Talk like an … Arctic oceanographer

Ocean circulation — the large-scale movement of water in the ocean, determined by wind, density and the Earth’s motion around its axis, that transports heat, freshwater, nutrients and carbon both at and below the surface

Ocean turbulence — small-scale, intermittent and patchy movements of water in the ocean that irreversibly mix water properties like heat and salt

Ocean acidification — as the ocean absorbs more carbon dioxide from the atmosphere, its pH level is reduced, causing it to become more acidic

The Arctic Ocean is undergoing rapid change as the climate warms. Sea ice, which in the past covered most of its surface in both winter and summer, is shrinking significantly, allowing the ocean to absorb more heat from the sun. Freshwater from rivers, rain and melting glaciers is entering the Arctic Ocean at a growing rate, and, at the same time, its deep waters are heating up as warmer waters enter from the Atlantic and Pacific Oceans.

These changes are affecting how heat and freshwater are stored and transported inside the ocean, with important implications for Arctic Ocean ecosystems, the people who live in the Arctic region and global climate. Understanding the fate of the Arctic Ocean’s increasing stores of heat and freshwater is key to understanding how the system will change in the future.

For much of her career, Professor Stephanie Waterman from the University of British Columbia has been working to improve our understanding of how the ocean mixes. “Ocean turbulence is responsible for the irreversible mixing of seawater,” says Stephanie. “Quantifying how ocean turbulence mixes heat, salt, dissolved gases and nutrients is key to understanding how it works.”

Measuring ocean turbulence

Stephanie uses autonomous ocean-observing robots called ocean gliders to measure turbulence in the ocean. “We equip our gliders with specialised sensors that can make rapid and sensitive measurements of small fluctuations in ocean motion that give us information about ocean turbulence,” she explains. “Our gliders can map these and other ocean properties over an extended area at a high level of detail, resulting in beautiful pictures of ocean structure.”

Ocean gliders don’t have motors; instead, they adjust their buoyancy to rise and sink through the water, using fixed wings to convert some of this vertical motion into horizontal motion. This type of propulsion requires minimal power, so gliders can collect data over long periods of time and large distances. Moving the glider in this way also reduces vibrations, making gliders extremely quiet platforms and allowing them to observe tiny fluctuations in ocean properties. “This is key to ensuring that we are measuring the turbulence of the ocean, rather than the motion of the glider,” explains Stephanie. “It allows gliders to detect extremely low levels of turbulence, like those we often see inside the Arctic Ocean.”

Stephanie’s glider is pre-programmed to navigate to specified locations using an internal compass, surfacing at set times to transmit the collected data and receive updated instructions from Stephanie and her team back home via satellite communication. “The mission can be adapted in real-time based on what the glider is seeing or changing conditions, like storms or drifting sea ice,” explains Stephanie.

The Beaufort Gyre

The Beaufort Gyre is an enormous swirl of polar water that holds much of the freshwater released into the Arctic Ocean. “The freshwater stored in the Beaufort Gyre is periodically released into the North Atlantic Ocean, where it impacts important ocean processes,” says Stephanie. “These processes form much of the Earth’s deep ocean water and drive global ocean circulation that transports water and heat around the globe.”

Every summer, researchers from the Joint Ocean Ice Study (JOIS) and Beaufort Gyre Observing System (BGOS) programme travel aboard a research vessel, the Canadian Coast Guard Ship (CCGS) Louis S. St-Laurent, on an expedition to collect water samples and make observations of ice and ocean properties in the gyre. They also deploy and maintain autonomous instruments that remain in the water and take samples year-round. For example, ice-tethered profilers are buoys that are anchored to, and drift with, the sea ice. Below the ice, a sensor travels up and down a wire to a depth of 750 metres multiple times a day making measurements of the water properties. The data recorded are then reported back to shore via satellites.

The JOIS/BGOS programme has been making these observations since 2003. “To understand how this important system works, and how and why it is changing, we require consistent and regular measurements of a variety of parameters at similar locations year-after-year,” explains Stephanie. “The measurements taken by the JOIS/BGOS programme allow us to understand decades-long changes to the structure of the Beaufort Gyre. This understanding of how the system is changing on these timescales is critical in helping us better predict how it will change in the future.”

In the summer of 2024, JOIS/BGOS scientists deployed Stephanie’s glider at the beginning of their expedition and collected it at the end, several weeks later. During that time, the glider made near-continuous measurements of ocean turbulence within the gyre.

What has Stephanie learnt about the Arctic Ocean?

“Our glider observations in the Beaufort Gyre give us important insights into how mixing in the Arctic Ocean differs from mixing in the lower-latitude oceans,” explains Stephanie. In general, the Arctic Ocean is much less turbulent than other oceans. As a consequence, heat stored in the water column tends to remain at depth and not be transferred to shallower waters and the sea ice above. “However, the near-continuous observations of the glider allowed us to catch a small number of patchy and intermittent turbulent mixing events that are responsible for most of the mixing of heat and salt that we observe,” continues Stephanie.

Stephanie’s work is a small part of a much larger effort to document and understand climate change in this region. The JOIS/ BGOS programme has observed and studied significant changes in all elements of the Beaufort Gyre system over the last two decades. “Significant sea ice losses have been accompanied by an intensification of the Beaufort Gyre circulation and a significant increase in both the heat and freshwater stored in the gyre,” says Stephanie. “The programme has also documented changes in biological productivity, increases in ocean acidification and a marked decrease in dissolved oxygen.”

Communicating the impacts

Stephanie believes that communicating research findings to a wide variety of stakeholders is a vital part of her role as an environmental scientist. “Information about how the environment is changing is critical to people who live in the region and are dependent on the environment for their livelihood, safety and culture,” explains Stephanie. “It is also critical to people everywhere, as changes in the Arctic region highlight the magnitude of humans’ impact on the climate system and the urgency to act to address human-caused climate change.”