Adapted from article on www.news.bbc.co.uk                                                           21 February 2006

POPULATION CENTRES • Population totals about 740,000 • Range widely over Southern Ocean • Largest groups on Macquarie, Kerguelen, and South Georgia • Have enjoyed protection since end of industrial hunting in late 1950s • So named because of their size and trunk-like snout • Dominant males control harems of up to 50 females

Elephant seals on South Georgia have been recruited to the cause of science.

Equipped with computerised tags stuck to their heads, the animals have been collecting new information about conditions in the Southern Ocean. As the animals swim for thousands of km and dive down to 2,000m, their tags record details of temperature, depth and the salinity of the water. When the seals pop up to breathe, the computers transmit the information to scientists in Scotland via satellite.

"These animals can go to places in the ocean that we very often can't go", said a spokesmanfrom the Sea Mammal Research Unit at the University of St Andrews. The unit is running this project in parallel with other projects using sea lions, tuna, and even sharks to gather ocean data.

The elephant seals' information has provided new insights into:

1. the habits and habitat both of the elephant seal and its prey species, squid
2. ocean circulation.

Getting information about varying seal populations

South Georgia's elephant seal population of 400,000 is the biggest group and has been relatively stable since the end of large-scale hunting in the 1950s. But the groups centred on the islands of Macquarie and Kerguelen have not fared so well. Why this is so may emerge from an analysis of the data gathered by the seals.

System shut-down

There is no doubt about the seals' diving prowess. Adults will spend perhaps more than 90% of their time far below the surface, for 30 minutes to an hour at a time. "They must have some way to reduce their metabolic rate when they are diving, shutting down most of their systems and resting as they go," said Martin Biuw of the Sea Mammal Research Unit. "So, they would go to sleep in transit and then they wake up down at 1,500m and hope there is squid there for them to eat."

The scientists stress the animals are not bothered by the data loggers carried on their heads. The boxes are attached with an epoxy glue and simply fall off after about a year during the moulting season.

Learning about "ocean fronts"

There are three main processes that make the oceans circulate:

1. tidal forces
2. wind stress
3. density differences in the seawater.

The circulation driven by density differences is called the thermohaline circulation, because the density of sea water is determined by its temperature (thermo) and its salinity or saltinesss (haline). This mass movement of water around the globe that helps redistribute the energy in our climate system is also called the Great Ocean Conveyor (Belt) .

The information provided by the elephant seals has significantly improved our understanding of the processes of heat exchange within the Southern Ocean and between this region and the rest of the world. The Southern Ocean plays a critical role in the behaviour of the Great Ocean Conveyor.

The South Georgia seals have helped trace the positions of "ocean fronts" in unprecedented detail. These are like the weather fronts you have in meteorology, only they are in the ocean. These fronts show where cold water is coming from the deep ocean up to the surface, or where warm water and nutrient-rich water is brought down into the deep ocean. Knowing where these fronts are helps us to understand what happens to the global conveyor in this part of the Southern Ocean.

The seals' tracked journeys have thrown new light on their wandering, where they go to feed and how they seem to use the frontal systems to navigate and find their food.

Will the Great Ocean conveyor stop again and cause another ice age?

Once considered incredible, the notion that climate can change rapidly is becoming respectable. A 2003 report cites "rapidly advancing evidence (from, e.g., tree rings and ice cores) that Earth's climate has shifted abruptly and dramatically in the past."

As the world warmed at the end of the last ice age about 13,000 years ago, melting ice sheets appear to have triggered a sudden halt in the Conveyor, throwing the world back into a 1,300 year period of ice-age-like conditions called the "Younger Dryas."

Will it happen again? Researchers are scrambling to find out. In 2004, an expedition set sail from Great Britain to place current-monitoring sensors in the Atlantic Ocean that will check the Gulf Stream for signs of slowing. The voyage is the latest step in a joint US / UK research project called Rapid Climate Change, which began in 2001. Another international project, called SEARCH (Study of Environmental ARctic CHange), kicked off in 2001 with the goal of more carefully assessing changes in Arctic sea ice thickness.