Slick answers after an oil spill are hard to find

As BP struggles to control the oil spill threatening the Gulf of Mexico, we look at past disasters in search of positive signs for hope.

A Saudi journalist bends down to look at a pool of oil on the stained Persian Gulf beach 29 January 1991 near the Kuwait-Saudi border. The United States has sent a team of experts to deal with the threat of several oil spills to the Saudi coastline.
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News travelled slowly in 1979. It was Thursday, June 7, before the first press reports that a test well 80 kilometres off the coast of Mexico had caught fire four days earlier and was spewing 30,000 barrels of oil a day into the Gulf.

At first, the rig's operator seemed to regard the blowout almost as good news. "It goes to show how rich that oilfield is," a spokesman for Petroleos Mexicanos said. His mood wouldn't last. It would take more than nine months to cap the Ixtoc 1 well. The slick would dwarf the 880,000 barrels that had flowed from the Torrey Canyon, the supertanker that had run aground off Cornwall, England in 1967, and even the 1.7 million barrels lost from the Amoco Cadiz, the crude carrier that sank off Brittany in France in 1978, creating the largest oil spill to date.

By March 23, 1980, some 290 days later, three million barrels of oil had escaped into the Gulf of Mexico. It remains the world's worst accidental oil spill. Until this week, estimates of how much oil has been pouring into the Gulf of Mexico since the exploratory well under Transocean's Deepwater Horizon blew out on April 20, destroying the rig and killing 11 crewmen and injuring 17 others, ranged from 12,000 to 19,000 barrels a day. At the upper rate, Deepwater Horizon would take the title from Ixtoc 1 on or around September 25, but on Thursday a US government panel estimated the true volume to be as much as 30,000 barrels a day.

For the past week or so, BP has been capturing some of the leaking oil - as much as 15,000 barrels on Tuesday alone - but it cautions that its containment cap has "never before been deployed at these depths and conditions, and its efficiency and ability ? cannot be assured". The story of the struggle to check the Ixtoc 1 leak - a mere 50 metres below the surface, compared with the 1,500 metres under the Deepwater Horizon - was told in a paper published in the technical journal Ambio in 1981. Events then were ominously similar to today.

Both rigs were semi-submersibles engaged in exploration drilling, the most dangerous part of the business. Back in 1979, the high pressure frustrated attempts to close the blowout preventer; next, an attempt was made to force steel and lead balls into the well head - similar to BP's failed "junk shot". Most were blown out, although the flow was reduced. Next, a 300-tonne "Sombrero" was placed over the leak to funnel oil up through a hose to the surface, but this was abandoned in December when rough seas crippled the device. BP is now in trying a similar technique to siphon off oil to the surface.

In the end, what saved the day was the drilling of two relief wells; BP is doing the same but says they won't be ready until August. In 1979, work started in the middle of June but it was March the following year before mud could be pumped through, plugging the leak long enough for the well to be sealed with concrete. As bad as it was, the Ixtoc 1 spill was overshadowed in January 1991 when Iraqi forces deliberately dumped an estimated 11 million barrels of oil from Kuwait's Sea Island terminal into the Arabian Gulf, an event that remains the world's worst oil spill.

Even with the revised figure of up to 30,000 barrels a day, it seems unlikely that BP's disaster will come close to matching the volume of the Kuwait spill - to do so, the leak would have to continue unchecked, and at its highest rate well into 2011. But however long it takes to shut it down, it could be many years before the environmental impact is known. At first, the damage to the Arabian Gulf did not appear too bad. In March 1993, the UN's Intergovernmental Oceanographic Commission (IOC) announced the optimistic results of a study that had been sponsored by Unesco and countries including Kuwait, Qatar, Saudi Arabia and the UAE.

"Given the phenomenal quantities of oil that were spilled into the Gulf, the results were rather cheering," Chidi Ibe of the IOC told the media. Coral reefs "appeared to be in good condition" and fish stocks showed "few unequivocal oil pollution effects attributable solely to the 1991 oil spills". However, members of the International Oil Spill Conference, a forum for response professionals from around the world, working with the Saudi government, took a closer look at the bays of Dafi and Musallamiyah on the kingdom's coast. They found a more worrying story.

All habitats showed "little improvement or recovery from their condition one year earlier", they reported in 1993. In some areas the oil, instead of being washed off the beaches, as expected, had "migrated deeper, up to twice the depths in 1992". One of those researchers was Jacqueline Michel, a geochemist who specialises in marine pollution studies and who is president of Research Planning, a consulting firm in the US state of South Carolina. She and her colleagues returned to the Arabian Gulf 12 years after the spill; in 2003 they found that "the oil from the 1991 oil spill has persisted along most of the Saudi Arabian shoreline between the Kuwaiti border and Abu Ali Island", with an estimated eight million cubic metres of oiled sediment along 803km of the coast.

There had been only "limited removal by natural processes in the 12 years since the spill" and "oil residues ? continue to have toxic effects on intertidal communities". It is a problem that still has not been solved. Michel is currently in Louisiana as part of the scientific support team put together by the US National Oceanic and Atmospheric Administration to help the Coast Guard and other agencies deal with the oil as it washes ashore. She brings lessons from the other Gulf with her, but not preconceptions.

"One of my favourite sayings is, 'I haven't been to the same spill twice'," she says. "Every spill is a unique combination of events - oil type, volume, weather conditions, effectiveness of shoreline clean-up - which is the first phase of recovery; tides, wind, waves and overall sensitivity of the environment." Although, when it comes to oil spills size isn't necessarily everything, in the Arabian Gulf in 1991 the sheer volume was compounded by the geographical vagaries of the region.

"Under certain conditions, oil will undergo a range of weathering processes," says Michel. "Evaporation is a primary process, removing 10 to 50 per cent of the oil." The oil from the blowout in the Gulf of Mexico, for example, "is expected to weather by evaporation and dissolution by 30 to 50 per cent. The Gulf War oil spill was expected to evaporate by about 10 to 20 per cent; however, natural dispersion was very low because of the low wave conditions."

Nature may have some tricks up its sleeve. According to the Deepwater Horizon operations centre, the imminent onset of the hurricane season in the Gulf of Mexico could be a mixed blessing. "The high winds and seas will mix and 'weather' the oil which can help accelerate the biodegradation process" but, on the other hand, "Storm surges may carry oil into the coastline and inland". And although leaks are often manmade, oil is not, and ecosystems have been dealing with it for countless millennia. Last year, Nasa released a photograph taken over the Gulf of Mexico on May 13, 2006, by the Moderate Resolution Imaging Spectroradiometer on its Terra satellite. It showed a vast and entirely natural oil slick, southwest of New Orleans.

In January 2005, Christopher Reddy, director of the Coastal Ocean Institute at the Woods Hole Oceanographic Institution in Massachusetts, found himself in the middle of one such slick, a mile off the California coast. "Big oil patties floated about," he wrote later in Oceanus, the Woods Hole magazine. "The air smelled like diesel fuel. By any definition, it was a classic oil spill. But we were the only boat in the area - no Coast Guard, no oil booms, no throngs of clean-up crews ? and no shipwreck."

The spill was "entirely natural. The oil had seeped from reservoirs below the seafloor, leaked through cracks in the crust about 45 metres under water". It was the first chance he had had to study the phenomenon of natural seeps, which are thought to account for about half the oil that ends up in the coastal environment - "five times as much oil as is delivered by accidental spills". In the sediment on the Santa Barbara seafloor, he and his colleagues found at least eight times as much oil as had spilled into Prince William Sound in Alaska in 1989 from the Exxon Valdez. They also found that nature and microbes, "astonishing and voracious little critters", had done "an amazing job" on breaking down the oil.

But nature wreaks its own havoc. Some of the estimated "few hundred" barrels of oil a day that seep into the Santa Barbara Channel end up oiling beaches. And, says John D Romero of the US Minerals Management Service, while "some organisms like crabs and some species of fish co-exist in areas with concentrations of natural oil seeps - under specific weather conditions, oil is entrained and can get large numbers of birds oiled."

One slick attributed by the state of California to natural seepage a few years ago is thought to have killed 5,000 birds. In the Arabian Gulf in 1991, nature worked against any clean-up. The oil was carried into a sheltered bay where it accumulated on flats riddled by burrowing crabs and worms; many burrows are still flooded with liquid oil. As a result, says Michel, it "penetrated into sediments that normally would not be very porous, deeply into muddy sediments where natural degradation processes are quite low, as reflected in the fact that the oil persists now for nearly 20 years".

The signs are, she says, that the US shoreline will be better off. Because the BP spill has to travel 50 to 100 miles before it reaches the shore, it will already have undergone extensive weathering by the time it gets there. "The oil also has emulsified, meaning that it has mixed with water and formed a viscous, thick oil that does not readily penetrate into the sediments." Under these conditions, "clean-up can be very effective because the oil is mostly on the surface. In contrast, the Gulf war spill penetrated deeply into the sediments and has weathered much more slowly."

The best strategy, she says, "is to remove the oil as quickly as possible; early and efficient shoreline clean-up can be an important factor in speeding the rate of shoreline habitat recovery. That is one lesson that was learnt in the Gulf War spill." Lessons learnt from other spills have shown that defining "worst" by volume alone does not take account of the unpredictable impacts of oil leaks. The fallout from the Ixtoc 1 spill, as measured 10 years later in a 1982 assessment for the US Bureau of Land Management, was limited. No trace of the spill was found in sediment in the South Texas Outer Continental Shelf area, although signs of oil from the well were detected in particles in suspension in the water column. But although low levels were found in many shrimp samples, only in one case was this linked to the Ixtoc 1 leak.

By contrast, life in Prince William Sound, Alaska, has never been the same since the oil tanker Exxon Valdez ran aground on Bligh Reef on March 24, 1989, spilling 250,000 barrels. Last year the Exxon Valdez Oil Trustee Council, set up after the spill to manage the US$900 million (Dh3.3billion) compensation fund and restoration projects, issued its 20th anniversary status report. Over the past two decades, wrote Craig Tillery, a former member of the trustee council, "we have made significant progress in restoration of areas impacted by the spill ? Yet the area has not fully recovered.

"In some areas, Exxon Valdez oil still remains and is toxic. Some injured species have yet to recover to pre-spill levels. This long-term damage was not expected at the time of the spill." The good news about the Deepwater Horizon saga is that it is the world's first multimedia oil disaster and, by the time it is over, the world and its experts will know a great deal more about coping with such events than ever before.

Thanks to the limited communication technology of the time, the Ixtoc 1 spill remained distant and witnessed by few; the monitoring of the environmental outrage of 1991, and efforts to clean it up, were hampered by the fog of war. Every step of BP's efforts in the Gulf of Mexico, however, is there for all to follow, documented in photographs and live video footage, Tweets, SMS alerts and RSS feeds. Subscribers can follow events on the response team's YouTube channel - and the disaster even has its own Facebook page, with tens of thousands of "fans".

Scientific experts from around the world continue to converge on the scene, armed with sophisticated sensors, autonomous vehicles and marine gliders, "to measure flow rates, map plume dispersion, characterise hydrocarbons in the water column, and provide high density data and meta-data in real time", said Susan Avery, president of Woods Hole, in a statement issued last week. The upshot, she said, was that this would be "the most immediately and intensively studied oil spill in history".