A long-extinct sand tiger shark’s teeth provide new insights into global climate change and tectonic plate movements. The study is published in the journal Paleoceanography and Paleoclimatology.
Sharks have been inhabiting Earth’s oceans for over 400 million years, recording the planet’s history. A new study of isotopes in the teeth of one of them will help resolve a long-standing dispute over the depth and timing of the Drake Passage discovery. 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 Eocene focus on the Southern Ocean, where tectonics and water circulation reduced heat transfer and reduced greenhouse gas emissions 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 water surrounding them, so there are limited species 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 worldwide. 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. The water temperature recorded by their teeth remained constant over time, despite the apparent movement of continents and changes in ocean circulation.
It is believed that the opening of this strait 1000 km wide and 3 km deep led to the fact that the Earth’s climate changed from a greenhouse to a glacial one. 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 can track the transport of water 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 colleagues used shark teeth collected around Seymour Island near Antarctica for isotope analysis. Isotopes are found in the environment and, together with food, enter various organisms and accumulate in their bones and teeth (while forming). The amount of these isotopes (and their percentage) depends primarily on the area’s geological features.
The results of this work combine shark paleontological studies, geochemical analysis for environmental reconstruction, and new global climate models to figure out the depth and timing of the Drake Passage discovery. Shark teeth contain a lot of data. The scientists conclude their potential should be seen as part of geological reconstructions by other researchers to study the ancient climate.