Scientists working in the Gulf of Mexico have found that contaminants from the massive 2010 Deepwater Horizon oil spill lingered in the subsurface water for months after oil on the surface had been swept up or dispersed. In a new study, they also detailed how remnants of the oil, black carbon from burning oil slicks and contaminants from drilling mud combined with microscopic algae and other marine debris to descend in a “dirty blizzard” to the seafloor.
The work, published May 30 in the Proceedings of the National Academy of Sciences, confirms that contaminants found in the water column and on the seafloor were indeed from the Deepwater Horizon spill, and not from the many natural oil seeps in the Gulf. The initial dispersal of materials in the water made pollutants hard to detect, but the eventual accumulation of “marine snow” concentrated the toxins on the seabed, where they can enter the food web, possibly affecting fish and corals in deep waters.
The sampling site and schematic of sediment trap array deployed in 2010/2011 and 2012/2013, with NOAA Okeanos Explorer bathymetry data included.
The findings suggest that the ecological effects of oil spills could last longer than previously thought. The paper comes on the heels of the most recent spill, detected May 12. About 88,200 gallons of oil were released from an underwater pipeline operated by Shell about 90 miles off the coast of Louisiana, according to news reports. Much of the oil has been recovered, and there are as yet no reported impacts on wildlife. But scientists are just beginning to assess the effects.
“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 of the Lamont-Doherty Earth Observatory, an environmental chemist who is lead author of the study.
Some researchers have contended that contaminants found on the seafloor are coming from natural oil seeps. But Yan and colleagues used various “fingerprinting” techniques to confirm the hydrocarbons in the water were derived from crude oil of the kind leaking from the Deepwater Horizon site. The presence of barium and the distribution of olefin compounds, two key components in drilling mud, confirmed the contaminants were associated with the spill.
“It’s kind of like a smoking gun that pins down the source,” Yan said.
The study also sheds light on why these contaminants can stay so long—five months—in the water column. “The deposition of hydrocarbons was largely controlled by the particle sources, which are available sporadically,” Yan said. “Hydrocarbons, especially high molecular weight ones, were adsorbed tightly to fine particles. These fine particles can linger in the water column for weeks.” But a bloom of diatoms, microscopic marine plants, acted as a “dust bunny” to accumulate the particles and carry them below after the diatoms died, he said.
“Normally we don’t think of oil as sinking,” said co-author Uta Passow, a biological oceanographer at the Marine Science Institute at the University of California Santa Barbara. “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.”
Though it’s tough to measure exactly how much of the spilled oil winds up on the seafloor, Passow said it could be substantial. “I would argue it’s probably more than 10 percent, probably even more than 15 percent,” she said. That could add up to millions of gallons.
Other studies have documented how the oil and other contaminants dispersed, and have established that petroleum hydrocarbons from the spill have accumulated on the seafloor. Scientists also have known that phytoplankton, microscopic marine plants, play a role in delivering the oil to the seafloor. In the new study, the researchers describe how that happens. The paper “provides a likely mechanism for the impact to deep sea corals discovered outside of the depth range and most likely flow path of the Deepwater plume of oil and gas that formed during the spill,” said Chuck Fisher, a marine biologist at Penn State who was not involved in the study. Fisher’s work documented damage to corals following the spill.
Between April 20 and July 15, 2010, about 200 million gallons of crude oil gushed into the Gulf of Mexico from a blown well beneath the Deepwater Horizon oil rig—the largest marine oil spill in U.S. history. Some of the oil was recovered, evaporated or was deliberately burned at the surface. Some washed ashore; still more was broken down by chemical dispersants and consumed by bacteria. But a large portion, perhaps a quarter, has been unaccounted for. Although the oil was undetectable in surface waters within a few weeks, the deeper environmental consequences were unclear because the mechanisms that transport petroleum hydrocarbons to the ocean floor were not well understood.
Yan and his colleagues used sediment traps to collect diatoms and other matter slowly sinking through the water and found contaminants clinging to the tiny particles, including black carbon left over from burning oil slicks, and barium and synthetic fibers of olefin, which are used in drilling mud. The researchers were “shocked” to find the barium Yan said, because it was assumed that the contaminant would settle quickly near application sites.
The team deployed a sediment trap roughly 4.5 miles from the capped well and captured sinking material from August 2010 to October 2011. According to the researchers, the black carbon continued to sink for two months after the oil fires were extinguished, while other contaminants, including barium, accumulated for at least five months.
“The traps collected this material months after everyone thought the leak was over,” Passow said. “The material stays in the water much longer than people think.” And because drilling mud and oil are present whenever drilling is going on, contaminants could be winding up on the bottom in other situations, as well, she said.
“Considering the widespread use of drilling mud at hundreds of ocean drilling sites around the world, the environmental implications of such an unexpectedly long residence time of barium in the water column is significant and worthy of further investigation,” the paper’s authors write. The researchers found that the movement of contaminants from the water column to the seafloor was intensified during August and September 2010 by an exceptionally large bloom of diatoms. These phytoplankton produce a mucous, particularly when dying, that acts as a glue for other particles in the water. As this “marine snow” sank, it carried the contaminants from the oil spill to the seafloor.
It’s unclear whether the oil itself played a role in precipitating the diatom bloom. A study earlier this year by another Lamont researcher, Ajit Subramaniam, found phytoplankton thriving above natural oil seeps in the Gulf. While the oil itself doesn’t seem to help the phytoplankton, turbulence from the seeps brings nutrients up from the deep that do.
Subramaniam said that water management authorities increased discharge of the Mississippi River to push the Deepwater Horizon oil plume away from the shore, and that may have pushed nutrients out into the Gulf that could have fueled the diatom bloom.
“There were people out there measuring hydrocarbons,” Subramaniam said. But they didn’t find any in the water, and “by August-September, the word on the street is the show’s over, we can all go home.” But the new study “shows they just weren’t looking for the right things.”
The study may prove helpful in planning future responses to spills, how to measure their impact, and how to contain damage to the environment and associated food systems and ensure food safety. Yan said the team is currently studying what happens to the oil seeping naturally in the Gulf through the Ecosystem Impacts of Oil and Gas Inputs to the Gulf project.
New NOAA Report Examines National Oil Po
Live Feed from the E/V Nautilus: ECOGIG
NOAA, Partners Predict Possible Record-S
Saab Seaeye’s Panthers Picked for Gulf
Teledyne Oil & Gas Announces the Release
New Exploration Opportunity - Offshore M
Ocean Specialists Inc. Achieves Major
International Conference Set to Discuss
OceanGate Inc. Dives on Oil Platform for
Study Describes How an Oil Slick Could I
Research Finds More than 50 Fish Species
BP Makes Gulf of Mexico Environmental Da
Gulf of Mexico Research Initiative Annou
NOAA Announces Regulations to Protect Ma
CSA Ocean Sciences Inc. Awarded Gulf of
Completion of Deep Water Pipeline Equipm
BOEM and Louisiana Coastal Marine Instit
Gas and Oil Discoveries in the Askja Pro
Major Reductions in Seafloor Marine Life
Yara Acquires German Company Specialized
Professor and Graduate Students From Nov
Tracking the Last Mile Before Oil Meets
OIL & GAS UK Discuss New Offshore Well I
New £8 Million Training Center for the O
Deepwater Horizon: Identifying Harmful E
A Quantum Change in Offshore Oil and Gas
When Whales and Oil Rigs Meet
New Tool Available to Help Track Spilled
Starts Up Na Kika Phase 3 in Deepwater G
UTEC Expands Houma Team To Benefit Gulf
Scientists Train the Next Generation on
DeepWater Buoyancy Delivers Flotation Te
State of the Gulf of Mexico” Summit to F
Florida State University: Researchers Fi
Gulf Coast Energy Resources High Bidde
Powerful MacArtney MERMAC Winch System f
Tankers Stack Up in Port of Houston in W
New Study Shows Heart Abnormalities in F
Pellerin Energy Group Sets Record In Dee
Virtual explorers' Invited to the Depths
Gas and Oil Discovery in the Valemon Are
OceanWorks International Delivers Additi
NOAA Releases Expansion Proposal for Gul
Total Discovers Oil in Deep Offshore Ivo
CSA GeoPortal Aids Rapid Oil Spill Respo
European Seafloor Survey Reveals Depth o
UGA Research Examines Fate of Methane Fo
Study Evaluates Synthetic Aperture Radar
Sonar Could Spot Oil Spills Hidden by Ar
Seafloor Experts Publish New View of Zon
Joint Finnish-Swedish Surveillance Opera
Secretary Jewell Announces Award of Firs
CSB Releases New Computer Animation of 2
Apache Completes Sale of Lucius and Heid
NOAA, Partners Predict an Average ‘Dea
Statoil Opens New Research Center – a Mi
CAMAC Energy Discovers Multiple Oil and
BW Offshore has signed contract with Pre
Woods Hole Group Awarded Multi Year Oper
Study at Deepwater Horizon Spill Site Fi
OSIL Multi-Corers in CSA Ocean Sciences
Shell announces first oil from Cardamom
Teledyne Oil & Gas Announces Record Cont
New Map Exposes Previously Unseen Detail
Harvey Gulf Continues Strategic Growth w
Subsea Pipeline Pressure Isolation Prote
BMT Appoints New Sales Manager for Offsh
MTN Builds Houston Team to Expand on 20
Pulse Motion and Strain Monitoring Syste
Highly Distributed Oil & Gas Workforces
Guildford and Aberdeen Based Kongsberg O
DNV GL Win Multi Service Contract from M
Ocean Installer’s Normand Vision Ready f
February - Feature Story - Teledyne Oil
A Mile Deep, Ocean Fish Facing Health Im
LATC Marine Brings Next Generation Damen
Brazilian Offshore Oil Field Takes Nexan
Neptune Awarded 5-Year Offshore Diving C
Join a Plastic Pollution Research Voyage
Seafloor Sensors Record Possible Eruptio
NOAA Announces New Deepwater Horizon Oil
NOAA Announces Long-Term Gulf of Mexico
Emerging Markets Communications Showcase
The Harte Research Institute Honors Hero
New Tools Aiding Storm Prediction, Incre
Bob The Drifter Inspires Singapore Class
NOAA, Partners Predict an Average ‘Dead
Elastec Launches New Offshore Oil Spill
OceanWorks International Receives 2nd Se
ION Launches MexicoSPAN in Mexico’s Offs
Millions from BP Settlement to Benefit T
ASV Completes 10 Days of Passive Acousti
ASV Completes 10 Days of Passive Acousti
BOEM to Offer Almost 22 Million Acres in
3D at Depth Transforms Upstream Oil and
Tampnet to Acquire Telecom Infrastructur
The American Sea: A Natural History of t
Study Offers New Insights on Hurricane I