Newswise — It’s been six years since the Deepwater Horizon oil spill occurred in the Gulf of Mexico and scientists are still working to understand how oil and other pollutants move in the ocean. The incident, which occurred in April 2010, is considered the largest accidental marine oil spill in history.

University of Delaware’s Helga Huntley is among more than 40 scientists studying this problem as a member of the Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE).

“In order to improve models and forecasts, ultimately for oil spill response, we have to get the chain of causation, or cause and effect, right,” said Huntley, an assistant research professor with the College of Earth, Ocean, and Environment’s School of Marine Science and Policy.

In 2012, CARTHE scientists deployed 300 untethered buoys, called drifters, into the Gulf of Mexico to simulate an oil spill. The drifters reported their location every 5 minutes via satellite GPS as they floated along with surface currents, allowing researchers to compile maps of the devices’ paths. At the same time, the scientists took measurements about the ocean’s salinity and temperature. When combined, the data gave researchers a glimpse into what happens to material in the ocean.

As they analyzed the data, the scientists learned that small-scale ocean currents play a major role in the spread of pollutants at the ocean surface. They also realized that more information was needed to fully understand the physics driving this dispersion.Huntley recently discussed CARTHE’s latest field experiment, called LASER, conducted in January 2016.

Q: Tell us about CARTHE’s latest field experiment— LASER.

Huntley: We got a great start with the GLAD drifter experiment in 2012. Now with LASER in early 2016, we wanted to fill in the gap and have more contextual observations so that we can better understand the dynamics that affect the behavior of objects drifting in the ocean.

To do this we tracked two different types of material in the Gulf of Mexico, drifters and bamboo plates. The drifters, which were about two feet tall, sit at the water’s surface but are equipped with a drogue to capture the velocity or flow over that surface layer of the ocean. We also tracked bamboo plates that sampled the very thin layer between the surface of the ocean and the air. The drogued drifters and bamboo plates sample slightly different water masses and one of our goals with the LASER experiment is to see if that matters.

Q: Was LASER just a repeat of the GLAD experiment? Huntley: Part of the purpose of LASER was a wintertime version of GLAD, to test whether the drifters behave differently in different seasons. We’ve already discovered that the drifters moved around pretty quickly. Many drifters stayed in the area off Louisiana and Mississippi, where they were deployed, some went to the western Gulf and a few drifters came out through the Straits of Florida. In fact, one of my colleagues at the University of Miami actually picked up a drifter that had washed ashore!

But LASER was much more than that. GLAD had 300 drifters overall; LASER had over 1,000 biodegradable drifters that we deployed over several experiments; two large dense deployments and several smaller, targeted deployments for specific purposes. Also, this time around, we added more localized observations with the bamboo plates, and we had a more comprehensive suite of other measurements, including hundreds of miles of temperature and salinity sections from a towed instrument, about 500,000 very detailed images of the sea surface temperature field taken from aircraft, wave data from an X-band radar, and measurements of vertical motion from 3D Lagrangian floats.

Q: What caused the drifters to move so quickly?

Huntley: There are some strong ocean currents in the Gulf of Mexico, and a portion of our drifters got caught up in one of these systems. Also, multiple strong atmospheric fronts passed through the area during the fieldwork, which had an effect on the drifter distribution. It was a successful experiment that provided us a better idea of how the dispersion might vary in this surface layer of the ocean, depending on the season.

Q: Why is the surface layer of the ocean important?

Huntley: Oil really concentrates in a very thin layer at the ocean surface, on the order of microns to a few centimeters thick. To mimic this, the researcher team tossed roughly 10,000 biodegradable bamboo plates into the ocean over several experiments to represent oil floating on the surface. Then, we took pictures with a camera mounted on a helium-filled balloon, called an aerostat, tethered to the ship. By combining these images with geographic coordinates, we hope to trace individual plates to learn more about the plates’ velocity over time.

Q: Why are the bamboo plates’ movements of scientific interest?

Huntley: It tells us something about what happens to material that floats on the ocean surface, and hopefully, on analysis, we can gain insight into the physics that drives this activity and verify that what we see in the models is realistic compared to what actually happens on the ocean surface.

Q: What else did you look at?

Huntley: We also added a focused sampling of a specific water feature in one of the smaller deployments. In this case, we targeted an oceanic front, a boundary in the ocean with water of different temperature and/or salinity from one side to the other.

The classic picture that oceanographers have is that oceanic fronts collect drifting objects in the ocean and then spread the objects out along the front. In our experiment we observed the drifters collect in clusters and then break up and separate into new clusters, consistent with the theory. It’s great to have data that we can analyze to get a better understanding of the mechanisms and time-scales involved.

Q: Does the work you are doing only apply to oil?

Huntley: While the overarching goals of the project are motivated by having a planned response in the event of another oil spill, the models can apply to anything that floats on the surface of the water. One example might be using these same techniques to understand where plastic comes from in the ocean, how it travels and where it ends up. At the same time, the Coast Guard uses drift data during search and rescue operations, and oceanographers use models to track algae and their blooms and how they spread out. So, drift predictions are important for all kinds of applications.

If we can better understand the physics of what’s happening in the Gulf of Mexico, we can apply the information in our models to other areas of the ocean. The characteristics that result from the local conditions would be different, but the underlying physics would be the same.

About LASER and CARTHECARTHE researchers returned to the Gulf of Mexico in January-February 2016 to conduct the LAgrangian Submesoscale ExpeRiment (LASER). LASER builds upon the vast amount of data that was collected during the 2012 GLAD experiment to understand the small scale ocean currents in the open ocean environment near the DeSoto Canyon, as well as how oil or other pollutants might be transported via these currents.

The largest-scale experiment of its kind, LASER brought together an unprecedented collection of aircraft surveillance, remote sensing, real-time data-assimilating models, and advanced Lagrangian transport analysis methods operating in unison in order to guide massive Lagrangian sampling (with up to 1000 drifters and 10,000 drift cards) of upper ocean processes controlling transport of hydrocarbons in the environment.

The research was made possible by a grant from the Gulf of Mexico Research Initiative (GoMRI). The GoMRI is a 10-year, $500 million independent research program established by an agreement between BP and the Gulf of Mexico Alliance to study the effects of the Deepwater Horizon incident and the potential associated impact of this and similar incidents on the environment and public health.

The CARTHE program includes over 43 principal investigators from 27 universities and research institutions, including ten from Gulf of Mexico states, and three new international partners. Together these scientists are engaged in novel research through the development of a suite of integrated models and state-of-the-art computations that bridge the scale gap between existing models and natural processes.

About UD’s College of Earth, Ocean, and EnvironmentUD’s College of Earth, Ocean, and Environment (CEOE) strives to reach a deeper understanding of the planet and improve stewardship of environmental resources. CEOE faculty and students examine complex information from multiple disciplines with the knowledge that science and society are firmly linked and solutions to environmental challenges can be synonymous with positive economic impact.

The college comprises the School of Marine Science and Policy, Department of Geography and Department of Geological Sciences.

CEOE brings the latest advances in technology to bear on both teaching and conducting ocean, earth and atmospheric research. Current focus areas are ecosystem health and society, environmental observing and forecasting, and renewable energy and sustainability.