Ancient shark teeth lost in Antarctica millions of years ago recorded Earth’s climate history

Tens of million years ago, sand tiger sharks hunted in the waters off the Antarctic Peninsula, gliding over a thriving marine ecosystem on the seafloor below. All that remains of them today is their sharp pointed teeth, but those teeth tell a story.
They’re helping solve the mystery of why the Earth, some 50 million years ago, began shifting from a “greenhouse” climate that was warmer than today toward cooler “icehouse” conditions.
Many theories about this climate shift focus on Antarctica. There is geologic evidence that both the Drake Passage, which is the water between South America and the Antarctic Peninsula, and the Tasman Gateway, between Australia and East Antarctica, widened and deepened during this time as Earth’s tectonic plates moved.
The wider, deeper passages would have been necessary for the waters of the major oceans to come together and the Antarctic Circumpolar Current to form.
That current, which flows around Antarctica today, traps cold waters in the Southern Ocean, keeping Antarctica cold and frozen. The now-extinct sand tiger shark species Striatolamia macrota was once a constant in the waters around the Antarctic Peninsula, and it left exquisitely preserved fossil teeth on what is now Seymour Island near the tip of the peninsula. By studying the chemistry preserved in these shark 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.
The temperatures recorded in shark teeth are some of the warmest for Antarctic waters and verify climate simulations with high atmospheric carbon dioxide concentrations.
Oxygen captured in very sharp teeth Sand tiger sharks have sharp teeth that protrude from their jaw to grasp prey. A single shark has hundreds of teeth in multiple rows. Over a lifetime, it sheds thousands of teeth as new ones grow. Important environmental information is encoded within the chemistry of each tooth and preserved there over millions of years.
For example, the outer layer of a shark’s tooth is composed of an enameloid hydroxyapatite, similar to enamel in human teeth. It contains oxygen atoms from the water the shark lived in.
By analyzing the oxygen, we can determine the temperature and salinity of the surrounding water during the shark’s life.
The teeth from Seymour Island show that the Antarctic waters – at least where the sharks lived – stayed warmer longer than scientists had estimated. (PTI)