Scientists have discovered troubling evidence that warm deep-ocean water is slowly moving closer to Antarctica, increasing the risk of melting the continent’s giant ice shelves from below.
The new study, led by researchers at University of Cambridge with collaborators from universities in California, analyzed decades of ocean measurements and found that a huge mass of warm water called circumpolar deep water has expanded and shifted toward Antarctica over the past 20 years.
The findings were published in Communications Earth & Environment.
Scientists have long worried about this possibility, but until now there was not enough detailed ocean data to clearly detect the trend.
Lead author Joshua Lanham said the discovery is concerning because the warm water can flow underneath Antarctic ice shelves and melt them from below, weakening the natural barriers that hold back glaciers and inland ice.
These ice shelves are extremely important for the planet. Antarctica’s ice sheets contain enough frozen freshwater to raise global sea levels by around 58 meters if they were to melt completely.
The Southern Ocean surrounding Antarctica plays a major role in Earth’s climate system. It absorbs much of the extra heat trapped by greenhouse gases caused by human activity.
In fact, scientists estimate that more than 90 percent of the excess heat from global warming ends up stored in the ocean.
For decades, scientists relied mainly on research ships that crossed the Southern Ocean every several years, collecting measurements of temperature and salinity. While these missions provided valuable snapshots, they were too limited to fully track long-term changes.
To solve this problem, the researchers combined ship measurements with data from thousands of robotic drifting devices known as Argo floats. These instruments move through the upper ocean and continuously collect information about ocean conditions.
The team then used machine learning techniques to merge the two sets of data into a detailed monthly record covering the last 40 years. This allowed them to clearly see the warm water gradually moving closer to Antarctica.
Professor Sarah Purkey from Scripps Institution of Oceanography compared the process to turning on a hot tap in a cold bath. In the past, Antarctica’s ice shelves were surrounded by a layer of very cold water that helped protect them. Now, ocean circulation patterns appear to be changing, allowing warmer water to move in.
The changes may also affect the massive global system of ocean currents that moves heat, carbon, and nutrients around the world. Near the poles, cold dense water normally sinks deep into the ocean, helping drive this giant “conveyor belt” of currents, including the Atlantic Meridional Overturning Circulation.
Climate models have predicted that global warming and increasing freshwater from melting ice could weaken these currents. The new study suggests those changes may already be happening in the Southern Ocean.
Lanham said the findings show this is no longer just a future scenario predicted by computer models. The changes are already being observed in the real world, with potentially major consequences for sea levels and the global climate system.
