Sharks could cope with climate change

Some shark species may be able to cope with the rising temperature and the subsequent decrease of water salinity, a new study has found.
The study of sharks that lived in warm Arctic waters millions of years ago suggests that some shark species could handle the falling Arctic salinity that may come with rising temperatures.
The Arctic is of special interest today because it is increasing in temperature at twice the global rate.
No one knows exactly what effect climate change could have on various species; scientists believe some species will be at risk, though others might thrive.
According to study leader Sora Kim, from the University of Chicago, past climate change in the Arctic can serve as a proxy to better understand our current climate change and aid future predictions.

The Eocene epoch, she said, is like 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."

Kim and Jaelyn Eberle from the University of Colorado, studied shark teeth from a coastal site on Banks Island.
This allowed them to better understand the changes in ocean water salinity across a broader geographic area during a time of elevated global temperatures.
Shark teeth are one of the few available vertebrate marine fossils for this time period. They preserve well and are incredibly abundant.
Kim isolated and measured the mass ratio of oxygen isotopes 18 to 16 found in the prepared enameloid (somewhat different from human tooth enamel) of the shark teeth.

Sharks constantly exchange water with their environment, so the isotopic oxygen ratio found in the teeth is directly regulated by water temperature and salinity.
With assumptions made about temperatures, the group was able to focus on extrapolating salinity levels of the water.
"The numbers I got back were really weird. They looked like fresh water," Kim said.
"As more freshwater flows into the Arctic Ocean due to global warming, I think we are going to see it become more brackish," said Eberle.
Because the teeth are 40 to 50 million years old, many tests were run to eliminate any possible contaminates, but the results were still the same.

These findings suggest that sharks may be able to cope with rises in temperature and the subsequent decrease of water salinity. It has long been known that sharks are hardy creatures.
They have fossil records dating back some 400 million years, surviving multiple mass extinctions, and have shown great ecological plasticity thus far.
The findings were published in the journal Geology.