US: Arctic turtle fossil suggests global warming

The fossil of a tropical, freshwater Asian turtle (Photo: University of Rochester) found in Arctic Canada indicates that animals migrated from Asia to North America directly across a freshwater sea floating atop the then-warm, salty Arctic Ocean, new research suggests.

Published in the latest edition of the journal Geology, the research also suggests a rapid influx of carbon dioxide from volcanoes caused a super-greenhouse effect about 90 million years ago.

"We've known there's been an interchange of animals between Asia and North America in the late Cretaceous period, but this is the first example we have of a fossil in the High Arctic region showing how this migration may have taken place," says John Tarduno, a professor of geophysics at the University of Rochester in New York and leader of the Arctic expedition.

"We're talking about extremely warm, ice-free conditions in the Arctic region, allowing migrations across the pole."

The fossil was found in 2006, and Tarduno and Donald Brinkman of the Royal Tyrrell Museum of Canada, later named it Aurorachelys, or aurora turtle. The turtle strongly resembled a freshwater Mongolian species, which raised questions about how it came to be in the marine waters of the North American Arctic.

Tarduno says volcanic events could have produced a series of islands that would have given the turtles - and other species - the ability to island-hop from ancient Russia to Canada. In addition, numerous rivers from the adjacent continents would have poured fresh water into the ancient Arctic sea.

Since fresh water is lighter than marine water, it would have rested on top of the salty ocean water allowing a freshwater animal such as the aurora turtle to migrate with relative ease. He says the volcanic activity that created the islands could also have contributed to the warm climate that enabled the turtle to survive in the Arctic circle.

"The warming may have been caused by volcanoes pumping tremendous amounts of carbon dioxide into the Earth's atmosphere. There's evidence that this volcanic activity happened all around the planet - not just the Arctic. If it all happened on a short enough timescale, it could cause a super-greenhouse effect."