Workers removing tar balls from the Alabama coast. Credit: Reuters

Laboratory tests have confirmed that oil washed ashore during Hurricane Isaac on the Louisiana coast was indeed from the 2010 BP Deepwater Horizon spill.

About 100 pounds of tar balls were also collected from the Alabama coast after Hurricane Isaac.  Those samples are still being tested.

Read more about oil washed ashore by Hurricane Isaac from the Associated Press.

How does this happen exactly?

When a large hurricane such as Isaac stirs up the ocean’s surface with its strong winds, it creates large-scale upward motion in the depths of the ocean called “upwelling”.  This upward motion can bring deep water up towards the surface of the ocean.

In this case, oil from the BP spill that had dispersed in deeper sections of the Gulf was forced up to the surface, washing tar balls ashore once again.