Antarctica’s Southern Ocean comprises approximately 10 percent of the total oceans and is home to some of the most rare, vulnerable, and critical ecosystems in the world. Millions of penguins call this place home, as do seabirds, fish, seals, whales, and the region’s keystone species, krill. This invertebrate is vital prey to many of the other species and acts as a major carbon sink for the Southern Ocean, sequestering 23 million tons of carbon each year.
Scientists have shown that the region is vital to marine life far from the icy continent: upwellings and currents pull nutrient-rich waters from deep in the Southern Ocean and transport them to distant ecosystems.
But this essential ecosystem is under threat due to climate change and fishing activities. Now, on the 60th anniversary of the signing of the Antarctic Treaty—which directly led to the creation of the Commission for the Conservation of Antarctic Marine Living Resources (CCALMR) and launched the effort to conserve marine life in the Southern Ocean—six studies show the urgency of continuing that mission.
Emperor penguins likely to go extinct
Antarctica is home to millions of emperor penguins but may not be for long: The rapid warming of the Southern Ocean region, driven by climate change, could render them extinct by the end of the century, according to a study led by seabird ecologist Stephanie Jenouvrier and published in Global Change Biology. The rise in temperatures is melting sea ice, which emperor penguins use to access open water so they can find food for their chicks.
“If global climate keeps warming at the current rate, we expect emperor penguins in Antarctica to experience an 86 percent decline by the year 2100,” says Jenouvrier. “At that point, it is very unlikely for them to bounce back.”
Krill range shrinking due to climate change
Because of krill’s importance to the Southern Ocean, any change in the population is cause for concern. A study by Angus Atkinson and an international group of researchers analyzing 90 years of data, published in the journal Nature Climate Change, found that the center of the krill population near the Antarctic Peninsula has shifted about 440 kilometers (nearly 275 miles) southward, and that the number of juveniles has dropped since 1970. This news has huge implications: As warming waters and sea ice loss force krill to retreat toward the continent—where the landmass blocks further southward movement—their available habitat decreases, which might lead to further drops in their numbers, and cascading impacts on the entire Southern Ocean food web.
As krill decline, so might predators
Climate change could also reduce krill biomass, or the total weight of krill, and the abundance of their predators in some areas of Antarctica’s Scotia Sea and off the Antarctic Peninsula, according to a study published in the journal PLOS One.
Led by Emily Klein, the authors looked at how this reduced krill biomass might affect penguins, seals, whales, and fish that feed primarily on krill. The study found that penguins were the most sensitive to such changes, and projected that future warming would cause penguin abundance to decline by up to 30 percent in the Antarctic Peninsula and Scotia Sea region.
The team also found that current rates of krill fishing further threaten some predators.
Mass die-off of Adélie penguin chicks
A study in Frontiers in Marine Science showed that, out of thousands in a colony of Adélies in the D’Urville Sea/Mertz region of East Antarctica, no chicks survived the 2013-14 breeding seasons and only two survived the 2016-17 season, largely because the sea ice did not recede as it usually does. Adélies nest on land and the unusually large amount of sea ice coupled with uncommon rain events, both of which the authors speculated was due to climate change, meant the penguins had to travel farther to the ocean in search of food. That caused chicks to starve and weakened the parent left behind. These mass die-offs were the only two seen in 40 years of monitoring this colony of about 36,000 individuals.
Krill are a major carbon sink
Krill, as individuals and massive swarms—some of which cover up to 100 square kilometers—play a critical role in the carbon cycle of the Southern Ocean. According to recent research led by Emma Cavan at Imperial College London, krill feed on carbon-filled phytoplankton at the ocean’s surface and then release a “rain” of dense fecal pellets that can sink quickly to the deep sea. This carbon transport can be huge, as carbon that reaches depths of about 800 to 1,400 meters in the Southern Ocean enters deep-water currents, where it remains for decades. Krill also move between shallow and deep areas multiple times daily to feed, which may increase the chance of fecal pellet export deep into the water column.
Krill feeding can also break down plankton cells, releasing nutrients such as iron and ammonium that can stimulate additional plankton growth and facilitate uptake of atmospheric carbon dioxide into the surface layer of the ocean.
Marine reserves proven to help build resilience
Marine protected areas (MPAs) act as climate refugia for wildlife and their habitat, and provide reference zones for scientists studying changes in climate and the impact of industrial fishing. CCAMLR is considering designating three MPAs in the Southern Ocean.
A network of MPAs, combined with an ecosystem-based krill fisheries management system, would provide resilience against the threats affecting the Southern Ocean. The Intergovernmental Panel on Climate Change’s recent report on the ocean and cryosphere (ice-covered regions) supports these solutions. MPAs can preserve biodiversity and the Southern Ocean’s ability to store carbon, while ecosystem-based management of fisheries can help sustain krill—and their predators.
The science is clear. Global leaders need to take action and implement these key solutions.
Andrea Kavanagh directs The Pew Charitable Trusts’ campaign to protect Antarctica’s Southern Ocean.