Ancient Shark Teeth Explains Climate Shift on Antarctica

Some 50 million years ago, the Earth's 'greenhouse climate' shifted from a much warmer and uniform than today toward cooler 'icehouse' conditions, and shark teeth from millions of years ago could tell us how.

Geologic evidence from Antartica was recorded during a particular time, one of them being the Drake Passage and Tasman Gateway that widened and deepened as Earth's tectonic plates moved. This impacts the currents on where the waters of major oceans come together which flows around Antarctica today, trapping cold waters in the Southern Ocean, which explains why Antarctica is cold and frozen.

To solve the mystery of earth's ancient climate, the now-extinct sand tiger shark species Striatolamia macrota shall provide. Their species once roamed around the Antarctic Peninsula waters constantly, and left exquisitely preserved fossil teeth on what is now Seymour Island near the tip of the peninsula.

Scientists hope to find enlightenment of the ancient phenomenon through examining the chemistry preserved in these shark teeth.

Information Trapped in Shark's Teeth

"My colleagues and I found evidence of when the Drake Passage opened, which allowed the waters of the Pacific and Atlantic oceans to mix, and what the water felt like at the time," wrote Sora Kim, Assistant Professor of Paleoecology, University of California, Merced on Science Alert.

"The temperatures recorded in shark teeth are some of the warmest for Antarctic waters and verify climate simulations with high atmospheric carbon dioxide concentrations."

A single shark has hundreds of teeth in multiple rows which are sharp enough to grasp prey, and can grow new ones immediately once they are shed. Researchers typically collect and encode important environmental information preserved there over millions of years.

One of them is enameloid hydroxyapatite which composes the outer layer of a shark's tooth, just like the enamel in human teeth. Since it contains oxygen atoms from the water the shark lived in, the temperature and salinity of the surrounding water during the shark's life could be determined.

The teeth recovered from Seymour Island suggests that the Antarctic waters stayed warmer longer than scientists had estimated.

Second clue can be extracted from the element neodymium, which holds and replaces other elements in the outer enameloid of the tooth during early fossilization. The ratio of two different neodymium isotopes in shark's teeth detects the sources of the water where the shark died.

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Tooth Size And Chemistry 'Yielded Surprising Clues To The Past'

The 400 teeth from Seymour Island, varied in all ages, juvenile to adult, living between 45 million to 37 million years ago, suggests that "sharks' water temperature then was similar to the water temperatures where modern sand tiger sharks can be found today."

"It is possible that the ancient sand tiger sharks also migrated, and when Antarctic waters cooled off, they headed north to warmer waters at lower latitudes."

Finally, the neodymium in the fossil implies that the Drake Passage opening, delayed cooling effect, and chemical and tectonic evidence are factors that caused complex interactions between Earth's systems, affecting climate shift.

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