Antarctica, a landmass located at the Earth’s southernmost point, is profoundly shaped by water in its most extreme forms. It stands as the planet’s largest reservoir of freshwater, holding approximately 70% of all freshwater found on Earth. This vast amount is primarily locked within its immense ice sheets, which cover nearly 98% of the continent. The presence of water in both solid and liquid states, influenced by the continent’s frigid temperatures, defines Antarctica’s unique environment.
The Continental Freshwater System
The East and West Antarctic Ice Sheets dominate the continent’s surface. The East Antarctic Ice Sheet, significantly larger and thicker, averages 2,226 meters in depth and reaches elevations over 4,000 meters. In contrast, the West Antarctic Ice Sheet is smaller and rests on bedrock largely below sea level, making it more susceptible to changes. These ice sheets consist of compressed layers of snow that have transformed into dense glacial ice over millennia.
Within these massive ice sheets, glaciers and ice streams flow outward from the interior towards the coast. Ice streams are fast-moving corridors of ice, advancing over 1,000 meters annually and spanning up to 50 kilometers in width. They discharge about 90% of the continent’s ice into the surrounding ocean. This flow is influenced by the ice’s thickness and underlying terrain.
During the brief Antarctic summer, seasonal surface meltwater forms temporary streams and lakes along the continent’s edges and on floating ice shelves. Satellites have observed over 65,000 such meltwater lakes around the ice sheet’s margins. Recent research indicates that over half of this meltwater exists as slush, which absorbs more solar heat than solid ice or snow, potentially impacting ice shelf stability. These surface melt features indicate dynamic changes on Antarctica’s icy exterior.
Hidden Subglacial Lakes and Rivers
Beneath Antarctica’s thick ice sheets lie extensive networks of liquid water, including over 400 identified subglacial lakes, with estimates suggesting thousands more await discovery. These liquid environments persist due to a combination of factors: immense pressure from the overlying ice lowers water’s freezing point, and geothermal heat from the Earth’s crust warms the ice sheet’s base. This geothermal heat is a primary factor in maintaining the liquid state of these lakes, particularly where ice is thickest.
Lake Vostok, located beneath approximately 4 kilometers of ice in East Antarctica, is the largest known subglacial lake, comparable in surface area to Lake Ontario. This enormous freshwater body has been isolated from the Earth’s surface for at least 15 million years. Researchers study these unique, isolated environments to understand how life might adapt and thrive under extreme conditions, such as complete darkness and immense pressure.
The potential for unique microbial ecosystems within these lakes offers insights into astrobiology and the possibility of life on other celestial bodies like Jupiter’s moon Europa. While drilling into Lake Vostok has occurred, scientific efforts prioritize preventing contamination of these pristine environments. Some subglacial lakes are “active,” meaning they periodically store and release water, influencing the dynamics of the overlying ice and potentially accelerating ice flow.
The Surrounding Southern Ocean
Encircling the Antarctic continent is the Southern Ocean, a unique marine environment characterized by extreme cold and high nutrient levels. This ocean experiences a pronounced annual cycle of sea ice, which expands dramatically during winter, nearly doubling the continent’s size, and then largely retreats in the summer. These fluctuating ice conditions shape the ocean’s physical and biological characteristics.
A defining feature of the Southern Ocean is the Antarctic Circumpolar Current (ACC), the world’s largest ocean current. The ACC flows unimpeded clockwise from west to east around Antarctica, transporting up to 173 million cubic meters of water per second. This powerful current acts as a barrier, isolating Antarctica’s climate and its distinctive marine life from warmer waters further north.
The ACC’s continuous flow contributes to the upwelling of nutrient-rich deep waters, particularly at the Antarctic Convergence where colder Antarctic waters meet warmer subantarctic waters. This upwelling supports a highly productive marine ecosystem, fostering abundant phytoplankton, krill, and the diverse marine life that relies on them. Strong westerly winds primarily drive this current’s movement.
Antarctic Bottom Water Formation
The Southern Ocean is also the origin of Antarctic Bottom Water (AABW), the densest water mass in the world’s oceans. AABW forms in specific coastal regions, such as the Weddell and Ross Seas. The process begins during harsh polar winters as extensive sea ice forms.
As seawater freezes, it expels salt into the remaining liquid water, a process called brine rejection. This rejected salt increases the salinity and density of the surrounding surface water. Intense cold temperatures further cool this briny water, making it exceptionally heavy. This cold, dense water then sinks to the ocean floor, cascading down the continental slope.
Once formed, AABW spreads northward, occupying the deepest parts of all major ocean basins, typically below 4,000 meters. This deep flow is a primary driver of the global ocean “conveyor belt,” also known as thermohaline circulation. AABW ventilates the deep ocean, transporting oxygen and nutrients across vast distances and influencing global climate patterns over long timescales.