Disturbing find at bottom of ocean triggers worrying weather prediction

It was previously thought such a change would take hundreds of years.

The world’s coldest, densest mass of ocean water is critical to the Earth’s temperature regulation. And worryingly, it’s shrinking.

Antarctic Bottom Water is formed by cold winds at a handful of sites around Antarctica. The exceptionally salty water sinks to the seafloor, filling depths below 4000 metres as it spreads to basins connected to the Southern Ocean.

Its flow helps the world’s oceans circulate and this assist them in storing heat and absorbing carbon. If this process is affected, then it will be bad news for humankind, because oceans have so far absorbed 90 per cent of the heating created by human activities and around a third of extra carbon pollution created since the Industrial Revolution.

In the foreground we see the backs of two men in helmets. It is snowing. A Conductivity-Temperature-Depth (CTD) is being hauled in. It is dark.
A Conductivity-Temperature-Depth (CTD) is dropped into the ocean to measure water conditions in Antarctica. Source: Mike Meredith, BAS

How was the ocean data collected?

Researchers from British Antarctic Survey published findings in the journal Nature Climate Change that long-term changes to winds and sea ice are impacting the water’s production in the Weddell Sea. The study follows the release of a new map that shows major changes to the borders of Antarctica and the Arctic due to climate change.

The study was formulated using ship-based observations, satellite data, and expeditions to measure ocean temperature and saltiness. Researchers found shrinkage of 20 per cent volume over the past three decades in the sections they analysed.

What does this mean for me?

Lead author Dr Shenjie Zhou said the study reveals how “sensitive” the Antarctic is to climate change. “It highlights the complex interplay between atmosphere and sea ice which needs to be properly represented in climate models in order for us to confidently predict how it may respond in the future,” he said.

It was previously believed changes to the deep ocean took centuries, but co-author Dr Alessandro Silvano said the study shows they can happen in just a few decades. “The shrinking of deep waters in Antarctica can have far-reaching consequences, from reducing the ability of the ocean to absorb carbon associated with human activities to decreasing the oxygen supply to abyssal waters, affecting deep ecosystems,” he said.

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