Imagine if all the oxygen were sucked out of the air where you lived. Pretty terrifying, right? This is a major problem for marine life in areas of the ocean where dead zones form. Dead zones develop when dissolved oxygen at the bottom of the coastal shelf reaches critically low concentrations that are harmful to the organisms living there. A “dead zone” develops every summer in coastal waters off the Texas and Louisiana coast, and has been a major concern of scientists for decades.
Mapping the region affected by low-oxygen bottom water is essential to understanding the dynamics of dead zones. This is not an easy task. Each year a research vessel maps the hypoxic region of the Texas-Louisiana shelf (hypoxia refers to low-oxygen conditions), but the marine environment is constantly changing, and during the week it takes for a ship to traverse the region experiencing hypoxia, the shape of the dead zone has changed.
Below: Bottom oxygen simulations for August – September 2010 on the Texas/Louisiana Shelf. Harmful low -oxygen concentrations form mobile patches. Simulation made by the Physical oceanography Numerical Group (PONG) at Texas A&M University using the Regional Ocean Modeling System for the Texas-Louisian shelf.
To better inform direct sampling in the field from a research vessel, scientists use mathematical models that simulate ocean currents and conditions to approximate the formation and changes within dead zones. These ocean models resemble the atmospheric models used to predict weather and are based on equations that describe physical processes, all interpreted by powerful computers. One advantage of using models is the ease with which scientists can run experiments where some mechanisms or environmental conditions within the model are altered. The model responds to these changes, giving scientists important insight to the processes at work within marine environments. For example, scientists can explore how the area of the hypoxic region will change if the freshwater input from the Mississippi river increases or decreases, or how storms of different strengths can disturb the hypoxic region by mixing the water on the Texas-Louisiana shelf. Models are not perfect; they are often limited by data or do not capture all the dynamics of marine ecosystems, but models and field observations, when used to complement one another, greatly improve scientists’ understanding of marine systems.
This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.
Script Author: Veronica Ruiz Xomchuk
Editor: James M. Fiorendino
Contributing Professor: Dr. Kathryn Shamberger