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UVic Scientist helps us understand the tiny Arctic organisms at the base of the food web

Diana Varela, professor of biology at the University of Victoria
Diana Varela, professor of biology at the University of Victoria, is a global expert in phytoplankton, the micro-organisms at the base of the food web

For twenty years, Diana Varela has been exploring the Arctic – revelling in the views from the decks of icebreakers doubling as research vessels.

“Standing on the ice at 84° North gives a sense of the unknown, the extremes,” says the University of Victoria biological oceanographer. “It’s very appealing to me. The sense of discovery, of awe, is unbeatable.”

But while the views are a bonus, the real reason Varela is there is to dip deep into the circumpolar seas to learn more about diatoms. The single-celled organisms are part of the larger phytoplankton group, the free-floating algae that are the foundation of marine food webs and responsible for 50 per cent of all carbon captured by photosynthesis and for producing half of the oxygen in our atmosphere. Diatoms, as part of that group, are responsible for about 20 per cent of all carbon taken up and oxygen produced on Earth.

“Diatoms are unique,” she says, “because their cell cover is largely silicon, the most abundant element in the Earth’s crust after oxygen.”

The microscopic engines of life on earth

A particular isotope, silicon-32, gives her a very accurate way to measure the population growth and characteristics of some of the thousands of diatom species. Varela, arguably the pre-eminent marine silicon-32 scientist in Canada and one of a handful in the world, is able to correlate her findings about diatoms to their environments.

“Phytoplankton productivity, how many of the creatures there are and how efficiently they conduct their carbon/oxygen processes," she explains, "can vary with time of year, nutrient levels, grazing by zooplankton, ice cover and also by climate-induced changes such as ocean acidity."

Detecting change in Arctic waters

So Varela and her students collect water samples from places like the Bering and Chukchi seas of the Pacific Arctic and the Atlantic sector of the Arctic Ocean north of Svalbard, as well as the Antarctic and Galápagos. They measure diatom content to learn how many individual organisms are there, how much carbon dioxide they use and which of 200,000 species they belong to. With 20 years of data, the scientists are seeing some trends.

Norwegian research vessel Kronprins Haakon sits in the ice n the ice north of the Arctic Circle
Norwegian research vessel Kronprins Haakon in the ice north of the Arctic Circle

What happens when diatoms decline?

Under the ice north of Svalbard last May, for example, numbers were unexpectedly low for the time of year, which meant fewer nutrients for animals further up the food chain. On the other hand, the shallow waters of the Bering and Chukchi seas are generally very productive in the spring, so they’re high-nutrient feeding areas for whales, fish, birds and other animals. However, Varela’s research is showing a trend; even in the North Pacific, she's seeing a decrease in diatom biomass and more smaller organisms compared to larger ones.

This is significant because it means less food for the whole marine ecosystem. It also signals changes to ocean chemistry with potential links to the climate. When diatoms die, they drift to the sea floor, carrying with them the carbon that their cells naturally contain. In the near term, this stores carbon out of the atmosphere. Over geologic-scale time periods though, these sediments have become petroleum deposits which have long attracted interest for their use as fuel.

Following the science from Svalbard to the Galápagos

Varela regularly collaborates with Fisheries and Oceans Canada and other Canadian scholars along with international partners in Norway, Argentina, France and the US. Her reputation earned her berths on Canada’s Three Oceans expedition during the 2007 International Polar Year, Geotraces Arctic cruises in 2009 and 2015 and the Canada C3 (Coast to Coast to Coast) in 2017, among many others over the past two decades. 2025 was doubly busy with the University of Tromsø-led trip north of Svalbard in the spring, quickly followed by a Galápagos expedition in August.

“My students and I study the Arctic a lot because that's where many research opportunities are to understand how phytoplankton and diatoms thrive under changing oceanic conditions,” Varela says. “When you start going to these places, they're fascinating. You get enthralled.”

 

Rachel Goldsworthy