Rifted continental margins, which separate thick continental crust from thin oceanic crust, lay at the oceanward edge of continents and are formed during continental break-up to form new oceans.
Understanding where rifted continental margins are located and how they form are important both for the science of plate tectonics, for finding oil and gas reserves at continent-ocean margins such as in the Arctic, and for territorial claims under the UN law of the sea process.
Now geophysicists at Liverpool University in England have developed new satellite remote sensing exploration methods to map crustal thickness and locate the distal deep water extremities of continental crust at the ocean-continent transition(1).
Professor Nick Kusznir at the University's Department of Earth and Ocean Sciences explains what drove his research: "The very deep waters between continents and oceans are now the frontier exploration target of the oil and gas industry. As oil and gas resources on land become progressively exhausted, our future oil and gas supplies will increasingly come from sedimentary basins at rifted continental margins. While deep water oil and gas exploration at rifted continental margins is very expensive it can produce enormous rewards as illustrated by recent major oil and gas discoveries offshore Brazil, Angola and Gulf of Mexico. With deep-water exploration wells costing up to US$200m each, understanding where the continental crust stops and oceanic crust starts is critically important to this exploration effort."
The new geophysical exploration method uses the inversion of satellite and other gravity anomaly data to map oceanic and rifted continental margin crustal thickness, and to predict ocean-continent transition location.
The new method has been successfully applied, in collaboration with the oil and gas industry, to map crustal thickness and ocean-continent transition for many of the world's ocean margins including to the Arctic Ocean - an area of potentially conflicting territorial interests - to produce the first set of comprehensive crustal thickness maps and ocean-continent transitions for that ocean. And conflicts there are likely to be, as the US Geological Survey estimates that the Arctic may be home to 30 per cent of the planet's undiscovered natural gas reserves and 13 per cent of its undiscovered oil. In addition, much of the reserves are projected in be in less than 500metres of water (Fig.1). However, while countries including Canada, Greenland/Denmark, Norway, Russia and the US jockey for exploration positions, the World Wildlife Fund (WWF) has renewed its call for a time-out on offshore drilling in the Arctic.
In its new report Lessons not learned: 20 years after the Exxon Valdez disaster, little has changed in how we respond to oil spills in the Arctic, the organisation wants development to be put on hold until technologies improve to ensure adequate clean-up of an oil spill are available. WWF is also calling on the Obama administration to permanently protect Alaska's fish-rich Bristol Bay from drilling.
Bill Eichbaum, WWF's vice president for marine and arctic policy, said: "Sea ice is disappearing and open water seasons are lasting longer, creating a frenzy to stake claims on the Arctic's rich resources - especially oil and gas development. Oil spills can be devastating to Arctic marine environments given the current lack of oil spill response capabilities. We need a 'time-out' until protections are in place."
WWF, which has the world's largest Arctic conservation programme, also recommends that the most vulnerable and important areas of the Arctic be deemed permanently off-limits to oil and gas development. Such no-go zones should be based on the sensitivity and productivity of special priority areas, where oil spill response would be virtually impossible to clean up or where any spill would cause irreparable long-term damage.
These areas include Bristol Bay in the southeastern Bering Sea in Alaska, known as America's fish basket, where more than 40 per cent of all wild seafood is caught in the US. Oil and gas development in the bay is estimated to bring in US$7.7billion over the 25-40 year lifetime experts predict it would take to extract the resources. By comparison, says the WWF, the renewable fisheries of the Bristol Bay region are valued at US$50-$80billion over that same time period.
Among the WWF's other main recommendations are:
- Response gap analyses should be performed throughout the Arctic to better understand the factors contributing to the lack of information and timing about where local conditions exceed the limits of spill response systems. These should be integral components of feasibility and assessment studies for oil operations and part of contingency planning.
- All Arctic states should conduct comprehensive risk assessments of industrial activities, such as shipping and petroleum development, along with climate change-induced impacts on the marine environment.
- Arctic states should upgrade investments to improve existing technologies and spill response mechanisms with enhanced involvement of local communities and stakeholder groups who have a vested interest in spill response outcomes.
- Arctic states should initiate a conservation plan that assesses the health, biodiversity and functioning of Arctic ecosystems, including impacts of industrial activities. Adopting a precautionary approach, this plan would use extensive spatial planning to determine permanently protected areas as well as guiding decisions about whether, when, where and how industrial activities should take place.
(1) For more see Geophys. J. Int. (2008) doi: 10.1111/j.1365-246X.2008.03803.x