Seals collect treasure trove of data on ocean currents


Scientists enlisted some unusual assistants to help find out what is going on 5,000 metres beneath Antarctica's oceans. Anthea Batsakis reports. 


Southern male elephant seals became research assistants when fitted with state-of-the-art miniaturised, satellite-linked conductivity-temperature-depth sensors in Prydz Bay Antarctica.
Clive R. McMahon

Melting ice shelves in Antarctica’s Prydz Bay could eventually have disastrous effects on the world’s ocean currents, new data – collected by elephant seals – show.

As ice melts, it dilutes the saltier water at the bottom of the ocean, which affects ocean currents worldwide.

Too much fresh water could lead to “doomsday scenario” – and shut down the Earth’s ocean circulation system – says Guy Williams from the University of Tasmania, the lead author of a new study published in Nature Communications, although he admits the disaster could be tens of thousands of years in the making.

Antarctic research is rarely a simple exercise, particularly if you’re investigating currents thousands of metres below the surface. But that’s where scientists find the key to Earth oceanic circulation, in what’s known as bottom water – the extremely salty water around 5,000 metres deep.

It forms when Antarctic water on the surface freezes and leaves the salt in the water. The dense surface water sinks to the ocean floor.

The constant sinking, mixing and upwelling puts the Earth’s ocean conveyor belt system into gear – although the exact mechanism is not completely understood.

But with ice shelves – the big floating slabs of ice that fringe the frozen continent – crumbling, the system is at risk.

Understanding how the fresh water dumped by melted ice affects bottom water formation is important if we are to understand ocean circulation and how it might change in the future, says Williams.

Under one scenario he is considering, the salty bottom water dilutes so much that it does not have sufficient density to reach the ocean floor. That would reduce the conveyer belt system, creating a stagnant, dead layer at the bottom of the ocean, which would devastate the deep-water ecosystem.

To better understand the dynamics involved, Williams and his colleagues turned to Prydz Bay, one of four known places in Antarctica that produces bottom water.

The problem, though, was it was too dangerous for humans to access, particularly in the winter.

So to investigate the depths of the chilly Antarctic seas, Williams and his team enlisted the help of native research assistants – southern elephant seals, which thrive in the icy waters where they feed on fish and squid.

They were fitted with devices that measured salinity, temperature and dive depth, sending back a staggering 100,000 measurements (a previous attempt by researchers alone managed just 90), painting a complete picture of the processes involved.

The data allowed scientists to divide the water into three layers: warm water interacting with the ice shelves, salty water beneath the sea ice and freshwater injection areas beneath the glaciers.

“The elephant seals were going to places we’ve never been before and some places we might not ever get to any other way,” Williams says.

“While they’re not the same quality as the ship-based data, the sheer mass of it is a huge step forward in our observations, really filling in the gaps of areas we had no information about before.”

  1. http://nature.com/articles/doi:10.1038/ncomms12577
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