Seals can be a powerful tool for exploring ocean conditions

A new study led by Japan’s National Institute of Polar Research (NIPR) has investigated the continental shelves of Antarctica by attaching CTD-Satellite Relay Data Loggers with glue to the heads of eight Weddell seals between March and September 2017. The method was used due to the difficulty of conducting oceanographic observations by ship in continental shelf areas covered by landfast ice.

The continental shelves of Antarctica are some of the most biologically productive areas in the world’s oceans due to the large amounts of nutrients resulting from the interactions between ocean, sea ice, and ice shelves. 

In East Antarctica, sea ice production is most abundant in the coastal polynyas (areas of open, unfrozen seawater surrounded by ice). Outside these polynyas, a large amount of landfast ice (sea ice attached to the shore) provide an excellent habitat for predators such as Weddell seals or emperor penguins.

The exchanges between deep warm waters coming from off-shelf areas, coastal polynyas, and seasonal sea-ice zones play a crucial role in biological production throughout continental shelf areas. However, since these regions are practically inaccessible by ship, in recent years, researchers have begun deploying oceanographic data logging equipment to marine animals such as seals in order to record features such as conductivity, temperature, and depth.

“Previous studies using instruments strapped to migrating southern elephant seals and resident Weddell seals – a deep diving predator – had shown some interesting physical processes in Antarctic areas, but even here, there has barely been anything investigating coastal areas covered by landfast ice,” said study lead author Nobuo Kokubun, an assistant professor of Oceanography at NIPR.

By using data collected from sensors attached on the heads of eight Weddell seals, Professor Kokubun and his colleagues have found that warm and low salinity water appeared in the subsurface during autumn, and the depth of the warm water increased as the season progressed. 

The scientists have also discovered that seasonally prevailing easterly wind during autumn caused a significant flow of off-shelf surface warm waters and additional prey onto the continental shelf.

The study suggests that using seals with oceanographic sensors attached to them can be a powerful tool for exploring oceanographic and ecological conditions on Antarctic continental shelves covered with landfast ice, where access by ship is nearly impossible.   

The study is published in the journal Limnology and Oceanography.

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By Andrei Ionescu, Earth.com Staff Writer