According to the latest prediction from NOAA, 2012 Gulf of Mexico hypoxic zone could range from a low of approximately 1,197 square miles to as much as 6,213 square miles. The wide range is the result of using two different forecast models. The forecast is based on Mississippi River nutrient inputs compiled annually by the U.S. Geological Survey (USGS).
The smaller dead zone forecast was generated by researchers from the University of Michigan. Their model is based on spring nutrient inputs from the Mississippi River which are significantly lower than average due to drought conditions throughout much of the watershed.
The larger dead zone forecast is from Louisiana Universities Marine Consortium and Louisiana State University scientists. The Louisiana forecast model includes prior year’s nutrient inputs which can remain in bottom sediments and be recycled the following year. Floods in 2011 and low flows in 2012 influenced the “carryover effect” for the 2012 prediction.
Hypoxic zones, also known as "dead zones" are said to be caused by nutrient pollution and other factors that deplete oxygen in seawater. Fish and other marine life are sometimes unable to survive at or near the seafloor where hypoxic zones exist.