Isotopes in the teeth of an ancient shark show how the climate changed during the Eocene

Sharks have been inhabiting Earth's oceans for over 400 million years, recording the history of the planet. New research on isotopes in

teeth of one of them will help to solve a long-standing dispute aboutthe depth and timing of the opening of the Drake Passage. It is an intercontinental strait that connects the southern Atlantic and Pacific oceans. To the north of the strait is the southernmost point of the South American continent and the entire American continent - Diego Ramirez Island and Cape Horn, and on the opposite side - the South Shetland Islands. By the way, it is the Drake Passage that is one of the most stormy places on the planet.

Many explanations for climate change in the Eoceneare concentrated in the Southern Ocean, where tectonics and water circulation have reduced heat transfer and reduced greenhouse gas emissions have led to glaciation. To date, few studies have focused on marine vertebrates at high latitudes to reveal the paleoecological and paleoecological implications of this climate transition.

The body temperature of sharks is regulated by the surroundingwater, therefore, limited species live in the cold polar regions. There have been periods of time in the past (eg, the Eocene geological period, 56-33.9 million years ago) when the Earth was much warmer and sharks were abundant in ocean waters around the world. For example, fossilized shark teeth have been found in Eocene sediments in Antarctica. Scientists have analyzed their chemical composition. This gave them clues about how the climate changed in the Eocene. The study found that sand tiger sharks of all ages lived in the Drake Passage area, and the temperature of the water recorded by their teeth remained constant over time, despite the apparent movement of continents and changes in ocean circulation.

It is believed that it was the opening of this strait1000 km wide and 3 km deep led to the fact that the climate on Earth changed from greenhouse to glacial. However, data analyzed by female paleoecologist Sora Kim of the University of California and her colleagues show otherwise.

“By analyzing isotopes in shark teeth, we cantrack the transfer of water masses between ocean basins and see when a passage has opened. However, we see no evidence of climate change at the time. This will force people to reconsider their hypotheses, ”explains Kim.

Scientists used to conduct isotopicanalysis of shark teeth collected around Seymour Island near Antarctica. Isotopes are found in the environment and, along with food, enter various organisms, accumulate in their bones and teeth (while they are forming). The amount of these isotopes (and their percentage) depends primarily on the geological features of the area.

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