Elephant seal
Southern ocean
Vital oceanographic data to better understand the world climate can be hard to obtain,
especially at high latitudes where sea ice and harsh weathers render the navigation of ships and buoys difficult and prevent satellite sensing. Yet, there is a living probe that roams these areas of the world all year round: elephant seals! In the Southern Ocean they can carry miniature oceanographic platform to complement data obtained by more traditional means.
Time-depth recorder
Thanks to technological advances there is now a plethora of physical and geochemical
parameters that can be monitored by the elephant seals: temperature, salinity, dissolved oxygen, pH… Name it! Together with other information delivered by GPS and time-depth
recorder (localization) or by accelerometers and magnetometers (precise path and activities of the seals), it is possible to record parameters to a level of precision which is compatible with measures taken by physicists. And with a transmitting system added to the logger data
can even be sent almost real time.
Challenging seal
While it sounds straightforward, getting the seals to cooperate can be challenging. A beast of several hundreds of kilos at best – 3 tons in case of a male – requires sedation to be handled and a mini crane system to be weighed. At least, one would think there is ample choice on such a huge body to attach the logger but to get a clear communication with satellite to transmit data the top of the head is often the best spot. And on such a thin fur only glue can keep the logger in position until it is retrieved or until the next mould of the fur where the patch of glue will be discarded… together with the logger.
Resistant divers
Elephant seals are extraordinarily adapted to marine life. They can dive down to 2 km and swim many thousands of kilometers, crossing entire oceanic basin, above and under the sea ice, they surely are precious oceanographic auxiliaries. While the seals dive all through
the 24 h of the day they do spend enough time at the surface between two dives for summarized data (simplified data) to be sent to the satellite. And as these animals return to land (the subantarctic islands scattered in the Southern Ocean) to breed or mold there is also an non-negligible chance of recapturing the animal and recover the logger with the complete dataset. For the latter, international collaboration is paramount as the seal can
sometimes pop up on another island where a different research team can recover the logger!
Plenty information
Whether summarized data or the complete dataset are recovered, there
is plenty of information to deal with. Series of scripts are applied to the raw data to make them compatible with the international standards of
oceanographic data.
Data interpretation
Temperature profils
All data are georeferenced (latitude and longitude), as well as depth-annotated so that 3D profiles of a given parameter can be reconstructed along the route followed by the elephant seal. For example, temperature profiles against depth can reveal the presence or absence of thermocline, a rupture in the temperature decrease with depth that is often associated with high biological productivity. And when temperature profiles are displayed along the route of the seal this gives scientists a view of the different water masses and their dynamics in the Southern Ocean.
Combining data
International collaboration is not only a sine qua non condition for recapturing seals. The approach using elephant seals as oceanographic bioplatforms is actually repeated by many research teams across the globe that are organized in a consortium. This consortium is the first provider of oceanographic data at high latitudes, especially in the southern hemisphere where almost 90% of data collected south of 60°C come from the seals!
