Deep-ocean impact of the Deepwater Horizon explosion revealed

Other researchers on the team include the paper's lead author, Assistant Professor of Chemistry Helen White of Haverford College, Erik Cordes of Temple University, and Timothy Shank and Christopher German of the Woods Hole Oceanographic Institution (WHOI), which operates the Navy-owned submersible Alvin. Fisher, Cordes, Shank and German are co-authors of the study, along with 10 other scientists from WHOI, Penn State, Temple and the U.S. Geological Survey.

The study's findings are significant for a number of reasons, White said.

"These biological communities in the deep Gulf of Mexico are separated from human activity at the surface by 4,000 feet of water. We would not expect deep-water corals to be impacted by a typical oil spill, but the sheer magnitude of the Deepwater Horizon oil spill and its release at depth make it very different from a tanker running aground and spilling its contents. Because of the unprecedented nature of the spill, we have learned that its impacts are more far reaching than those arising from smaller spills that occur on the surface."

The study grew out of an initial research cruise to the Gulf, led by Fisher in late October 2010 -- approximately six months after the Deepwater Horizon oil spill. This expedition was part of an ongoing study funded by the Bureau of Ocean Energy Management and the National Oceanic and Atmospheric Administration's Ocean Exploration and Research program. Using the remotely operated vehicle (ROV) Jason II, the team examined nine sites at distances greater than 20 kilometers from the Macondo Well and found deep-water coral communities unharmed. However, when the ROV explored another area 11 kilometers to the south west of the spill site, the team was surprised to discover numerous coral communities covered in a brown flocculent material and showing signs of tissue damage.

"We discovered the site during the last dive of the three-week cruise," said Fisher, a biologist and the chief scientist of this mission. "As soon as the ROV got close enough to the community for the corals to come into clear view, it was clear to me that something was wrong at this site. I think it was too much white and brown, and not enough color on the corals and brittle stars. Once we were close enough to zoom in on a few colonies, there was no doubt that this was something I had not seen anywhere else in the Gulf: an abundance of stressed corals, showing clear signs of a recent impact. This is exactly what we had been on the lookout for during all dives, but hoping not to see anywhere."

These coral communities were 4,300 feet deep, in close proximity to the Macondo well, which had been capped three months previously after spilling an estimated 160 million gallons of oil into the Gulf. Because the timing and unprecedented nature of this observation suggested that the damage observed visually resulted from the Deepwater Horizon oil spill, the scientists rapidly organized a second research cruise, which began on Dec. 8, 2010, barely a month after their return to land following their initial discovery.

Joining this second research cruise, again headed by Fisher, was White, whose expertise as a geochemist was key to the interdisciplinary effort. This rare opportunity for the researchers to return to a deep-water site so quickly for the subsequent study was made possible with funding from the National Science Foundation's RAPID Collaborative Research grant program, which aids scientists seeking to respond quickly to urgent issues such as natural disasters or crises resulting from human activity.

To examine the deep water, the team used the autonomous underwater vehicle Sentry to map and photograph the ocean floor, and the deep-submergence, 3-passenger, robotic-armed vehicle Alvin to get a better look at the distressed corals. During six dives in Alvin, the team collected sediments and samples of the corals and filtered the brown material off of the corals for analysis.

To identify the oil found in the coral communities, White worked with Christopher Reddy and Robert Nelson at WHOI using an advanced technique called comprehensive two-dimensional gas chromatography, which was pioneered at WHOI by Reddy and Nelson for use in oil spill research. The method, which separates oil compounds by molecular weight, allows scientists to essentially "fingerprint" oil and determine its source.

This exacting petroleum analysis, coupled with the analysis of 69 images from 43 individual corals at the site -- performed by Pen-Yuan Hsing, a graduate student of Fisher's at Penn State -- yielded strong evidence that the coral communities were impacted by oil from the Macondo well spill.

Fisher said these findings confirm a serious impact from the spill on the animal communities in the deep sea more than seven miles from the Macondo well. He added, "Our ongoing work in the Gulf will allow us to better understand the long-term effects of the spill on the deep sea, and to constrain the footprint of the impact zone for deep-water corals around the Macondo well."