Southern Ocean threat to ice sheet
The Southern Ocean is one of the most important yet least understood regions of the planet when it comes to determining how global warming may affect the future of humanity, thanks to its capacity to absorb huge quantities of heat and carbon dioxide, and melt swathes of the Antarctic ice sheet.
In recent years, understanding how the Southern Ocean is changing as a result of increased greenhouse gas emissions has taken on greater urgency as scientists have learned more about the fragility of large parts of the Antarctic ice sheet, since glaciers extending into the sea are being eroded by relatively mild waters below.
Like removing a doorstop, the collapse of these ice shelves can free up inland ice to move into the sea, raising global sea levels and harming coastal communities.
Now a new study, published this week in Nature Communications, finds that beneath the surface layer of waters circling Antarctica, the seas are warming much more rapidly than previously known.
Furthermore, the study concludes, this relatively warm water is rising towards the surface over time, at a rate three to 10 times what was previously estimated. This means that there is a greater potential for the waters of the Southern Ocean, which are absorbing vast quantities of added heat and carbon dioxide from the atmosphere as a result of human activities, to help destabilise parts of the Antarctic ice sheet.
The observations in the study, conducted by researchers at institutions in France and Australia, come from 25 years of temperature measurements taken aboard the French Antarctic resupply vessel L’Astrolabe, from the surface down to about 2600 feet deep. The data, which includes more than 10,000 vertical temperature profiles, was gathered during multiple transits per year from Hobart in Tasmania to the Dumont d’Urville research station in Antarctica.
The researchers found that warming under the sea surface within waters near Antarctica, stands out from naturally occurring trends, with temperatures increasing at a rate of about 0.072 degrees Celsius (0.04C) per decade.
At the same time, the relatively warm water, usually located under a colder layer, is rising towards the ocean’s surface at the rate of about 130 feet per decade.
Part of the reason for concern is because within these waters, seemingly small shifts in temperature can have dramatic implications. Subsurface waters flowing around Antarctica are typically below freezing, but because of the pressures involved at depth and the water’s salt content, the freezing point can be lower than 0C (32F). This makes otherwise cold waters capable of melting ice.
The study states that the temperature changes found in the shipbased data matches the magnitude of changes found in the A mu nd se nB el ling ha us en Sea sin West Antarctica, where Antarctica’s most dramatic ice loss is already happening.