Oceanographic instruments attached to the heads of Antarctic elephant seals have assisted scientists better understand the role melting ice shelves are having in regulating global ocean temperatures. During their foraging dives the animals collected data and helped researchers to identify a new source of bottom water production in East Antarctica.

An Antarctic elephant seals carries a small oceanographic instrument on his head. The instrument collects data during foraging dive and is only glued on. It falls off during the annual moult when the animal sheds hair and outer layers of skin in large patches. Picture: Clive R. McMahon
An Antarctic elephant seals carries a small oceanographic instrument on his head. The instrument collects data during foraging dive and is only glued on. It falls off during the annual moult when the animal sheds hair and outer layers of skin in large patches. Picture: Clive R. McMahon

Research published in the journal 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.”

This map shows the thermohaline circulation, also known as the
This map shows the thermohaline circulation, also known as the "ocean conveyor belt". This collection of currents is responsible for the large-scale exchange of water masses in the ocean. The entire circulation pattern takes ~2000 years. In this graph the oceans are shown as a single body of water. Blue paths represent deep-water currents, while red paths represent surface currents. Picture: Avsa, Wikipedia commons

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.”

Antarctic bottom water is formed in the Weddell and Ross Seas, off the Adélie Coast and by Cape Darnley. Surface water cools in polynyas and below the ice shelf. It is the densest water mass of the World Ocean. Two years of additional data collection has enabled scientists to confirm Prydz Bay in East Antarctica as a secondary contributor to the Cape Darnley Antarctic bottom water. Picture: David Barringhaus
Antarctic bottom water is formed in the Weddell and Ross Seas, off the Adélie Coast and by Cape Darnley. Surface water cools in polynyas and below the ice shelf. It is the densest water mass of the World Ocean. Two years of additional data collection has enabled scientists to confirm Prydz Bay in East Antarctica as a secondary contributor to the Cape Darnley Antarctic bottom water. Picture: David Barringhaus

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.

Juvenile southern elephant seals huddle together. When fully grown they will spend up to 80% of their lives in the ocean. They can hold their breath for more than 100 minutes and dive to depth of more than 1550 m. Picture: Katja Riedel
Juvenile southern elephant seals huddle together. When fully grown they will spend up to 80% of their lives in the ocean. They can hold their breath for more than 100 minutes and dive to depth of more than 1550 m. Picture: Katja Riedel

Source: Australian Antarctic Division