Quirks & Quarks

The horn of the unicorn of the sea reveals a dirty secret about arctic pollution

Researchers can read Narwhal tusks like the rings in a tree trunk. And they're showing alarming concentrations of mercury as the climate warms.

Narwhal tusks show a dramatic increase in mercury, despite diet changes suggesting otherwise

A pod of narwhals surfaces in northern Canada. (THE CANADIAN PRESS/AP Photo/Kristin Laidre, NOAA, files)

Narwhals are often called the unicorns of the sea. Not only are these whales rare, almost mythical creatures that spend their lives hidden under the arctic ice, but also, because of their long, spiralled tusks — actually an extended tooth — that can protrude three metres from their heads.

Now an international team of researchers has discovered that a narwhal's tusk can provide valuable insight into the changing conditions in the Arctic.

"Like a tree trunk, there's rings that grow incrementally every year," Jean-Pierre Desforges said to Quirks & Quarks host Bob McDonald. "We can take samples from and analyze a number of different things."

Cut-through narwhal tusk displaying the individual year rings. The researchers purchased the tusks from Inuit hunters in Greenland. (Rune Dietz)

The team analyzed stable isotopes to look at mercury levels and diet changes over the past 50 years, as top level predators like the narwhal primarily absorb mercury through their diet. They found that since the year 2000, even though their diet changed to eat prey that were lower in mercury, the amount of mercury the narwhals absorbed increased dramatically.

"There's obviously some other source of mercury going on here that's not coming from the diet. And we suspect that it's either a combination of increased emissions of mercury globally, or change in the way that mercury is moving within the Arctic ecosystem," said Desforges.

The paper was recently published in the journal Current Biology.

Jean-Pierre Desforges is a post-doctoral research fellow in the department of Natural Resource Science at McGill University. You can listen to his conversation with Bob McDonald at the link above.


Produced and written by Amanda Buckiewicz

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