Scientists have found that 71 of the 162 ice shelves surrounding Antarctica have reduced in volume over 25 years, releasing 7.5 trillion tonnes of meltwater into the oceans. The study found that almost all ice shelves on the western side experienced ice loss, while most on the eastern side remained the same or increased in volume. Over the 25 years, almost 67 trillion tonnes of ice was exported to the ocean, while 59 trillion tonnes of ice were added to the ice shelves, resulting in a net loss of 7.5 trillion tonnes. Dr Benjamin Davison, a research fellow at the University of Leeds, said that the mixed picture of ice-shelf deterioration is due to ocean temperature and currents around Antarctica.
The western half of Antarctica is exposed to warm water, which can rapidly erode the ice shelves from below, while much of East Antarctica is protected from nearby warm water by a band of cold water at the coast. Dr Davison believes human-induced global warming is a key factor in the loss of ice, as natural variation in climate patterns would have seen some signs of ice regrowth on the western ice shelves.
Ice shelves are weakening, leading to increased ice loss from glaciers. The Getz Ice Shelf experienced the largest ice losses, with 1.9 trillion tonnes lost over 25 years. The Pine Island Ice Shelf lost 1.3 trillion tonnes, with 450 billion tonnes due to calving and the remaining 1.3 trillion tonnes due to melting from the underside. The Amery Ice Shelf gained 1.2 trillion tonnes, surrounded by colder waters. Researchers analyzed over 100,000 satellite radar images to assess the health of ice shelves. If ice shelves disappear or diminish, it will have significant impacts on the ice system in Antarctica and global ocean circulation.
Over the 25-year study period, 66.9 trillion tonnes of freshwater went into the Southern Ocean around Antarctica from the ice shelves alone. This is because dense salty water sinks to the ocean floor as part of the global ocean conveyor belt. Freshwater from Antarctica dilutes the salty ocean water, making it fresher and lighter, which takes longer to sink and can weaken the ocean circulation system. A different study published in Nature Climate Change suggests that this process may already be underway. Professor Anna Hogg, from the University of Leeds, said the study has generated important findings, indicating that ice shelves are not cyclical advances and retreats but are experiencing steady attrition due to melting and calving.
Antarctica is experiencing significant ice shelf deterioration, with 48 losing over 30% of their initial mass over 25 years. This is evidence of Antarctica’s changing climate due to warming. The study provides a baseline measure for further changes that may emerge as the climate gets warmer. Information about Antarctica’s situation has largely come from the CryoSat-2 and Sentinel-1 satellites, which can monitor the continent even during cloudy and long polar nights.
CryoSat-2, launched in 2010, was the first European Space Agency Explorer mission and the first dedicated to monitoring Earth’s polar ice sheets and glaciers. The satellites have enabled scientists to track year-by-year changes in Antarctica. Dr. Mark Drinkwater, Head of Earth and Mission Science at the European Space Agency (ESA), said that monitoring and tracking climate change across the continent requires a satellite system that captures data routinely throughout the year. Sentinel-1, along with historical data from its predecessors ERS-1, -2, and Envisat, has revolutionized our ability to take stock of floating ice shelves and assess the health of the Antarctic ice sheet.