Part Two
ANTARCTICA – GEOLOGY
During this lecture, the renowned geologist Keith Mountain spoke to us about plate tectonics, how the continent came to be, and how Antarctica became isolated by the Antarctic Circumpolar Current (ACC), all the while providing fascinating insights into oceanography and geology.
He started off by explaining what exactly the word Antarctica refers to geographically. The Antarctic Treaty applies to all territory south of 60° S, where all territorial claims are frozen, effectively making Antarctica the world’s only international continent. While this political boundary lies at 60° S, the Antarctic Convergence, also known as the Antarctic Polar Front, represents the biological or oceanographic boundary.
Normally located between 55° and 60° S, the convergence shifts seasonally, moving by as much as 160 kilometres north or south. Within this zone, warmer, more saline subtropical waters flowing south collide with colder, denser, and less salty polar waters moving north. This broad, invisible boundary forms a well-defined oceanic frontal system characterised by upwelling, as the colliding water masses churn nutrients up to the surface. This nutrient-rich upwelling creates one of the most productive marine ecosystems on the planet, supporting vast numbers of krill, which in turn sustain a profusion of foraging seabirds, seals, and cetaceans.
Alfred Wegener, one of the pioneers of Earth sciences, postulated that Antarctica, along with several other continents, was once part of a supercontinent called Gondwana. By observing how these landmasses fit together like pieces of a jigsaw puzzle, he developed the theory of continental drift.
This idea was later supported by fossil evidence, including Glossopteris plant fossils found across multiple continents, as well as geological data made accessible once drilling technology allowed scientists to study the continent’s deeper layers. Around 120 million years ago, South America and Australia drifted away from Antarctica, isolating the continent climatologically, oceanographically, and geologically. This separation allowed cold waters to fully encircle the continent, setting the stage for the frozen world we know today.
As South America separated from Antarctica, the Scotia Plate, a minor tectonic plate situated between the South American and Antarctic Plates, formed alongside the opening of the Drake Passage. Flowing through this passage and over the Scotia Arc, which includes island chains such as the Falkland Islands, is the Antarctic Circumpolar Current. This immense ocean current flows clockwise around the continent and is the largest current on Earth, transporting as much water as all the world’s rivers combined. By preventing warmer waters from reaching Antarctica, the ACC acts like a planetary moat, thermally isolating the continent and allowing its ice sheet to persist. In doing so, it plays a crucial role in regulating global climate and ocean circulation, meaning that changes here ripple far beyond the Southern Ocean.
Today, the icy continent covers over 14 million square kilometres, accounting for roughly 10% of the Earth’s land surface and about 20% of the Southern Hemisphere. Approximately 98% of Antarctica is covered by a massive ice sheet, with an average thickness of around two kilometres.
In some areas, particularly in East Antarctica, the ice may reach up to four kilometres thick, its immense weight depressing the underlying bedrock by as much as 500 metres. Beneath this ice lie mountain ranges, deep valleys, and hundreds of subglacial lakes, some of which have been sealed off from the surface for millions of years. These hidden lakes, such as Lake Vostok, may host microbial life adapted to extreme cold, pressure, and darkness, making Antarctica one of the closest analogues on Earth to environments scientists hope to study on moons like Europa.
As if that weren’t impressive enough, during winter, sea ice forms at temperatures between -1.7 and -1.9 degrees Celsius due to the salt content lowering the freezing point of seawater. This seasonal sea ice does not add to sea level, but it does effectively double the size of the continent, drastically altering global heat exchange between the ocean and atmosphere. Despite all this ice, Antarctica is technically a desert, receiving less annual precipitation than many of the world’s hottest deserts, with most of its ice having accumulated slowly over hundreds of thousands of years.
He also threw in some staggering statistics. About 71% of the Earth’s surface is covered by water, totalling roughly 1.386 billion cubic kilometres. Of this, 97% is saltwater, while the remaining 3% is freshwater. Around 70% of that freshwater, and roughly 90% of the world’s ice, is locked away in Antarctica. Ice cores drilled here act as time capsules, trapping bubbles of ancient atmosphere and allowing scientists to directly measure past concentrations of carbon dioxide and other gases going back more than 800,000 years. It’s from these frozen records that we know current greenhouse gas levels are unprecedented in human history. Crazy.
The continent, he continued, is divided into West and East Antarctica by the Transantarctic Mountains, with a rift system on the western side driving volcanic activity.
Notable features include the Ellsworth Mountains at the base of the Antarctic Peninsula, which host the continent’s highest peak at 4,892 metres; Mount Erebus on Ross Island, the southernmost active volcano on Earth, which erupts frequently; and Dome Argus, one of the coldest places on the planet, where temperatures can plunge to around -90 degrees Celsius.
Across these regions, a mix of igneous, metamorphic, and sedimentary rocks can be found, along with rare minerals that are uncommon elsewhere in the world. Some rocks buried beneath the ice date back 1.5 to 2.5 billion years, while much younger volcanic formations remain exposed at the surface, undergoing constant freeze-thaw cycles that fracture rock and shape the landscape.
West Antarctica, though considerably smaller than its eastern counterpart, has an ice sheet comparable in size to that of Greenland. This ice sheet has already begun to destabilise, with glaciers accelerating, calving icebergs, and thinning into floating ice shelves that remain in direct contact with warming ocean waters. East Antarctica, which holds the vast majority of the continent’s ice, is currently far more stable. Were it to melt entirely, global sea levels would rise by approximately 58 metres, compared to around five metres if the West Antarctic Ice Sheet were to collapse completely.
Even partial melting would have profound consequences, altering ocean circulation, shifting climate systems, and reshaping coastlines worldwide. What happens in Antarctica does not stay in Antarctica.
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