Hydrocarbons and petroleum are almost synonymous in environmental science. After all, oil reserves account for nearly all the hydrocarbons we encounter. But the few hydrocarbons that trace their origin to biological sources may play a larger ecological role than scientists originally suspected.
A team of researchers at UC Santa Barbara and Woods Hole Oceanographic Institution investigated this previously neglected area of oceanography for signs of an overlooked global cycle. They also tested how its existence might impact the ocean’s response to oil spills.
“We demonstrated that there is a massive and rapid hydrocarbon cycle that occurs in the ocean, and that it is distinct from the ocean’s capacity to respond to petroleum input,” said Professor David Valentine(link is external), who holds the Norris Presidential Chair in the Department of Earth Science at UCSB. The research, led by his graduate students Eleanor Arrington(link is external) and Connor Love(link is external), appears in Nature Microbiology(link is external).
In 2015, an international team led by scientists at the University of Cambridge published a study demonstrating that the hydrocarbon pentadecane was produced by marine cyanobacteria in laboratory cultures. The researchers extrapolated that this compound might be important in the ocean. The molecule appears to relieve stress in curved membranes, so it’s found in things like chloroplasts, wherein tightly packed membranes require extreme curvature, Valentine explained. Certain cyanobacteria still synthesize the compound, while other ocean microbes readily consume it for energy.
Valentine authored a two-page commentary on the paper, along with Chris Reddy from Woods Hole, and decided to pursue the topic further with Arrington and Love. They visited the Gulf of Mexico in 2015, then the west Atlantic in 2017, to collect samples and run experiments.
The team sampled seawater from a nutrient-poor region of the Atlantic known as the Sargasso Sea, named for the floating sargassum seaweed swept in from the Gulf of Mexico. This is beautiful, clear, blue water with Bermuda smack in the middle, Valentine said.
Obtaining the samples was apparently a rather tricky endeavor. Because pentadecane is a common hydrocarbon in diesel fuel, the team had to take extra precautions to avoid contamination from the ship itself. They had the captain turn the ship into the wind so the exhaust wouldn’t taint the samples and they analyzed the chemical signature of the diesel to ensure it wasn’t the source of any pentadecane they found.
What’s more, no one could smoke, cook or paint on deck while the researchers were collecting seawater. “That was a big deal,” Valentine said, “I don’t know if you’ve ever been on a ship for an extended period of time, but you paint every day. It’s like the Golden Gate Bridge: You start at one end and by the time you get to the other end it’s time to start over.”
The precautions worked, and the…