NOAA's Response and Restoration Blog

An inside look at the science of cleaning up and fixing the mess of marine pollution

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Science of Oil Spills Training Now Accepting Applications for Spring 2016

Two people closely examining rocks and seaweed on a shoreline.

These classes help prepare responders to understand the environmental risks and scientific considerations when addressing oil spills, and also include a field trip to a local beach to apply newly learned skills. (NOAA)

NOAA‘s Office of Response and Restoration, a leader in providing scientific information in response to marine pollution, has scheduled Science of Oil Spills (SOS) classes in two locations in spring 2016:

  • Mobile, Alabama the week of March 28, 2016
  • Ann Arbor, Michigan the week of May 16, 2016

We will accept applications for these classes as follows:

For the Mobile class, the application period will be open until Friday, January 22. We will notify accepted participants by email no later than Friday, February 5.

For the Ann Arbor class, the application period will be open until Friday, March 11. We will notify accepted participants by email no later than Friday, March 25.

SOS classes help spill responders increase their understanding of oil spill science when analyzing spills and making risk-based decisions. They are designed for new and mid-level spill responders.

These trainings cover:

  • Fate and behavior of oil spilled in the environment.
  • An introduction to oil chemistry and toxicity.
  • A review of basic spill response options for open water and shorelines.
  • Spill case studies.
  • Principles of ecological risk assessment.
  • A field trip.
  • An introduction to damage assessment techniques.
  • Determining cleanup endpoints.

To view the topics for the next SOS class, download a sample agenda [PDF, 170 KB].

Please understand that classes are not filled on a first-come, first-served basis. We try to diversify the participant composition to ensure a variety of perspectives and experiences, to enrich the workshop for the benefit of all participants. Classes are generally limited to 40 participants.

For more information, and to learn how to apply for the class, visit the SOS Classes page.

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NOAA Is Supporting Oil Spill Response in Kentucky After Tugs Collide on Mississippi River

On the evening of September 2, 2015, two tug boats collided on the Mississippi River near Columbus, Kentucky, spilling slurry oil into the river.

Early reports, which later may be corrected, indicate an estimated 120,500 gallons of oil were released from a hole in the cargo tank of a barge being towed by the tug Dewey R during the collision. The spill and ensuing response closed the river between mile markers 938 and 922, south of Paducah, Kentucky, but the waterway was reopened to vessel traffic as of September 8.

At the request of the U.S. Coast Guard, NOAA’s Office of Response and Restoration is supporting the response and sending oil spill and data management experts to the scene of the spill. NOAA scientific support coordinators are providing a variety of information for the response, including river flow forecasts, chemistry of the spilled oil, a submerged oil assessment (because this heavier oil may sink), and other information to help determine where the spill will go and what can be done to protect our waterways and keep commerce moving.

The natural resource agencies also are beginning to assess potential impacts to natural resources, a first step to determining whether restoration is needed as a result of the spill.

Updates from NOAA about this oil spill may be available on IncidentNews.

What Is Slurry Oil?

Slurry oil is a residual oil resulting from the refining process and when spilled, most of it will sink or become suspended in the water column. A U.S. Coast Guard overflight the morning of September 3 revealed a floating sheen of oil four to five miles downstream of the discharge, which is not unexpected with this type of heavy oil.

Learn more about different types of oil and their behaviors when spilled and read about a 2005 slurry oil spill in the Gulf of Mexico.

How Is an Oil Spill in a River Different Than One in the Ocean?

From dams and density to muddy waters and vegetation, rivers offer a very different environment than the ocean during an oil spill.

Read more about the kinds of unique challenges we have to consider during an oil spill in a river.

More Information About Oil Spills

Find basic information related to oil spills, cleanup, impacts, and restoration, as well as NOAA’s role during and after oil spills.

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Podcast: What Was It Like Responding in the Aftermath of Hurricane Katrina?

On today’s episode of Diving Deeper, we remember one of the most devastating natural disasters to hit U.S. shores: Hurricane Katrina, which made landfall 10 years ago this week.

What was it like working in New Orleans and the surrounding area in the wake of such a storm?

In this podcast, we talk with Charlie Henry and Dave Wesley, two pollution responders from NOAA’s Office of Response and Restoration who were working in the area in the aftermath of not just one massive hurricane, but two, as Hurricane Rita swept across the Gulf Coast just a few short weeks later.

Hear about their experiences responding to these storms, find out which memories stand out the most for them, and reflect on the toll of working in a disaster zone:

Learn more about our work after Hurricanes Katrina and Rita, explore the progress made in the 10 years since, and see photos of the destruction these storms left across the heavily industrialized coast of the Gulf of Mexico.

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How Do Oil Spills out at Sea Typically Get Cleaned Up?

This is a post by Kate Clark, Acting Chief of Staff with NOAA’s Office of Response and Restoration.

Close up of skimming device on side of a boat with oil and boom.

Skimmers come in various designs but all basically work by removing the oil layer from the surface of the water. (U.S. Coast Guard)

Whether for hanging a picture on the wall or fixing a leaky faucet, most people keep a common set of tools in their home. While some tools get more use than others, it’s good to have an array on hand to handle most repair jobs. The same is true for responding to oil spills.

Like a home repair job, each oil spill has unique aspects that call for careful consideration when deciding which tool to use. Responders keep an array of response methods in their toolkit for dealing with oil in offshore waters: skimming and booming, in situ burning, and applying dispersants.

Let’s get to know a few of those tools and the situations when they might be the most appropriate method for dealing with oil spills out at sea.

Skimming: Take a Little off the Top

Skimming is a process that removes oil from the sea surface before it reaches sensitive areas along a coastline. Sometimes, two boats will tow a collection boom, allowing oil to concentrate within the boom, where it is then picked up by a “skimmer.” From whirring disks to floating drums, skimmers come in various designs but all basically work by removing the oil layer from the surface of the water. These devices attract oil to their surfaces before transferring it to a collection tank, often on a boat. Ideal conditions for skimming are during the day when the oil slick is thick and the ocean surface is fairly calm.

The success of a skimming operation is dependent on something known as the “encounter rate.” Much like a vacuum picks up dirt from your carpet, a skimmer has to come in direct contact with the oil in order to remove it from the surface and, even then, it will still pick up some water. That’s why responders will often refer to the volume of oil removed via skimming as gallons of an oil-water mixture.

In Situ Burning: Burn After Oiling

Plumes of smoke from two fires burning oil on the ocean surface.

Burning oil “in place” (in situ) on the water’s surface requires gathering a layor of oil thick enough to sustain the burn. (NOAA)

In situ burning is the process of burning spilled oil where it is on the ocean (known as “in situ,” which is Latin for “on site”). Similar to skimming, two boats will often tow a fire-retardant collection boom to concentrate enough oil to burn. Burning is sometimes also used in treating oiled marshes.

Ideal conditions for in situ burning are daylight with mild or offshore winds and flat seas. The success of burning oil is dependent on corralling a layer of oil thick enough to maintain a sustained burn. Any burn operation includes careful air monitoring to ensure smoke or residue resulting from the burn do not adversely impact people or wildlife.

Chemical Dispersants: Break It Up

Releasing chemical dispersants, usually from a small plane or a response vessel, on an oil slick breaks down the oil into smaller droplets, allowing them to mix more easily into the water column. Smaller droplets of oil become more readily available to microbes that will eat them and break them down into less harmful compounds.

However, using dispersants has its drawbacks, shifting potential impacts to the marine life living in the water column and on the seafloor. Because of this, the decision to chemically disperse oil into the water column is never made lightly. This decision is often made so that much less oil stays at the surface, where it could affect birds and wildlife at the ocean surface and drift onto vulnerable coastal habitat like beaches, wetlands, and tidal flats.

Ideal conditions for chemical dispersion are daylight with mild winds and moderate seas. Chemical dispersion is never done close to the shore, in shallow waters, near coastal communities, or when there is a potential for winds to carry the chemical spray away from its intended target.

Natural dispersion can and does occur when waves at the ocean surface have enough turbulent energy to allow surface oil to mix into the water column. Applying chemical dispersants can expedite this process when there is an imminent threat associated with allowing the oil to stay on the surface.

Graphic showing methods for responding to oil spills at sea. Plane applying chemical dispersants: Chemical dispersion is achieved by applying chemicals to remove oil from the water surface by breaking  the oil into small droplets. Burning oil surrounded by boom: Also referred to as in situ burning, this   is the method of setting fire to freshly spilled oil, usually while still   floating on the water surface. Booms: Booms are long floating barriers used to   contain or prevent the spread of spilled oil. A boat skimming oil: Skimming is achieved with  boats equipped with a floating skimmer designed to remove thin layers of oil from   the surface, often with the help of booms.One Size Does Not Fit All

You may have noticed that each of these tools has one common factor limiting its effectiveness: daylight, or more precisely, visibility. Being able to see the spilled oil, often over large areas of the ocean, is critical to being able to clean it up. That means these tools become ineffective at night, during certain seasons, or in regions where prolonged darkness, fog, or clouds are the norm.

Table showing the conditions which may affect the use of different oil spill response methods at sea (skimming, burning, dispersing). Conditions are sunlight, wind, rough seas, cold, and nearshore.

Conditions which may affect the use of different oil spill response methods at sea.

Rough seas can be prohibitive for skimming and burning since these methods rely on calm conditions and collection booms to gather (and keep) oil in one place. High winds can often rule out burning and aerial dispersion as an option.

While these techniques perform best under certain, ideal conditions, responders often have to make do with the variety of conditions going on during an oil spill and can and do use these tools under less-than-ideal conditions. Their effectiveness also depends on factors such as the type or state of the spilled oil or the environment it was spilled in (e.g., sea ice).

Just like your home repairs, the job sometimes calls for a non-traditional tool or creative fix. The continued development of alternative response methods and technologies for cleaning up oil is critical for addressing oil spills in geographic areas or conditions that the traditional toolbox is not equipped to fix.

Kate Clark is the Acting Chief of Staff for NOAA’s Office of Response and Restoration. For nearly 12 years she has responded to and conducted damage assessment for numerous environmental pollution events for NOAA’s Office of Response and Restoration. She has also managed NOAA’s Arctic policy portfolio and served as a senior analyst to the National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling.

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Who Thinks Crude Oil Is Delicious? These Ocean Microbes Do

This is a post by Dalina Thrift-Viveros, a chemist with NOAA’s Office of Response and Restoration.

Edge of oil slick at ocean surface.

There are at least seven species of ocean bacteria that can survive by eating oil and nothing else. However, usually only a small number of oil-eating bacteria live in any given part of the ocean, and it takes a few days for their population to increase to take advantage of their abundant new food source during an oil spill. (NOAA)

Would you look at crude oil and think, “Mmm, tasty…”? Probably not.

But if you were a microbe living in the ocean you might have a different answer. There are species of marine bacteria in several families, including Marinobacter, Oceanospiralles, Pseudomonas, and Alkanivorax, that can eat compounds from petroleum as part of their diet. In fact, there are at least seven species of bacteria that can survive solely on oil [1].

These bacteria are nature’s way of removing oil that ends up in the ocean, whether the oil is there because of oil spills or natural oil seeps. Those of us in the oil spill response community call this biological process of removing oil “biodegradation.”

What Whets Their Oily Appetites?

Communities of oil-eating bacteria are naturally present throughout the world’s oceans, in places as different as the warm waters of the Persian Gulf [2] and the Arctic conditions of the Chukchi Sea north of Alaska [3].

Each community of bacteria is specially adapted for the environment where it is living, and studies have found that bacteria consume oil most quickly when they are kept in conditions similar to their natural environments [4]. So that means that if you took Arctic bacteria and brought them to an oil spill in the Gulf of Mexico, they would not eat the oil as quickly as the bacteria that are already living in the Gulf. You would get the same result in the reverse case, with the Arctic bacteria beating out the Gulf bacteria at an oil spill in Alaska.

Other factors that affect how quickly bacteria degrade oil include the amount of oxygen and nutrients in the water, the temperature of the water, the surface area of the oil, and the kind of oil that they are eating [4][5][6]. That means the bacteria that live in a given area will consume the oil from a spill in the summer more quickly than a spill in the winter, and will eat light petroleum products such as gasoline or diesel much more quickly than heavy petroleum products like fuel oil or heavy crude oil.

Oil-eating microbes fluorescing in a petri dish.

This bacteria, fluorescing under ultraviolet light in a petri dish, is Pseudomonas aeruginosa. It has been used during oil spills to break down the components of oil. (Credit: Wikimedia user Sun14916/Creative Commons Attribution-ShareAlike 3.0 Unported license)

Asphalt, the very heaviest component of crude oil, is actually so difficult for bacteria to eat that we can use it to pave our roads without worrying about the road rotting away.

What About During Oil Spills?

People are often interested in the possibility of using bacteria to help clean up oil spills, and most oil left in the ocean long enough is consumed by bacteria.

However, most oil spills last only a few days, and during that time other natural “weathering” processes, such as evaporation and wave-induced breakup of the oil, have a much bigger effect on the appearance and location of the oil than bacteria do. This is because there are usually only a small number of oil-eating bacteria in any given part of the ocean, and it takes a few days for their population to increase to take advantage of their abundant new food source.

Because of this lag time, biodegradation was not originally included in NOAA’s oil weathering software ADIOS. ADIOS is a computer model designed to help oil spill responders by predicting how much of the oil will stay in the ocean during the first five days of a spill.

However, oil spills like the 2010 Deepwater Horizon well blowout, which released oil for about three months, demonstrate that there is a need for a model that can tell us what would happen to the oil over longer periods of time. My team in the Emergency Response Division at NOAA’s Office of Response and Restoration has recognized that. As a result, version 3 of ADIOS, due to be released later in 2015, will take into account biodegradation.

My team and I used data published in scientific journals on the speed of oil biodegradation under different conditions to develop an equation that can predict how fast the components of oil will be consumed, and how the speed of this process can change based on the surface area-to-mass ratio of the oil and the climate it is in. A report describing the technical details of the model will be published in the upcoming Proceedings of the Arctic and Marine Oilspill Program Technical Seminar, which will be released after the June conference.

Including oil biodegradation in our ADIOS software will provide oil spill responders with an even better tool to help them make decisions about their options during a response. As part of the team working on this project, it has provided me with a much greater appreciation for the important role that oil-eating bacteria play in the long-term effort to keep our oceans free of oil.

I know I’m certainly glad they think oil is delicious.

Dalina Thrift-ViverosDalina Thrift-Viveros is a Seattle-based chemist who has been providing chemistry expertise for Emergency Response Division software projects and spill responders since 2011, when she first started working with NOAA and Genwest. When she is not involved in chemistry-related activities, Dalina sings with the rock band Whiskey River and plays sax with her jazz group, The Paul Engstrom Trio.

Literature cited

[1] Yakimov, M.M., K.N. Timmis, and P.N. Golyshin. “Obligate oil-degrading marine bacteria,” Current Opinion in Biotechnology, 2007, 18(3), pp. 257-266.

[2] Hassanshahian, M., G. Emtiazi, and S.Cappello. “Isolation and characterization of crude-oil-degrading bacteria from the Persian Gulf and the Caspian Sea,” Marine Pollution Bulletin, 2012, 64, pp. 7–12.

[3] McFarlin, K.M., R.C. Prince, R. Perkins, and M.B. Leigh. “Biodegradation of Dispersed Oil in Arctic Seawater at -1°C,” PLoS ONE, 2014, 9:e84297, pp. 1-8.

[4] Atlas, R.M. “Petroleum Biodegradation and Oil Spill Bioremediation,” Marine Pollution Bulletin, 1995, 31, pp. 178-182.

[5] Atlas, R.M. and T.C. Hazen. “Oil Biodegradation and Bioremediation: A Tale of the Two Worst Spills in U.S. History,” Environmental Science & Technology, 2011, 45, pp. 6709-6715.

[6] Head, I.M., D.M. Jones, and W.F.M. Röling, “Marine microorganisms make a meal of oil,” Nature Reviews Microbiology, 2006, 4, pp. 173-182.

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Five Years After Deepwater Horizon, How Is NOAA Preparing for Future Oil Spills?

The Deepwater Horizon Oil Spill: Five Years Later

This is the ninth and final story in a series of stories over the past month looking at various topics related to the response, the Natural Resource Damage Assessment science, restoration efforts, and the future of the Gulf of Mexico.

Oil in a boat wake on the ocean surface.

Keeping up with emerging technologies and changing energy trends helps us become better prepared for the oil spills of tomorrow, no matter where that may take us. (NOAA)

When the Exxon Valdez tanker ran aground in Alaska and spilled nearly 11 million gallons of crude oil in 1989, the world was a very different place. New laws, regulations, and technologies followed that spill, meaning future oil spills—though they undoubtedly would still occur—would do so in a fundamentally different context.

This was certainly the case by 2010 when the Deepwater Horizon oil rig suffered an explosion caused by a well blowout in the Gulf of Mexico. Tankers transporting oil have become generally safer since 1989 (thanks in part to now-required double hulls), and in 2010, the new frontier in oil production—along with new risks—was located at a wellhead nearly a mile under the ocean surface.

Since that fateful April day in 2010, NOAA has responded to another 400 oil and chemical incidents. Keeping up with emerging technologies and changing energy trends helps us become better prepared for the oil spills of tomorrow, whether they stem from a derailed train carrying particularly flammable oil, a transcontinental pipeline of diluted oil sands, or a cargo ship passing through the Arctic’s icy but increasingly accessible waters.

So how is NOAA’s Office of Response and Restoration preparing for future oil spills?

The Bakken Boom

Crude oil production from North Dakota’s Bakken region has more than quadrupled [PDF] since 2010, and responders must be prepared for spills involving this lighter oil (note: not all oils are the same).

Bakken crude oil is highly flammable and evaporates quickly in the open air. Knowing the chemistry of this oil can help guide decisions about how to respond to spills of Bakken oil. As a result, we’ve added Bakken as one of the oil types in ADIOS, our software program which models what happens to spilled oil over time. Now, responders can predict how much oil naturally disperses, evaporates, or remains on the water’s surface using information customized for Bakken’s unique chemistry.

We’ve also been collaborating across the spill response community to boost preparedness for these types of oil spills. Earlier this year, NOAA worked with the National Response Team to teach responders about how to deal with Bakken crude oil spills, with a special emphasis on health and safety.

The increase of Bakken crude poses another challenge to the nation: spills from oil-hauling trains. There are few ways to move Bakken crude from wells in North Dakota to refiners and consumers across the country. To keep up with the demand, producers have turned to rail transport as a quick alternative. In 2010, rail moved less than five million tons of crude petroleum. By 2013, that number had jumped to nearly 40 million.

NOAA typically responds to marine spills, but our scientific experience also proves useful when oil spills into a navigable river, as can happen when a train derails. To help answer response questions for waterways at risk, we’re adding even more data to our tools for spill responders. Ongoing updates to the Environmental Response Management Application (ERMA), our online mapping tool for environmental response data, illustrate the intersection of railroads and sensitive habitats and species, which might be affected by a spill from a train carrying oil.

Our Neighbor to the North

Oil imports from Canada, where oil sands (also known as tar sands) account for almost all of the country’s oil, have surged. Since 2010 Canadian oil imports have increased more than 40 percent.

Oil sands present another set of unique challenges. This variety is a thick, heavy crude oil (bitumen), which has to be diluted with a thinner type of oil to allow it to flow through a pipeline for transport. The resulting product is known as diluted bitumen, or dilbit.

Because oil sands are a mixture of products, it’s not completely clear how they react in the environment. When this product is released into water, the oils can separate quickly between lighter and heavier parts. As such, responders might have to worry about both lighter components vaporizing into toxic fumes in the air and heavier oil components potentially sinking down into the water column or bottom sediments, becoming more difficult to clean up. This also means that bottom-dwelling organisms may be more vulnerable to spills of oil sands than other types of oils.

As our experts work to assess the impacts from oil sands spills (including the 2010 Enbridge pipeline spill in Michigan), their studies both inform restoration for past spills and help guide response for the next spill. We’ve been working with the response and restoration community around the country to incorporate these lessons into spill response, including at recent meetings of the West Coast Joint Assessment Team and the International Spill Control Organization.

Even Further North

As shrinking summer sea ice opens shipping routes and opportunities for oil and gas production in the Arctic, the risk of an oil spill increases for that region. By 2020, up to 40 million tons per year of oil and gas are expected to travel the Northern Sea route through the Arctic Ocean.

Responding to oil spills in the Arctic will not be easy. Weather can be harsh, even in August. Logistical support is limited, and so is baseline science. Yet in the last five years, NOAA’s Office of Response and Restoration has made leaps in Arctic preparedness. For example, since 2010, we launched Arctic ERMA, a version of our interactive response data mapping tool customized for the region, and released Arctic Ephemeral Data Guidelines, a series of guidelines for collecting high-priority, time-sensitive data in the Arctic after an oil spill. But we still have plenty of work ahead of us.

Ship breaking ice in Arctic waters.

The U.S. Coast Guard Cutter Healy breaks ice in Arctic waters. A ship like this would be the likely center of operations for an oil spill in this remote and harsh region. (NOAA)

During a spill, we predict where oil is going, but Arctic conditions change the way oil behaves compared with warmer waters. Cold temperatures make oil more viscous (thick and slow-flowing), and in a spill, oil may be trapped in, on, and under floating sea ice, further complicating predictions of its movement.

We’ve been working to overcome this challenge by improving our models of oil movement and weathering in icy waters and researching response techniques and oil behavior to close gaps in the science. This May, we also find ourselves in a new role as the United States takes chairmanship of the Arctic Council. Amy Merten of NOAA’s Office of Response and Restoration will chair the Arctic Council’s Emergency Prevention, Preparedness and Response Working Group, where we hope to continue international efforts to boost Arctic spill preparedness.

Expecting the Unexpected

After decades of dealing with oil spills, we know one thing for certain—we have to be ready for anything.

In the last five years, we’ve responded to spills from the mangroves of Bangladesh to the banks of the Ohio River. These spills have involved Bakken crude, oil sands, and hazardous chemicals. They have resulted from well blowouts, leaking pipelines, derailed trains, grounded ships, storms, and more. In fact, one of the largest spills we’ve responded to since Deepwater Horizon involved 224,000 gallons of molasses released into a Hawaiian harbor.

Whatever the situation, it’s our job to provide the best available science for decisions. NOAA has more than 25 years of experience responding to oil spills. Over that time, we have continued to fine-tune our scientific understanding to better protect our coasts from this kind of pollution, a commitment that extends to whatever the next challenge may bring.


Attempting to Answer One Question Over and Over Again: Where Will the Oil Go?

The Deepwater Horizon Oil Spill: Five Years Later

This is the first in a series of stories over the coming weeks looking at various topics related to the response, the Natural Resource Damage Assessment science, restoration efforts, and the future of the Gulf of Mexico.

Oil spills raise all sorts of scientific questions, and NOAA’s job is to help answer them.

We have a saying that each oil spill is unique, but there is one question we get after almost every spill: Where will the oil go? One of our primary scientific products during a spill is a trajectory forecast, which often takes the form of a map showing where the oil is likely to travel and which shorelines and other environmentally or culturally sensitive areas might be at risk.

Oil spill responders need to know this information to know which shorelines to protect with containment boom, or where to stage cleanup equipment, or which areas should be closed to fishing or boating during a spill.

To help predict the movement of oil, we developed the computer model GNOME to forecast the complex interactions among currents, winds, and other physical processes affecting oil’s movement in the ocean. We update this model daily with information gathered from field observations, such as those from trained observers tasked with flying over a spill to verify its often-changing location, and new forecasts for ocean currents and winds.

Modeling a Moving Target

One of the biggest challenges we’ve faced in trying to answer this question was, not surprisingly, the 2010 Deepwater Horizon oil spill. Because of the continual release of oil—tens of thousands of barrels of oil each day—over nearly three months, we had to prepare hundreds of forecasts as more oil entered the Gulf of Mexico each day, was moved by ocean currents and winds, and was weathered, or physically, biologically, or chemically changed, by the environment and response efforts. A typical forecast includes modeling the outlook of the oil’s spread over the next 24, 48, and 72 hours. This task began with the first trajectory our oceanographers issued early in the morning April 21, 2010 after being notified of the accident, and continued for the next 107 days in a row. (You can access all of the forecasts from this spill online.)

Once spilled into the marine environment, oil begins to move and spread surprisingly quickly but not necessarily in a straight line. In the open ocean, winds and currents can easily move oil 20 miles or more per day, and in the presence of strong ocean currents such as the Gulf Stream, oil and other drifting materials can travel more than 100 miles per day. Closer to the coast, tidal currents also can move and spread oil across coastal waters.

While the Deepwater Horizon drilling rig and wellhead were located only 50 miles offshore of Louisiana, it took several weeks for the slick to reach shore as shifting winds and meandering currents slowly moved the oil.

A Spill Playing on Loop

Over the duration of a typical spill, we’ll revise and reissue our forecast maps on a daily basis. These maps include our best prediction of where the oil might go and the regions of highest oil coverage, as well as what is known as a “confidence boundary.” This is a line encircling not just our best predictions for oil coverage but also a broader area on the map reflecting the full possible range in our forecasts [PDF].

Our oceanographers include this confidence boundary on the forecast maps to indicate that there is a chance that oil could be located anywhere inside its borders, depending on actual conditions for wind, weather, and currents. Why is there a range of possible locations in the oil forecasts? Well, the movement of oil is very sensitive to ocean currents and wind, and predictions of oil movement rely on accurate predictions of the currents and wind at the spill site.

In addition, sometimes the information we put into the model is based on an incomplete picture of a spill. Much of the time, the immense size of the Deepwater Horizon spill on the ocean surface meant that observations from specialists flying over the spill and even satellites couldn’t capture the full picture of where all the oil was each day.

Our inevitably inexact knowledge of the many factors informing the trajectory model introduces a certain level of expected variation in its predictions, which is the situation with many models. Forecasters attempt to assess all the possible outcomes for a given scenario, estimate the likelihood of the different possibilities, and ultimately communicate risks to the decision makers.

In the case of the Deepwater Horizon oil spill, we had the added complexity of a spill that spanned many different regions—from the deep Gulf of Mexico, where ocean circulation is dominated by the swift Loop Current, to the continental shelf and nearshore area where ocean circulation is influenced by freshwater flowing from the Mississippi River. And let’s not forget that several tropical storms and hurricanes crossed the Gulf that summer [PDF].

A big concern was that if oil got into the main loop current, it could be transported to the Florida Keys, Cuba, the Bahamas, or up the eastern coast of the United States. Fortunately (for the Florida Keys) a giant eddy formed in the Gulf of Mexico in June 2010 (nicknamed Eddy Franklin after Benjamin Franklin, who did some of the early research on the Gulf Stream). This “Eddy Franklin” created a giant circular water current that kept the oil largely contained in the Gulf of Mexico.

Some of the NOAA forecast team likened our efforts that spring and summer to the movie Groundhog Day, in which the main character is forced to relive the same day over and over again. For our team, every day involved modeling the same oil spill again and again, but with constantly changing results.  Thinking back on that intense forecasting effort brings back memories packed with emotion—and exhaustion. But mostly, we recall with pride the important role our forecast team in Seattle played in answering the question “where will the oil go?”


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