Ancient shark teeth helping solve mystery of Earth’s climate history
- The teeth from Seymour Island bear testimony that the Antarctic waters – at least where the sharks lived – stays warmer longer than scientists had estimated.
The sharp pointed teeth of sand tiger sharks, hunted in the waters off the Antarctic Peninsula some tens of millions of years ago, are now helping solve the mystery of why the Earth began shifting from a greenhouse climate that was warmer than today toward cooler icehouse conditions, reports news agency PTI.
A study by the University of California said that 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 and deeper passages were important for the ocean water to mingle and the Antarctic Circumpolar Current -- which flows around Antarctica today -- to form. The current traps cold waters in the Southern Ocean and helps keep Antarctica cold and frozen, the study revealed.
By studying the chemistry preserved in these shark teeth, University of California 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 among the warmest for the ocean in the Antarctic region and they 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 their prey. Over a lifetime, it sheds thousands of teeth as new ones grow. The chemistry of each tooth preserved there over millions of years is encoded with crucial environmental information.
The teeth from Seymour Island bear testimony that the Antarctic waters – at least where the sharks lived – stays warmer longer than scientists had estimated.
Another clue comes from the element neodymium, which absorbs and replaces other elements in the outer enameloid of the tooth during early fossilization. Each ocean basin has a distinct ratio of two different neodymium isotopes based on the age of its rocks. The ratio in the shark teeth allows the researchers to detect the sources of the water where the shark died.
The neodymium composition would not change under ideal conditions, experts said. However, if neodymium composition does change in fossil teeth over time, that indicates changes in oceanography.