Saanich Inlet research sheds new light on ocean dead zones

Oceanographers from around the world are hoping to learn more about the science of “dead zones,” thanks to a University of Victoria-led research project currently taking place in Saanich Inlet near Victoria.

Every two weeks since September, a research team on the UVic research vessel MSV John Strickland has been venturing into the inlet to collect water samples at various depths—roughly 300 litres per day—to measure the levels of everything from dissolved gases and trace metals to phytoplankton and microbes.

Because of the inlet’s unique topography—it’s a deep glacial fjord separated from adjacent waters by a shallow sill that restricts water inflow—it’s widely known as a natural laboratory for studies of “anoxic” or dead zones, areas in the ocean that are devoid of oxygen and marine life. The only lifeforms that can exist there are bacteria.

“The inlet is a natural dead zone, meaning it has low to no oxygen content for most of the year,” says Jeff Sorensen, a postdoctoral researcher in the School of Earth and Ocean Sciences. “We’re seeing dead zones expanding around the world, and that changes what species are able to live there, including a lot of fish and shellfish that people depend on to eat.”

While Saanich Inlet remains anoxic for much of the year, every fall water flows in over the sill and replenishes the oxygen supply. Marine life flourishes for a few months, but wanes again as the water’s oxygen content gets used up.

“In other locations where this kind of water exists there is no renewal process—there’s consistent anoxic water. That’s why Saanich Inlet is so perfect for study,” says Sorensen. “We know there’s a cascade of chemical reactions that happen as the oxygen is used up. We want to see how these reactions evolve over time and how they interact with each other.”

“Our main goal is to compare all these measurements to understand what happens over the course of the year as the oxygen content in the inlet changes,” says Roberta Hamme, a chemical oceanographer at UVic and lead investigator for the project.

Although the inlet’s anoxic conditions have been well-studied in the summer months, little work has been done in the winter. This project, which runs until next May, marks the first time that a wide range of measurements are being taken over the duration of the oxygen depletion process.

International interest 

About 30 researchers from UVic are involved, including graduate and undergraduate students. Local partners are Fisheries and Oceans Canada in Sidney and UVic’s Ocean Networks Canada, which is providing real-time data in between cruises from an instrument connected to its first internet-connected subsea observatory, installed in the inlet in 2006. The water samples are being collected close to that instrument.

Scientific interest in the project is international, with 20 research groups from Switzerland, Ireland, England, Spain, Brazil, the US and elsewhere in Canada signed on for water samples. “These are all world experts in their field who don’t have easy access to a natural dead zone like this,” says Sorensen.

The work is expected to shed new light not only on how dead zones evolve but on the role they play in climate change. Ironically, dead zones are more efficient at storing organic carbon in their depths, keeping it away from the atmosphere where it contributes to global warming.

“We need to understand the chemical reactions going on in these zones in a way that would allow us to model them and make predictions about what the future holds as these oxygen-poor zones around the world expand and have even greater anoxia,” says Hamme.

The project is funded by the Natural Sciences and Engineering Research Council.