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Researchers from Cambridge, UCLA, and Scripps published a study in Communications Earth & Environment confirming with two decades of data that Circumpolar Deep Water in the Southern Ocean is advancing towards Antarctica at 1.26 km/year, threatening to melt ice shelves from below and raise global sea levels.
Researchers from the University of Cambridge have confirmed for the first time what climate models had predicted for almost two decades: a mass of warm water in the depths of the Southern Ocean is moving towards Antarctica and threatens the stability of the ice shelves that protect the continent’s glaciers. The study, led by Joshua Lanham from Cambridge’s Department of Earth Sciences, in collaboration with the University of California (UCLA) and the Scripps Institution of Oceanography, was published on April 28, 2026, in the journal Communications Earth & Environment (Nature group) and demonstrates that the so-called Circumpolar Deep Water (CDW) has migrated poleward at an average rate of 1.26 kilometers per year over two decades of measurements in the Southern Ocean. “It’s concerning because this warm water can flow beneath Antarctica’s ice shelves, melting them from below and destabilizing them,” Lanham warned in an official statement released by the University of Cambridge.
Empirical confirmation transforms what was computational projection into observed data in the real ocean. By combining measurements from oceanographic vessels collected over decades with data from robotic Argo floats and machine learning techniques, Lanham’s team built a continuous monthly record of circulation in the upper layers of the Southern Ocean, down to 2,000 meters deep, demonstrating that the CDW not only approached the Antarctic continent but also increased in thickness during the analyzed period. To put what’s at stake into perspective: Antarctica’s ice contains enough freshwater to raise global average sea levels by about 58 meters according to NASA, and the ice shelves that CDW threatens to melt from below are the barriers that prevent continental glaciers from flowing into the ocean.
What is Circumpolar Deep Water and why does it threaten ice
Circumpolar Deep Water is a relatively warm, salty, and nutrient-rich mass of water that circulates at depth around Antarctica as part of the Antarctic Circumpolar Current. With temperatures above 0°C, CDW is warm enough to contribute significantly to the basal melt of ice shelves, a process where ocean heat erodes the base of the ice layer extending over the water, weakening the structure from the bottom up without the visible surface showing immediate signs of deterioration. Under normal conditions, a layer of cold, dense water protects the ice shelves from contact with CDW, acting as a thermal barrier between the deep ocean heat and the ice base.
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What the Cambridge study documented is precisely the erosion of this protective barrier. CDW is expanding and advancing towards the Antarctic continent, pushing away the cold layer that previously separated it from the ice, and the rate of 1.26 km per year observed over two decades in the Southern Ocean demonstrates that the phenomenon is not a temporary fluctuation but a consistent trend. When CDW reaches the base of the ice shelves, the result is accelerated melting that can destabilize entire glaciers, a process that, once initiated, can become irreversible on human timescales.
How scientists measured the advance of heat in the Southern Ocean
The study’s methodology is what gives it credibility that isolated computational projections lack. The researchers combined three data sources: periodic measurements from oceanographic vessels that have monitored the Southern Ocean for decades, continuous records from robotic Argo floats that automatically dive and measure temperature and salinity at multiple depths, and machine learning algorithms that integrated this information to generate an uninterrupted monthly overview of ocean circulation in the upper 2,000 meters over two decades. The combination of punctual ship data and continuous buoy monitoring allowed for the identification of patterns that neither source alone would reveal.
The use of machine learning was decisive in transforming sparse data into a coherent record. Oceanographic ship measurements occur approximately once per decade in many regions of the Southern Ocean, a frequency insufficient to identify migration trends like the one the study documents, and Argo floats, while providing continuous data, cover the ocean unevenly. Machine learning filled spatial and temporal gaps, generating a model that researchers validated against independent measurements, a process that assumed certain biogeochemical parameters remained stable during the period, a limitation the team explicitly acknowledges in the article published in Communications Earth & Environment.
What happens when warm ocean water reaches Antarctic ice
The cascade effect that CDW migration in the Southern Ocean can trigger follows a logic that glaciology has documented for decades. Ice shelves function as natural barriers that dam continental glaciers, preventing them from flowing into the ocean at the speed gravity would allow without obstruction, and when CDW penetrates beneath these shelves, basal melting progressively weakens them until their containment capacity is compromised. Without the shelves acting as a brake, continental glaciers accelerate towards the ocean and contribute directly to global sea level rise.
The potential volume involved is what makes the discovery in the Southern Ocean a matter of global interest. The 58 meters of sea level rise that the complete melting of Antarctica would produce according to NASA is an extreme scenario that no serious scientist projects for the short term, but the question the Cambridge study poses is not whether all the ice will melt: it is whether the CDW will destabilize specific ice shelves that protect glaciers already considered vulnerable. The Thwaites and Pine Island ice shelves in West Antarctica are the most monitored, but a complementary 2022 study published in Nature Climate Change by Herraiz-Borreguero and Naveira Garabato also showed significant CDW warming in East Antarctica, indicating that the threat of the warm ocean is not limited to one region.
What the advance of ocean heat means for Brazil
Antarctica may seem distant from Brazilian reality, but what happens in the Southern Ocean directly affects the country’s coastline. Any rise in average sea levels impacts coastal cities such as Rio de Janeiro, Recife, Santos, Florianópolis, and Salvador, where millions of Brazilians live in areas vulnerable to flooding, and the Brazilian Panel on Climate Change (PBMC) has already warned of risks to coastal infrastructure, including port terminals like Itaqui, Tubarão, Santos, and Paranaguá, through which the commodities that sustain the country’s trade balance flow. The oil and gas sector, with offshore operations in the pre-salt layers of the Campos and Santos Basins, is also indirectly affected by changes in ocean dynamics that alter currents, temperatures, and operating conditions.
The research reinforces the urgency of the energy transition that Brazil is debating in the context of its climate policies. The connection between greenhouse gas emissions, ocean warming, and Antarctic ice melt is a chain documented by science for decades, and the Cambridge study adds observational evidence that the process is underway, not a future projection. The decisions that governments and companies make now regarding emissions reduction, energy matrix diversification, and coastal infrastructure adaptation will directly impact the speed with which heat at the bottom of the ocean will continue to advance towards the ice that protects the world from a sea level rise that would transform maps.
And you, do you think Brazil is prepared to deal with sea level rise? Should this type of research influence our climate policies more? Leave your opinion in the comments.
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