VIENNA – On April 20, an explosion on Deepwater Horizon, a British Petroleum (BP)- operated oil rig in the Gulf of Mexico, led to the most publicized oil spill in decades. Another blowout in the same waters 31 years ago, farther south on the Mexican side of the Gulf, turned into the largest peacetime oil spill ever.
The platform where that accident happened, called Ixtoc 1, was operated by Pemex, the state-owned Mexican oil company. The two accidents and the spills they caused have a number of similar features, although marine oil spills in general have profoundly changed in character in the three decades between the two events.
Oil tankers used to be responsible for the bulk of oil that was spilled. Tank-washing gave rise to a huge number of small spills, and tanker accidents such as those involving the Torrey Canyon, Exxon Valdez, Metula, and St. Peter resulted in huge, concentrated spills. Blowouts were not infrequent, but most occurred on land or in shallow water, and most could be stopped relatively easily.
The ban on tank-washing, technical features such as double hulls and sectioning of tanks, introduction of one-way sea lanes and, most important, the use of Global Positioning Systems, have greatly reduced the amount of oil entering the sea from tankers.
Meanwhile, the technology used at drilling and production platforms has developed tremendously, but the challenges regarding depth, weather, and sediment structure have grown even more, as easy-to-exploit oil fields have been exhausted. Blowouts have become the most troublesome type of oil spills, and in deep water they tend to continue for a considerable time because of the difficulties faced in containing them.
After the explosions at Deepwater Horizon and Ixtoc, oil and gas under high pressure entered the water at the seabed. This resulted in a three-phase emulsion of oil, gas, and water that also contained sand and dirt particles.
The properties of this oil emulsion differ from normal crude oil. Some part of it will float on the surface, but parts may also form plumes at different depths in the water mass. Standard aerial or satellite imaging techniques to measure the quantity of oil spilled do not work well.
In the Ixtoc case, using such methods, Pemex (wanting to keep the loss figure low) estimated the spill to amount to a little under a half-million tons. A United Nations expert group that I led put the figure significantly higher. Similarly, whereas BP has been using a release figure of 800 tons per day From Deepwater Horizon, estimates by independent experts are many times higher.
Pemex tried to put a device called a “sombrero” over the Ixtoc leak to collect the oil at the ocean floor, but the plan failed because the structure could not be kept in place. Formation of methane hydrate was noted, but was not decisive. In the case of Deepwater Horizon, a huge dome could be put in place, despite the greater depth, thanks to deployment of modern unmanned underwater vehicles, robots, and positioning tools, but the formation of methane hydrates clogged the device and rendered it useless.
In both cases, efforts were made to burn off the oil from the ocean’s surface. But, as the 1967 Torrey Canyon experience showed – the stranded tanker was bombed with napalm – oil on water doesn’t burn well, and the emulsified oil called “chocolate mousse” hardly burned at all.
Whether or not to “disperse” oil has been a key strategic question since combating spills began in earnest in the 1960’s. The answer depends on whether the priority for protection is birds and beaches, or other forms of marine life such as fish, shrimps, and mollusks. If it’s birds and beaches, disperse; if it’s fisheries, don’t.
The decision has an obvious public-relations dimension. Oil-contaminated birds and beaches make appalling pictures, whereas dead fish and shrimp larvae go unnoticed by cameras.
The damage caused by the Ixtoc spill was huge. Beaches, mostly in Mexico but to some extent also in the United States, were hit, and birds succumbed in large numbers, despite the dispersion efforts. Because of the dispersion, shrimp, squid, and some fish populations suffered, with fisheries hit even harder.
Where the concentrations of un-weathered oil components are highest, water-breathing organisms die. In a much larger area, they become tainted and rendered useless as food products. In an even larger area – and for a much longer time – consumers reject the products.
After Ixtoc, the blow to the Mexican fisheries became a blessing in disguise. The dramatic reduction in fishing pressure allowed the devastated populations to recover, and five years later one had to look carefully to spot either remaining oil or damaged populations. The high temperatures of the Gulf of Mexico helped, as recovery proceeds much faster in warm waters than in cold.
It took nine months to cap the Ixtoc well. Drilling a release well finally did the job of stopping the flow of oil. Deepwater Horizon is still spewing oil into the Gulf of Mexico, even though BP has succeeded in inserting a smaller pipe into the main leakage to suck off part of the flow.
It is far too early to assess the ecological damage and economic losses to fisheries and tourism from the Deepwater Horizon spill. It is a safe bet that shrimp and squid populations will suffer, as they did in the Ixtoc case, but so is a close-to-complete recovery within a limited number of years.