Ancient shark teeth are providing researchers with a glimpse of the Arctic in the future.
When you picture the Arctic, chances are that an image of a polar bear standing on ice in the middle of cool blue water, with a white background is one of the first ones that will pop into your head. But, 38 to 50 million years ago, during the Eocene epoch, the Arctic was not that cold; it was more like a temperate forest with brackish water.
(The Antarctic was also warm during the Eocene epoch…polar regions of the southern Pacific Ocean were as warm as Florida is today.)
The Arctic is increasing in temperature at twice the global rate, which is why it is a particularly important area of study. By studying past changes, researchers will be better able to predict how climate change will impact the ecosystem.
In a news release, lead researcher Sora Kim, the T.C. Chamberlin Postdoctoral Fellow in Geophysical Sciences at the University of Chicago, explained that the Eocene epoch 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.”
Most marine records come primarily from deep-sea cores pulled from the central Arctic Ocean site called the Lomonosov Ridge. In this study, Kim and colleagues examined ancient shark teeth from a different coastal location on Banks Island. By collecting records from a new location, Kim and colleagues were able to get a better understanding of the changes in ocean water salinity across a broader geographic area during a time of elevated global temperatures.
Shark teeth preserve incredibly well and are very abundant, so Kim was able to measure the mass ratio of oxygen isotopes 18 to 16 found in the shark teeth. Because sharks constantly exchange water with their environment, the isotopic oxygen ratio in the teeth is directly regulated by water temperature and salinity. By making assumptions about temperature, researchers were able to determine salinity levels.
Kim was studying sand tiger sharks, which are known to prefer areas with high salinity, so she was surprised when the numbers she got back “looked like fresh water.”
This could be due to an increase in freshwater flowing into the Arctic Ocean as temperatures increase and ice melts.
The findings suggest that at least some sharks may be able to cope with increasing temperatures and decreasing salinity, which isn’t too surprising, as sharks have been swimming our oceans for more than 400 million years and survived multiple mass extinctions.
Kim hopes to expand her research to other locations in the Arctic and, hopefully, back in geological time in order to get a better picture of the ecology and evolution of sharks.
She noted that “working with fossils is tricky because you have to work within the localities that are preserved. You can’t always design the perfect experiment.”
To learn more:
- Read the full news release: Ancient shark teeth give clues to future of Arctic climate change.
- Find the full study here: Evidence from shark teeth for a brackish Arctic Ocean in the Eocene greenhouse.
- Check out this news release from CU-Boulder: Some sharks tolerated brackish Arctic Ocean 50 million years ago.
Copyright © 2014 by Marine Science Today, a publication of Marine Science Today LLC.