The Southern Ocean Helps Cool the Planet

The Southern Ocean surrounds the continent of Antarctica and connects with the Pacific, Indian, and Atlantic Oceans via the Antarctic Circumpolar Current (ACC), the world’s strongest ocean current, carrying an estimated 165 million to 182 million cubic meters of water every second, more than 100 times the flow of all the rivers on the planet. The ACC acts as the natural barrier between the relatively warmer waters of these oceans and the seasonally sub-zero waters of the Southern Ocean, essential for maintaining Antarctica’s icy temperatures and its unique population of endemic wildlife. Just as important, this current also allows the Southern Ocean to absorb heat from the waters coming in from the North Atlantic before circulating it back north, a vital process which regulates the earth’s climate. According to NASA scientists, the world’s oceans absorb 90% of the anthropogenic heat produced on Earth. The Southern Ocean alone is responsible for 60% of this ocean heat uptake, due in part to the strong westerly winds virtually uninterrupted by landmasses.

The Southern Ocean is an Immense CO2 Sponge

In addition to trapping excess heat, the Southern, observations from NASA research aircraft show that the Southern Ocean absorbs much more carbon from the atmosphere than it releases, making it a very strong carbon sink and an important buffer for some of the effects of human-caused greenhouse gas emissions.

When CO2 emissions enter the atmosphere, some of that gas is absorbed by the ocean. The cold waters of the Southern Ocean rise to the surface through a process called upwelling, absorbing the carbon before sinking again.

This conveyor belt of carbon from the surface to the ocean depths is helped along by the abundant marine wildlife inhabiting the Southern Ocean. According to new findings published recently (2019) in Nature Communications by scientists from the NOC and the British Antarctic Survey (BAS), Antarctic krill – which form one of the highest concentrations of animal biomass in the world – feed on the microscopic phytoplankton living near the surface and the underside of the sea ice. After feeding, their carbon-rich feces then sink in the cold waters, efficiently sequestering carbon.

And krill aren’t alone in this process.

The Incredible Biodiversity of Marine Wildlife in the Southern Ocean

Despite its reputation as a harsh environment for humans, Antarctica and the sub-zero waters of the Southern Ocean are home to one of the most biodiverse ecosystems in the world. According to Australian Geographic, the Southern Ocean is in fact home to more than 9,000 known species, many endemic to the region. And new ones are discovered with each scientific expedition.

Like Antarctic krill, many of these species play an important role in sequestering carbon, such as whales, the gentle giants of the Southern Ocean. Although almost hunted to extinction during the 20^th century, whale populations are slowly making a comeback thanks to the end of commercial whaling activities (including Japan’s illegal “scientific whaling” program which Sea Shepherd helped bring to an end in 2018). According to the IMF, the carbon capture potential of whales is “truly startling”.  The great whales accumulate an average of 33 tons of carbon in their bodies during their long lives. When they die, they take that CO2 to the bottom of the ocean, where they also become a food source for other organisms. For comparison’s sake, a tree absorbs only up to 48 pounds of CO2 a year. Unfortunately, populations of some species, such as blue whales, are still just 3% of their previous abundance, showing how protecting their habitat is more important than ever in the fight against climate change.

Whale species found in the Southern Ocean today include blue whales, fin whales, sei whales, Antarctic minke whales, humpback whales, sperm whales, Southern right whales, Cuvier’s beaked whales, and southern bottlenose whales. Other Antarctic cetaceans include several species of orca, hourglass dolphins, and long-finned pilot whales.

The Southern Ocean is home to seven of the world’s 17 penguin species (emperor, gentoo, bridled, chinstrap, Adélie, macaroni, and rockhopper) and six different species of seal (Ross, Weddell, crabeater, leopard, fur, and elephant). There are several dozen species of fish, including icefish and the highly-fished Patagonian and Antarctic toothfish. You won’t find any sharks in the sub-zero Antarctic waters, but there are squid, octopus, and thousands of different invertebrates, such as sponges, sea spiders, scale worms, starfish, and the famously abundant krill.

Antarctic krill are a keystone species in the Southern Ocean ecosystem, serving as the main food source for many species of whales, penguins, seals and sea birds such as Albatross. Fun fact: did you know penguin poop is often pink because of the krill they consume? Similarly, salmon gets its pink color from consuming krill…otherwise its flesh is naturally a greyish color. If you’re eating farmed salmon, you’re also indirectly consuming wild Antarctic krill. Which is bad news for the krill, and for all wildlife in the Southern Ocean.

Major Threats Facing the Southern Ocean’s Biodiversity

Climate change, ocean acidification, and tourism are putting the Southern Ocean’s biodiversity at risk, but there’s no bigger threat to the Antarctic ecosystem than fishing. Now that humans are no longer hunting seals and whales in the Southern Ocean, fishing is the main industry in Antarctic waters, with four main target species: krill, Antarctic toothfish, Patagonian toothfish, and mackerel icefish.

“Precautionary catch limits” were set in the 1990s, but these are outdated and do not take into account climate change and technological advances of fishing vessels, according to scientists. Furthermore, fishing activities are often concentrated in the very same areas where krill predators such as penguins, seals and whales are feeding, as seen in this week’s study published in Ecology where scientists from Stanford show close to 1,000 fin whales foraging near Antarctica while fishing vessels trawled for krill in their midst. “While there are indications that the Southern Ocean whale population is slowly recovering, we should not take this rebound for granted. These whales, and the ecosystems they rely on, face increasing pressures from commercial fishing and climate change,” said study co-author Earle Wilson, assistant professor of Earth system science at the Stanford Doerr School of Sustainability.

Shockingly, there are no laws preventing industrial super-trawlers from seeking out pods of whales feeding on dense patches of krill, then dragging their massive nets right through the middle of them to scoop up the krill by the ton (similar to how tuna fishing vessels used to target dolphins). In addition to practically stealing the food from their mouths, this can result in the whales’ injury or death by becoming entangles in the nets or ship strike.

In 2021 scientists from Stanford already concluded there is no longer enough krill in the Southern Ocean to support recovery of whale populations to pre-whaling numbers, even in the absence of krill fishing. Combined with the warming oceans and acidification, continuing to commercially exploit marine wildlife could be disastrous for the entire Antarctic ecosystem. And yet krill fishing is a booming industry.

According to a report published this January by Global Industry Analysts, the $531-million market for krill oil health supplements is projected to rise to $941 million by 2026, while fish farming (which uses krill as feed) is the world's fastest growing food sector, as global demand for fish is expected to double by 2050. In the face of climate change, do we really want to risk putting additional pressure on krill populations by expanding krill fishing for fish food and omega-3 supplements for humans? Read more about the importance of protecting krill here.

The Southern Ocean and its wildlife are a vital part of the earth’s climate system, so it is essential to protect and preserve it for future generations. Sign up here for our newsletter to get weekly updates from our campaign in the Southern Ocean and take action to protect Antarctica.