'Cyber seals' wearing head sensors help scientists uncover the mystery of the 'ocean engine' at the bottom of the Antarctic

Elephant seals wearing head sensors and swimming deep beneath Antarctic ice have helped researchers uncover how the ocean's coldest, deepest waters are formed - and how they affect our climate.

The tagged seals revealed unprecedented details about the 'Antarctic bottom water,' a dense, deep layer of water near the ocean floor that has a significant impact on the movement of the world's oceans.
Three sources of the water were known of, and the existence of a fourth suspected for decades, but the area was far too inaccessible - until now, thanks to the seals.

Elephant seals wearing head sensors and swimming deep beneath Antarctic ice have helped scientists better understand how the ocean's coldest, deepest waters are formed

'The seals went to an area of the coastline that no ship was ever going to get to,' said Guy Williams of the Antarctic Climate & Ecosystem CRC in Tasmania.

'This is a particular form of Antarctic water called Antarctic bottom water production, one of the engines that drives ocean circulation,' he told Reuters.

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The Antarctic bottom water surrounds Antarctica, with temperatures ranging from -0.8°C to 2°C.

It is the densest water mass of any part of the world's oceans.
It forms in the winter, when icy winds and temperatures freeze seawater into sea ice, expelling salt. The remaining salty, chilly water is denser than the water around it, and it sinks downward.

This deep current flows north, away from the continent, and transports oxygen and carbon dioxide around the planet.
Its flow is often used when calculating climate change simulations and referred to as the 'ventilation' of the oceans.

'What we've done is found another piston in that engine.'
Twenty of the seals were deployed from Davis Station in east Antarctica in 2011 with a sensor, weighing about 100 to 200 grams, on their head.

 

Each of the sensors had a small satellite relay which transmitted data on a daily basis during the five to 10 minute intervals when the seals surfaced.

'We get four dives' worth of data a day but they're actually doing up to 60 dives,' said Williams.

'The elephant seals ... went to the very source and found this very cold, very saline dense water in the middle of winter beneath a polynya, which is what we call an ice factory around the coast of Antarctica,' he added.

Southern Ocean Elephant seals are the largest of all seals, with males growing up to six metres (20 feet) long and weighing up to 4,000 kilograms (8,800 lbs).

The tagged seals, along with sophisticated satellite data and moorings in ocean canyons, all played a role in providing data from the extreme Antarctic environment, where observations are very rare and ships could not go

Scientists have long known of the existence of 'Antarctic bottom water,' a dense, deep layer of water near the ocean floor that has a significant impact on the movement of the world's oceans.
Previous studies have shown that there are 50-year-long trends in the properties of the Antarctic bottom water, and Williams said the latest study will help better assess those changes, perhaps providing clues for climate change modeling.

'Several of the seals foraged on the continental slope as far down as 1,800 meters (1.1 miles), punching through into a layer of this dense water cascading down the abyss,' he said in a statement.
'They gave us very rare and valuable wintertime measurements of this process.'

A Southern Ocean elephant seal wears a sensor on its head as it swims in the Southern Ocean, Antarctica