The Antarctic Circumpolar Current, also known as the Antarctic Circumpolar Current (ACC), is the most powerful ocean current on the planet. It literally circles Antarctica from west to east, pushed by strong westerly winds. It transports an impressive amount of water — about 173 million cubic meters per second — and connects three oceans: Atlantic, Pacific and Indian.
This huge flow of cold water regulates global temperatures, moves nutrients between oceans and plays an important role in the carbon cycle. In practice, it is one of the fundamental mechanisms of the “Earth-climate”. But something is changing.
According to an international study published in the journal Nature Communications130,000 years ago the ACC flowed three times faster than today. The data comes from samples of marine sediments taken at over 3,000 meters deep, in the Scotia Sea, north of Antarctica. The mission was led by the University of Bonn, in collaboration with researchers from five countries.
How the most powerful current on Earth has changed
To reconstruct the speed of the current in the past, scientists studied the size of the grains in the sediments deposited on the seabed. The reasoning is simple: the stronger the current, the longer the particles remain suspended in the water. When the current slows down, the finer ones are deposited. By analyzing the proportion between large and fine particles, one can understand how intense the current was in a certain period.
In the case of the ACC, the difference is clear. According to Michael Weber, geologist at the University of Bonn and coordinator of the expedition:
During the penultimate warm period – around 130,000 years ago – the current was more than three times faster than in recent millennia.
A surprising discovery, given that the climate back then was similar to that of today. So, what has changed?
What does the Earth’s orbit have to do with the speed of ocean currents?
The answer, the researchers explain, could lie in space. Specifically, in the way the Earth revolves around the Sun. Our planet follows an elliptical orbit that changes shape every 100,000 years or so. Furthermore, the tilt and rotation of the Earth’s axis change every 21,000 years. These two factors change the amount of solar energy that reaches different areas of the Earth — and this affects winds, including those that power the ACC.
According to the study, 130,000 years ago both of these astronomical factors were at their maximum, and this would have enhanced the westerly winds, making the current much faster. Not only that: the current would have moved further south, by about 600 kilometers, bringing warmer waters closer to the Antarctic ice sheets.
This may have contributed to a sea level rise of between 6 and 9 meters during the last interglacial period. For comparison: today, millions of people live less than one meter above sea level.
What does this study tell us about the future?
At present, Earth’s climate system, if left to act on its own, is expected to slowly shift the ACC northward, over centuries or millennia. But the latest climate models predict the opposite: a southward movement caused by ongoing climate change. The melting of Antarctic ice, which releases fresh, cold water into the oceans. This slows down the deep circulation and weakens the current.
According to scientists, understanding how much natural factors matter compared to those caused by man is an absolute priority today. For this reason, it will be necessary to combine past geological data with advanced climate simulations.
As Xufeng Zheng, professor at Hainan University and coordinator of the study, stated:
To understand where we are going, we must look back, but also forward. We need a dialogue between geology and climate science.
You might also be interested in:
