The Earth's largest and strongest ocean current is younger than researchers thought
A new study reveals that the Antarctic Circumpolar Current first started flowing 10 million years ago and not 30, as a consequence of permanent ice on Antarctica rather than its cause. Andreas Klocker contributed to the groundbreaking study published in the well-reputed journal Nature Geoscience.
The Antarctic Circumpolar Current. The strongest and largest ocean current on the planet with a crucial role for the global climate. So far, scientists thought it started flowing over 30 million years ago, leading to the formation of permanent ice on Antarctica. But, a new study reveals that this first happened 10 million years ago, as a consequence of permanent ice on Antarctica rather than its cause. Why is this important? We asked NORCE climate researcher Andreas Klocker who contributed to the groundbreaking study published in the well-reputed journal Nature Geoscience.
Why is it important to study the Antarctic Circumpolar Current?
– The Antarctic Circumpolar Current (ACC) is a strong and deep current circulating around Antarctica. It connects the three main ocean basins - the Atlantic, Pacific, and Indian, and it is crucial in regulating the ocean’s uptake of heat and carbon and regulates the transport of nutrients and energy to low-latitude regions.
– Consequently, it is important to study the dynamics of the Antarctic Circumpolar Current to understand how this current will change in a future climate.
Why is studying the “birth” of the current important, then?
– If we want to understand how the ACC will change in a future, warmer climate, much can be learned by reconstructing the circumpolar current’s evolution through Earth’s past climates.
One of the most significant changes in the strength of this current occurred ~10 million years ago when it reached a similar strength and depth to what is observed in today’s climate.
What did you find?
– First and foremost, we found that this current is not what caused Antarctic glaciation, but is rather the consequence of this ice formation.
– This study challenges the well-accepted hypothesis that plate tectonics, through the opening between Antarctica and the continents to the north, creating the openings known as Drake and Tasman Passage, led to the onset of the Antarctic Circumpolar Current.
What difference does this finding make?
– These results open up new perspectives on understanding the interaction between this current and Antarctic ice sheets. These results are therefore of great importance for understanding the future evolution of the ACC in a warming climate in which ice sheets are rapidly melting
How did you find out about this?
– We used rather innovative techniques. We analyzed fossil fish teeth and sediment grain size from sediment cores taken at the bottom of the Southern Ocean, spanning the last 31 million years.
– By combining these samples, we could trace the history of the ACC and determine when it developed to a similar strength to that observed in the modern climate.
What was your/NORCE’s role in the study?
– My role in this study was to strengthen the findings from the sediment cores with simulations from a high-resolution ocean model, showing that changes in the strength of the ACC, as estimated from sediment cores, were not driven by local changes in the bathymetry detail, but that climate-driven mechanisms drove the modern-like strong and deep ACC.
What can other scientists use the findings for?
– Other scientists can use these results as an important puzzle piece to understand the evolution of Earth’s climate through past warm and cold periods and use this to constrain future projections of a warming climate.
