‘Australia has one of the most unique currents’

A physical oceanographer, Jessica Benthuysen monitors real-time data on the temperature, salinity and currents of oceans thousands of kilometres from her desk in Perth. She has worked with the Australian Institute of Marine Science for the last decade, first in Townsville and now in Western Australia, using ocean observations and ocean models to understand more about marine heatwaves and the movement of the great ocean currents.

“Australia has one of the most unique currents in the world, the Leeuwin current, off the west coast, just off Perth,” she says. “It’s one of the only currents in the world that flows Pole-ward against the winds; usually currents off west coasts flow with the winds toward the equator with cooler water which is very nutrient-rich. The Leeuwin current is very warm and low in nutrients.”

The Leeuwin current brought Benthuysen to Australia. Originally from the United States, she completed her doctorate in physical oceanography in the Massachusetts Institute of Technology–Woods Hole Oceanographic Institution Joint Program. “It really set me on my path understanding the coastal oceanography around the US,” she says. “But then my interest extended beyond that to understanding what is happening in the southern hemisphere. I wanted to come to Australia to find out why the Leeuwin current flows the way it does.”

She wanted to test theories on how ocean currents along the bottom of continental shelves are affected by changes in density and topography and how these bottom currents can cause upwelling, which pushes nutrients up into sunlit areas where they support marine ecosystems.

Benthuysen arrived in Australia in 2010 and began her research as a post-doctoral fellow with the CSIRO in Tasmania. She had been living in Australia for less than a year when there was an unprecedented marine heatwave off the coast of Western Australia and waters of up to five degrees above normal were measured over a month, she says.

“That’s truly phenomenal – that doesn’t really happen. We discovered this warm water event was related to a surge of warm water from the Leeuwin current reaching record strength speeds, bringing warm fresh tropical water along the coast.”

The marine heatwave had a range of devastating effects including coral bleaching and the death of sea grass meadow. It affected aquaculture and fisheries industries in Western Australia, such as the western rock lobster industry, worth hundreds of millions of dollars.

Benthuysen wanted to know why the record-strength Leeuwin current had brought a surge of warm fresh water down the west Australian coast. On the other side of Australia, she has also investigated how the East Australian Current can bring cooler waters to the Great Barrier Reef via “upwelling”.

She now monitors data from a range of scientific equipment immersed in the oceans around Australia which can track temperatures and salinity at varying depths.

“The data is critical to understanding long-term changes around Australia,” she says, “and we can use it to determine whether a marine heatwave is related to atmospheric changes or changes in the currents, such as the Leeuwin current.”

The Australian