Video: Underwater thickness comparison

The fate of oil during the first day after an accidental oil spill is still poorly understood, with researchers often arriving on the scene only after several days. New findings from a field experiment carried out in the North Sea provide valuable insight that could help shape the emergency response in the immediate wake of disasters.

It is well known that oil and water don't mix. Less well known is the fact that when petroleum is spilled onto a water surface, a fraction of the oil immediately begins to evaporate into the air or dissolve into the seawater. These dissolved toxic hydrocarbons can threaten aquatic species, while evaporated compounds may pose a risk to rescue workers or populations downwind of an accident site. Publishing in the journal Environmental Science & Technology, a team of European and American researchers report on a unique study focused on the fate of hydrocarbons during the 24 hours that follow an oil spill.

Following a spill, oil suddenly finds itself in a radically new environment -- exposed to light, air, and the water surface after millions of years underground. "In its new environment, the oil immediately begins to change its composition, and much of that change happens on the first day," explains Samuel Arey, a researcher at EPFL and Eawag in Switzerland and corresponding author of the study. Oil is a complex mixture of many hydrocarbon compounds. Certain volatile compounds evaporate within hours, contaminating the overlying atmosphere. Others, such as toxic naphthalene, simultaneously dissolve into the seawater, posing a threat to aquatic life. Especially since the Exxon Valdez catastrophe in 1990, which released over 40,000 cubic meters of oil into the ocean, researchers have sought to evaluate to what extent marine species in the vicinity of an oil spill are exposed to toxic hydrocarbons. But this question has largely remained debated, because many of the hydrocarbons are dispersed into the water or the overlying air well before scientists arrive at the site.

In order to collect data on the immediate aftermath of an oil spill, the researchers collaborated with emergency response specialists of the Dutch Rijkswaterstaat to recreate a four cubic meter oil spill in the North Sea, in a shipping zone already burdened by pollutants, 200 kilometers off the coast of the Netherlands. By studying this relatively small oil release, they were able to gain a better understanding of what goes on in much larger spills, with findings that could be useful to assess the risks to underwater life, as well as to emergency response team workers at the sea surface.

No two oil spills are alike. Aside from the sheer volume of oil released onto the sea surface, the environmental impact of an oil spill depends on external factors, such as the wind, waves, and the temperature of the air and the water. The North Sea experiment, for instance, was carried out on a summer day with two-meter high waves. Within just over a day, the surface oil slick had almost dissipated. On a cooler day with less wind and smaller waves, the slick would have likely persisted longer.

Thanks to a computer model that was tested against the data collected in the North Sea, the researchers are now able to extrapolate their findings to larger spills and other environmental conditions. Results from the study will provide the researchers with tools to better assess the immediate impact of future disasters on humans and on the environment, as well as to plan the emergency response, even in settings that differ strongly from those encountered in the North Sea.

Source:  Public release, August 9, 2014.  Ecole Polytechnique Federale de Lausanne

A recent study investigated how surface waves contribute to the fate of plankton.  For the numerical modelling experiment, Deep-C researchers picked an example particle and region that is accessible for measurements in the field, and easy to model -- Northeast Arctic Cod eggs and larvae. While some of the results are specific for this species, the main results apply to all buoyant particles in the upper ocean (i.e. plankton and oil droplets) and to all regions wherever surface waves are present. By considering wave effects for particle transport and vertical mixing, the Deep-C researchers found that waves modified the fate of cod eggs by moving the buoyant particles closer to shore in the long term. They hypothesize that this mechanism also acts to concentrate biomass and pollutants, increasing their contact rates. Breaking waves are also responsible for mixing particles downwards, thereby flattening the vertical profile of particle concentrations. Understanding the involved processes for transport of plankton and oil in the upper ocean will hopefully serve our efforts to model oil spill accidents and impacts on the ecosystem. 

Reference:  Rohrs, J., Hakon Christensen, K., Vikebo, F., Sundby, S., Saetra, O., & Brostrom, G. (2014). Wave-induced transport and vertical mixing of pelagic eggs and larvae. Limnol. Oceangr., 59(4), 1213-1227.

Each summer, exciting scientific internships are available in a variety of fields studied by National Oceanic and Atmospheric Administration (NOAA) and Northern Gulf Institute (NGI) scientists including coastal science, fisheries management, climate change, ecosystem management, engineering and socio-economic data analysis. The NOAA-NGI Diversity Internship Program offers students from all scientific disciplines (including biological, physical, environmental, information, computer and social sciences as well as environmental justice), as well as education and engineering, are eligible for these competitive positions.

"Selected students work side-by-side with leading scientists and experts in their fields at their respective research institutions and laboratories," says Dr. Tina Miller-Way, Internship Program PI and Chair of the Discovery Hall Program at the Dauphin Island Sea Lab (DISL). "These internships offer a unique opportunity for on-the-job learning and enable students to explore career opportunities that match their academic and personal interests."

The NOAA-NGI Diversity Internship Program has been in existence since 2008: DISL has been the home of the program since 2010. To date, the program has hosted 64 interns at 18 locations across the northern Gulf.

This summer, the Deep-C Consortium is supporting two students selected for participation with scientists Drs. Richard Snyder (University of West Florida) and James Nienow (Valdosta State University) acting as their mentors and facilitating the interns' research:

Cynthia Kane (at left) interning at the University of West Florida used several microbiology techniques including polymerase chain reactions (PCR), gel electrophoresis, and clonal library creation to analyze water and sediment samples collected from the Gulf of Mexico to determine the different types of Archaea present. To learn more, read Cynthia's blog.

Chris Horruitiner (at right) interned at Valdosta State University (GA) to investigate the impacts of the Deepwater Horizon event on the phytoplankton populations in the DeSoto Canyon region of the northern Gulf of Mexico. Chris used a combination of net plankton samples (across the entire water column), pigment samples (for HPLC), and discrete Niskin bottle water samples from several depths across the water column analyzed using SEM and imaging flow cytometry to address how phytoplankton populations change with depth and with season in this area. To learn more, read Chris' blog.

NOAA-NGI internships last 10 weeks and are open to undergraduate and graduate students currently enrolled in a degree-granting program. There is an emphasis on selecting students from communities and institutions in the northern Gulf of Mexico region, and individuals from demographic groups underrepresented in the NOAA workforce are especially encouraged to apply. Visit the DISL website for information about future NOAA-NGI internship opportunities.