The Antarctic Sea, also known as the Southern Ocean, encompasses the expansive body of water surrounding the Antarctic continent. This marine environment is distinct, characterized by extreme conditions and its pristine, relatively undisturbed nature. It hosts a unique ecosystem.
Physical Characteristics of the Antarctic Sea
The Antarctic Sea experiences extremely low temperatures, around -1.8 degrees Celsius, due to its salinity. Sea ice forms annually, covering a vast area that expands from 2-4 million square kilometers in February to 19-20 million square kilometers in September, nearly 1.5 times the area of the Antarctic continent. Sea ice plays a significant role in the ecosystem, influencing heat and water vapor exchange and contributing to the formation of dense, cold, salty water.
The Antarctic Circumpolar Current (ACC) is the world’s largest ocean current, isolating the region and driving its unique climate and oceanography. This current also plays a role in upwelling, bringing warmer Circumpolar Deep Water (CDW) towards the surface, a heat source for ice shelf melt. The formation of dense bottom water, known as Antarctic Bottom Water (AABW), occurs when dense shelf water, produced during sea-ice formation, cascades down the continental slope and mixes with warmer deep water. This dense water then reaches the ocean bottom, influencing global ocean circulation.
Biodiversity and Adaptations
The Antarctic Sea supports diverse marine life with remarkable adaptations to its extreme conditions. Antarctic krill (Euphausia superba) are small crustaceans, about 6 cm long, forming dense swarms that can be seen from space. These swarms, sometimes reaching densities of 10,000-30,000 animals per cubic meter, serve as the primary food source for whales, seals, icefish, and penguins. Krill feed on microscopic phytoplankton and algae found on the underside of sea ice, and can shrink their bodies during periods of starvation to survive dark winter months when food is scarce.
Various whale species, such as blue, humpback, minke, and orcas, rely heavily on krill, consuming tens of millions of tonnes annually. Seals, including crabeater, Weddell, and leopard seals, also depend on krill for survival, with crabeater seals having evolved specialized multilobed teeth to sieve krill from the water. Penguins, like the emperor and Adélie, are also significant krill predators.
Fish species, such as icefish, have developed physiological adaptations to survive frigid waters. Adaptations include antifreeze proteins in their blood to prevent ice crystal formation, and some species lack hemoglobin, allowing them to thrive in oxygen-rich, cold waters. Many Antarctic animals possess thick blubber for insulation, and some have specialized metabolic rates to function in low temperatures.
Global Ecological Importance
The Antarctic Sea holds significant global importance, extending beyond its immediate ecosystem. It plays an important role in regulating global climate through processes like deep-water formation and carbon sequestration. Dense waters sinking from the Antarctic continental shelf isolate transported carbon from the atmosphere at depths of several kilometers for centuries to millennia. This process contributes to global ocean circulation and redistributes nutrients to other ocean basins.
The high productivity of the Antarctic Sea, especially its krill biomass, supports local marine life and contributes to global nutrient cycles. Krill, as a keystone species, transfer carbon from the surface to deeper waters through their feeding and excretory cycles, acting as a carbon sink. Estimates suggest krill remove tens of millions of metric tons of carbon annually. The relatively undisturbed state of the Antarctic Sea makes it a natural laboratory for scientific research, offering insights into oceanographic processes and ecosystem dynamics largely unaffected by human disturbance.
Current Challenges and Conservation
The Antarctic Sea faces threats, primarily from climate change. Ocean warming and the associated loss of sea ice directly impact the ecosystem, as sea ice provides a habitat for krill and influences ocean-atmosphere interactions. Ocean acidification, a consequence of increased carbon dioxide absorption, can reduce krill development and hatchling rates, leading to population declines. The West Antarctic Peninsula has experienced a 5-6°C increase in mean winter air temperatures and a decrease in winter sea-ice cover.
Overfishing, particularly of krill and toothfish, poses a challenge. The krill fishery has expanded due to rising demand for krill in animal feed, aquaculture, and human consumption. While catch limits are in place, regulations may need updating to reflect the changing marine environment and climate change impacts on krill stocks. Illegal, unregulated, and unreported (IUU) fishing also threatens species like the Patagonian toothfish, undermining conservation efforts.
International conservation efforts are underway to protect the Antarctic Sea. The Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), established in 1982, manages and protects the region’s marine resources. CCAMLR incorporates climate change considerations into its decisions and aims to implement an overarching climate change strategy. The designation of Marine Protected Areas (MPAs) is an important conservation tool, with MPAs already established. However, proposals for additional MPAs have faced delays due to ongoing negotiations.