For decades, the waters around Antarctica have witnessed unusual changes. From the 1970s up until about ten years ago, the continent’s sea ice was expanding, despite the ongoing climate change. However, in 2016, this ice suddenly and dramatically decreased and has not recovered since, as global temperatures appeared to catch up with the Southern Ocean. This loss of sea ice poses significant consequences for Antarctica’s extensive ice sheet, which, if lost, would raise sea levels by 190 feet.
Scientists have now pinpointed the factors behind this expansion and sudden contraction, aided by deep-diving robots. The primary elements involved are salinity, winds, and oceanic churn. “One of the key takeaways from the study is that the ocean plays a huge role in sort of modulating how sea ice can vary from year to year, decade to decade,” explained Earle Wilson, a polar oceanographer at Stanford University and lead author of a new paper on the research.
The data was collected by a network of machines known as Argo floats. These human-sized, torpedo-shaped devices dive thousands of feet to measure temperature and salinity, then return to the surface to send the data to a satellite. Their passive floating allowed them to gather long-term data on changing conditions.
Consider swimming in a lake: as you dive deeper, the water becomes suddenly colder because the sun only warms the surface. This phenomenon also occurs in oceans, though the cold layer is much deeper.
In Antarctica, the situation is reversed. There, the cold air cools the ocean surface, while warmer waters circulate below. The Argo robots detected this pattern during their vertical movements. This separation means more sea ice can form as the warmer water is kept away from the surface.
Before 2016, increased precipitation made the surface waters less salty compared to the denser, saltier waters below, creating stratification. This setup trapped heat in the deeper layers, causing it to accumulate.
Then, atmospheric changes intensified winds, which moved surface waters away from Antarctica and brought the deeper warmth to the surface. “What we witnessed was basically this very violent release of all that pent up heat from below that we linked to the sea ice decline,” Wilson stated.
This atmospheric shift was likely influenced by climate change: as the planet warms, temperature gradients develop in the atmosphere, strengthening and altering wind patterns. Scientists are still determining how much of this is due to natural variability versus human-induced carbon emissions since the Industrial Revolution.
Regardless, the system changed in 2016. Besides drawing up warm waters, the intensified winds may have broken up the ice by clumping blocks together and creating waves. “Recent research has shown that both atmospheric and oceanic warming is likely contributing to the sudden change in Antarctic sea-ice extent since 2016, and this paper helps to further develop the point that deeper ocean warmth is a significant player,” noted Zachary Labe, a climate scientist with Climate Central who was not involved in the study.
The reduction in sea ice has jeopardized other ice formations. The Antarctic ice sheet, which rests on land, is supported by ice shelves along the coast. These vital structures are being undermined by warming seas and violent underwater storms. If the surrounding sea ice is lost, these shelves lose a significant protective barrier, as floating ice absorbs wave energy. Moreover, sea ice reflects sunlight, which helps to lower local temperatures. Losing these ice shelves would accelerate the decline of a vast amount of ice on the continent.
While Argo floats have provided critical data, more measurements are urgently needed. “Overall, we need more international support to continue building observing networks across the Antarctic polar region, both for oceanic and atmospheric monitoring,” Labe emphasized. “This is critical given the rapid changes we are beginning to observe in this part of the world in a warming climate, with potentially significant consequences for global sea level rise.”
The pressing question is whether the current low sea ice levels are permanent or if atmospheric and oceanic conditions might eventually favor growth. This new research promises to help scientists refine models predicting changes in the Antarctic waters and the speed of these changes. Sea ice might experience cycles of sharp decline followed by growth, but “the long-term, multidecade trend will be negative,” Wilson predicted. “That would be my guess, but we don’t know for sure.”
