Topic: Earth Science

Scientists have discovered how and when the Antarctic Circumpolar Current formed. They found that it wasn't just opening ocean gateways between Antarctica, South America, and Australia that created it. Instead, a combination of factors including shifting continents and strong winds played a crucial role.

The Antarctic Circumpolar Current is one of the most important drivers of the global climate system. It carries more than 100 times the total flow of all the world's rivers combined. Scientists have long wondered how this immense current first developed. New research published in the journal Proceedings of the National Academy of Sciences has finally shed light on this mystery.

The study found that around 34 million years ago, during a period known as the Oligocene, Earth experienced a dramatic transformation from a warm greenhouse world to a cooler icehouse climate marked by expanding polar ice sheets. During this time, ocean passages between Antarctica, Australia, and South America widened and deepened.

The researchers used detailed climate simulations based on Earth's geography about 33.5 million years ago, when Australia and South America were positioned much closer to Antarctica. They combined these simulations with an Antarctic Ice Sheet model from a previous study, linking it with ocean, atmosphere, and land systems to track how currents evolved.

The results highlight the importance of the Tasman Gateway, a seaway between Antarctica and Australia. The strong westerly winds blowing directly through this gateway played a crucial role in the formation of the Antarctic Circumpolar Current.

The study also suggests that the Southern Ocean looked very different during this early stage. Even though ocean passages were already open, the current did not yet form a continuous loop. Instead, strong flow developed in the Atlantic and Indian regions, while the Pacific sector remained relatively calm.

Why It Matters

Understanding how the Antarctic Circumpolar Current formed is important for predicting future climate scenarios. As atmospheric CO2 levels continue to rise, scientists need to know how the current has changed over time to make accurate predictions about its impact on global temperatures.

Key Facts

• The Antarctic Circumpolar Current carries more than 100 times the total flow of all the world's rivers combined.
• Around 34 million years ago, Earth experienced a dramatic transformation from a warm greenhouse world to a cooler icehouse climate marked by expanding polar ice sheets.
• The Tasman Gateway, a seaway between Antarctica and Australia, played a crucial role in the formation of the Antarctic Circumpolar Current.
• Atmospheric CO2 levels were about 600 ppm during this period, which has not been reached again since.
• The study used detailed climate simulations based on Earth's geography about 33.5 million years ago to track how currents evolved.

Key Terms

Antarctic Circumpolar Current

A powerful ocean current that circles Antarctica without being blocked by land.

Implications

Understanding how the Antarctic Circumpolar Current formed is important for predicting future climate scenarios. As atmospheric CO2 levels continue to rise, scientists need to know how the current has changed over time to make accurate predictions about its impact on global temperatures.