Off the coast of Sydney, a vast and powerful ocean eddy is taking shape, stirring the waters of southeastern Australia. This isn’t a minor whirlpool but a massive, deep-reaching vortex, visible even from space, with the potential to disrupt marine life on a grand scale.
Recent research links these giant eddies to the creation of marine heatwaves, such as the one that hit Sydney from December 2021 to February 2022. The current formation, an even larger eddy located about 50 kilometers offshore, is a cause for concern among oceanographers. The CSIRO’s RV Investigator has just completed a 24-day voyage to study this “monster eddy,” revealing that it’s spinning at speeds of 8 kilometers per hour and harboring temperatures up to 3°C above the norm at depth.
Eddies are the ocean’s version of atmospheric storms, capable of being warm or cold, and significantly influencing marine life. Warm eddies often result in “ocean deserts” due to their low biological productivity, while cold eddies are more fertile, bringing up deep-sea nutrients that feed plankton. These eddies can trap warm water for extended periods, causing temperature-sensitive marine ecosystems to suffer during prolonged heatwaves.
Understanding the formation, movement, and dissipation of eddy currents is crucial as they can store vast amounts of heat and affect coastal sea levels. The East Australian Current, known for its instability, often feeds these warm eddies, which can grow to immense sizes. The current’s fluctuations can eventually form a coherent circle, trapping the eddy between other oceanic systems, much like atmospheric high-pressure systems can be pinned by surrounding weather patterns.
The research team deployed various instruments, including GPS-tracked buoys and Argo floats, to measure the eddy’s dynamics. These tools confirmed the eddy’s rapid internal currents and its relatively stationary position off the New South Wales coast. Satellite data and deep-sea measurements indicate that surface temperatures within the eddy have reached 23°C, which is 2 degrees above the monthly average, with even more extreme temperatures below the surface.
Like atmospheric systems, eddies act as heat engines, redistributing warmth across the ocean. While they eventually dissipate, releasing their heat into the atmosphere and surrounding waters, the timing of their disappearance is unpredictable. With summer approaching, the current mega eddy shows no signs of moving. If it drifts closer to the coast, it could spell disaster for the concentrated marine life there, potentially leading to a significant underwater crisis.