New research finds that melting ice in Antarctica is weakening the Antarctic Circumpolar Current (ACC) and could lead to worsening climate extremes, disrupting marine ecosystems, and reducing the ocean's ability to absorb carbon by 2050.
The melting ice sheets in Antarctica are weakening the ACC, a vital ocean current that regulates global climate and ocean circulation.
Scientists predict a 20% slowdown by 2050, which could exacerbate climate extremes, disrupt marine ecosystems and reduce the ocean's ability to absorb carbon. The slowdown could also allow invasive species to reach Antarctica and alter the food web.
Antarctica's giant current faces slowdown
According to a new study, melting glaciers are slowing down the Antarctic Circumpolar Current (ACC) — the strongest ocean current in the world.
This slowdown could have far-reaching consequences for the global climate, including rising sea levels, changing ocean temperatures, and disrupting marine ecosystems.
Researchers from the University of Melbourne and the NORCE research center in Norway estimate that in a high-carbon emissions scenario, the ACC could weaken by about 20% by 2050.
The increased influx of freshwater resulting from melting ice is expected to change the ocean's salinity and density, thereby disrupting circulation patterns in the Southern Ocean.
To understand these changes, researchers—including Associate Professor Bishacadette Gayan, Dr. Timur Sohil, and Dr. Andreas Kloker—used high-resolution simulations of the ocean and sea ice. Their analysis examined how changes in temperature, salinity, and wind conditions affect ocean currents and heat transfer.
Professor Gayan said: "The ocean is extremely complex and delicately balanced. If this 'engine' breaks down, it could have serious consequences, including more climate variability with greater extremes in some regions and acceleration of global warming due to a reduction in the ocean's ability to act as a carbon sink."
Invasive species threaten Antarctica
The ACC acts as a barrier to invasive species, such as southern kelp rafts or marine animals such as crustaceans or mollusks.
As the ACC slows and weakens, it is more likely that such species will reach the fragile Antarctic, with a potentially serious impact on the food web, which could, for example, change the menu available to Antarctic penguins.
The critical role of the ACC in global ocean circulation
The ACC, four times stronger than the Gulf Stream, is a vital part of the world's "ocean conveyor belt," which moves water around the globe and connects the Atlantic, Pacific, and Indian Oceans.
The researchers used Australia's fastest supercomputer, GADI, located at the Access National Research Infrastructure in Canberra. The basic model (ACCESS-OM2-01) was developed over a period of years by researchers from various Australian universities.
Slowdown expected even in low emissions scenarios
The projections examined in the study were made by a research team from the University of New South Wales (UNSW), who found that even a low emissions scenario could lead to a slowdown in ocean circulation.
Dr. Suhail said: "The 2015 Paris Agreement aimed to limit global warming to 1.5 degrees Celsius above pre-industrial levels. Many scientists agree that we have already reached this target, and it will likely warm further, with further impacts on the melting of ice in Antarctica."
The complexity of the ocean's reactions
The study, published in the journal Environmental Research Letters March 3, reveals that the impact of melting ice and ocean warming on the ACC is more complex than previously thought.
Professor Gayan said: "The melting ice sheets are pouring huge amounts of fresh water into the salty ocean. The sudden change in ocean salinity has many consequences—including weakening the Antarctic Bottom Water current and, according to this study, weakening the strong current that encircles Antarctica."
The new study contradicts previous studies that argued that the ACC may accelerate due to steeper temperature differences between different ocean latitudes.
Professor Gayane explained: "Previous ocean models have failed to adequately resolve small processes that control the strength of currents. This model is able to resolve such processes and shows a mechanism by which the ACC is expected to actually slow down in the future."
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