Whales assist in-depth ocean research

Smart tags attached to whales are providing valuable data from the ocean depths on crucial impacts related to climate change.

Sperm whales – those deep-diving, world-travelling giants of the ocean – have been called into service as research assistants to answer questions about climate change.

In the course of their in-depth research, they will also answer questions about basic oceanography and about cetacean behaviour.

And while researchers at Oregon State University (OSU) in the US confirm a painless, harmless and cost-effective way to exact detailed and otherwise-impossible scientific data from the once-threatened sperm, fin and blue whales, a physicist at the University of Washington has quietly proposed a new way of exploring ocean conditions without putting marine mammals at risk from sonar blasts.

Oceans play a decisive role in the management of the planetary climate. To explore that role, researchers need to know about surface and subsurface temperature, ocean chemistry, salinity and current flow in a vast body of water kilometres deep and covering 70% of the planet.

Expensive science

But oceanography is an expensive science, and there is a limit to what researchers can do with research ships, submersibles, satellite observation and robotic buoys such as the Argo oceanographic instruments.

For decades, scientists exploited the fact that sound travels faster in warmer water, and used sonar blasts to create acoustic profiles. But whales themselves communicate and navigate by sonar techniques, and the technique was abandoned in 2006 as a result of increasing concern about the impact of noise on the great creatures of the sea.

Some whale species, though, may be vulnerable to climate change. And in any case, whales are beginning to help climate scientists − directly or indirectly − take the measure of global change.

Whales are the fellow-mammals that know the ocean most intimately. And now they have begun to share that intimacy.

The OSU researchers report in Ecology and Evolution journal that a new kind of smart tag attached to a whale’s skin can record water depth, whale movement, body orientation, water temperature and light levels, and go on doing so for up to seven weeks at a time.

“This technology has even made whales our partners in acquiring data to better understand ocean conditions and climate change”

Then the tag detaches, floats to the surface, flashes its light-emitting diodes and transmits GPS quality location data, and bobs around until scientists can collect it.

Along with delivering oceanographic information in the kind of detail never before possible, the tag also maintains a record of the whale’s ups and downs. One recovered tag recorded more than 2,900 dives, and all of them delivered data about the water temperatures to depths of 1,600 metres.

“This provides us with a broad picture of whale behaviour and ecology that we’ve never had before,” says study leader Bruce Mate, a professor at the OSU Marine Mammal Institute. “This technology has even made whales our partners in acquiring data to better understand ocean conditions and climate change.

“It gives us vast amounts of new data about water temperatures through space and time, over large distances, and in remote locations. We’re learning more about whales, and the whales are helping us to learn more about our own planet.”

Zhongxiang Zhao, an oceanographer at the University of Washington’s Applied Physics Laboratory, reports in Geophysical Research Letters that he has devised a cheap way to monitor temperature through the ocean depths, using a technique in which no whales could be harmed.

Internal tidal waves are generated when currents, driven by the tide, pass over submarine ridges. Secondary waves – with wavelengths of 160 kilometres and speeds of 3 or 4 metres a second – make a telltale signature at the surface.

Climate change is warming the upper ocean more quickly than the waters at depth, and temperature affects the speed of internal tidal waves.

Internal waves

So, Dr Zhao says, the internal waves would leave their signature in tiny changes of height at the surface that could be recorded in satellite data.

An internal wave within the subsurface ocean could have a height change of 20 to 50 metres. This would be reflected in a surface height change of two centimetres. Careful reading of surface data variations could reveal changes in ocean temperature.

Analysis of two decades of ocean data has revealed a 1% increase in speed time along two tracks of the Atlantic Ocean. Importantly, Dr Zhao’s readings match data recorded by Argo buoys used by oceanographers.

He sees the approach as cheap, sustainable and harmless to whales, providing a tomography scan of the planet that offers a measure of ocean circulation.

“The internal tidal wave is a naturally occurring ocean phenomenon, so monitoring its long-term variability is very cheap,” Dr Zhao says.

“If you are a doctor, you are scanning the health of your patient. I am like a doctor scanning the Earth, and who can see if it is getting a temperature. This method offers a long-term, cost-effective, environmentally-friendly technique for monitoring global ocean warming.”