The Link Between the Southern Ocean and Climate Change

To investigate the interplay between climate change and the ocean, Irina Marinov, an assistant professor in the Department of Earth and Environmental Science, focuses her attention on the Southern Ocean, the waters that encircle Antarctica.

Though sometimes overlooked by scientists, the Southern Ocean below the 30th parallel takes up more than 60 percent of the anthropogenic heat produced on Earth and 40 to 50 percent of the anthropogenic carbon dioxide penetrating into the oceans.

“The Southern Ocean is emerging as being very, very important for regulating climate,” Marinov says.

In a recent line of work, Marinov and colleagues focused on one of the ocean’s deepest currents, called the Antarctic Bottom Waters. Acting as a conveyer belt around 6,500 feet below the surface, these bottom waters channel heat, carbon, oxygen, and nutrients from the Southern Ocean to oceans around the globe. The massive current has been shrinking in recent decades. Because the current “hides” heat and carbon from the atmosphere, climate scientists have feared that its slow-down could have repercussions for global warming.

Marinov and colleagues found that the surface of the Southern Ocean has become less salty over the last 60 years. And whereas the ocean has always been somewhat stratified, with deeper waters being saltier and denser, they found that these gradients had become more extreme over time.

Marinov explains that increased precipitation around Antarctica—a consequence of climate change—has made the ocean surface waters fresher, and thus less dense. These lighter waters are less prone to move down through the water column and mix with deeper waters.

The researchers’ models also point to some concerning implications for the future. A handful of the models indicate that growing levels of Southern Ocean fresh water could stop convection from occurring at all by 2030, and most of the models suggest convection will slow, reducing formation of the Antarctic Bottom Waters.

“This is worrisome,” Marinov says, “because if this is the case, we’re likely going to see less uptake of human-produced, or anthropogenic, heat and carbon dioxide by the ocean, making this a positive feedback loop for climate change.”

Marinov is involved with a new endeavor that will hopefully facilitate data collection from the farthest reaches of the Southern Ocean, allowing for more informed climate projections.

In this project, researchers will add special sensors to small, remotely controlled floats that dive deep into the ocean and resurface, transmitting information about the ocean’s conditions to scientists working thousands of miles away via satellite. In another effort, Marinov and colleagues hope to better understand how phytoplankton—tiny organisms that live at the ocean’s surface—figure into the ocean-climate picture.

“These new techniques will allow us to get essentially a global map of ocean biology and help us answer some important questions about how phytoplankton responds and contributes to fluctuations in climate,” she says. “Right now our models are way ahead of our ability to collect data, but we’re starting to catch up.”

Text by Katherine Unger Baillie
Video by Chip Murphy