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How Oil Feeds the Deep Sea

Positioned in front of a natural oil seep, this video camera is capturing images of the black oil bubbling up from beneath the sea floor. A light mounted to the frame helps see what is happening in the dark on the sea floor.


Deep Sea Systems/ Schmidt Ocean Institute

There can be catastrophic results when a large amount of oil is spilled into the ocean—as when the Deepwater Horizon rig exploded and spewed oil into the Gulf of Mexico in 2010. But did you know that a little bit of oil in the ocean is actually necessary for many organisms to survive? In the deep sea, there is no light, so oil and gas act as a source of energy for bacteria. These bacteria are in turn eaten by larger organisms, which are then eaten by even larger organisms, and so on, as you move up the food chain.

Generally the oil that feeds organisms in the deep sea isn’t spilled there by humans, but constantly leaks from reservoirs deep beneath the seafloor. The oil in these reservoirs is formed from organic matter (i.e. plants or animals) that has been buried over millions of years. Petroleum companies tap straight into these reservoirs to pull the oil to the surface, to be refined and sold. But at natural seeps, oil leaks out of these reservoirs little by little, slowly making its way through sediments to the seafloor.

This rainbow sheen on the sea surface is what it looks like when the oil bubbles make it to the sea surface.


MacDonald Lab, FSU

You can even find evidence of oil seeps on the ocean’s surface, where we can see continuous oil slicks miles above where the oil is released. When you go to these areas and look into the water from the ship, you can actually see oil bubbles come up and a rainbow sheen form on the surface… the smell is pretty pungent too! While most people associate such slicks with oil spills, they also form naturally from some of these seeps.

In the Gulf of Mexico, oil seeps are often associated with solid ice-like structures called gas hydrates, which accumulate on the bottom around the seep. Gas hydrate is made up of a gas molecule (often methane) trapped in a cage of water molecules. These gas-trapping cages are rigid in structure but very sensitive to temperature and pressure and will break apart if there is a drastic change. When they do break apart, the gas is released into the water. We see an abundance of wildlife including bacterial mats, ice worms (which burrow through the gas hydrates and graze on the bacteria), clams, crabs, eels, and fish living around these seep sites. 

One of my research goals is to determine how much oil and gas is released by these natural seeps. We use video cameras to film the exit points of oil bubbles at the sea floor. A video time-lapse camera is placed close to the seep site and is left to take video footage for extended periods of time. We deploy the cameras at depths of around 4,000 feet (1,200 meters), which is deeper than any diver can go. Instead, we use remotely operated vehicles (ROVs) controlled by pilots on a research vessel to place the camera in the right spot at the bottom of the ocean. I was even lucky enough to go down in the ALVIN submersible (from the Woods Hole Oceanographic Institute) this past year and see the bottom of the sea with my very own eyes! When we bring the camera back up, I use automated image processing techniques that I developed to count the bubbles filmed. Calculating the number and size of bubbles can give us an idea of how much oil and gas is released from natural seeps. 

Some areas have rapid bubble release, and some areas extremely slow. The amount of oil and gas in the bubbles also differs. Some natural seep areas release very oily bubbles, which we can identify by their dark brown color. Others have a much higher gas content, where you see shiny clear spheres bubbling out of the gas hydrate. We are still in the process of investigating exactly why we see such differences between the bubble releases at separate natural seep areas, but this bubble counting technique I have developed allows us to get a range of bubble release rates. By knowing where this oil and gas comes from, how it travels through the sediments to the sea floor, and how much oil and gas is being released, we can begin to understand the complex dynamics of these deep-sea seep systems. 

We know that the migration of this oil and gas is extremely important for deep-sea communities. The deep sea is often thought to be a barren, unfavorable place for life; however, we see a diverse congregation of organisms around these natural seeps. The presence and movement of oil and gas is essential for these organisms to flourish and could possibly give us insight to how the first life forms evolved on Earth. 

Our Research is funded by the Gulf of Mexico Research Initiative (GOMRI) through the Deep Sea to Coast Connectivity in the Eastern Gulf (DEEP-C) consortia and the Ecosystem Impacts of Oil and Gas Inputs to the Gulf (ECOGIG) consortia which are based at Florida State University and University of Mississippi respectively.

The Gulf of Mexico Research Initiative (GoMRI) is a 10-year independent research program established to study the effect, and the potential associated impact, of hydrocarbon releases on the environment and public health, as well as to develop improved spill mitigation, oil detection, characterization and remediation technologies. For more information, visit