Hurricane Alex rumbled through the Gulf of Mexico recently, disrupting efforts to capture or clean up the oil gushing from BP's Macondo well and giving a preview of what a powerful tropical cyclone might do at the ongoing environmental disaster. With everyone from the U.S. National Oceanic and Atmospheric Administration (NOAA) to Columbia University scientists predicting that this year’s hurricane season will be more active than normal, Alex is likely to foreshadow disruptions to come.
So what does a storm with the energy potential of 10,000 nuclear bombs do to an oil spill covering roughly 6,500 square kilometers?
"The oil is not going to be up in the clouds and raining down on people," says oceanographer Christopher Zappa of the Lamont-Doherty Earth Observatory at Columbia University. Or as the U.S. Environmental Protection Agency put it in a June 23 statement, "EPA has no data, information or scientific basis that suggests that oil mixed with dispersant could possibly evaporate from the Gulf into the water cycle."
Of course, sea spray and evaporating water will carry the oil and any chemical dispersants with them, but it probably won't be an apocalyptic sight or experience. "There likely will be little traces of the hydrocarbons in the water that is condensed to form rain, but it will likely make up less than normal pollution does," says research meteorologist Frank Marks, director of hurricane research at NOAA's Atlantic Oceanographic and Meteorological Laboratory in Miami, Fla. "The amount of water vapor evaporated that might contain hydrocarbons related to the spill will be very, very small." But it will be there. Already, the EPA states on its Web site that the agency has detected "pollutants associated with oil," such as volatile organic compounds, polycyclic aromatic hydrocarbons and hydrogen sulfide, in Gulf shore air in "low levels."
And this polluted air and water vapor certainly will be carried to the near shore and left as an oily residue on everything from trees to electrical transformers, just as the salt from seawater often coats several kilometers inland in the wake of a hurricane. "If there's oil in the water, it will be coming along with it to some extent," says marine physicist Rick Luettich of the University of North Carolina. "I don't know how significant the impact will be."
As of now, NOAA is predicting 14 to 23 named storms—the most tropical cyclones ever anticipated by the U.S. government agency in its several decades of forecasts. "A variety of things, all of which are conducive to the formation and propagation of tropical cyclones, are in place this year," Luettich says. "We have to look at the 2005 season. That is the only one we are aware of that seems to be comparable to what we're expecting could happen this year." In that year, Hurricanes Katrina and Rita caused their own dispersed oil slicks in the Gulf of Mexico, along with devastating New Orleans and the Gulf Coast—and there were 28 storms, all told. In 2010, sea surface temperatures—the primary fuel of hurricanes—are already higher than in 2005. "It's actually at unprecedented levels," Greg Holland, director of the National Center for Atmospheric Research's Earth System Laboratory, testified to Congress on June 30. "It's a combination of global warming and natural variability."
Already storms have caused lightning strikes on the Deepwater Horizon rig pumping oil from the broken well, shutting the rig down, and even the relatively minor Hurricane Alex halted relief efforts, preventing the skimming or burning of roughly 60,000 barrels of oil over three days. "The weather hits us on several fronts: one, in our inability to recover and, two, it does break down that boom and make it more permeable [to oil]," said Rear Admiral Paul Zukunft of the U.S. Coast Guard during a July 2 press briefing on the impacts of Alex, including the suspension of skimming and burning as well as the displacement of the boom protecting the coastline. "Unfortunately, Mother Nature has voted against us as we're staging up this response."
Dispersal and movement
First and foremost, according to scientists, hurricane-force winds in excess of 119 kilometers per hour further mix and disperse the oil itself. "A lot of it will get mixed in the water column," Luettich says. "That will help disperse it a bit and help it be degraded more quickly, so that's probably a good thing,"
Not so good: "It's also going to move the oil," adds Zappa, including both the oil slick visible at the surface and the invisible oil plumes in the seawater. How exactly it moves the oil—whether sending it surging inland or pushing it further out to sea—will depend on exactly where the storm hits. Hurricanes in the Northern Hemisphere always spin counterclockwise. So a tropical cyclone that passes to the left (or west) of the bulk of the oil spill would push it closer to shore, while one that passes to the right (or east) would push it further out to sea. "A hurricane that went right up the west coast of Florida, a lot of the oil would be on the left-hand side of that, so it might get drawn offshore," Luettich notes. "A hurricane on Katrina's path would push a lot of stuff onto shore, given where a lot of the oil is right now."
He continues: "A hurricane like Ike [in 2008] could move that oil pretty large distances. It could take oil that is near the Mississippi Delta or even east of it and move it around to the Texas coast so Galveston could see it."
Luettich's simulations contradict mathematical modeling by NOAA of the likely movements of the ongoing oil spill, which shows a low probability of Texas being impacted and a general movement of the oil toward the east—in the absence of a hurricane.
Of course, a storm doesn't even have to come close to the slick to cause havoc, as Alex proved. "The main thing [hurricanes] do is generate waves, and those waves travel long distances," Luettich says. "They can have an impact on skimming and other efforts to stop the oil."
Alex's top winds of 160 kilometers per hour and the storm's path hundreds of kilometers south of the slick were enough to push tar balls to Galveston, Texas, and even into Lake Pontchartrain in Louisiana. "There is a good chance that the large circulation of Hurricane Alex contributed to westward advection of some of the tar balls related to the oil spill toward Louisiana and Texas," Marks says. But "it would be very hard to attribute the tar balls arriving only to the presence of Alex."
And if oil continues to need to be pumped from the ocean floor, operations will have to be shut down some 120 hours before a storm, according to Coast Guard Rear Admiral Thad Allen, who is directing the government's efforts to contain and clean up the oil spills. A new capped blowout preventer that BP has installed may avert that in future.
Oil, paradoxically, also has the effect of calming rough seas—as has been reported or demonstrated by scientists from Aristotle to Benjamin Franklin. A small amount of oil can dampen a large amount of waves, due to the differing surface tensions of the two fluids.
In fact, a German experiment reported May 15, 1989, in the Journal of Geophysical Research (pdf) found that oil does indeed depress waves, primarily by dampening short waves that then cannot transfer their energy to longer waves. "If you put oil on the surface, oil damps out small waves very effectively," Zappa says. But "they found this at regular winds, 20 knots at maximum, not a hurricane."
Oil also dampens evaporation. But given that the oil slick, despite covering 6,500 square kilometers, is still three to four times smaller than a hurricane, it is not expected to dampen the power of an onrushing storm. "The hurricane is going to be so strong that it would break up any slicks and cause them to be patchy. It's not going to have too much of an impact on evaporation," Zappa says. "That's the idea, but we don't know for sure."