Revealing shifts in Earth's mightiest ocean current over millions of years
by Robert Schreiber
Berlin, Germany (SPX) Mar 28, 2024

The Antarctic Circumpolar Current (ACC), the planet's most formidable oceanic flow, responsible for moving volumes of water a hundredfold greater than the cumulative discharge of all terrestrial rivers, has exhibited significant natural variability over the aeons, newly analyzed sediment core data reveals. These variations align with major climatic shifts, influencing both global temperature distribution and the carbon dioxide sequestration capabilities of the oceans.

During cooler periods in the Pliocene and the following Pleistocene epoch, the ACC's flow rate diminished, correlating with the expansion of the West Antarctic Ice Sheet. Conversely, during warmer intervals, the current accelerated, causing the ice sheet to retreat. "This dynamic of ice loss is linked to augmented heat conveyance towards the south," explains Dr. Frank Lamy of the Alfred Wegener Institute's Marine Geology Division, highlighting the ACC's pivotal role in modulating Earth's climate and the Antarctic Ice Sheet's stability.

The recent expedition aboard the drilling vessel JOIDES Resolution, helmed by Lamy and Prof. Gisela Winckler from Columbia University's Lamont-Doherty Earth Observatory, ventured into the remote South Pacific. Their mission: to extract sediment cores from the ocean floor, deep within the ACC's domain, free from terrestrial influence. These cores, dating back 5.3 million years, provide unprecedented insights into the ACC's historical flow rates and its response to past climate phases.

Spanning the Pliocene, Pleistocene, and the current Holocene epoch, the sediment analyses enable a comprehensive study of the ACC's evolution. Initial findings suggest an intensification of the ACC with the onset of global cooling in the Pliocene, attributed to an increasing temperature gradient between the Equator and Antarctica, stimulating robust westerly winds. However, a subsequent decline in the current's strength coincided with a major climatic transition and significant atmospheric and oceanic circulation changes, including a reduction in atmospheric CO2 levels and oceanic cooling.

Further research delineates a tight linkage between ACC strength and glacial cycles over the last 800,000 years, with the current's speed surging by up to 80 percent during warmer periods marked by higher CO2 concentrations. Conversely, ice ages saw a decrease in flow rate by up to 50 percent. These fluctuations not only affected the current's velocity but also its position, influencing the Southern Ocean's upwelling of nutrient-rich waters and the consequent CO2 storage in ocean depths.

Research Report:The study underscores the intricate relationship between the ACC and global climate dynamics, including potential implications for future climate scenarios. As anthropogenic influences continue to reshape the planet's climate, understanding the historical behavior of the ACC is critical for forecasting its future role in global heat distribution, carbon dioxide management, and the impacts on Antarctic ice melt.

Related Links
Alfred Wegener Institute
Beyond the Ice Age