Although isolated from other continents, Antarctica is connected to the rest of the world through oceanic and atmospheric circulations. Antarctica and the surrounding Southern Ocean are key drivers of Earth’s oceanic and atmospheric systems. A critically important feature is that about 90 per cent of Earth’s ice (approximately 26.9 million cubic kilometres) (Fretwell et al. 2013) is found here, and 70 per cent of all available fresh water is locked up in the Antarctic ice sheet. If melted, this would raise sea levels by 58 metres (Fretwell et al. 2013, Vaughan et al. 2013).
Equally important is the Southern Ocean that surrounds the Antarctic continent. The International Hydrographic Organization considers the parallel of 60°S to be the northern limit of the Southern Ocean (IHO 2002); however, Australia reserves the right to extend the Southern Ocean limits to the southern shores of Australia from Cape Leeuwin in the west and South East Cape in Tasmania (IHO 2002). South of 60°S, the Southern Ocean extends across some 22 million km2, averages about 3300 metres depth and reaches depths of 7000 metres; it encompasses about 6 per cent of the world’s ocean volume (Eakins & Sharman 2010). The Southern Ocean is the only ocean that encircles the globe uninhibited by land masses. The Southern Ocean connects the 3 main ocean basins (Atlantic, Pacific and Indian) and creates a global circulation system that is largely driven by the Antarctic Circumpolar Current (ACC)—the world’s largest current. The ACC flows from west to east around Antarctica and generates an overturning circulation that transports vast amounts of heat. The ACC also takes up a significant amount of carbon dioxide (CO2) from the atmosphere (Rintoul et al. 2001).
In winter, surface waters near Antarctica freeze to form sea ice. When sea ice forms, salt is forced out of the forming ice (brine rejection), making the water below the ice more saline and therefore denser. In a few places around Antarctica, the resulting cold and salty waters are sufficiently dense to sink to the deep ocean and form Antarctic bottom water. This dense bottom water sinks and spreads northwards to supply oxygen to the deep layers of the ocean, and warmer waters flow south to replace it. The southwards flow at mid-depth also compensates for the northwards flow of lighter waters. The formation and circulation of Southern Ocean water masses provide a key link in the global ‘conveyor belt’ of ocean currents that controls climate by transporting heat and other properties.
For our entire planet, atmospheric pressure, humidity, air temperatures and wind patterns are interconnected and greatly influenced by processes in the Southern Ocean.
As well as playing an important role in influencing weather patterns, the Antarctic environment provides valuable information about climate change. Antarctic continental ice contains climate records extending back more than 800,000 years, which have been obtained from ice cores. Moreover, the Antarctic environment and biosphere are highly sensitive indicators of present-day environmental change. Predictions made in the 1980s and 1990s about climate change and its effects in the polar regions in the 21st century have largely been confirmed (Singh et al. 2016). The major difference between previous predictions and recent observations is that the forecast change appears to be occurring at a faster rate than originally expected—for example, significant ice loss has already been observed from glaciers and the major ice sheets of Greenland and Antarctica (Vaughan et al. 2013). In the case of Greenland and parts of West Antarctica, there is evidence that this loss is accelerating (Rignot et al. 2011, Vaughan et al. 2013, Sutterley et al. 2014). Until recently, the western Antarctic Peninsula region had been warming 2 to 3 times faster than the global average (Turner et al. 2014); 3 of the 12 ice shelves in the peninsula region have retreated significantly, and 4 have collapsed, amounting to a loss of about 18 per cent of the floating ice (Cook & Vaughan 2010). However, in East Antarctica, which has been shielded from the effects of global warming by the ozone thinning commonly known as the ‘ozone hole’ (Perlwitz et al. 2008), the warming is less than the global average (Turner et al. 2014). The regional differences in the responses to climate warming and variability highlight the complexity of the processes currently affecting Earth’s environment.