Apr 7, 2026 03:08 AM
https://www.eurekalert.org/news-releases/1122610
PRESS RELEASE: It transports far more than 100 times as much water as all of the Earth's rivers combined: The Antarctic Circumpolar Current rushes around the southern continent unhindered by land masses and is therefore a fundamental component of the climate system.
In a recent study published in the journal Proceedings of the National Academy of Sciences, a research team led by the Alfred Wegener Institute describes how and when this mighty ring current developed in Earth's history. Surprising finding: it took more than the opening of the ocean passages between Antarctica, and South America and Australia.
Earth’s climate underwent its last drastic change around 34 million years ago during the transition into the Oligocene - cooling from a largely ice sheet-free greenhouse climate to our current icehouse climate, in which large areas of the poles became increasingly glaciated with permanent ice. At this time, the ocean passages between Australia, Antarctica and South America widened and deepened, the Antarctic Circumpolar Current (ACC) developed and the formation of the Antarctic Ice Sheet began.
The CO2 concentration in the atmosphere at that time was around 600 ppm - a value that has not been reached ever since, but could be exceeded again by the end of this century in some climate scenarios. “In order to predict the possible future climate, it is necessary to look into the past with simulations and data to understand our Earth in warmer and more CO2-rich climate states than today,” says Hanna Knahl, climate modeller at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) and lead author of the study, which now appears in the Proceedings of the National Academy of Sciences (PNAS).
“But careful, the climate of the past can of course not be projected 1:1 onto the future. Our study shows that the circumpolar current in its ‘infancy’ influenced the climate very differently than today’s fully developed ACC does.”
For the current study, Hanna Knahl and her colleagues analysed the formation of the ACC. To this end, climate simulations were created with the continental configuration from 33.5 million years ago, when Australia and South America were still much closer to Antarctica. For these simulations, the team coupled the Antarctic Ice Sheet from a 2024 Science study with the ocean, atmosphere, and land masses to analyse how the ocean currents around Antarctica developed. The simulated currents were then compared with data-based reconstructions from this period.
Hanna Knahl explains: “There were already indications that the wind in the Tasman Gateway played an important role in the formation of the ACC. Our simulations can clearly confirm this: Only when Australia had moved further away from Antarctica and the strong westerly winds blew directly through the Tasman Gateway, the current could fully develop.”
Surprisingly, at that time the Southern Ocean may have been divided into two completely different parts. Although the ocean passages around Antarctica were already open, the model only simulates a strong current in the Atlantic and Indian sectors, while the Pacific sector remained much calmer... (MORE - details, no ads)
PRESS RELEASE: It transports far more than 100 times as much water as all of the Earth's rivers combined: The Antarctic Circumpolar Current rushes around the southern continent unhindered by land masses and is therefore a fundamental component of the climate system.
In a recent study published in the journal Proceedings of the National Academy of Sciences, a research team led by the Alfred Wegener Institute describes how and when this mighty ring current developed in Earth's history. Surprising finding: it took more than the opening of the ocean passages between Antarctica, and South America and Australia.
Earth’s climate underwent its last drastic change around 34 million years ago during the transition into the Oligocene - cooling from a largely ice sheet-free greenhouse climate to our current icehouse climate, in which large areas of the poles became increasingly glaciated with permanent ice. At this time, the ocean passages between Australia, Antarctica and South America widened and deepened, the Antarctic Circumpolar Current (ACC) developed and the formation of the Antarctic Ice Sheet began.
The CO2 concentration in the atmosphere at that time was around 600 ppm - a value that has not been reached ever since, but could be exceeded again by the end of this century in some climate scenarios. “In order to predict the possible future climate, it is necessary to look into the past with simulations and data to understand our Earth in warmer and more CO2-rich climate states than today,” says Hanna Knahl, climate modeller at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) and lead author of the study, which now appears in the Proceedings of the National Academy of Sciences (PNAS).
“But careful, the climate of the past can of course not be projected 1:1 onto the future. Our study shows that the circumpolar current in its ‘infancy’ influenced the climate very differently than today’s fully developed ACC does.”
For the current study, Hanna Knahl and her colleagues analysed the formation of the ACC. To this end, climate simulations were created with the continental configuration from 33.5 million years ago, when Australia and South America were still much closer to Antarctica. For these simulations, the team coupled the Antarctic Ice Sheet from a 2024 Science study with the ocean, atmosphere, and land masses to analyse how the ocean currents around Antarctica developed. The simulated currents were then compared with data-based reconstructions from this period.
Hanna Knahl explains: “There were already indications that the wind in the Tasman Gateway played an important role in the formation of the ACC. Our simulations can clearly confirm this: Only when Australia had moved further away from Antarctica and the strong westerly winds blew directly through the Tasman Gateway, the current could fully develop.”
Surprisingly, at that time the Southern Ocean may have been divided into two completely different parts. Although the ocean passages around Antarctica were already open, the model only simulates a strong current in the Atlantic and Indian sectors, while the Pacific sector remained much calmer... (MORE - details, no ads)