A long-term study has issued a stark warning that Antarctica is being melted from below as deep ocean heat moves closer to the continent's fragile ice shelves. Scientists have been tracking the movement of a mass known as the 'circumpolar deep water' (CDR) for decades. This flow of relatively warm water is typically trapped far from the ice sheets, at depths of around 1,600 feet (500 metres) beneath the ocean surface.
However, researchers have observed that strong winds in the Southern Ocean are now gradually dragging the CDR towards the surface. Although these waters are only about 2°C (35.6°F), they are sufficiently warm to begin weakening the Antarctic ice shelves. These vast floating platforms of ice act as a barrier, holding back Antarctica's inland ice sheets and glaciers, which contain enough freshwater to raise global sea levels by 190 feet (58 metres).
Changing Ocean Circulation
Senior author Professor Sarah Purkey, from the Scripps Institution of Oceanography, explained the significance of the findings. 'In the past, the ice sheets were protected by a bath of cold water, preventing them from melting. Now it looks like the ocean's circulation has changed, and it's almost like someone turned on the hot tap and now the bath is getting warmer!'
The study reveals that over the past 40 years, the CDR has become thicker and moved closer to Antarctica. While climate models had previously predicted that deep ocean heat could expand and shift towards the continent, there was insufficient data to confirm this phenomenon until now. The challenge has been that high-quality data from the Southern Ocean is collected only about once per decade by passing ships.
Innovative Data Collection
To overcome this limitation, researchers utilised a global array of floating probes known as 'Argo' floats, which continuously gather data as they drift through the upper ocean. By combining this information with ship-based data, the team created a detailed record of monthly snapshots spanning over four decades. For the first time, this clearly showed that deep ocean heat is encroaching on Antarctica.
This process not only directly contributes to the melting of ice shelves but also pushes back the grounding line—the point where the ice meets the bedrock. This exposes more ice to warm water, creating a 'positive feedback loop' that accelerates ice loss.
Global Consequences
While the exact cause of the deep water movement remains uncertain, researchers suggest it may result from a combination of natural variations and human-induced climate change. However, the effects of this change will be felt worldwide. Senior author Professor Ali Mashayek, a climate scientist at the University of Cambridge, told the Daily Mail: 'The immediate impact is sea level rise with complex geographical patterns, impacting coastal communities. That impact can be regionally compounded by local currents, tides, and storms, creating extreme sea level events such as floods.'
Professor Mashayek added that this melting could also interfere with the formation of key ocean currents. When water meets ice around the poles, extremely cold, dense, salty water forms and sinks deep into the ocean, drawing down heat, carbon, and nutrients, and driving the global 'conveyor belt' of ocean currents. These currents include the vast Atlantic Meridional Overturning Circulation (AMOC), which powers the Gulf Stream and distributes heat and water across the Atlantic.
Threat to Ocean Currents
Warming air temperatures and freshwater runoff from melting glaciers weaken this process and threaten to destabilise AMOC. New data indicates that cold water production will also decline around Antarctica, causing even more warm water to move towards the ice shelves to fill the void. The resulting slowdown in ocean circulation will limit the ocean's ability to absorb carbon and heat from the atmosphere, leading to faster global warming.
Lead author Dr Joshua Lanham stated: 'We can now see this scenario is already emerging in the observations. This isn't just a possible future scenario suggested by models; it's something that is happening now, bringing wider implications for how carbon, nutrients and heat are cycled through the global ocean.'
AMOC Collapse Fears
Although the study does not fully examine the consequences for AMOC, it comes amid growing fears that this key ocean current may collapse completely. A separate study from the University of Bordeaux predicted that AMOC is on track to weaken by 50 per cent by the end of this century, a more severe decline than the previously estimated 32 per cent. If AMOC were to fail, it would radically alter the Gulf Stream and could plunge Northern Europe and the UK into a new Ice Age, with London experiencing winter extremes of -20°C (-4°F) and three months of the year below freezing.
