THE flow of oil from the Deepwater Horizon spill in the Gulf of Mexico may now have been stemmed, but there is an altogether bigger problem lurking on the seabed, a legacy of the greatest ever loss of shipping.
In the next decade or so, up to 20 times the amount of oil that leaked from Deepwater Horizon will start to ooze, and in some cases gush, from rusting wrecks scattered about the sea floor. And these leaks will continue for the next 50 years and beyond (see 鈥淲hy wartime wrecks are slicking time bombs鈥�).
Unlike the Deepwater Horizon leak, we鈥檙e not talking about an isolated eruption in a specific spot. With more than 8500 of the time bombs around the world waiting to disgorge oil from their tanks, new leaks could develop at the rate of more than one a week.
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Most of these wrecks date from the second world war. In many cases, no one knows their precise position. And in most cases no one has a clue how much oil is still trapped in these rusting hulks.
There are some known hotspots, though. The Gulf of Mexico is one, where German U-boats were particularly active in the months following the US鈥檚 entry into the war. Another is Chuuk Lagoon in the Federated States of Micronesia, which was the Pacific base of the Japanese fleet. Then there are the wrecks from the attack on Pearl Harbor and the battle of Guadalcanal.
In many cases, the first anyone will know about these leaks is when oiled seabirds and sea mammals start washing up on their beaches and fisheries fail because oil slicks have polluted spawning grounds. This is a problem that most governments are completely unprepared for. They have ignored these wrecks for seven decades. But recent leaks, such as the one this year from the 69-year-old wreck of the Darkdale 鈥� a British tanker which sank off the island of St Helena in the south Atlantic 鈥� should be a wake-up call. These wrecks can no longer be ignored.
鈥淕overnments have ignored these wrecks for seven decades. They are completely unprepared鈥�
The US at least is a little ahead of the game. It has an embryonic programme for removing oil from sunken vessels. It aims to identify those wrecks that threaten environmentally sensitive areas and the wrecks that are known to be a serious risk because they are in danger of breaking up.
But this programme only applies to the 1700 or so wrecks in US coastal waters. Other countries should follow the US鈥檚 lead, pinpoint their own high-risk wrecks and develop a strategy for dealing with them.
Governments also need to buy time. Fortunately there is a relatively cheap way of doing this. Sacrificial anodes, which are already standard on oil rigs, can be installed on fuel tanks to arrest corrosion and delay the day when something more must be done.
Ultimately, though, governments will have to foot the bill. Rich nations will have to accept responsibility for their wrecks and help poorer countries. How else can Micronesia, where 27 per cent of the population live below the poverty line, cope with the 50-plus Japanese wrecks in Chuuk Lagoon?
One central lesson of the Deepwater Horizon disaster is to anticipate catastrophic failure and take necessary preventive action. However expensive it may be to remove oil from a wreck, it is likely to be more costly to clear up after a major leak.