The Antarctic Circumpolar Current (ACC), the most powerful ocean current on Earth, is slowing down due to the rapid melting of Antarctic ice sheets. Scientists project a 20% slowdown by 2050, a shift that could disrupt global climate patterns, intensify extreme weather, and threaten marine ecosystems. The weakening of the ACC also risks allowing invasive species to reach Antarctica, altering the fragile food web of the region.

The Antarctic Circumpolar Current

The ACC is a massive conveyor belt that moves water around the globe, connecting the Atlantic, Pacific, and Indian Oceans. More than four times stronger than the Gulf Stream, it regulates global climate by transporting heat, carbon dioxide, and nutrients across the world’s oceans. This circulation plays a crucial role in stabilizing weather patterns and supporting marine life.

However, they release massive amounts of freshwater into the ocean. This disrupts the density-driven circulation of the ACC, leading to a weakening of the current. Scientists from the University of Melbourne and NORCE Norway Research Centre warn that under a high-emissions scenario, the ACC could slow significantly, reshaping ocean circulation and global climate.

Why Is The Current Slowing Down?

Using high-resolution ocean and sea ice simulations, researchers have confirmed that as the ocean becomes less salty and less dense, the engine that powers the Antarctic Circumpolar Current (ACC) is slowing down.

According to Dr. Taimoor Sohail and Associate Professor Bishakhdatta Gayen, “the ocean is extremely complex and finely balanced. If this current ‘engine’ breaks down, there could be severe consequences, including more climate variability, with greater extremes in certain regions, and accelerated global warming due to a reduction in the ocean’s capacity to act as a carbon sink.”

Also, the disruption of ocean circulation could lead to the breakdown of deep ocean currents, affecting marine ecosystems worldwide. These changes threaten the stability of ocean life, impacting everything from fish populations to the broader marine food web that sustains biodiversity across the planet.

The Rise Of Invasive Species in Antarctica

Beyond climate disruption, a weaker ACC could also open the door for invasive species to reach Antarctica. Normally, the strong current acts as a natural barrier, preventing marine life from crossing into the icy continent.

As the ACC slows, kelp rafts, shrimp, and mollusks from other regions could make their way into Antarctic waters, potentially disrupting local ecosystems. Scientists fear these species could outcompete native Antarctic organisms, leading to shifts in the food web and threatening species like penguins, krill, and fish that depend on specific environmental conditions.

A Shift From Acceleration To Slowdown

For years, some climate models suggested that global warming would accelerate the ACC, as the increasing temperature difference between the poles and the tropics would strengthen the current. However, the latest high-resolution models suggest the opposite: the overwhelming effect of ice melt weakens the current instead.

This contradicts earlier predictions and highlights the complexity of Earth’s climate systems. The researchers emphasize that many past models did not fully account for small-scale ocean processes.

Can We Prevent The Slowdown?

Limiting global warming remains the only viable solution to preventing the ACC from weakening further. According to Dr. Sohail, if carbon emissions remain high, the slowdown will continue, even under more conservative climate projections.

The 2015 Paris Agreement aimed to limit warming to 1.5°C above pre-industrial levels, but recent studies suggest that this threshold has already been reached. ” Many scientists agree that we have already reached this 1.5 degree target, and it is likely to get hotter, with flow-on impacts on Antarctic ice melting,” noted Dr. Sohail.