What Is the Antarctic Circumpolar Current and How Did It Form?

The Antarctic Circumpolar Current is the largest and most powerful ocean current on Earth, carrying more water than every river on the planet combined — and new research reveals that scientists had its origins completely wrong for decades.

What Makes the Antarctic Circumpolar Current So Remarkable?

No other ocean current comes close to matching the scale of the Antarctic Circumpolar Current (ACC). It is the only current on Earth that flows in a continuous ring around an entire continent — Antarctica — with no landmass anywhere along its path to slow it down or redirect it. That unobstructed loop allows it to build into something almost incomprehensible in scale.

The ACC plunges nearly 2.5 miles (about 4 kilometers) below the ocean surface, extending from the water’s surface all the way down to the seafloor. It flows through three major ocean basins — the Atlantic, Pacific, and Indian — connecting them into one continuous system. The volume of water it moves dwarfs every river on Earth put together.

Why Is the Drake Passage So Important?

The Drake Passage — the roughly 500-mile (800-kilometer) gap separating the southern tip of South America from the Antarctic Peninsula — has long been considered the key to understanding the ACC. For decades, the leading scientific assumption was straightforward: when the Drake Passage tore open approximately 30 million years ago as tectonic plates shifted, it created the opening the current needed, and the Antarctic Circumpolar Current was born.

It was a tidy, logical explanation. It became textbook science. And according to new research, it was wrong.

What Did Scientists Get Wrong About Its Formation?

A landmark study overturned the long-held gateway hypothesis. Researchers found that the modern Antarctic Circumpolar Current likely did not form when the Drake Passage opened. Instead, the powerful, deep-reaching current we see today may have developed millions of years after the passage was already open — meaning the physical opening of the gateway and the birth of the current were two entirely separate events driven by different forces.

This distinction matters enormously. It means the factors that actually gave rise to the ACC — possibly including changes in wind patterns, ocean chemistry, or global temperatures — are not the ones scientists have been studying and modeling. The old assumption shaped climate reconstructions, ice sheet models, and our understanding of Antarctic glaciation. All of that now needs to be revisited.

How Does the ACC Regulate Earth’s Climate?

The Antarctic Circumpolar Current is not just a curiosity of ocean geography — it is one of the planet’s most critical climate regulators. It acts as a thermal barrier, isolating Antarctica from warmer waters to the north and helping keep the continent locked in ice. Without it, warm ocean water could reach Antarctic shores far more easily, accelerating ice loss.

The ACC also drives the global ocean conveyor belt, redistributing heat, carbon, and nutrients across all of Earth’s oceans. Weather systems on every continent are influenced — directly or indirectly — by the circulation patterns the ACC helps maintain. A significant weakening of this current would send ripple effects through climate systems worldwide.

Why Does This Discovery Change So Much?

Science is built on models, and models are only as good as the assumptions underneath them. When a foundational assumption — like “the Drake Passage opening created the ACC” — turns out to be wrong, every model built on top of it becomes suspect. Climate scientists now have to reconsider how and when Antarctica became the frozen continent it is, and what forces are truly capable of disrupting the current that keeps it that way.

Understanding the ACC’s real origin story is not just an academic exercise. As the planet warms and Southern Ocean dynamics shift, knowing what actually controls this current could be critical to predicting what comes next.