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2012 Gulf of Mexico 'Dead Zone' Forecast

Published on: 06/21/2012

2012 Gulf Hypoxia in Brief

  • Forecast:1,197 to 6,213 square miles
  • Results of preliminary June survey cruise find area to be 295 mi2
  • August 1: Results of mid-summer survey cruise

NOAA Hypoxia Forecast
In June 2012 scientists from the National Centers for Coastal Science-fundedNorthern Gulf of Mexico Ecosystems and Hypoxia Assessment (NGOMEX)programissued a divergent outlook for the size of the Gulf of Mexico dead zone this summer. TheUniversity of Michiganmodel predicts a hypoxic zone size to measure 1,197 mi2, with a 95% confidence interval of 0 -3,938 mi2, while a Louisiana State University(LSU) model predicts the hypoxic zone to measure 6,213 mi2.

Both models incorporate spring nutrient and flow data from the Mississippi River that point towards a small dead zone size given dry spring conditions in portions of the Midwest. However, the LSU model also incorporates a parameter that accounts for the possibility of stored nutrients in the northern Gulf, such as in bottom sediments.

With the record Mississippi River flooding that occurred in 2011, the possibility of this 'legacy' effect proved a significant factor in the LSU forecast model. The occurrence of flooding in 2011 followed by dry conditions in 2012 will provide a unique opportunity to assess the influence, if any, of legacy nutrient loads on the size of the dead zone.

Like weather forecasts, this prediction is based on the results of multiple forecast models that are used to develop an integrated, or ensemble, forecast of the size of the hypoxic zone. While each model can individually provide useful information, the ensemble approach improves prediction accuracy. The two models used to develop the ensemble forecast employ a statistical approach to relate nutrient loadings and river discharge from the Mississippi and Atchafalaya Rivers to the areal extent of the hypoxic zone.

Both forecast models have been validated with results from long-term surveys of the mid-summer hypoxia survey cruise conducted byLouisiana Marine Consortium(LUMCON). In addition to forecasts, both models also inform the Gulf of Mexico Hypoxia Task Force on the amount of nutrient reductions required in order to meet the Task Force coastal goal of a maximum hypoxic zone size of 1,930 mi2.

Measuring the Hypoxic Zone Size and Validating the Forecast
Since 1985, LUMCON has conducted a NOAA-supported mid-summer cruise timed to measure the extent of the hypoxic zone at its maximum size in late-July. This cruise continues to serve as the primary metric to assess progress of the Gulf Hypoxia Task Force. In support of this cruise, which can be subject to tropical storms and other weather patterns that can aerate the water column, two additional NOAA-supported survey cruises were recently added by Texas A&M. These cruises take place in June and August. Results from the June survey found the hypoxic zone measured 295 mi2. Although June is relatively under studied, this is much smaller than would typically be expected. In addition NOAA's Fishery Service is currently taking oxygen measurements in conjunction with their summer ground fish survey in the Gulf of Mexico and, while not specifically designed to determine the size of the hypoxic zone, this cruise provides additional observations on the extent of the hypoxic zone. Results of this cruise are posted in near real-time through Hypoxia Watch and further indicate a relatively small.

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