New Delhi, Oct 30: Scientists from the Indian Institute of Science (IISc), Bengaluru, and the UK warned on Wednesday that a massive body of water flowing from Antarctica into the Indian Ocean has undergone a complete transformation in its fundamental characteristics over the last decade. This shift signals a potential major impact on the entire global climate system.
By conducting an in-depth analysis of ocean and satellite data spanning over 20 years, the scientists have demonstrated that the massive loss of Antarctic ice is causing an unprecedented, significant upheaval in the depths of the ocean. They noted that the changes occurring over the past few decades within this vast water mass—which connects the icy southern continent to the rest of the world—took a drastic turn after 2016.
“For decades, this water mass remained ‘super-stable.’ However, since 2016, this trend has completely reversed. Due to the rapid melting of Antarctic sea ice, the deep ocean water has become saltier, denser, and has shifted to greater depths,” stated Baishakhdutta Gayen, a key member of the research team at IISc. What is ‘Antarctic Intermediate Water’?
Oceans absorb 90 percent of the excess heat that accumulates in the atmosphere due to global warming. Consequently, any significant change in the characteristics of the oceans has a direct impact on the global climate.
The Southern Ocean—often referred to as the ‘engine room’ of the Earth’s climate system—is covered by Antarctic ice and plays a crucial role in determining the depth and structure of the world’s oceans. It contains major water masses that transport vast quantities of heat and carbon across the globe.
This significant variation was discovered by scientists Baishakhdatta Gayen and Kaushik Mishra from the Centre for Atmospheric and Oceanic Sciences (CAOS) at the Indian Institute of Science (IISc), along with Alberto Naveira Garabato from the University of Southampton, while they were studying ocean circulation patterns near Antarctica.
The water mass they studied is known as ‘Antarctic Intermediate Water’. Located at a depth of 700 to 1,200 meters below the ocean surface, this layer separates the heat-absorbing upper ocean from the deeper ocean below. Water from the Southern Ocean flows northward into the Atlantic, Indian, and Pacific Oceans, carrying characteristics acquired near Antarctica to tropical oceans thousands of kilometers away.
A Shift in Ocean Balance in 2016
Each year, as ice melts during the spring and summer, it adds fresh water to the ocean surface. From the 1970s until 2015, this water mass was becoming progressively fresher and lighter. However, the situation has changed completely since 2016, following a sharp decline in the amount of sea ice.
Scientists have examined 20 years of measurements from ‘Argo’—an international robotic network that records ocean temperature and salinity—alongside satellite observations and ocean analyses covering the period from 2004 to 2024. While all three datasets indicate that the water was becoming fresher until 2015, they confirm that since 2016, Antarctic Intermediate Water has been becoming saltier, denser, and deeper. The most pronounced changes among these have been observed in the South Atlantic Ocean.
Although the ultimate consequences of this oceanic shift are not yet fully understood, it has the potential to significantly impact the South Asian monsoon. “Previous research has established a strong link between the heat absorbed by the Southern Ocean and the dynamics of the South Asian monsoon winds. Therefore, we must closely monitor this trend over the next decade at the very least,” stated Gayen. This significant and concerning research paper has been published in the globally renowned journal *Nature Climate Change*.