Gulf oil spill: Where has the oil gone?

"The sheer volume of oil that's out there has to mean there will be some very significant impacts," says Jane Lubchenco, administrator of the National Oceanic and Atmospheric Administration (NOAA). "We've already seen some of those impacts play out in ways that are more obvious, more visual, because they're at the surface, but what we have yet to determine is the full impact that the will have not just on the shorelines or on the wildlife, but beneath the surface."

While the baking-hot temperatures break down the volatility of the spill, toxicity is still a concern. While hundreds of animal autopsies have been inconclusive as to the cause of death, oil and its byproducts are extremely difficult to locate in animal tissue since they break down very quickly, says Mr. Shirley.

For many on the coast, the disappearing oil isn't a mystery at all.

Many suspect it has settled either on the bottom or in mid-layers of the Gulf. (There's little evidence the oil has drifted to the bottom, says Ms. Lubchenco at NOAA.) Gulf Coast residents remain concerned about the long-term health of the Gulf fishery, even as NOAA recently reopened some fishing grounds that were closed because of the spill. Locals' concern is that out-of-sight oil will be out-of-mind oil for BP and the Coast Guard.

Three dozen NOAA vessels are currently working to track the oil spill and major research cruises are being put together to study the effects of the BP oil spill in the Gulf. The biggest question for many scientists is the Gulf's environmental resilience: Whether the oil spill in some parts of the Gulf brought some local ecologies to a tipping point where they simply can't recover.

"We'll continue to stumble upon caches of this oil," says Shirley. "Some of it will be in deep water, some of it will be in a few hundreds of feet as this oil combines with other organic compounds and sediment. We'll find other pools of oil that are exposed, some of which will be in mousse or asphalt, some of it in the form of liquid oil covered over with sand or sediment."

Experts look to the 1979 Ixtoc blowout off Mexico's Yucatan Peninsula for clues to how oil disperses and degrades in the Gulf. While fisheries in the nearby area completely rebounded two years after the spill, a return expedition this year by Texas A&M researcher Wes Tunnell, who studied the Ixtoc spill, showed some species, especially oysters, never fully recovered.

Within minutes of arriving on site, Mr. Tunnell found asphalt and tar blocks from the Ixtoc spill wedged into coral in the same places they had been 20 years ago. When researchers broke open the blocks, they got fresh whiffs of petroleum hydrocarbons, Shirley says. "It's tough stuff, that's why we put it on roads."

Related:

• Gulf oil spill's environmental impact: How long to recover?
• Gulf oil spill: the 51 minutes that led to disaster
• Gulf of Mexico oil spill: How bad is it?

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