Defying all predictions, the Gulf of Mexico's annual "dead zone" failed to break the size record this year, although the reason may have more to do with luck, scientists say.
Scientists back from their usual seven-day cruise to gauge the size of the dead zone -- the vast expanse of ocean along the Louisiana and Texas coast where oxygen levels drop so low as to drive away or kill all marine life -- reported over the weekend that the area measures 6,765 square miles, about 300 square miles larger than Hawaii.
That is bigger than average but not quite the record-breaker predicted to form as a result of the massive pulse of pollution-saturated water that the flooded Mississippi River dumped into the Gulf this spring.
Researchers had predicted that the Mississippi River's waters would wash across farmland and soak up a heavy dose of nitrogen and phosphorus, nutrients in fertilizer that fuel the growth of algae, whose growth and subsequent mass die-off and decay, in turn, suck dissolved oxygen out of the water. The result, they said, would likely be a dead zone that would measure between 8,500 and 9,421 square miles, breaking the size record by as much as 10 percent (Greenwire, June 14).
The result is no cause to celebrate.
Chief scientist Nancy Rabalais of the Louisiana Universities Marine Consortium (LUMCOM) reported in a statement issued yesterday that "the major disruptor of the size was Tropical Storm Don that followed the Research Vessel Pelican across the Gulf of Mexico towards Texas and whipped up the winds and waves."
The mixing action from such storms replenishes dissolved oxygen levels in the water, at least temporarily reducing the size of the dead zone.
"It would have been the largest if we had been out there at the right time, I suppose," Rabalais said in a phone interview this morning.
The dead zone will likely re-form as the waters calm, said Rabalais. The scientists will set out again for their regularly scheduled two-day follow-up cruises in August and September to take additional measurements before the zone recedes in the fall, although the official size verdict likely will not change.
Since the 1970s, when scientists first began studying it, the Gulf dead zone has grown steadily larger to become the second-largest in the world as fertilizer use on cropland in the Corn Belt has increased, making life difficult for fishermen, crabbers and shrimpers along the Louisiana coastline who are forced to either wait it out or venture the 60 or so miles from the coastline to go beyond the zone and find their catch (Greenwire, May 26).
The largest dead zones by far have been produced in the past decade, including the record 8,500-square-mile zone in 2002. Five of the past 10 years have seen dead zones form in the Gulf that were larger than the one measured this year.
The zone usually stretches from the mouth of the Mississippi Delta west to Galveston, Texas, hugging the coastline where the shallower, warmer waters make for ripe hypoxia-forming conditions. Big storms can weaken dead zones and have done so, said Rabalais, who recalled that Hurricane Katrina stirred oxygen back into the water after it ripped through the Gulf. But the dead zone quickly regrouped.
"We were out there about two weeks later," Rabalais said. "It had settled back out, and there was hypoxia."
Click here to read the statement.
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