Research on sea ice may inform spill cleanup strategies

Although sea ice is often thought to block the flow of oil through ocean water, a team of researchers at the University of Alaska Fairbanks is studying how oil can percolate into ice. This has implications for the methods and policies used to clean up oil spills in the Arctic.

“Ice has always been considered a physical barrier to oil,” said Kyle Dilliplaine, a master’s student at the School of Fisheries and Ocean Sciences. Many oil cleanup crews even think of ice as an aid to cleanup. A lot of policies are built on the ease of cleaning up the oil when it gets ‘corralled’ by sea ice. But the science is not always behind it. It’s not that easy.”

Dilliplaine is studying how microscopic organisms within sea ice affect the ability of oil to flow into the ice, in collaboration with SFOS Assistant Professor Eric Collins, International Arctic Research Center Professor Hajo Eicken, and SFOS Affiliate Faculty Rolf Gradinger and Bodil Bluhm. They artificially grew sea ice in experimental chambers filled with seawater and added tiny organisms, or biota, to the ice. Then they “spilled” oil in the water under the ice to see how the oil could spread.

A horizontal cross section of a chunk of ice shows how oil can percolate into channels and pores. Photo by Kyle Dilliplaine.

The researchers have three years of funding from the Coastal Marine Institute through the Bureau of Ocean and Energy Management.

Sea ice is not solid like river or lake ice. When salt water freezes, freshwater crystals form, leaving the salts behind in liquid brine. Seawater brine can be seven times the salinity of normal seawater. As the ice continues to grow, some of this brine forms channels that drain into the ocean at the bottom of the ice, and some brine remains inside the ice. Biota living within the brine channels create mucus to protect themselves against the cold, salty liquid. Mucus production is thought to block some of the brine from draining from the ice, which increases the number of brine channels and quantity of liquid in the ice. This makes the ice even more porous.

Oil can flow into the brine channels and into the pores around ice crystals. “When the sea ice is more porous because of these microbes, oil just has to overcome a little pressure to get through that first layer,” said Dilliplaine. The more porous sea ice is, the easier it is for oil to percolate in.

Thin layers of oil directly under sea ice can also get incorporated into growing ice. The ice may simply grow crystals around the oil, trapping the oil inside the ice structure.

Cleanup crews use a combination of radar and remote sensing technology to detect oil in arctic water. In a nearshore environment, where water motion is more predicable, it is common to cut holes in the ice and use plywood slots as a barrier to prevent oil from spreading underneath the ice, explained Jessica Starsman, an environmental protection specialist with the Alaska Department of Environmental Conservation. Oil removal can involve a combination of skimming oil from the surface, using dispersants to break down oil and burning the oil from the surface.

These methods can be effective at removing oil from the surface of the water, but do not address oil that remains inside the sea ice.

Researchers are just beginning to study the ability of oil to remain in sea ice for longer than one winter season. When oil layers get incorporated into new, growing ice, it is often assumed that this ice will melt in the spring, releasing the oil back into the water. Additionally, oil trapped inside of sea ice is often not a top priority for cleanup crews because it represents a low proportion of the overall oil in a spill, Starsman said.

Diagram of seawater chambers used to conduct the study. Each of the letters represents a feature used to help regulate salinity and ice formation in the chamber. A = LED light; B = data logger; C = thermistor string; D = salinometer/temperature probe; E = photosynthetically active radiation (PAR) sensor; F = pump; G = heater; H = pressure release bladder.

At UAF, Dilliplaine and SFOS student Mark Oggier built chambers that are one meter tall and 60 by 60 centimeters on the sides. The researchers made seawater using a product available for home saltwater aquariums. Next, they slowly grew ice at the top of the chambers. Dilliplaine explained that this process required a number of components—to maintain constant salinity, each chamber had an antifreeze bladder to prevent pressure buildup in the tanks, a small pump to maintain consistent temperatures in the tank and prevent uneven ice buildup, and a heater to prevent too much ice from crystalizing in the chambers.

Sea ice biota were extracted from about 200 ice core samples taken near Barrow, Alaska. Getting the biota to inhabit the ice proved challenging. Initially, Dilliplaine drilled some holes in the ice and put the biota on very fine ice crystals in the water near the surface of the ice. The biota was unable to move as more ice crystalized, and the organisms became trapped in the new ice. On the second attempt, he created a biota slush of water and ice, which he placed just underneath the ice in the chamber.  The slush combination was successful in getting organisms to slowly establish on the ice, while preventing them from freezing into the ice altogether.

To simulate a continuous-flow oil spill, Dilliplaine pumped oil into the water and let it pool underneath the ice. To represent oil dispersal by wave action, he placed a small pump under the ice that blew out oil droplets slowly over time.

Dilliplaine found that the oil inhibited the growth of algae and mucus production. “In the control tank with no oil, we saw a 30-fold increase in the amount of algal pigment—which is often used as a indicator for quantifying the mass of algae on ice—from the beginning to the end of the experiment,” he said. Algal pigments like the chlorophylls are capable of absorbing ultraviolet light, allowing the algae to photosynthesize.

Kyle Dilliplaine checks on his sea ice chambers in the cold, dark room where all of the study's lab work took place. Photo by Marc Oggier.

However, bacteria production remained relatively constant.  Dilliplaine speculates that there was likely a die-off of existing bacteria alongside an increase in oil-degrading bacteria, which would thrive after the spill. He plans to do additional genetic testing to learn about how the composition of bacteria on the ice may have changed.

Sea ice cover in the Arctic Ocean is projected to continue to decrease. This will increase the variability of sea ice motion as well as ship traffic, both of which are likely to increase the number of marine accidents in the Arctic. Understanding the influence of sea ice on the motion of spilled oil will become increasingly crucial as the potential for arctic spills increases. Dilliplaine stressed the importance of understanding that ice is not a barrier to oil movement. “We can’t think about the ice as a physical barrier that can help us with our cleanup. It might actually be working pretty far against us.”

ADDITIONAL CONTACT:

Kyle Dilliplaine, 412-926-2872, kbdilliplaine@alaska.edu

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