You might have heard about the huge ocean whirlpool that's swirling just 50 kilometres off Sydney’s coastline. It's a ‘monster eddy’, a 400-kilometre-wide vortex of warm ocean water that is spinning close to Sydney's coast at 8 kilometres an hour, with deep underwater temps that are 3 degrees celsius above normal.
Yes, it does sound like a watery black hole and/or plot line from a Hollywood sea-apocalypse movie. Here's what it means for the waters along Australian's eastern coastline and those who call it home.
What is an eddy?
Scientists call a ‘spinning body of water’ an eddy. They can be small currents in rivers and creeks, but ocean eddies can be massive, stretching kilometres-wide and deep. They can even be visible from space.
In the ocean, eddies are like underwater storms. They can be cold or hot, and shape underwater life, while also creating extreme ocean weather.
Unlike cold eddies, which draw up rich nutrients for plankton from the icy depths of the ocean, warm eddies are desert-like currents that don’t house much life. They work through amassing heat, storing it, and taking it to wherever they get spun in the ocean.
They can store a lot of heat for a long time, but they do eventually let it go back into the atmosphere after blending with surrounding colder currents.
Why does this monster eddy mean for Sydney and our ocean life?
Researchers at UNSW and the CSIRO have found that the current, massive water vortex off Sydney could trigger a coastal marine heatwave. A coastal marine heatwave makes water temperatures rise rapidly, which in turn, has an impact on marine ecosystems and sea life, which are sensitive to temperature changes. There's a possibility it could lead to mass marine mortalities around Sydney and along Australia’s east coast.
The monster eddy is currently being squished between cold waters from the south, but it is being fed by the warm east Australian current (also known as the EAC in Finding Nemo). Researchers from UNSW have found that the water in this eddy is holding 30 per cent more heat than is normal in this part of the ocean.
The cold currents around it are stopping it being able to whirl away and dissipate in deeper waters, meaning it's possible it will come closer to the coast. This happened in December 2021, and it triggered a record-breaking marine coastal heatwave that impacted marine life. Let's hope we don't see a repeat.