Antarctic Intermediate Water Is Becoming Saltier: A new study published in Nature Climate Change has found that Antarctic Intermediate Water (AAIW) has become saltier and denser since 2015, following a sharp decline in Antarctic sea ice. The findings highlight potential changes in ocean circulation, water layering, and carbon exchange between the ocean and the atmosphere.
Scientists from the Indian Institute of Science (IISc), the University of Melbourne, and the University of Southampton conducted the research. The team found that a long-term trend of decreasing salinity in AAIW reversed after 2015, coinciding with a substantial decline in Antarctic sea ice.
What Is Antarctic Intermediate Water (Antarctic Intermediate Water Is Becoming Saltier)?
Antarctic Intermediate Water is a major water mass that forms in the Southern Ocean surrounding Antarctica and spreads northward into the Atlantic, Indian and Pacific Oceans.
It generally flows hundreds of metres below the ocean surface and plays an important role in regulating the ocean’s vertical structure, including the distribution of temperature, salinity and density.
Because AAIW transports the influence of the Southern Ocean into distant regions, changes in its properties can affect ocean conditions far beyond Antarctica.
According to Kaushik Mishra, the study’s lead author and a PhD student at IISc’s Centre for Atmospheric and Oceanic Sciences (CAOS), changes in this water mass can carry Antarctic environmental changes into other parts of the world’s oceans.
You can also watch a video regarding Antarctic Intermediate Water Is Becoming Saltier here:
How Has Antarctic Sea Ice Changed Since 2015?
During the Antarctic winter, particularly between May and July, sea ice forms across the Southern Ocean. As temperatures rise, some of this ice melts, releasing freshwater into the surrounding ocean.
For decades before 2015, Antarctic Intermediate Water had been becoming fresher. However, the study found that this trend reversed after a sharp decline in Antarctic sea ice.
The researchers linked this change to two major processes:
- Reduced freshwater input: Less freshwater associated with sea ice melt changes the salinity balance of the upper ocean.
- Increased upward movement of deep water: More warm, salty water moves upward from deeper ocean layers, contributing to higher salinity in the water that feeds AAIW.
Together, these processes increase the salinity and density of Antarctic Intermediate Water.
Why Does Freshwater From Melting Sea Ice Matter?
Freshwater released by melting Antarctic sea ice helps maintain a relatively fresh layer of cold water near the ocean surface. During winter, a cold water layer known as Winter Water forms in the Southern Ocean. It plays an important role in developing Antarctic Intermediate Water.
This surface water mixes with deeper water, contributing to the formation of water masses that later spread northward. When the freshwater contribution decreases, and saltier deep water moves closer to the surface, the balance changes. As a result, the water contributing to AAIW becomes saltier and denser.
These changes can affect how different ocean layers interact and circulate.
What Did the IISc Study Find?
The researchers analysed ocean temperature and salinity measurements, satellite observations of Antarctic sea ice and other ocean datasets.
They also used information from Argo, an international network of robotic floats that measure ocean conditions below the surface.
The study reported an increase in AAIW salinity of approximately 0.0048 grams per kilogram per decade around the Southern Ocean, with greater changes in certain regions.
The findings indicate that AAIW freshening reversed after 2015, alongside major changes in Antarctic sea ice conditions.
Bishakhdatta Gayen, the corresponding author and an Associate Professor at IISc’s Centre for Atmospheric and Oceanic Sciences, said the research initially focused on how intermediate water flows and mixes in the Indian Ocean sector and how its properties change over time.
As the researchers examined the observations, they identified changes in AAIW and investigated their relationship with changing sea ice conditions.
How Could Saltier Antarctic Intermediate Water Affect Climate Change?
Increasing AAIW salinity and density could have important implications for ocean stratification and the global carbon cycle.
1. Changes in Ocean Stratification
Ocean stratification refers to the arrangement of water into layers with different temperatures, salinities, and densities. Changes in salinity and density can affect how these layers mix and interact, potentially influencing ocean circulation and heat transport.
2. Potential Impact on Carbon Storage
The study also highlights concerns about the ocean’s ability to retain stored carbon. Changes in ocean layering and circulation can affect how carbon moves between deeper waters and the surface. Under certain conditions, this may allow more stored carbon to escape into the atmosphere, contributing to global warming.
However, the precise impact on the global carbon cycle depends on several interacting ocean processes and requires continued observation.
3. Effects Beyond Antarctica
AAIW spreads through the Atlantic, Indian and Pacific Oceans. Changes in its temperature, salinity, and density can therefore carry the effects of changing Antarctic conditions into distant ocean regions.
This makes monitoring intermediate water masses important for understanding broader changes in the global ocean system.
Also read: RMS CET 2026 Correction Window Opens.
Why Is Monitoring the Ocean Beneath Antarctic Sea Ice Important?
Satellite observations provide valuable information about the extent and concentration of sea ice. However, understanding the consequences of sea ice changes also requires measurements beneath the ocean surface.
The IISc-led research highlights the importance of combining satellite observations with ocean temperature and salinity measurements.
Argo floats are particularly valuable because they provide information about ocean conditions below the surface, helping scientists track changes that cannot be understood through sea ice observations alone.
Continued monitoring could help researchers better understand how Antarctic sea ice changes affect ocean circulation, water-mass formation and carbon storage.
Conclusion
The IISc-led study published in Nature Climate Change reveals that Antarctic Intermediate Water has become saltier and denser since 2015, reversing decades of freshening.
The researchers linked this shift to declining Antarctic sea ice, reduced freshwater input and the increased upward movement of warm, salty deep water.
Because AAIW connects the Southern Ocean with the Atlantic, Indian and Pacific Oceans, changes in this water mass could affect ocean circulation, stratification and the global carbon cycle.
The findings underline the need for continued observations of both Antarctic sea ice and the ocean beneath it to better understand the changing climate system.