Deepwater Horizon oil spill leaves 'dirty blizzard' in Gulf waters

New research details how containments from the 2010 Deepwater Horizon oil spill lingered under the surface of the Gulf of Mexico for months after oil on the surface had been cleaned up or dispersed. These containments—including remnants of oil and black carbon from burning oil slicks—combined with debris to descend to the seafloor in what the study refers to as a “dirty blizzard.”

Published in Proceedings of the National Academy of Sciences, the study details how the mingling of microscopic algae and other natural debris and oil containments can make pollution difficult to detect.

The dispersal of the oil in the Gulf of Mexico originally obfuscated the amount of these containments, but the “marine snow” that formed from the debris and oil eventually forced pollutants onto the seabed.

From here, pollutants could enter the food chain of deep-sea fish or coral, suggesting that oil spills can have even longer-lasting ecological effects than previously assumed.

“We knew oil pollutants can be carried downward by marine snow, but we didn’t expect the pollutants to stay in the water for such a long time,” said Beizhan Yan, an environmental chemist and the lead author of the study.

Hydrocarbons, or organic compounds made of hydrogen and carbon, were able to transfer from the oil spill in the Gulf of Mexico and adhere to microscopic marine plants called diatoms. When these blooms of diatoms died, the accumulated pollutant particles were able to sink below the surface with the dead plant matter. Using sediment traps, Yan and his colleagues were able to collect diatoms and other sinking ocean debris 4.5 miles away from the capped oil well between August 2010 to October 2011. Yan and his colleagues discovered that containments on the particles were still detectable five months after the oil leak was thought to be contained.

This phenomenon explains why containments were able to stay beneath the water’s surface for months before sinking to the seafloor without being detected.

The study also confirms that the containments found along the seafloor come from the Deepwater Horizon spill, and not from the natural oil seeps within the Gulf of Mexico.

Though some researchers have asserted in the past that seafloor level containments come from these natural oil seeps, the study’s use of “fingerprinting” techniques found that the hydrocarbons in the water linked the contaminants to the kind of crude oil that leaked out of the Deepwater Horizon site. With the further discovery of barium and distributed olefin compounds, two key elements of drilling mud, the study’s researchers were able to confirm the containments were caused by the oil spill.

“Normally we don’t think of oil as sinking,” said Uta Passow, a biological oceanographer and co-author of the study. “People in the past have not really ever considered oil coming to the seafloor, especially very, very deep. We now know how the oil gets down there in large amounts and affects the communities that live there.”

While it is difficult to measure how much oil from the spill actually found its way to the seafloor, Passow believes the amount to be substantial.

“I would argue it’s probably more than 10 percent, probably even more than 15 percent,” she said.

Passow’s estimated amount of oil from the spill on the seafloor would be in line with the large amount of oil left unaccounted for after final efforts to clean up the spill had been made.

Deepwater Horizon oil rig’s 2010 oil leak was the largest marine oil spill in U.S. history, with around 200 million gallons of crude oil gushing into the Gulf of Mexico in a three-month period.

There were many different attempts to clean the oil; recovery, breaking the oil down with chemicals, evaporation and burning oil on the water’s surface were all used as techniques. Some oil even washed ashore. However, even though oil had disappeared completely from the Gulf’s surface a few weeks after the leak had been repaired, scientists feared the long-term ecological consequences.

Yan and his colleagues’ study reveals just how prolonged the aftereffects of an oil spill can be, confirming that oil particles can find their way to the seafloor and into the food chain that exists there months after the initial spill.

This new research may serve to help plan a more comprehensive oil cleaning plan for future spills, as well as be helpful in measuring and understanding the further environmental impact oil spills have on regions like the Gulf of Mexico.

With the recent oil spill in the Gulf of Mexico on May 12, in which 88,200 gallons of crude oil were released from an underwater pipeline, Yan’s research may prove more relevant than ever. As time progresses, the aftereffects of these spills will only continue to appear.