As if a giant sponge had failed at the planet's southern extreme, the Southern Ocean is becoming saltier, losing ice at an alarming rate, and allowing deep heat to return to the surface, in a change capable of disrupting the circulation that regulates temperature, carbon, and storms across all Earth's oceans.

As if a giant sponge had failed at the planet’s southern extreme, the Southern Ocean is becoming saltier, losing ice at an alarming rate, and allowing deep heat to return to the surface, in a change capable of disrupting the circulation that regulates temperature, carbon, and storms across all Earth’s oceans.

Written by Valdemar Medeiros

Published on 29/04/2026 at 20:59

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2025 Study Reveals Southern Ocean Became Saltier, Lost Climate Efficiency, and May Affect Global Ocean Circulation.

According to the University of Southampton, a study published on June 30, 2025, in the Proceedings of the National Academy of Sciences revealed that the Southern Ocean has entered a completely different state from what it maintained for decades, with abrupt changes not predicted by climate models. Using European satellite data collected between 2015 and 2024, Dr. Alessandro Silvano and his team documented an unexpected reversal: the ocean surface around Antarctica, which had been progressively becoming colder and fresher since the early 1980s, started to become warmer and saltier from 2015 onwards.

During the same period, Antarctica lost a sea ice area equivalent to the size of Greenland, marking one of the largest environmental transformations recorded in recent decades. The two changes began to interact in a feedback loop that is not yet fully understood by science.

Southern Ocean Acts as Planet’s Main Climate Regulator by Absorbing Heat and Carbon Dioxide

To understand the importance of this change, it is necessary to comprehend the role of the Southern Ocean in the global climate system.

ARTICLE CONTINUES BELOW

Salinity-Dependent Water Stratification Maintains Thermal Equilibrium and Allows Heat Storage in the Depths

The functioning of this system depends on a specific physical equilibrium. In regions close to freezing, such as the Southern Ocean, water density is primarily controlled by salinity.

Saltier water is denser and sinks. As it sinks, it transports heat and carbon to the depths, where they are stored for long periods.

For decades, the system functioned stably. Ice melt released fresh water to the surface, forming a less dense layer that floated over saltier waters. This process created stratification that kept heat trapped in deep layers and favored surface freezing in winter.

Increased Salinity Since 2015 Breaks Stratification, Allowing Deep Heat to Rise to the Surface

From 2015 onwards, this equilibrium was disrupted. Surface salinity increased, reducing the stratification that separated the ocean layers.

As a result, heat stored in the depths began to rise more easily to the surface. This process triggered a feedback loop: less ice generates less fresh water, which increases salinity, allowing more heat to rise, further hindering ice formation.

Collapse of Antarctic Sea Ice Reinforces Warming Cycle and Alters Ocean Dynamics

Sea ice entered an accelerated decline. From 2022 onwards, minimum extent records were repeatedly registered.

The summer of 2023 presented the lowest sea ice extent ever observed in satellite records. This reduction reinforces the surface warming process and profoundly alters ocean dynamics.

Return of Maud Rise Polynya Indicates Profound Change in Weddell Sea Ocean Circulation

One of the most striking signs of this transformation was the return of the Maud Rise polynya. This opening in the sea ice, which had not occurred since the 1970s, reappeared with great extent in the Weddell Sea.

Polynyas allow direct heat and gas exchange between the deep ocean and the atmosphere, intensifying convection and altering the thermal balance.

The Southern Ocean plays a central role in thermohaline circulation. This system distributes heat, salt, and carbon throughout all the oceans on the planet.

Changes in stratification and deep water formation can modify this system, with global impacts.

Upwelling of deep waters releases heat and carbon dioxide accumulated over decades

With the breakdown of stratification, warmer, carbon-rich deep waters began to rise. This results in the release of stored heat and a reduction in the ocean’s capacity to absorb new CO₂ emissions.

Since the 1980s, the Southern Ocean showed a trend of surface cooling and reduced salinity.

This trend was reversed in less than a decade. The speed of the change was considered unexpected by the scientific community.

Causes of change include ice loss, altered winds, and warming of intermediate layers

Researchers point to multiple factors to explain the change. Among them are the reduction of sea ice, changes in wind patterns, and accumulated warming in the intermediate layers of the ocean.

Oceano Austral está ficando mais salgado, perdendo gelo — Southern Ocean is getting saltier, losing ice

Changes in the ocean impact atmospheric patterns. Regions like New Zealand already show signs of increased storms. Other areas of the Southern Hemisphere may also be affected.

Global ocean circulation influences the temperature of the South Atlantic. This dynamic is linked to the South Atlantic Convergence Zone, which regulates rainfall in Brazil. Changes in this system can affect precipitation regimes.

Continuous monitoring with satellites and sensors is essential to understand the phenomenon’s evolution

The University of Southampton highlights the need for constant monitoring. Satellites and autonomous instruments are fundamental for tracking changes in salinity, temperature, and ice.

The available data does not yet allow determining if the change is reversible. The system may return to its previous state or enter a new climatic regime. The observed change raises questions about the future of the climate system.

In your view, can the ocean still recover its balance, or are we facing a permanent transformation?

2025 Study Reveals Southern Ocean Became Saltier, Lost Climate Efficiency, and May Affect Global Ocean Circulation.

Southern Ocean Acts as Planet’s Main Climate Regulator by Absorbing Heat and Carbon Dioxide

Salinity-Dependent Water Stratification Maintains Thermal Equilibrium and Allows Heat Storage in the Depths

Increased Salinity Since 2015 Breaks Stratification, Allowing Deep Heat to Rise to the Surface

Collapse of Antarctic Sea Ice Reinforces Warming Cycle and Alters Ocean Dynamics

Return of Maud Rise Polynya Indicates Profound Change in Weddell Sea Ocean Circulation

Upwelling of deep waters releases heat and carbon dioxide accumulated over decades

Causes of change include ice loss, altered winds, and warming of intermediate layers

Continuous monitoring with satellites and sensors is essential to understand the phenomenon’s evolution

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2025 Study Reveals Southern Ocean Became Saltier, Lost Climate Efficiency, and May Affect Global Ocean Circulation.

Southern Ocean Acts as Planet’s Main Climate Regulator by Absorbing Heat and Carbon Dioxide

Salinity-Dependent Water Stratification Maintains Thermal Equilibrium and Allows Heat Storage in the Depths

Increased Salinity Since 2015 Breaks Stratification, Allowing Deep Heat to Rise to the Surface

Collapse of Antarctic Sea Ice Reinforces Warming Cycle and Alters Ocean Dynamics

Return of Maud Rise Polynya Indicates Profound Change in Weddell Sea Ocean Circulation

Upwelling of deep waters releases heat and carbon dioxide accumulated over decades

Causes of change include ice loss, altered winds, and warming of intermediate layers

Continuous monitoring with satellites and sensors is essential to understand the phenomenon’s evolution

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