Seals help solve Antarctic bottom water mystery

Prydz Bay
Two years of additional data has enabled scientists to confirm Prydz Bay as a secondary contributor to the Cape Darnley Antarctic bottom water. (Photo: David Barringhaus)
Elephant sealsElephant seal with instrument

Oceanographic instruments attached to Antarctic elephant seals have helped scientists better understand the role melting ice shelves are having in regulating global ocean temperatures. 

Research published today in Nature Communications has used elephant seals to demonstrate that fresh water from Antarctic’s melting ice shelves slows the processes responsible for the formation of deep-water ocean currents that regulate global temperatures.

The research paper, led by Dr Guy Williams from the Institute of Marine and Antarctic Studies and Antarctic Climate and Ecosystems CRC, said the findings were significant for the global climate.

“Antarctica and the Southern Ocean are like a beating heart, producing deep and powerful currents of cold water that drive global ocean mixing and regulate atmospheric temperatures,” Dr Williams said.

“These currents begin with intense sea ice formation around the Antarctic continent in winter, which creates cold, salty and dense water that sinks and flows away from the continent in large volumes.

“If this production of Antarctic bottom water weakens, it leads to changes in global ocean circulation patterns that can, in turn, lead to changes in the global climate.”

In 2011, researchers discovered a fourth source of Antarctic bottom water off Cape Darnley in East Antarctica. The latest research includes an additional two years of data and shows that Prydz Bay makes a secondary contribution to Cape Darnley Bottom Water.

An additional two years of data from the biotagged seals provided comprehensive spatial and seasonal oceanographic coverage of the region.

“However we found that the contribution from Prydz Bay is less salty and dense due to the influence of fresh water by nearby ice shelves,” Dr Williams said.

“We can easily imagine that the production of these global ocean currents will slow as the rate of ice shelf melting all around Antarctica continues to increase.”

As part of the Integrated Marine Observing System (IMOS) and with the support of the Australian Antarctic Program, elephant seals were equipped with small oceanographic instruments on their heads, designed to collect data while they foraged to depths up to 1800m.

When the seals surface, their sensors relay information back to land via satellite, and the near real-time data is made available via the Global Telecommunication System of the World Meteorological Organization for immediate use. IMOS also makes the data available via their data portal. The oceanographic data collected by the seals is also used for ecological research into their behaviour and aids in conservation

“This study would have been virtually impossible without help from the seals, who can gather oceanographic data from areas that tend to be very difficult to access in research ships,” Dr Williams said.