Antarctica drives a global network of ocean currents called the “overturning circulation” that redistributes heat, carbon and nutrients around the globe. The overturning is crucial to keeping Earth’s climate stable. It’s also the main way oxygen reaches the deep ocean.

But there are signs this circulation is slowing down and it’s happening decades earlier than predicted. This slowdown has the potential to disrupt the connection between the Antarctic coasts and the deep ocean, with profound consequences for Earth’s climate, sea level and marine life.

Deep-ocean animals are adapted to low oxygen conditions but still have to breathe. Losses of oxygen may cause them to seek refuge in other regions or adapt their behaviour. Models suggest we are locked in to a contraction of the “viable” environment available to these animals with an expected decline of up to 25%. Slowdown of the overturning may also intensify global warming.

A paper published in the journal Nature Climate Change, uses real-world observations to decipher how and why the deep ocean around Antarctica has changed over the past three decades. The measurements reported show the overturning circulation has slowed by almost a third (30%) and deep ocean oxygen levels are declining. This is happening even earlier than climate models predicted.

Dense water formed near Antarctica, known as Antarctic bottom water (AABW), drives deep ocean circulation and supplies oxygen to the abyssal ocean. Observations show that AABW has freshened and contracted since the 1960s, yet the drivers of these changes and their impact remain uncertain.

To read a review click here and for the full paper click here