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Huge phytoplankton bloom off southern Australia

There's a remarkable story in those beautiful blue swirls in the waters off southern Australia, as viewed by satellite this Thursday, December 5.

For those who know their Dutch post-impressionist masters, the scene is reminiscent of Vincent van Gogh’s famous work The Starry Night. But this is not art. It's nature at its absolute finest.

Extensive phytoplankton bloom east of the Great Australian Bight, brought about by seasonal upwelling. pic.twitter.com/cFWTykSrie

— Andrew Miskelly (@andrewmiskelly) December 3, 2024

The swirls are caused by a phytoplankton bloom – a sudden and relatively rapid increase in the population of the microscopic algae called phytoplankton near the surface of the ocean.

Image: Well, obviously we had to include Van Gogh's The Starry Night for comparison. Source: Wikimedia Commons.

Such blooms are not uncommon in southern Australian waters in late spring and early summer. They are caused by an upwelling of nutrient-rich cold water from depths of the ocean, and often last a week or two.

Being a type of algae, phytoplankton are plants – unlike their tiny cousins zooplankton, which are microscopic animals. But plants need nutrients to help with photosynthesis, so when the upwelling occurs, phytoplankton want a piece of the action.

Image: The bloom is clearly visible in the waters between King Island (off NW Tasmania) and Kangaroo Island (south of Adelaide).

As for the greeny-blue colour of the bloom, that's down to the chlorophyll – yes, the same pigment that makes tree leaves green.