Anatomy of an Oil Spill:

Science from the Gulf of Mexico

On April 20, 2010, the Deepwater Horizon oil rig exploded, killing eleven people and setting off the largest marine oil spill in world history. A few days later, underwater cameras revealed that oil and gas were leaking from the ocean floor about 42 miles off the coast of Louisiana. The oil well leaked 4.9 million barrels of oil before it was capped nearly 3 months later on July 15, 2010.

The Disaster

The Deepwater Horizon rig sat 42 miles off the Louisiana shore, pumping oil up from deep beneath the seafloor. On the night of April 20, a bubble of methane gas escaped from the well and shot up the pipe towards the surface, causing an explosion and fire. This tragically took the lives of 11 rig workers, while 115 others were successfully evacuated. Crude oil and gases, buried deep beneath the seafloor, began leaking from the oil well 5,000 feet down. Wind, waves and currents spread the oil across the ocean’s surface to form a slick, which eventually covered around 5,000 square miles—about the size of Connecticut.

The Cleanup

The rig sank on April 22 after burning for more than a day. Workers did their best to stop the oil from washing up on the Gulf shore, where it would be even more difficult to remove from fragile coastal ecosystems. Some wildlife, such as birds and sea turtles, got stuck in the surface slick during cleanup, endangering their lives.

Dispersants

On April 26, BP began adding dispersants to the oil. Dispersants are like strong soaps, which cause the oil to break down and mix with water more easily to speed up its natural biodegradation. As they combined, the oil became less buoyant, forming additional underwater plumes while preventing the droplets from floating to the surface and spreading to the coasts. But dispersants can also enter the food chain and potentially harm wildlife.

The Open Ocean

The oil spill occurred more than 40 miles offshore, which was lucky in some ways, as less oil was able to reach fragile coastal ecosystems. But it still interacted with wildlife in the open ocean. It was eaten by organisms big and small, some of which are better able to clear it from their bodies than others. And out in the open, it ran into any developing eggs or larvae carried by the waves—the effects of which we won't know for years to come.

The Deep Sea

As much as 20 percent of the spilled oil may have ended up on and buried beneath the seafloor, where it interacted with wildlife such as deep-sea corals, fish, mollusks and microscopic foraminifera. When the buried oil is brought back to the surface, it can expose animals to dangerous chemicals again. In addition to the oil and dispersants that fell to the seafloor, sediment was left behind during attempts to plug the leaking well. Understanding how the oil spill affected the seafloor may take many years because it's difficult to access and observe.

The Coast

Thirty days after the leak, oil began washing up on the shores of Louisiana. Marshes and estuaries are the worst places that oil can end up. They are difficult to clean without killing the marsh grass itself, and serve as nurseries for young ocean animals. Sometimes the oil becomes buried beneath the mud, where it is slowly released back into the water over decades. In heavily oiled areas of marsh, erosion rates doubled in the years after the spill and little recovery has been observed since. We won't know the full effects of oil in the marshes for years after the spill, when the larvae that would have been exposed to oil are grown up and caught in fisheries.

Today

The Deepwater Horizon oil spill leaked oil and gas into the Gulf of Mexico for 87 days until the well was capped on July 15, 2010. Today, Gulf seafood is safe to eat and the Gulf is recovering better than expected. Scientists continue to study the effects of the spill and develop technologies to improve upon the cleanup methods and response for any future spills that occur.