A closer look at Earth’s history shows that melting ice sheets temporarily increased stratification in the Southern Ocean.
A new study finds that during the last two major deglaciations, the shifts from ice ages to warmer interglacial periods, meltwater released from the Antarctic ice sheet strengthened layering in the Southern Ocean. This enhanced stratification reduced the mixing of surface and deep waters and slowed the circulation of the global ocean.
The findings underscore the powerful influence of the Antarctic ice sheet on ocean dynamics and, in turn, on the global climate system. The research was led by François Fripiat of the Max Planck Institute for Chemistry and the Université Libre de Bruxelles, in collaboration with scientists from Princeton University and the Alfred Wegener Institute.
Over the past three million years, Earth has cycled repeatedly between extended glacial intervals and warmer interglacial phases. During glacial periods, vast ice sheets spread across much of the Northern Hemisphere, reaching into parts of Europe. Deglaciations marked the gradual retreat and loss of these massive ice sheets, reshaping ocean circulation and climate patterns worldwide.
Much attention for the North Atlantic, less for the Southern Ocean
Scientists have long examined how melting ice in the Northern Hemisphere affects the North Atlantic.
“While the impact of melting large Northern Hemisphere ice sheets on North Atlantic circulation has been studied for decades and is recognized for its major climatic consequences, the specific role of Antarctica on the Southern Ocean that surrounds it remains largely unknown,” explains François Fripiat.
In the North Atlantic, freshwater released from the Greenland ice sheet is thought to weaken the Atlantic Meridional Overturning Circulation (AMOC), a major ocean current system that helps keep Europe relatively warm.
By contrast, the Southern Ocean has received far less attention, despite its central role in the climate system. Encircling Antarctica, it links the Atlantic, Indian, and Pacific Oceans and acts as a hub for global ocean circulation. It is also the primary region where the atmosphere exchanges gases with the deep ocean, a massive carbon reservoir that holds roughly one hundred times more carbon dioxide than the atmosphere.
These exchanges depend largely on ocean stratification, that is, the way water masses are organized into layers that are more or less well mixed. “The ocean can be compared to a huge machine that redistributes heat and carbon on a planetary scale. When this machine becomes stratified, its operation slows down, with direct consequences for the climate,” explains François Fripiat.
Diatoms as a climate archive
For the study recently published in the journal Proceedings of the National Academy of Sciences (PNAS), the researchers analyzed sediment cores taken from the Southern Ocean. Their data is based on the isotopic composition of organic matter preserved in the shells of diatoms.
These microscopic shells of marine algae are found in large numbers in the Southern Ocean sediments and serve as a natural archive of past environmental conditions.
Impact of Ice-Sheet melt on ocean mixing
The results show that during deglacial periods, ocean stratification intensified strongly near Antarctica, driven by large inputs of freshwater from ice-sheet melting. At the same time, farther north near the polar front, the combined action of these freshwater inputs and the westerly winds promoted enhanced upwelling of deep waters, maintaining a certain degree of ocean ventilation on a global scale.
“Our data show that the climate system did not completely grind to a halt. Even when the ocean near Antarctica became more stratified, other mechanisms still allowed deep waters to rise and exchange with the atmosphere, notably under the influence of winds. These exchanges may have released CO₂ into the atmosphere, contributing to the warming that ended ice ages,” explains François Fripiat.
Far from being a simple icy desert, Antarctica thus appears as one of the invisible conductors of Earth’s climate system. Understanding its mechanisms means better anticipating the planet’s future.
Reference: “Deglacial stratification of the polar Southern Ocean” by François Fripiat, Daniel M. Sigman, Xuyuan E. Ai, Cédric Dumoulin, Simone Moretti, Anja S. Studer, Bernhard Diekmann, Oliver Esper, Thomas Frederichs, Frank Lamy, Ling Liu, Frank Pattyn, Mareike Schmitt, Ralf Tiedemann, Gerald H. Haug and Alfredo Martínez-García, 2 February 2026, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2502076123
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7 Comments
For several decades, there has been speculation about global warming slowing, or even halting, the Atlantic Meridional Overturning Circulation (AMOC). Most speculations seem to be in the category of ‘not impossible’ warnings, i.e. “could.” There have even been some papers that claim the extant circulation has already slowed. However, the currents are not fixed in concrete channels. They wander and vary in strength with time. If some have failed to find it, it could simply mean that they didn’t look in the right place! Lack of evidence is not evidence against something! However, it should be noted that a couple of papers, whose summaries have been published here — https://scitechdaily.com/defying-doomsday-forecasts-critical-ocean-current-is-still-going-strong-after-60-years/ and https://scitechdaily.com/how-the-florida-current-has-defied-changes-for-40-years/ — disagree with the claims of slowing or even cessation of the AMOC.
In Science, one cannot simply ignore counter evidence. It must be demonstrated with evidence and logic that the conclusions are faulty misinterpretations or other error(s) before one can legitimately dismiss the counter claims. In the case of the AMOC, because of its wandering, false-positives (claims of current where there is none) are unlikely, whereas, false-negatives (claims of cessation when the core location has only shifted) are much more likely.
It seems to me that many researchers are too quick to assume that the evidence for supporting the consensus paradigm — the AMOC is weakening as it did during the early-Pleistocene interglacials — instead of considering T. C. Chamberlain’s ‘Method of Multiple Working Hypotheses,’ to properly explain the empirical data.
Basically what you are looking at is the beginning of the day of the Lord. “The day of the Lord so cometh as a thief in the night…” The elements shall melt with fervent heat. Therefore what manner of person ought you to be.
I thought that the day of the Lord was over 2,000 years ago. However, to stay on topic, this is a science website, NOT an online Sunday School.
Perhaps, on occasion, the convergence of the two should be respected and given contemplation…
As long as there is evidence that the alleged ‘convergence’ isn’t just coincidence. Do you have such scientific evidence that you can present? When researchers can’t agree on which hypothesis is correct, it is hubris for laymen to decide to pick the one the agrees with their religious beliefs.
God’s Word predicts that in the last days of the world “…nations will be in distress, with the seas and the waves roaring. ” In a process i call Cataclysmic Interoperable Dysfunctionalism-driven by increasing heat-oceanic, atmospheric, cyrospheric and geophysical realms of adversely affected materials negatively engage each other. The result is ever increasing out of whack, disjointed operation of the world’s major forces. This may ultimately result in the disruption of the world’s oceans.
Have you heard the phrase “word salad?” It is a skill that some have mastered to use a lot of words to say nothing of value.