Southern Ocean Ecosystem

• Category: Marine and Oceanic Biomes.
• Geographic Location: Antarctica.

• Summary: The Southern Ocean and its surrounding, mostly ice-covered land area are home to an abundance of marine life that thrives on the cold, oxygen-rich waters.

The Antarctic Ocean—or the Southern Ocean, as it is usually known—is approximately 13.7 million square miles (35.5 million square kilometers) in area, or twice the size of the United States. It is the world's fourth-largest ocean. Because of its unique position and characteristics, the Southern Ocean plays a unique role in regulating the global climate.

Encircling the continent of Antarctica, the Southern Ocean is formed by the convergence of the Pacific, Atlantic, and Indian Oceans as they flow together around Antarctica—the coldest, windiest, and driest of all the world's continents. The Southern Ocean encompasses the Amundsen Sea, the Bellinghausen Sea, part of the Drake Passage, the Ross Sea, a small section of the Scotia Sea, and the Weddell Sea. The deepest point of the Southern Ocean is 27,737 feet (8,454 meters) below sea level, at the South Sandwich Trench.

The waters of the Southern Ocean are characterized by the Antarctic Circumpolar Current (ACC), also known as the Wind Drift Current. As it travels eastward at about 5.4 million cubic feet (153 million cubic meters) per second, this current transports a higher volume of water than any other current in the world, amounting to about 100 times that transported by all the world's rivers. The ACC is the only current that encircles the globe. The Antarctic Convergence, the globe-circling region where the ACC waters blend with the somewhat warmer waters of the other oceans, is a band about 20 to 30 miles (32 to 48 kilometers) wide, ranging between 48 degrees south and 61 degrees south.

Fish Species

Even though the land area of the Antarctic is covered with snow and ice, the biome of the Southern Ocean supports a wealth of plant and invertebrate animal life. The most abundant groups of fish in the Southern waters are the Antarctic cod and the ice fish, and research tends to concentrate on these two species.

Upwelling currents Within the Southern Ocean cause rich nutrients to be pulled up from the seabed to the surface to nourish the microscopic algae (plankton) that live near the surface water layers. Krill, small shrimplike crustaceans, feed on the plankton and are eaten by the fish, whales, seals, and birds that live in the Southern Ocean. These cold waters are considered as much as four times more productive per acre (hectare) than any other ocean in the world. The abundant krill that teem in the surface waters are responsible for the red color sometimes observed here. Squid and octopus are also essential links in the ocean's food chain because they nourish sperm whales, seals, penguins, seabirds, and fish. Estimates place the number of squid consumed by whales alone at 55 million tons annually.

Because krill are so plentiful and high in protein, efforts have been made to use them to solve food shortages in some of the poorer nations of the world. However, the idea has proved to be largely impractical because of the need for rapid processing and distribution. However, both Japan and Russia have begun to perfect methods of using krill for other commercial purposes.

Biodiversity

Marine mammals that live in the Southern Ocean are no strangers to human activity. During the 18th and 19th centuries, the seals of the Southern Ocean were exploited for their furs, ultimately being classified as protected. By the 21st century, these seals have begun a comeback. These seals cannot breed in the water; thus, they head toward land or pack ice during mating seasons. Antarctic seals are larger than those that live in the Arctic, partly due to the easy availability of food and fewer predators in the area.

The polar winter of the Antarctic generally lasts from November to March and is when violent storms occur. Daylight is absent, and the coastal waters become icebound. When the polar winter ends, more than one hundred million seabirds arrive in the Southern Ocean to breed on the mainland or offshore islands. The albatross, the largest of all flying seabirds, is one of the most distinctive. Other species include fulmars, prions, petrels, and shearwaters; more widespread species include shore birds, skuas, gulls, terns, and penguins. Because ice-free land is scant along the shores of the Southern Ocean, these birds tend to breed in large concentrations. When they sense the return of polar winter, the seabirds move to the open sea, sometimes temporarily populating the pack ice.

The penguin may be the most emblematic animal in the Southern Ocean. However, the various species are widely celebrated popularly under considerable environmental pressures. For example, the Emperor penguin colony of Terre Adélie in east Antarctica shrank by 50 percent in the 1970s and has yet to recover from that loss. The direct cause was the diminishing acreage of sea ice. As these birds breed and nurture their young on the sea ice, the problem is exacerbatedbecause much of their diet also depends on the ice. The fish, squid, and krill that Emperor penguins consume eat the specialized plankton that grows on the underside of sea ice floes. Incremental rise in sea temperature has been enough toupset the balance of this food web.

Seven species of penguins are classified as Antarctic penguins, and more penguins than any other bird species live on this continent. Unlike most birds, penguins do not fly; they use their feet as propellers to move through the waters. The most common species is the Adélie, which may be 24 to 28 inches (60 to 70 centimeters) tall, and the Emperor, which grows to four feet (1.2 meters) in height and can weigh up to 95 pounds (43 kilograms). Some concentrations of penguins may include as many as 180,000 birds. The nests of the Adélie are built of stone; just one or two eggs are incubated in these nests at a time.

Environmental Stresses

Despite its isolation, the Southern Ocean is not immune to some of the same environmental stresses threatening ecosystems worldwide. According to some estimates, the Southern Ocean serves as a massive storehouse for carbon dioxide (CO2), with up to one-third of all CO2 stored by the world's oceans present here. However, scientists are warning that the Southern Ocean is losing its capability to serve as a buffer for the rest of the world because global warming has accelerated the production and accumulation of CO2 while simultaneously reducing the ability of the Southern Ocean to absorb it, due to altered temperature and salinity regimes.

Recent studies show the Southern Ocean is facing unprecedented challenges. In the past decade, scientists have observed record-low Antarctic sea ice levels, with 2023 marking the lowest extent ever recorded. This dramatic loss of sea ice affects not just Emperor penguins and other ice-dependent species, but disrupts the entire food web, from krill to whales. Climate change is also making the Southern Ocean more acidic as it absorbs increasing amounts of carbon dioxide, threatening krill populations that form the foundation of the Antarctic ecosystem. Despite these challenges, there have been some conservation successes - the creation of several large Marine Protected Areas has helped protect some key breeding and feeding grounds, though more international cooperation is needed to establish additional protected zones.

Human industrial activity has also contributed to the hole in the atmospheric ozone layer over the Antarctic, which tends to add to warming in its regional climate. This depleted-ozone area allows more solar ultraviolet radiation to penetrate the surface waters, which some research suggests has reduced the amount of plankton here by as much as fifteen percent and likely has altered the DNA of some fish species.

The exploitation of fishing grounds has become a major problem. Australian scientists have sent out an international call for help because of the increased levels of fishing piracy in the Southern Ocean. One such casualty is the highly prized Patagonian toothfish (Dissostichus eleginoides) and its relative, the Antarctic cod (Dissostichus mawsoni), which are considered a delicacy in both Japan and the United States—where they are marketed as "Chilean sea bass." These fish, known to commercial fishers as the "white gold of Antarctica," have both been placed on the seafood red list of fish to avoid, posted by Greenpeace International. Armed surveillance ships are, in some cases, being used to protect Patagonian toothfish, which are an integral part of the diets of sperm whales and elephant seals.

A "collateral" casualty of the practice of using long-line baited hooks that stretch out for miles over the surface of the Southern Ocean are some 100,000 seabirds a year. Attracted to the bait, the birds go after the hooks and are trapped as they are pulled below the surface. According to some sources, the great albatross and petrels may have recently joined the ranks of the most endangered birds on the planet due to such practices.

Bibliography

El-Sayed, Sayed Z. Southern Ocean Ecology: The Biomass Perspective. Cambridge University Press, 1994.

Forcada, Jaume, and Philip N. Trathana. “Penguin Responses to Climate Change in the Southern Ocean. Global Change Biology, vol. 15, no. 7, 2009.

Gabbatt, Adam."National Geographic Recognizes New Southern Ocean, Bringing Global Total to Five." The Guardian, 10 June 2021, www.theguardian.com/environment/2021/jun/10/new-ocean-global-total-five-national-geographic. Accessed 11 Nov. 2024.

Lowen, James. Antarctic Wildlife: A Visitor's Guide. Princeton University Press, 2011.

Roberts, Leslie Carol. The Entire Earth and Sky: Views on Antarctica. University of Nebraska Press, 2008.

Turner, John. Climate Change in the Polar Regions. Cambridge University Press, 2011.

Santana-Falcón, Y., et al. "Irreversible Loss in Marine Ecosystem Habitability After a Temperature Overshoot." Communications Earth & Environment, vol. 4, no. 343, 2023, doi:10.1038/s43247-023-01002-1. Accessed 9 Nov. 2024.