If you were able to stand on the bottom of the seafloor and look up,
you would see flakes of falling organic material and biological debris
cascading down the water column like snowflakes in a phenomenon known as
Recent disasters like the Deepwater Horizon oil spill in the Gulf of
Mexico, however, have added a new element to this natural process: oil.
During these events, the natural marine snow interacts with oil and
dispersants to form what’s known as marine oil snow as it sinks from the
surface through water column to the seafloor sediments.
The danger with marine oil snow is that it transfers oil and its
negative impacts from the water column to the sediments on the bottom of
the seafloor, delivering a more diverse suite of oxygenated compounds
to sediments and deep-sea ecosystems. These oxygenated forms of many oil
compounds are more toxic to organisms in the sediments than are the
While this result may lessen the impact on near-surface organisms
like fish and birds and shellfish, it transfers the oil to the deep
ocean where it impacts fauna, deep corals, and fish down there, where
adverse impacts were documented after the Deepwater Horizon oil spill.
The University of Delaware’s Andrew Wozniak conducted research to
investigate the fate and accumulation of marine oil snow in the Gulf of
Mexico, the results of which were recently published in the Environmental Science and Technology journal.
Wozniak, assistant professor in the School of Marine Science and
Policy in UD’s College of Earth, Ocean and Environment, conducted the
research while a research faculty member at Old Dominion University. He
said that to recreate the conditions of the Gulf of Mexico, he and his
collaborators used 100-liter glass tanks filled with seawater collected
from the Gulf.
In addition to the seawater, they added plankton collected from
coastal waters directly before the initiation of the experiment. They
also added the kind of oil spilled during the Deepwater Horizon
disaster, along with the chemical dispersant used to break it up, and
monitored the tanks for four days.
Particles in the tanks formed on the surface, in the water column
and the rest sank to the bottom. Wozniak collected the particles that
sank and isolated the oil component to conduct a chemical analysis.
When they performed the chemical analysis and compared it to the
initial oil, the samples differed in a way that could be attributed to
Wozniak said this occurred as the marine oil snow sank through the water column.
When an event like an oil spill occurs, the phytoplankton and
bacteria in the ocean interact with the oil — which is bad for them —
and they release extracellular polymeric substances (EPS) which collects
“It’s kind of a defense mechanism and because that EPS is sticky, it
gets that oil aggregated and hopefully protects them from the oil,”
The result of the EPS protection is a base particle for other substances to glom onto.
“If something with enough density like minerals form on it, then
they’ll sink and that’s when you get that marine oil snow,” said
By looking at the degraded material at the bottom of the mesocosms,
Wozniak could see that as the oil sank through the water column, it
provided a microhabitat for microbes and microbes that prefer
hydrocarbons and oil-like compounds proliferated.
In addition to supporting that community of bacteria, it also keeps a
portion of oil that has been changed — potentially for the worse — in
“It may have consequences for the toxicity of the oil because it
oxygenates compounds,” said Wozniak. “The oxygenated forms of some of
the compounds, like Polycyclic Aromatic Hydrocarbons, tend to be more
toxic and so it may have important implications for future study for
what’s happening in sediments or deep coral reefs.”
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