Snorkeling along a coral reef near Veracruz, Mexico, in 2002, Texas biologist Wes Tunnell spotted what looked like a ledge of rock covered in sand, shells, algae and hermit crabs. He knew, from years of research at the reef, that it probably wasn't a rock at all. He stabbed it with his diving knife. His blade pulled up gunk.
"Sure enough, it was tar from the Ixtoc spill," Tunnell said.
Twenty-three years earlier, in 1979, an oil well named Ixtoc I had a blowout in 150 feet of water in the southern Gulf of Mexico. The Mexican national oil company Pemex tried to kill the well with drilling mud, and then with steel and lead balls dropped into the wellbore. It tried to contain the oil with a cap nicknamed The Sombrero. Finally, after 290 days, a relief well plugged the hole with cement and the spill came to an end — but only after polluting the gulf with 138 million gallons of crude.
That remains the worst accidental oil spill in history — but the Deepwater Horizon blowout off the Louisiana coast is rapidly gaining on it.
The spill has now been partially contained with the cap that BP engineers lowered onto the mile-deep geyser Thursday night. That means roughly a quarter to half of the flow is being piped to a surface ship, the national incident commander, Coast Guard Adm. Thad Allen, said Saturday. BP hopes to improve the rate captured in coming days. If official government estimates are correct, 23 million to 47 million gallons of oil have spewed so far.
Ecosystems can survive and eventually recover from very large oil spills, even ones that are Ixtoc-sized. In most spills, the volatile compounds evaporate. The sun breaks down others. Some compounds are dissolved in water. Microbes consume the simpler, "straight chain" hydrocarbons — and the warmer it is, the more they eat. The gulf spill has climate in its favor. Scientists agree: Horrible as the spill may be, it's not going to turn the Gulf of Mexico into another Dead Sea.
But neither is this ecological crisis going to be over anytime soon. The spill will have ripple effects far into the future, scientists warn.
"This spill will be lasting for years if not decades," said Doug Inkley, senior scientist at the National Wildlife Federation.
Some of the immediate effects of a spill are obvious — witness the gut-wrenching images of soaked and suffocating seabirds in the gulf. But some types of ecological damage are hard to measure and can take years to document. Many of the creatures that die will sink to the bottom, making mortality estimates difficult. Damage to the reproduction rate of sea turtles may take years to play out.
The Exxon Valdez spill of 11 million gallons killed as many as 700,000 sea birds and 5,000 sea otters initially, but even 21 years later, populations of sea otters in areas of Prince William Sound haven't recovered. The Pacific herring population collapsed after the spill for reasons that remain in dispute among scientists. Two intensely studied pods of killer whales in the sound suffered heavy losses in the spill and have struggled since. One of the two pods has no more reproductive females. It is doomed to extinction.
And the oil?
"It's still sitting there," said Stan Rice, program manager for habitat studies at the National Oceanographic and Atmospheric Administration's Auke Bay Fisheries Lab. "It's still liquid, you can still smell it and touch it."
The degradation of oil slows over the years. The microbes move on, as the large and complex compounds that remain, known as the asphaltenes, are too hard to digest. What's left tends to be dense, tar-like, largely inert and attractive only to people who like to pave roads.
By 2003, there were still 21,000 gallons of oil in Prince William Sound, Rice reports in a recently published study on the lingering effects of the Exxon Valdez spill. The oil can be found by someone scraping three to six inches below the surface of the beach. Rice writes that an oil spill will be "over" when the oil itself is gone, the litigation has been settled and there are no continued negative effects in the environment.
"The Exxon Valdez spill does not meet any of these three criteria," he wrote.
The oil drifting north from the Ixtoc spill not only wiped out hundreds of million of crabs on Mexican beaches but, also far to the north, managed to killed 80 percent of the segmented worms and shrimp-like crustaceans that live in the sand of Texas beaches, according to Tunnell, a biologist at Texas A&M University at Corpus Christi. But the tiny animals have rapid reproductive cycles, and in about two and a half years they had recovered, he said. Poor government funding limited research on the broader ecological impact of the spill, however: "We don't have any comprehensive, good scientific studies of what happened."
There are on record since 1970 about 1,700 spills from tankers in which at least 2,100 gallons of oil were discharged into water. Scientists have been monitoring the effects of some of them for decades, including a 189,000-gallon spill that occurred off Cape Cod in September 1969.
Five years after that spill, fiddler crabs in the oiled marsh were sluggish and reproduced poorly. In many cases they dug burrows too shallow to protect themselves over the winter.
Astonishingly, many of those problems remained 35 years later, when a graduate student, Jennifer Culbertson, surveyed the marsh. She found that the fiddler crabs reacted slowly to startling motions, apparently the result of a narcotic effect of oil that still formed a visible layer four inches below the marsh surface. (A similar clumsiness has been seen in juvenile spot fish when they chew on sediments contaminated with compounds from oil.) When the crabs burrowed down and hit the layer of 40-year-old oil, they veered horizontally.
"The marsh is still waging chemical warfare several inches below the surface," said Christopher M. Reddy, a chemist at the Woods Hole Oceanographic Institute in Massachusetts who helped supervise Culbertson's research.
Beaches get scrubbed by waves and storms, but marshes can develop tar mats lasting decades, Tunnell said. He said the beaches are a 3 on a scale of 1 to 10 in terms of sensitivity to oil spills, but the marshes are a 10. Attempts to clean a marsh will backfire. After the huge Amoco Cadiz spill of 68 million gallons off Brittany in 1978, French authorities scraped the top off the oiled marshes. It was a mistake: Most never came back.
Although many scientists and officials have warned that the marshes are in danger, one scientist who has studied oil spills in Louisiana marshes said that these wetlands are generally able to recover if human intervention doesn't make the situation worse.
"The vegetation itself generally recovers in a year, although sometimes it may take three or four," said Irving A. Mendelssohn, a biologist at Louisiana State University. Only if oil sinks in deep, or if repeated oilings kill off new shoots, does the marsh die, he added.
That's not just a biological change but a geological one, points out LSU professor Edward Overton. "Biological stocks can be replenished a lot easier than land loss," he said.
Every oil spill has unique features, from the geography to the chemical makeup of the oil, which can vary dramatically in toxicity. The Deepwater Horizon spill has the distinction of being the deepest blowout in history. Also unique has been the huge quantity of chemical dispersants sprayed on the surface and at the leak on the seafloor. There's little scientific understanding of how the dispersants might affect the deep-water ecosystem.
Coral reefs, only recently studied, can take centuries to develop in the cold, oxygen-poor depths; there are several such reefs directly beneath the oil slick. Deep plumes of oil have been reported in preliminary research by scientists on research vessels. As bacteria feast on the oil they could deplete the oxygen levels further, creating unusually deep "dead zones."
"If you're a creature that can't move, it's not good," Overton said.
In the years to come, scientists will study this spill in the same way they have studied the Exxon Valdez disaster. The gulf ecosystems may survive, but they'll likely have changed in certain details, according to LSU biologist Kevin R. Carman.
"Undoubtedly, life will get a foothold," he said. "The question is how different it will be."