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8 months ago
22
A massive vortex of ocean water encircling Antarctica, a swirling volume 100-times larger than all the world's rivers combined, is getting faster due to climate change.
At least, that's the finding a new study that examined the past 5.3 million years of this polar ocean vortex's behavior, using sediment cores samples take from Earth's roughest and most remote waters.
As one co-author of the new research, a geochemist at Columbia University, put it, 'This is the mightiest and fastest current on the planet.'
'It is arguably the most important current of the Earth climate system.'
Sea ice plays an important role maintaining the Earth's energy balance while helping keep polar regions cool due to its ability to reflect more sunlight back to space. Pictured above, some of that very same sea ice, in the water off Cuverville Island in the Antarctic
That geochemist, Dr. Gisela Winckler of Columbia's Lamont-Doherty Earth Observatory, said that the new study 'implies that the retreat or collapse of Antarctic ice is mechanistically linked to enhanced ACC flow.'
It's 'a scenario,' she said, 'we are observing today under global warming.'
Driven by the continuous westerly winds, the ACC rotates clockwise around the southernmost icy continent at a speed of approximately 2.5 miles per hour, swirling along with it about 6 billion cubic-feet of water per second.
Geologists currently believe that the conditions for creating the vortex first emerged after Antarctica separated from Australia 34 millions years ago, during tectonic shifts in the Eocene epoch.
But the vortex, scientists say, only got into its modern grove 12-14 million years ago.
Above is map of simulated ocean velocities at 328 feet below the surface, with the bluish gray areas showing weaker current and the white areas showing the stronger currents of the Antarctic Circumpolar Current (ACC) vortex. ACC behavior here was derived from the satellite 'altimetry16.' The white stars above denote the research team's sediment core drilling sites
In 2021, French explorer and environmentalist Jean-Louis Etienne announced a Polar Pod that will complete two circuits around Antarctica every three years, carried by the Antarctic Circumpolar Current, for similar polar research
What is sea ice?
Sea ice is simply frozen ocean water. It forms, grows, and melts in the ocean.
It floats on the surface of the sea because it is less dense than liquid water.
In contrast, icebergs, glaciers, ice sheets, and ice shelves all originate on land.
Sea ice is estimated to cover around 7 per cent of Earth's surface and about 12 per cent of the world's oceans.
The lion's share of sea ice is contained within the polar ice packs in the Arctic and Southern oceans.
These ice packs undergo season variations and are also affected locally on smaller time scales by wind, current and temperature fluctuations.
About 40 scientists from a dozen countries contributed to new study, published Wednesday in Nature, some aboard drill ship the JOIDES Resolution which was deployed to retrieve sediment samples from the ocean floor.
The research vessel conducted a two-month tour in the darkness of South Pole's winter (May to July 2019) near Point Nemo over 1,600 miles from the nearest piece of surface land, the Pitcairn Islands.
Waves over 60-feet high threatened the JOIDES as its crew drilled and dredged up 500- to 650-ft sediment cores for their study of the vortex's many millenia of activity.
Advanced X-ray techniques helped the researchers analyze the changing particle sizes of the ancient deep-ocean sediment.
Smaller particles, the reasoned, settle more during times of slower current, while only larger particles will have the weight to fall to the ocean floor during faster ACC currents.
After years of study, the core samples revealed multiple eras of changing ACC speed that matched known shifts in Earth's climate.
The project was then able to match this new data to prior studies of the West Antarctic Ice Sheet, raising stark evidence that the ACC's fast-flow periods corresponded to known moments when Antarctica's glacial ice shrank.
'This loss of ice can be attributed to increased heat transport to the south,' Dr. Frank Lamy, the study's lead author, said.
'A stronger ACC,' Dr. Lamy, who teaches at Germany's Alfred Wegener Institute warned, 'means more warm, deep water reaches the ice-shelf edge of Antarctica.'
English (US)