The world’s sharks already are in big trouble, with 25 percent of shark species now threatened with extinction, according to the International Union for Conservation of Nature. So some have worried that climate change would only add to sharks’ plight, because they might not be able to adapt to decreasing salinity in Arctic waters, caused in part by melting ice on land and increased precipitation.

But a new study  offers some hope that sharks in the Arctic be able to cope.

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The study, published online in the journal Geology, looked at fossil sand tiger shark teeth found on Banks Island, the westernmost part of the Canadian Arctic archipelago. The teeth date back to the Eocene epoch 38 to 53 million years ago, when the region had a temperate climate and its water had a lower salinity.

That period is a  ”deep-time analogue for what’s going to happen if we don’t curb CO2 emissions today, and potentially what a runaway greenhouse effect looks like,” according to the study’s lead author, University of Chicago marine scientist Sora Kim.

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Kim did an an analysis of the ratio of oxygen isotopes in the teeth — a measure that tends to reflect ocean temperature and salinity. She found that the numbers indicated the water had such low salinity that it practically looked like freshwater. Nevertheless, the sand tiger sharks — part of a group called lamniform sharks, which prefer high salinity — had managed to live in the region.

The results suggest that sharks may be able to cope with rising temperatures and decreasing salinity that scientists expect to see in the Arctic of the future. That may have added significance, because a 2013 study shows that warming elsewhere in the oceans is pushing sharks and other marine species increasingly northward.

Photo: Sand tiger sharks such as this one may be able to cope with climate change’s effects, according to a new study. Credit: UND77, via Wikimedia Commons