Three years after the Deepwater Horizon drilling rig spewed millions of gallons of oil into the Gulf of Mexico, scientists are still determining how much damage was done and where all the oil went.
A team of scientists funded by a 10-year, $500 million "Gulf of Mexico Initiative" grant from BP is examining the effects of the oil spill on the ecosystem of the gulf.
One of those scientists is University of Florida geology professor Thomas Bianchi, who focuses on detecting trace amounts of oil in the water 900 to 1000 meters below the surface.
"We're still seeing traces of a signature of what is definitely from the Deepwater Horizon oil," Bianchi said. "But it's not in the form of traditional oil measurements. So if you go and you collect the water and look for various types of hydrocarbons using traditional methods, you won't see it. It'll be below levels of detection."
The Deepwater Horizon explosion and subsequent oil spill was the largest in United States' history, discharging gas and crude oil from an ocean depth of about 5,000 feet.
The spill is unique to study, Bianchi said, because most oil spills occur at the ocean's surface where sunlight, wind, currents and waves play a role in breaking down the oil's chemical composition.
What Bianchi has found is that even deep below the surface, the spill has transformed its chemical signature, becoming part of the dissolved organic matter. Scientists like Bianchi are now determining whether this organic matter is still toxic.
Because the oil is not exposed to the sunlight, it is likely being consumed by microbes deep below the surface, he said. This makes the oil a part of the food web.
"(Oil levels) are dropping, which means they are actually being metabolized or consumed," Bianchi said, "and the question is: Where is that actually moving? From the bacteria up through the food web, who's doing it?"
Texas A&M Corpus Christi scientist Paul Montanga published a paper earlier this year that examined the impacts of the oil spill on the Gulf ecosystem. He found the amount of small microbes called Benthos have decreased near the spill site.
Bianchi cautioned that scientists need to consider whether this decrease is due to oil coming from the spill or from the ocean's natural oil seeps.
"Natural seeps in the Gulf of Mexico have been leaving tar balls on the beach and residues of oil contamination, so to speak, on our beaches long before humans ever walked the shores," Bianchi said. "These go back millions of years and they're natural seeps, so basically, the oil is literally leaking out of the bottom of the ocean."
In order to determine if the residual oil being detected is from the spill and not natural sources, a Texas A&M study tested the oil for barium — a chemical associated with drilling. The study linked the oil to the Deepwater Horizon rig.
On the surface, David Godfrey, executive director of the Sea Turtle Conservancy, said the sea turtle population is attempting to stabilize.
The Deepwater Horizon incident occurred in the middle of nesting season, Godfrey said, and hundreds of thousands of turtles were impacted by the oil spill, either by being directly killed by the oil or having their food supply compromised.
"Very likely, only one out of 1,000, or one out of 10,000 hatchlings survives to reach adulthood," Godfrey said. "If thousands and thousand of adults were killed by the spill, you have to produce a whole lot of hatchlings and give them 30 years to grow up before you begin to actually replace adult turtles that were harmed by the spill."