Despite the fact that there is only one global ocean, the immense body of water that spans 71 % of the Earth is split into specific areas. For a variety of historical, cultural, geographical, and scientific reasons, the borders between these territories have altered over time.
The Atlantic, Pacific, Indian, and Arctic oceans have been named historically. Most countries currently recognize the Southern (Antarctic) Ocean as the fifth ocean. The United States Board on Geographic Names recognizes it as the body of water that stretches from Antarctica’s coast to 60 degrees South latitude. In 2000, the International Hydrographic Organization (IHO) was asked to suggest the ocean’s limits. However, because not all countries are in agreement on the proposed borders, the IHO was yet to be ratified. However, the National Geographic Society designated the body of water encircling Antarctica as the Southern Ocean on June 8, 2021.
The character of the Southern Ocean has shifted over time. Over the course of years of investigation, scientists have deduced its significance, as well as its ecological richness and uniqueness, which make it vital to the planet’s health. As a result, this article focuses on the new fifth ocean, which is a massive reservoir of natural diversity, as well as its significance for global climate.
Assessing Patterns of Heat and Carbon Storage
Let’s start with the ability of the Southern Ocean to store surplus heat and carbon. The world’s oceans absorb more than 90% of the extra heat and a third of the additional carbon dioxide produced by the combustion of fossil fuels.
The Southern Ocean, south of 30°S, is thought to account for 75–22% of worldwide oceanic heat uptake and 30–40% of global oceanic carbon uptake from the atmosphere. The subsequent storage of excess heat (Q′) and carbon (C′) in the Southern Ocean can have a substantial impact on large-scale marine ecosystems by providing feedback on oceanic heat intake and carbon buffering capability. The net change in temperature and dissolved inorganic carbon (DIC) in the ocean as a result of the increased surface flux and interior redistribution of the preindustrial temperature and DIC are referred to as excess heat and carbon, respectively.
Two important findings are highlighted based on recent data and a high-resolution climate model: In the Southern Ocean, the spatial patterns of Q′ and C′ storages differ greatly, and the circulation change is a key factor in creating this difference. The consequences of these discoveries are twofold. To begin, understanding the Q′ and C′ patterns is critical for effectively simulating seawater chemistry. Changes in oceanic seawater chemistry, particularly ongoing ocean acidification, are heavily reliant on regional patterns of Q′ and C′ storage, which essentially determine CO2 buffering capability and have the potential to disrupt marine ecosystems. Second, the preponderance of passive transport on C′ storage suggests that models with a lower resolution would be able to reproduce the C′ storage while still accurately representing the mean state of the ocean circulation.
The ACC, or Antarctic Circumpolar Current, is the world’s most powerful ocean current. It encircles Antarctica and stretches from the sea surface to the ocean’s depths. Because it keeps Antarctica cool and frozen, it is essential for the planet’s health. As the world’s climate heats, it is also changing. As we move north, away from Antarctica, the water temperature rises gently at first, then quickly across a severe gradient. This barrier is kept in place by the ACC. The ACC also contributes to the meridional (or global) overturning circulation, which transports deep waters from the North Atlantic south into the Southern Ocean. The ACC transports it around Antarctica as Circumpolar Deep Water. South of the Polar Front, it steadily climbs toward the surface. Some of the water then travels northward and sinks north of the Subarctic Front once it has resurfaced. The remaining portion goes to Antarctica, where it is turned into the densest water in the ocean, sinking to the seafloor and flowing northward as Antarctic Bottom Water. These are the primary processes by which the oceans absorb heat and carbon dioxide before storing it in the deep ocean.
Interplay Of Global Currents
The strong westerly winds that blow almost continuously across the Southern Ocean, causing equally enormous waves, are known as the Roaring Forties, Furious Fifties, and Screaming Sixties. As a result, the ocean surface becomes extremely active and difficult to monitor. However, the heat and carbon exchanges that occur across this complex interface are crucial on a global scale, and oceanographers have created tools expressly for this difficult environment.
One must conceive in three dimensions to truly appreciate the Southern Ocean. In eddies, water with different characteristics mingles horizontally and vertically. Deep cool water from the North Atlantic rises back up toward the surface, while colder polar water masses mix northward and sink back beneath. The wind and the form of the seafloor lead this complicated interplay. Only three significant constrictions exist to the north: the 850-kilometer-wide Drake Passage, as well as the submerged Kerguelen and Campbell Plateaus. The ACC brushes up against Antarctica to the south. By bringing relatively warm — and warming — Circumpolar Deep Water into contact with the ice bordering Antarctica, the ocean performs yet another essential function in the global climate system.
The Antarctic Circumpolar Current relies heavily on circumpolar deep water (CDW). CDW is located near the shelf break in the Amundsen Sea, where the continental shelf serves as a large topographic barrier to the majority of the deep water. In the southern high latitudes, the Southern Annular Mode (SAM) is the primary mode of atmospheric variability. In recent years, the SAM has shifted towards positive polarity, implying lower pressure over the Antarctic and higher pressure at mid-latitudes, owing to increases in greenhouse gases and the ozone hole. A positive SAM is related to substantial warming, strengthening of the westerlies, and a shift in storm paths across the Antarctic Peninsula. More Circumpolar Deep Water will move onto the Antarctic continental shelf as a result of stronger westerlies and a positive SAM; it will lead to increased heat transport and melting at the grounding line and beneath ice shelves.
As a result, increased upwelling of warm, salty Circumpolar Deep Water is melting away the ice shelves’ bases and the grounding lines of some of Antarctica’s largest, most fragile glaciers and ice streams, causing significant far-reaching, and irreversible changes.
Annual Fluctuation of Sea Ice Cover
The annual cycle of sea ice growth and melting around Antarctica is one of our planet’s defining rhythms and a key feature of the Southern Ocean. In this way, the two polar areas are diametrically opposed. The Arctic Ocean is a small, deep-sea, i.e., bordered by land and has just a few limited entrances. On the other hand, the Antarctic Peninsula is a vast landmass surrounded by water, with a continental shelf. In these areas, sea ice covers 15 million square kilometres and advances and retreats every year.
The rhythm of Antarctic Sea ice has followed less evident patterns than the clear and dramatic fluctuations in the north. It was really gently spreading northward in the face of a warming ocean until around 2016 when it unexpectedly began to contract. Hence, climate experts were intrigued by this because such massive, unexpected, and rapid shifts are uncommon.
The amount of sea ice that covers Antarctica changes dramatically from year to year. In fact, in 2014, the Antarctic Sea ice cover reached a new high. This was a hint. Since sea ice cover changes significantly from year to year and decade to decade, longer-term melting due to global warming may go undetected. The next piece of information came from records that had been broken far from Antarctica. In the tropical eastern Indian Ocean in the spring of 2016, sea surface temperatures and rainfall reached new highs. This occurred in conjunction with a significant negative Indian Ocean Dipole (IOD) event that delivered warmer waters to Australia’s northwest. While IOD phenomena influence rainfall in south-eastern Australia, it also created a wind pattern over the Southern Ocean that was especially conducive to sea ice reduction. These northerly surface winds not only drove the sea ice back towards the Antarctic continent, but they were also warmer, assisting in the melting of the ice. The key places where sea ice disappeared were almost exactly matched by these northerly winds. The westerly winds that surround Antarctica dropped to record lows later in 2016. As a result, the ocean surface warmed, resulting in reduced sea ice cover. The weaker winds began over Antarctica in an area known as the stratospheric polar vortex. As a result, the sequential influence of IOD and then stratospheric factors contributed to the record decreases in 2016 and continues to affect year-to-year changes even now.
When one considers the annual cycle of Antarctic Sea ice, one may believe that it merely grows and melts in place as the seasons change. However, the majority of the sea ice formation takes place in polynya, or sea ice factories near the shore, where cold and swift Antarctic winds generate and blow away new sea ice as quickly as it develops. This procedure returns us to the topic of global ocean circulation. When the new ice forms, the salt from the freezing saltwater is forced out and mixed with the seawater beneath it, resulting in colder, saltier seawater that sinks to the bottom and drains northward.
Growth And Persistence of Life in Sub-Zero Ocean
At first look, Antarctica appears to be a harsh, almost desolate landscape of ice and snow, dotted with seabirds and seals. However, diving beneath the surface shows an ocean teeming with life and intricate ecosystems, ranging from single-celled algae and tiny spineless invertebrates to well-known top predators like penguins, seals, and whales.
More than 9,000 marine species have been identified in the Southern Ocean, and expeditions and studies continue to uncover new ones. Life in the Southern Ocean is difficult to investigate. Waves can reach heights of more than 20 meters, and icebergs and sea ice can be found amid them. The water temperature is frequently below freezing: freshwater freezes at 0°C, whereas saltwater freezes at around -2°C. Although scuba diving is possible, remote sampling is used for a lot of studies on life in the Southern Ocean. To look at and collect samples, marine scientists employ robotic tools, including remotely operated underwater vehicles, grabs, and dredges, as well as grabs and dredges to bring up bottom-dwelling creatures. Every expedition unearths new species, some of which could be commercially useful, but all of which are critical components of the Southern Ocean ecosystem. Our understanding of the region’s variety is rapidly developing.
In 2012, Huge numbers of new marine species were identified in the hot, dark habitat surrounding hydrothermal vents on the deep-sea floor near Antarctica by scientists. This came as a shock to the team, as some experts had speculated that the Southern Ocean vents could serve as a link between other ocean vents, allowing animals to propagate across the oceans over thousands or millions of years. However, the current study shows that the Southern Ocean’s harsh circumstances may instead operate as a barrier to spread.
In 2018, a German research team used hot water to boreholes in the Ekström ice shelf and gathered samples from two locations on the seabed beneath. According to the samples, the ecosystem is home to 77 species, which is more than all prior research below Antarctica’s ice combined discovered. The researchers believe there is enough algae moved beneath the ice shelf from open water to support a healthy food web. The annual growth of four of the species was strikingly close to that of similar organisms in open marine Antarctic shelf environments, according to microscopy of samples. According to current theories on what life could live beneath ice shelves, as you get further away from open sea and sunlight, all life becomes less abundant. Small mobile scavengers and predators, like as fish, worms, jellyfish, and krill, have been found in these ecosystems in previous investigations. Filter-feeding creatures, on the other hand, which rely on food from above, were expected to be among the first to go beneath the ice.
Even in 2021, on rocks near Bharati, an Indian research site in the Larsemann Hills in eastern Antarctica, researchers from the Central University of Punjab have identified a new moss species. The finding of the new moss species is significant, according to the researchers, because such species are important elements of the Antarctic ecosystem, contributing to carbon cycling through organic matter accumulation and release, as well as providing habitat and food for invertebrates. The researchers called the species’ Bryum bharatiense’ since it was discovered near Bharati station. It’s a single-stemmed plant with dark green bottom stems and brown upper stems. The moss species was discovered in a location with a lot of penguin faeces. They believe that such faeces may include nutrients that are beneficial to animals.
One-Of-A-Kind Food Chain
Primary producers (organisms at the start of the food chain) in the Southern Ocean range from single-celled algae – such as diatoms with finely sculpted silica shells – to enormous macroalgae like kelp. Kelp and other huge seaweeds can only thrive in areas where icebergs don’t scrape the seafloor frequently. Diatoms come in a wide variety of shapes and sizes, and some species can be found on the underside of sea ice. Ice algae are a major food source for krill, tiny crustaceans that play a vital role in the food webs of the Southern Ocean.
Invertebrates account for more than 90% of the species found in the Southern Ocean. Moreover, half of the species are only found in this ocean. In northern, warmer waters, these invertebrates are frequently much larger than their relatives. This condition is known as “polar gigantism,” and it can be found in a variety of animals, including big sea spiders, massive sponges, and scale worms the size of a forearm. Nobody knows why Antarctic invertebrates develop to such enormous sizes, but it could be due to high oxygen levels, sluggish growth rates, or the lack of essential predatory groups like sharks and brachyuran crabs.
Antarctic krill move between the algae primary producers and the distinctive top predators we connect with Antarctica in the marine food chain. Baleen whales acquire a lot of their energy from large gulps of swarming krill (10,000–30,000 individual animals per cubic meter), and pink streaks in penguin and seal excrement indicate that they like these delectable crustaceans as well. The Southern Ocean is rich in fish and cephalopods (squid and octopus), which provide food for deep-diving marine mammals like elephant seals. Some fish species have adapted to the oxygen-rich freezing seas to the point that they no longer generate red blood cells, instead of producing antifreeze substances in their blood to enable them to live in sub-zero temperatures.
Ecosystem Evolving with Environment Change
Over 21,000 visitors and scientists visit Antarctica every year, bringing pollution, diseases, and exotic species with them. The Antarctic Treaty entered into force on June 23, 1961, to limit human impacts on Antarctic ecosystems and to assist with political negotiations. The treaty governs all activities south of 60 ° S latitude and provides a protocol for environmental preservation.
Warming ocean temperatures, a decline in sea ice, and falling ice shelves are all signs of global climate change and ocean acidification in the Southern Ocean. With warming, plastic pollution, and non-native species making their way to Antarctic waters from beyond the huge polar barrier, research is increasingly proving that even the far-flung Southern Ocean is not entirely sealed off from the rest of the globe. Rafts of floating seaweeds from outside the Antarctic can cross the Southern Ocean and reach Antarctic coastlines; even some non-native animals swim their way to the coast. They don’t appear to be able to withstand Antarctica’s harsh climate right now, but that may change as the planet warms. The distinctive plants and animals of Antarctica will be put under a lot of stress when new species move in and set up shop. However, everything isn’t doom and gloom. Since the Antarctic Treaty came into force more than four decades ago, we’ve seen how governments can work together to tackle problems in the Antarctic. Antarctic Marine Protected Areas are one example. This kind of international cooperation should offer us hope not only for the Southern Ocean’s future, but also for the world’s other major concerns.
Vulnerable Habitat Needs Protection
Humans are, without a doubt, the most ferocious predators in the Southern Ocean. Despite its remoteness, the seas surrounding Antarctica have been widely exploited by humans in the 200 years or so since its discovery. Human activity has been widespread in Antarctica, particularly in ice-free and coastal areas, yet biodiversity is concentrated in these places. As a result, much of the continent’s key biodiversity sites are not captured in wilderness zones, which are parts of the continent entirely unaffected by human activity.
Fish and krill (which are harvested for food or dietary supplements) have been the main targets in recent years, and as a result, certain species’ populations have plummeted. When more indirect effects like ocean warming and acidification mix with fishing, it can result in decreased krill populations, which can lead to fewer top predators like whales. Because these waters do not belong to any one country, fishing in the Southern Ocean is difficult to manage. The Commission for the Conservation of Antarctic Marine Living Resources now administers quotas that limit catches to assist in regulating the impact of fisheries.
More marine protected areas are also being established by this international organization. Critical elements of the food web (such as krill) could be exploited to the point that ecosystems collapse if these measures to regulate captures are not made. Expanding the network of Antarctic Specially Protected Areas to incorporate additional wilderness and inviolate areas where politicians would ban human activity could help to protect the Antarctic wilderness. When considering how we will use Antarctica in the future, we should weigh the benefits of science and tourism against the importance of preserving pristine wilderness and protected places.
Environmental impact evaluations, which are required for all activities in the region, might be used to do so expressly. Impacts on a site’s wilderness value are rarely taken into account at the moment.
In Antarctica, we have an opportunity to safeguard some of the world’s most intact and untouched environments, as well as avoid future deterioration of the continent’s outstanding wilderness value.
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