Antarctica sits on a massive slab of continental rock roughly the size of the contiguous United States and Mexico combined, while the Arctic is an ocean basin filled with seawater and covered by a relatively thin layer of floating ice. That geological reality is the entire reason one qualifies as a continent and the other does not. The distinction sounds simple, but what lies beneath each polar ice cap turns out to be far more interesting than most people expect, involving ancient supercontinents, mountain ranges hidden under miles of ice, a powerful ocean current that acts as a thermal fence, and even networks of lakes that fill and drain in the dark.
Rock Versus Ocean
A continent, at its most basic, is a large continuous mass of land distinguished from islands and ocean floor by its size and the type of crust it rides on. Continental crust is thick, relatively buoyant, and composed of lighter rocks like granite. Oceanic crust is thinner, denser, and made mostly of basalt. Antarctica checks every box for continental crust. Strip away its ice sheet and you find bedrock, mountain ranges, lowland plains, and river valleys carved by glaciers over millions of years. The Arctic Ocean, by contrast, is a deep basin of oceanic crust floored by basalt, fringed by the continental shelves of North America, Europe, and Asia. The sea ice floating on top of the Arctic Ocean is frozen seawater, typically a few meters thick even at its winter maximum. Antarctica’s ice sheet, on the other hand, is freshwater ice piled on top of land, reaching thicknesses of over four kilometers in places.
This is not a matter of opinion or convention. Geophysical surveys have confirmed for decades that a continent-sized block of ancient rock sits beneath the Antarctic ice. The bedrock of East Antarctica in particular is a craton, one of the oldest and most stable pieces of continental crust on Earth, dating back billions of years. The Arctic seabed, meanwhile, is geologically young ocean floor interrupted by underwater ridges and plateaus. No amount of ice accumulation could turn an ocean basin into a continent, and no amount of melting could turn Antarctica into one either. The land is already there.
How Antarctica Got Where It Is
Antarctica was not always an isolated frozen landmass at the bottom of the world. It was once part of Gondwana, the southern supercontinent that also included what are now South America, Africa, India, and Australia. As Gondwana broke apart over tens of millions of years, the individual pieces drifted to their current positions. Antarctica ended up centered on the South Pole, a geographic lottery that would have profound consequences for its climate.
The tectonic history of the continent itself is more complex than a single block drifting south. East Antarctica and West Antarctica are geologically distinct regions that have moved relative to each other. Recent marine magnetic data from the Central Basin between the Hallett Ridge and Iselin Bank revealed oceanic crust that formed roughly 53 to 43 million years ago, pushing the onset of East-West Antarctic motion about 10 million years earlier than scientists had previously established. That timing coincides with the uplift of the Transantarctic Mountains and the end of seafloor spreading in the Tasman Sea, which redirected tectonic forces southward into the Ross Sea region.1PubMed Central. Revising the tectonic chronology of East–West Antarctica since the breakup of East Gondwana In other words, Antarctica is not one simple block but a jigsaw of tectonic pieces welded together and then partially pulled apart by the same forces that rearranged every other continent.
The Arctic has no equivalent story. There is no hidden continent beneath the Arctic Ocean waiting to be recognized. The ocean basin formed as North America, Europe, and Asia rifted apart, creating a deep-water basin that happened to end up at the top of the planet. The surrounding landmasses belong to other continents. The ice floating on the Arctic Ocean is not sitting on top of anything solid.
What Antarctica Looks Like Without Its Ice
If you could magically remove Antarctica’s ice sheet, you would not find a flat plain. You would see a continent with dramatic topography: mountain ranges, deep valleys, plateaus, and basins that in some cases drop well below sea level because the sheer weight of the ice has pressed the bedrock downward. One of the most striking features is the Transantarctic Mountains, a range stretching roughly 3,500 kilometers across the continent. Geophysical surveys combining subglacial topography and gravity measurements have confirmed that these mountains formed as a flexural uplift along the edge of the East Antarctic craton, essentially the ancient core of the continent bowing upward as the crust nearby stretched and thinned.2Journal of Geophysical Research: Solid Earth. Uplift of the Transantarctic Mountains and the bedrock beneath the East Antarctic ice sheet
Mapping this hidden landscape has been a long-running challenge. Ice-penetrating radar from aircraft, seismic surveys, and satellite-based techniques have all contributed. A recent continental-scale mapping effort used the physics of ice flow combined with ice surface data from satellites and geophysical ice-thickness observations to produce the most detailed picture yet of what lies underneath, resolving features as small as two to thirty kilometers across and revealing previously unknown patterns of subglacial roughness and landforms.3PubMed. Complex mesoscale landscapes beneath Antarctica mapped from space The picture that emerges is of a real, complex, geologically diverse continent, not a featureless platform propping up an ice sheet.
The Arctic Ocean floor has its own interesting geology, including mid-ocean ridges and sediment layers that tell stories about past climates. But none of that makes it a continent. The ocean floor is oceanic crust, and no matter how many features it has, it remains an ocean basin.
The Circumpolar Current and Antarctica’s Thermal Isolation
Antarctica’s status as a continent is a geological fact, but its ice-covered character is partly the product of its ocean. The Antarctic Circumpolar Current, or ACC, is the most powerful ocean current on Earth, flowing eastward around the entire continent without interruption by any landmass. It exists because Antarctica is completely surrounded by open water at the latitudes where the current flows, a situation that has persisted since the last land bridges connecting Antarctica to South America and Australia pulled apart tens of millions of years ago.
The ACC acts as a thermal barrier. By circling the continent, it minimizes the amount of warm subtropical surface water that can reach Antarctic shores, effectively locking the continent inside a cold ring of ocean.4Palaeogeography, Palaeoclimatology, Palaeoecology. Antarctic circumpolar current’s role in the Antarctic ice system: An overview Without this current, warmer waters from lower latitudes would deliver far more heat to Antarctic coastlines, and the ice sheet would look very different.
The Arctic has no equivalent barrier. Warm currents from the Atlantic, particularly the North Atlantic Drift, flow into the Arctic Ocean and deliver heat from lower latitudes. The Arctic is also surrounded by continents and large islands that channel these currents rather than blocking them entirely. This is one of the reasons the Arctic is significantly warmer than Antarctica at comparable latitudes, and why Arctic sea ice is thinner, more seasonal, and more vulnerable to climate shifts than the Antarctic ice sheet.
Why the Two Poles Have Such Different Climates
Even though both poles receive the same minimal sunlight during their respective winters, Antarctica is far colder than the Arctic. The interior of the East Antarctic Plateau holds the record for the coldest temperatures ever measured on Earth, dropping below minus 89 degrees Celsius. Arctic winter temperatures, while brutally cold by any human standard, rarely approach that extreme.
Several factors explain this gap, and they all trace back to the continent-versus-ocean distinction. First, land cools faster and holds less heat than water. The Arctic Ocean, even when covered by ice, stores enormous amounts of thermal energy in its water column and releases it slowly. Antarctica’s rock and ice have no such reservoir. Second, Antarctica’s average elevation is the highest of any continent, roughly 2,500 meters above sea level when you include the ice. Higher altitude means colder temperatures. The Arctic Ocean is at sea level. Third, the Antarctic polar vortex, the ring of cold stratospheric winds that encircles the continent each winter, behaves differently from its Arctic counterpart. Studies of decades of atmospheric data show that in the Arctic, a larger polar vortex tends to be colder and stronger, while in Antarctica, that same relationship does not hold in the same way.5Journal of Geophysical Research: Atmospheres. Arctic and Antarctic polar vortices 1957–2002 as seen from the ERA‐40 reanalyses The Antarctic vortex is generally more stable and persistent, which helps maintain extreme cold over the continent for longer periods.
The combined effect is stark. Antarctica is not just colder than the Arctic; it is colder in a fundamentally more stable way, because the underlying continent, the surrounding current, and the atmospheric dynamics all reinforce each other.
When Antarctica Had Forests
One of the most striking pieces of evidence for Antarctica’s continental nature is its fossil record. Fossil wood is abundant in Cretaceous and early Tertiary sediments of the northern Antarctic Peninsula region, representing vegetation that once grew at high latitudes during periods when the polar regions were far warmer than today. These fossils tell a story of a continent that experienced dramatically different climates over geological time: cool conditions during the Early Cretaceous, peak warmth during the Coniacian to early Campanian stages, and then a cooling trend through the Maastrichtian and Palaeocene, evident from progressively narrower growth rings in the wood.6Palaeogeography, Palaeoclimatology, Palaeoecology. Cretaceous and early Tertiary climates of Antarctica: evidence from fossil wood
These are not scrubby bushes clinging to life at the edge of ice. The fossils include large trees that grew in forests, supported by soils, in a climate warm enough for sustained plant growth. Dinosaur fossils, ancient amphibians, and a wide range of marine organisms have also been found on the continent. Antarctica’s fossil record is, in fact, one of the clearest demonstrations that continental positions change over time and that climate is not fixed. The same piece of continental crust that now sits beneath kilometers of ice once supported lush ecosystems.
The Arctic Ocean floor also contains sediment records of past warm periods, including times when the surface was ice-free and supported planktonic life very different from what lives there today. But sediment cores from an ocean floor are a fundamentally different kind of evidence than fossil forests rooted in bedrock. One tells you about conditions in a body of water; the other tells you about a landscape where plants and animals lived on solid ground.
Hidden Lakes Beneath the Ice Sheet
Perhaps the most surprising thing about Antarctica’s continental bedrock is that it hosts an active hydrological system entirely hidden beneath the ice. Subglacial lakes, bodies of liquid water trapped between the bedrock and the overlying ice sheet, have been known since the 1970s, but the scale and dynamism of the system continue to surprise researchers.
A decade of satellite altimetry data from CryoSat-2 identified 85 active subglacial lakes across the continent, meaning lakes that are measurably filling or draining on timescales of years. Of these, about a third showed only one-directional activity during the study period, either only filling or only draining, while the rest cycled through both phases. The median drainage event lasted about 2.2 years, with recharge taking roughly 3.5 years.7The Cryosphere. Analysis of long-term dynamic changes of subglacial lakes in the Recovery Ice Stream, Antarctica Some of these lakes are connected to each other in cascading networks. In the Recovery Ice Stream alone, researchers identified a drainage event that cascaded through ten connected lakes over a distance of about 1,000 kilometers, revealing a highly interconnected plumbing system beneath the ice.
Active subglacial lakes have even been found near the coast, under slowly moving ice close to the grounding line where the ice sheet meets the ocean. Laser altimetry data from ICESat and ICESat-2 satellites, combined with elevation models, revealed seven such lakes in the Dronning Maud Land region that actively fill and drain over periods of several years and appear to discharge meltwater across the grounding line into the ocean.8The Cryosphere. Evidence of active subglacial lakes under a slowly moving coastal region of the Antarctic Ice Sheet This means the continent’s hidden water system is not confined to the deep interior; it reaches all the way to the edges where ice meets sea.
Nothing comparable exists in the Arctic. Floating sea ice does not create the pressure conditions needed to trap liquid water beneath it in the same way. You need a continent, with its thick ice sheet bearing down on bedrock, to generate the insulating pressure and geothermal heat that keep these lakes liquid. The subglacial lake system is, in a sense, one of the most vivid illustrations of what it means for Antarctica to be a continent rather than a frozen ocean.
The Legal and Practical Weight of Being a Continent
The distinction between continent and ocean has real-world consequences beyond geology classrooms. Antarctica’s status as a landmass is the foundation of the Antarctic Treaty System, signed in 1959, which designates the continent as a zone for peaceful scientific research and suspends all territorial claims. The treaty’s Environmental Protocol, added in 1991, bans mineral resource extraction on the continent. These protections exist in part because Antarctica is land, and land can be claimed, fought over, and exploited in ways that open ocean cannot.
The Arctic, being an ocean, falls under a different legal framework entirely. The United Nations Convention on the Law of the Sea governs the Arctic Ocean, and the nations surrounding it, including Russia, Canada, the United States, Norway, and Denmark via Greenland, have the right to claim exclusive economic zones and extended continental shelves under that body of law. There is no equivalent of the Antarctic Treaty for the Arctic. The seabed beneath the Arctic Ocean is subject to competing national claims, and its resources, including oil, gas, and minerals, are actively being assessed and, in some areas, extracted.
This legal divergence flows directly from the physical one. A continent with no indigenous population and no historical sovereignty created the political space for an international treaty. An ocean surrounded by powerful nations with overlapping maritime claims did not. If the Arctic had a continent at its center, or if Antarctica were an ocean, the political and legal landscape of both regions would be unrecognizable.
Common Misconceptions About Polar Geography
A surprisingly persistent misconception is that both poles are essentially the same, just cold white expanses at the top and bottom of the globe. In reality, they are almost perfect opposites. Antarctica is land surrounded by ocean; the Arctic is ocean surrounded by land. Antarctica’s ice is mostly on land and contains about 26.5 million cubic kilometers of frozen freshwater; Arctic sea ice is frozen saltwater floating on the ocean, and even at its winter peak it holds a tiny fraction of that volume. If all of Antarctica’s ice melted, global sea levels would rise by an estimated 58 meters. If all Arctic sea ice melted, the direct effect on sea level would be negligible, because floating ice already displaces its own weight in water.
Another common confusion involves the poles and their wildlife. Polar bears live only in the Arctic; penguins live almost exclusively in the Southern Hemisphere, with most species found in or near Antarctica. This is not a coincidence. The ecological isolation created by the Southern Ocean and the ACC means that Antarctic species evolved in near-total separation from northern ecosystems. The Arctic, connected to surrounding continents, has far more overlap with temperate ecosystems, which is why land predators like bears, wolves, and foxes thrive there while Antarctica’s largest permanent land animal is a midge about six millimeters long.
People also sometimes assume that because the Arctic is “just ice,” it is less important or less geologically interesting than Antarctica. The Arctic Ocean floor preserves a rich record of tectonic and climatic history, and the ecosystems sustained by Arctic sea ice are ecologically critical. The point is not that one pole matters more than the other. It is that they are fundamentally different kinds of places, and understanding why requires knowing what sits at the bottom of all that ice.