How did Earth’s most powerful ocean current form?

What is it about?

Today, the Antarctic Circumpolar Current (ACC) is the most powerful ocean current on our planet Earth. It rushes around the southern continent unhindered by land masses and represents a fundamental component of the climate system. Our paper studies the early development of the ACC when the ocean passages between Antarctica, South America and Australia opened. We show that the opening of these ocean passages alone was not enough to establish the current. As long as the westerly winds - the main driver of the ACC - did not blow through the Tasman Gateway directly, only part of the circumpolar current could develop. To understand this link, we simulated the climate with the continental configuration from 33.5 million years ago, when Australia and South America were still much closer to Antarctica. At that time, also the CO2 concentration in the atmosphere was higher than today, which makes this climate very special. The Antarctic Ice Sheet was much smaller than today and the climate was transitioning from a greenhouse world into the world with permanently ice-covered polar ice caps, which we know today.

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Photo by Tikun Mendez on Unsplash

Photo by Tikun Mendez on Unsplash

Why is it important?

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. But caution Is needed, 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. This understanding is crucial, as the formation of the ACC has strongly driven carbon uptake by the ocean. This reduction in the concentration of greenhouse gases in Earth’s atmosphere thus had the potential to initiate the cooler climate of the so-called Cenozoic Ice Age, which continues to this day with permanently ice-covered polar ice caps, in which warm and cold periods alternate. This new knowledge will therefore help us to more reliably interpret recent changes in Southern Ocean circulation.

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