NEW ORLEANS (AP) – The summer “dead zone” off Louisiana’s coast is likely to be about 40 percent larger than average this year, state and federal scientists say. The scientists are predicting that the layer of cool water above the ocean floor for about 6,700 square miles – an area about half the size of Maryland – will hold too little oxygen to support sea life. The dead zone has averaged about 4,800 square miles since 1990. The record of 8,500 square miles, about the size of Israel, was in 2002. This year’s prediction was released as Louisiana Universities Marine Consortium director Nancy Rabalais, who has studied the phenomenon since 1985, measured the hypoxic (low-oxygen) area. The research ship left Thursday, and began measurements Friday, said R. Eugene Turner, the LSU scientist who led the forecast team. The forecast, by scientists at LUMCON, the National Oceanic and Atmospheric Administration and Louisiana State University, is based on the amount of nitrates measured during May in the Mississippi and Atchafalaya rivers. There’s no way to pinpoint why this year’s nitrate levels were higher than those in previous years, Turner said Monday. What is known is that agricultural runoff in the vast area drained by the Mississippi River contributes most of the nitrogen, phosphorus and other nutrients. Those feed a population boom of algae; as the algae die, they fall to the bottom. Their decay consumes oxygen faster than currents can bring it down from the surface. Scientists have several models for predicting the size of the dead zone. LSU’s model is the most accurate, but is still experimental, said a news release sent Friday and again Monday by the NOAA. Turner said the study is providing information about how the amounts of nutrients and the layers of warmer and cooler water in the Gulf of Mexico affect the size of the dead zone.