Gulf, causing oxygen levels to drop and depriving marine life of oxygen.
“When this happens, the coastal waters become stratified, meaning that the lighter freshwater will stay at the surface and cap the saltier, and heavier, ocean water beneath,” Steve DiMarco, a Texas A&M scientist who’s researched the phenomenon for more than a decade, said.
According to NOAA, a “dead zone” is a common term for hypoxia, which refers to reduced levels of oxygen in the water. Nutrient pollution from farm fertilizers is cited as the most common cause of a dead zone. The fertilizers stimulate algae over-growth that decomposes and depletes oxygen:
Less oxygen dissolved in the water is often referred to as a “dead zone” because most marine life either dies, or, if they are mobile such as fish, leave the area. Habitats that would normally be teeming with life become, essentially, biological deserts.
Hypoxic zones can occur naturally, but scientists are concerned about the areas created or enhanced by human activity. There are many physical, chemical, and biological factors that combine to create dead zones, but nutrient pollution is the primary cause of those zones created by humans. Excess nutrients that run off land or are piped as wastewater into rivers and coasts can stimulate an overgrowth of algae, which then sinks and decomposes in the water. The decomposition process consumes oxygen and depletes the supply available to healthy marine life.
Dead zones occur in many areas of the country, particularly along the East Coast, the Gulf of Mexico, and the Great Lakes, but there is no part of the country or the world that is immune. The second largest dead zone in the world is located in the U.S., in the northern Gulf of Mexico.