Study reveals that heat from the deep ocean is approaching Antarctica

    A decades-long study using oceanographic data provides the first evidence that heat from the deep ocean has moved closer to Antarctica, threatening the fragile ice shelves surrounding the continent.

    The upwelling of warm Circumpolar Deep Water is a fundamental process for the global climate system, transporting heat, nutrients and carbon towards the poles and Antarctica’s ice shelves.
    The upwelling of warm Circumpolar Deep Water is a fundamental process for the global climate system, transporting heat, nutrients and carbon towards the poles and Antarctica’s ice shelves.

    A study led by the University of Cambridge, with collaborators from the University of California, compiled long-term ocean measurements collected by ships and robotic floating devices to show that a warm water mass known as Circumpolar Deep Water has expanded and shifted towards the Antarctic continental shelf over the past 20 years. Previously, scientists did not have enough ocean observations to detect the warming trend.

    The importance of ice shelves and the imminent change

    Ice shelves play an important role in holding back Antarctica’s ice sheets and glaciers, which together store enough fresh water to raise sea levels by around 58 metres.

    This is the first time scientists have observed the shift in deep ocean heat across the entire Southern Ocean. Previous observations of the Southern Ocean, which surrounds Antarctica, were limited to transects recorded by ships roughly once every decade. This information, collected as part of a long-running international programme, provided detailed snapshots of temperature, salinity and nutrients throughout the water column, but without continuous data scientists faced greater uncertainty about long-term changes in heat distribution.

    In this study, scientists investigated physical and chemical properties of seawater obtained from repeated observations carried out from ships in order to classify Southern Ocean water masses and demonstrate changes in the abundance of warm water south of the Antarctic Circumpolar Current over the past two decades.
    In this study, scientists investigated physical and chemical properties of seawater obtained from repeated observations carried out from ships in order to classify Southern Ocean water masses and demonstrate changes in the abundance of warm water south of the Antarctic Circumpolar Current over the past two decades.

    To fill the gaps in the record, the researchers, including scientists from the Scripps Institution of Oceanography and UCLA, supplemented the ship measurements with publicly available data collected by a global network of autonomous drifting floats. These floats, known as Argo floats, provide continuous snapshots of the ocean, although the programme has not been running for as long as ships have been collecting detailed hydrographic sections.

    Combining data from Argo buoys and ships

    Using machine learning, the researchers combined data from the Argo floats with long-term patterns extracted from ship measurements to build a new record that captures detailed monthly snapshots over the past four decades, allowing them to uncover the shift in warm waters.

    “In the past, the ice shelves were protected by a layer of cold water, preventing them from melting. Now it appears that ocean circulation has changed, and it is almost as if someone has turned on the hot water tap and now the bathtub is heating up!”
    Sarah Purkey, professor and one of the lead authors of the study at the Scripps Institution of Oceanography.

    It makes sense that this warm water mass is expanding, said Purkey. More than 90% of the excess heat from global warming is stored in the ocean, with the Southern Ocean absorbing most of the anthropogenic heat.

    These changes could affect the entire globe, not just Antarctica

    The findings do not only have implications for Antarctic melting and sea level rise, said Professor Ali Mashayek, one of the lead authors of the study from Cambridge’s Department of Earth Sciences. “The Southern Ocean plays a key role in regulating global heat and carbon storage, so changes in heat distribution in this region have broader implications for the global climate system.”

    These changes suggest an increase in heat flow towards the Antarctic shelf, with implications for basal ice shelf melting and sea level rise.
    These changes suggest an increase in heat flow towards the Antarctic shelf, with implications for basal ice shelf melting and sea level rise.

    In the icy waters around the poles, extremely cold and dense water forms and sinks into the depths of the ocean. As the water sinks, it absorbs heat, carbon and nutrients, setting in motion a global “conveyor belt” of currents, including the Atlantic Meridional Overturning Circulation (AMOC), which transports water around the Atlantic.

    Climate models, including those used by the IPCC, indicate that rising air temperatures and the influx of fresh water from melting ice are reducing the formation of this dense water in the North Atlantic, which could lead to a weakening of the AMOC.

    Similar changes have recently been predicted for the Southern Ocean. Climate models suggest that the production of cold, dense water will decline around Antarctica, causing the warmer Circumpolar Deep Water to move towards the continent to fill the space left by the reduction in cold water.

    References of the news

    Lanham, J., Purkey, S., Srinivasan, K. et al. Poleward migration of warm Circumpolar Deep Water towards Antarctica. Communications Earth & Environment (2026).