Video: See how rusting ships can be prevented from leaking oil

Editorial: Defuse this oil time bomb

Thousands of ships sunk in the second world war are seeping oil – and with their rusty tanks disintegrating, “peak leak” is only a few years away

THE battle for Guadalcanal was one of the pivotal moments of the second world war. The Japanese occupied Guadalcanal, the largest of the Solomon Islands, in August 1942. When the Americans landed a few months later, the Japanese set out to reinforce their troops by sea. The struggle for naval supremacy that followed was confused and bloody, but by February 1943 the battle was over and the Japanese had evacuated their remaining troops.

The battle has a hidden legacy, however. Before the war, the stretch of water north of Guadalcanal was called Sealark Sound. Now it is known as Iron Bottom Sound, because of the number of wrecked ships there. One of these is the 6800-tonne Japanese freighter Hirokawa Maru, lying stranded off what would otherwise be an idyllic, palm-fringed Pacific island beach. Every now and then the ship leaks oil, threatening coral reefs, marine life and subsistence fishing.


Compared with the spill from BP’s Deepwater Horizon field in the Gulf of Mexico, the oil from the Hirokawa Maru is a drop in the ocean. But this is not an isolated case of one ship blackening the shores of one Pacific island. The second world war saw the greatest-ever loss of shipping: more than three-quarters of the oil-containing wrecks around the globe date from the six years of this war. Sunken merchant ships are scattered around trade routes, the victims of attack by U-boats and other craft aiming to disrupt enemy nations’ supply lines (see map). Then there are the naval ships sunk during great engagements such as the attack on Pearl Harbor and the battle of Chuuk Lagoon, the Japanese base in the Pacific where the US sank over 50 Japanese ships. In some locations these hulks are already leaking oil, threatening pristine shorelines, popular beaches and breeding grounds for fish. This year, for example, oil has begun to leak from the Darkdale, a British naval tanker that sank in 1941 near the island of St Helena in the south Atlantic Ocean. It was carrying more than 4000 tonnes of oil when it went down.

So how long have we got before there is a sharp increase in leakage from this lost fleet, and how big a problem could it be? What, if anything, can we do about it – and who will foot the bill?

Mystery cargoes

Trevor Gilbert of the Australian Maritime Safety Authority, Dagmar Etkin of Environmental Research Consulting in New York state, and their colleagues have compiled the first global database of these polluting wrecks. In 2005 they told the International Oil Spill Conference in Miami that there are 8569 potentially polluting wrecks, 1583 of which were oil tankers. No one can know for sure how much oil is held in these ships. “Many wrecks may have lost oil when being sunk due to major structural damage,” says Rean Gilbert of the Queensland-based consultancy Sea Australia, a leading authority on wrecks of the second world war. Regardless of whether they were carrying oil as cargo, these ships all contain “bunker fuel”, a heavy oil that can devastate marine life and fisheries. How much bunker fuel they have depends partly on how far they had travelled since they last refuelled. But experience with modern wrecks, such as the oil tanker Prestige, which split in two off the coast of Spain in 2002, shows that most will have at least some oil on board.

There may be huge uncertainties about exactly how much oil is out there, but no one doubts that it dwarfs any single previous maritime spill. Etkin and Trevor Gilbert put the figure at somewhere between 2.5 million tonnes and 20 million tonnes. Even the lower estimate is more than double the amount of oil thought to have been spilled into the Gulf of Mexico by the Deepwater Horizon accident and more than 60 times that of the Exxon Valdez (see diagram).

After 70 years at the bottom of the ocean, these wrecks will soon start to leak. “There is ample evidence that there are a large number of wrecks in US coastal waters that are, in essence, spills waiting to happen,” says Etkin. Doing nothing is fast ceasing to be an option. Ian MacLeod, based at the Western Australia Maritime Museum in Welshpool, is an authority on marine corrosion and has worked on the wrecks in Chuuk Lagoon. “It’s not hopeless but it is getting desperate,” he says. “I think we are going to see a sharp increase in the number of leaking ships in five to 10 years’ time.”

“There is evidence that a large number of wrecks in US coastal waters are spills waiting to happen”

In recent years there has been a steady trickle of leaks. In August 2001, a sunken US military oil tanker, the USS Mississinewa, began to leak into Ulithi Lagoon, in Yap state, part of the Federated States of Micronesia. The tanker had been carrying 20,000 tonnes of aviation fuel and fuel oil when it was sunk on 20 November 1944. And there it stayed for 57 years, a largely forgotten wreck lying in about 35 metres of water. Then in 2001 a typhoon struck and the islanders woke up to find thick fuel oil smeared over their beaches.

Quite when a wreck will leak oil depends largely on how fast its steel corrodes. “One millimetre a decade is the long-term average for corrosion,” says MacLeod. “We’ve got a pretty good handle on this now.” Marine engineers normally reckon that a ship would lose its structural integrity once its steel plate has lost between a quarter and a half its thickness. Most ships sunk during the second world war were made of plate between 19 and 25 millimetres thick.

However, the rate of corrosion depends hugely on the circumstances of individual wrecks. “It is vital to inspect and measure,” says Rean Gilbert. “What may be true of one wreck is not necessarily the same for another.” Most of the second world war wrecks were damaged when they were sunk, which is likely to have compromised their structural integrity. Any holes might also allow local currents to maintain a constant supply of oxygenated water, accelerating corrosion.

What’s more, the use of different metals in ships can set up galvanic coupling, essentially creating a battery with the steel plate as the anode. This causes the steel plate to be eaten away, even if no other metals are in contact with it. “On one US wreck we found very high corrosion rates within 5 to 10 metres of the carpenters’ store. When we investigated we found the store had 5000 copper nails in it,” MacLeod says. On the other hand, accretions of calcium carbonate and organisms such as barnacles can form a protective coating on the steel that retards the rate of corrosion – though violent storms can strip off this coating.

A lot depends on how a wreck is lying on the seabed. If it is not sitting upright, the rate of corrosion can be a lot higher due to the stresses placed on its structure. “Ships are designed to float, not to be wrecked,” MacLeod says.

‘Peak leak’ soon

The crucial question is just when a wreck has reached the point at which it will start to gush oil. “We don’t have a lot of the answers,” admits Lisa Symons, who heads a team at the US National Oceanic and Atmospheric Administration (NOAA) in Silver Spring, Maryland, responsible for potentially polluting wrecks. But the general picture is clearer. As steel plates corrode and lose their strength they reach the point where the next storm will trigger a catastrophic release of oil. MacLeod believes that in five to 10 years we will enter a period of “peak leak”, which he expects to last for 50 years or so.

For most countries, these old wrecks are out of sight and out of mind, until they start to leak. In the early 1990s oil started to come ashore in NOAA’s Gulf of the Farallones marine sanctuary, south of San Francisco. Initially blamed on pollution from passing ships, it continued to come ashore sporadically throughout the 1990s. In late 2001 there was another spill that went on for months. It killed about 50,000 seabirds and eight sea otters, and polluted 100,000 square kilometres of tidal marshes. Chemical tests showed that the oil was not from Alaska – the usual type carried by tankers passing the Californian coast – and that it matched previous mystery spills. So NOAA turned its attention to eight wrecks off the Californian coast. Divers and satellite imagery eventually pinpointed the source as the wreck of the Jacob Luckenbach.

“For most countries, these old wrecks are out of sight and out of mind, until they start to leak”

Although not a wartime wreck, the Jacob Luckenbach is of a similar vintage, having sunk after a collision in 1953. Fifty years later, researchers found that the ship rocked from side to side on the seabed every time there was a heavy storm, releasing oil. NOAA and the US coastguards decided it would be best to remove the oil, so in 2003 salvors bored holes in the ship’s tanks and heated the oil with steam lances to lower its viscosity, then pumped it out. This technology for removing oil, known as hot tapping, is well established but it can be expensive, depending on the state of the wreck. Emptying the Jacob Luckenbach cost $19 million.

It is important to NOAA to understand the potential impact of leaks on fisheries and marine sanctuaries, and their timescale, says Symons. Partly as a result of the Jacob Luckenbach incident, NOAA set up its Resources and Undersea Threats (RUST) database. This is a catalogue of the wrecks around the US coast that could cause oil spills, together with what is known about their oil load, location and state of corrosion. It lists some 1700 of these wrecks, their oil carried either as cargo or as bunker fuel. Taken together, they could potentially leak more than 15 times the amount of oil spilled by the Exxon Valdez. The wrecks are not evenly distributed around the coast: there are hotspots such as the Gulf of Mexico, where German U-boats were particularly active in the months after the US joined the war.

The US is one of the few countries to have started planning for peak leak. “NOAA is working to narrow down our list of RUST sites to determine those which are of greatest potential threat to economic and environmental resources,” says Symons.

In 2009, the American Salvage Association (ASA) helped to set up the Wreck Oil Removal Program to identify high-risk wrecks that could threaten the US coastline, either damaging the marine environment or threatening economic interests such as fisheries and tourism. Etkin, the ASA and the not-for-profit North American Marine Environmental Protection Association successfully persuaded Congress to give $1 million to WORP in 2010. “The first phase of the project is to do a risk assessment – the probability of leakage multiplied by the consequences of leakage,” says Etkin. As part of this work, NOAA is organising a workshop of the world’s leading corrosion experts at Newport News, Virginia, in October. The aim is to develop standard tests for deciding what to do about any given wreck. Ultimately, though, it is the US coastguard that will decide whether to remove oil from a wreck.

Close to the top of WORP’s list of priorities is likely to be the Coimbra, a British tanker that was torpedoed by a U-boat in 1942 and sank off the coast of Long Island, New York, in 55 metres of water. Carrying a cargo of 11,000 tonnes of lubricating oil, the tanker broke into three parts and has been a chronic source of oil pollution over many years.

Away from the US, in the Pacific about 85 per cent of the wrecks are Japanese and the rest are mostly American. In the Mediterranean, Atlantic and Indian Oceans about half the wrecks are British and 16 per cent American, says Rean Gilbert. In general, most wrecks are the responsibility of the owners, but outside the armed forces not many of these owners still exist. And flag states are reticent about accepting liability. The British government, for example, failed to reply to New Scientist’s questions about the Coimbra.

The cost of dealing with these wrecks is daunting. It cost about $5 million to pump 6000 tonnes of oil from the USS Mississinewa, for example. The cost of cleaning up the oil once it has leaked is also dismaying. In 1999 Etkin put it at between $2300 and $17,000 per tonne of oil, depending on a wreck’s depth and location. “As the situation in the Gulf of Mexico has made abundantly clear, once the oil spills it is a very expensive exercise to clean it up,” says Rean Gilbert. Poorer countries face exceptional difficulties here. The Federated States of Micronesia and the Solomon Islands are among the world’s most impoverished countries, with little leverage when it comes to persuading richer countries to take responsibility for their wrecks.

While the cost of pumping the oil out of all of the world’s rusting hulks would be enormous, it is possible to spread the cost as well as carry out surveys to identify those most at risk of creating a serious spill, says MacLeod. But the first step should be to put so-called sacrificial anodes on bunker-fuel tanks. A sacrificial anode is a piece of metal that alters the local electrochemistry and then slowly dissolves. This not only halts the corrosion of the steel it is attached to but also raises the local pH of the seawater, encouraging protective marine deposits to grow. “It will gain you some breathing space,” says MacLeod. “What we need is time.”