The
"dead zone" is a region in the northern Gulf of Mexico
where each summer low levels of oxygen in the water adversely
affect marine life living near the ocean bottom. The area - this
year more than 4800 square miles - has been studied and tracked
since it was discovered more than 20 years ago and is believed
to have generally increased in size during the 1990s. In 2003,
NOAA awarded researchers at Texas A&M University, Louisiana
State University, and Texas A&M University at Galveston a
three-year grant to investigate the principal mechanisms responsible
for initiating and sustaining the dead zone. Dr. Steven DiMarco
of the Department of Oceanography is the lead investigator and
project manager.
Hypoxia
- the technical term for low dissolved oxygen concentrations in
water - can result in huge fish kills and can adversely affect
many types of marine life where it is present. Many scientists
believe the dead zone is caused by extensive fertilizer runoffs
from the Mississippi River, which flows into the Gulf and cause
plankton blooms. The plankton then die and decay, consuming oxygen
in the water in the process. Under certain conditions, this could
in turn lead to massive loss of marine life. Additionally, the
presence of light wind conditions, warm temperatures, and large
amounts of freshwater, which are typical during summer in the
Gulf of Mexico, further enhance the conditions for hypoxia to
occur.
In 2005, the TAMU-led team conducted four one-week long oceanographic
cruises into the dead zone on the TAMU-operated Research Vessel
(R/V) GYRE. A total of 45 scientists, including 25 students, participated
in the cruises. The researchers found that high winter river discharge
provided conditions for the early onset of the hypoxia in March.
The hypoxia persisted in the region despite low river discharge
for most of the spring and summer. Eventually, the passage of
several large storms, including Tropical Storm Cindy, and Hurricanes
Dennis, Katrina, and Rita, ultimately broke up and dispersed the
hypoxia.
A
realistic computer ocean model of the northern Gulf has been developed
as part of the project. The goal of the computer modeling is to
assist in the interpretation of the field observations and isolate
and investigate the physical and biological causes of hypoxia.
The model has been very successful reproducing the basic characteristics
of the timing and spatial coverage of hypoxia.
