Shrimp-Like Fossil Confirms Antarctica Was Once Warmer

Windswept and frigid, Antarctica's Dry Valleys region is among the most inhospitable on Earth. But it wasn't always that way.

Scientists have discovered the fossil of a 14 million-year-old crustacean lurking in the sediments of an ancient lake. Together with well-preserved mosses, these tiny cousins of shrimp -- called Ostracods -- offer new evidence that the icy continent was once much warmer.

Led by Mark Williams of the University of Leicester in the United Kingdom, a team of researchers sifted through sediments left by the ancient Lake Boreas, looking for signs of Antarctica's climate history. What they found stunned them.

"One of my students working on a microscope said 'could there be little eyes staring back at me?'" Allan Ashworth of North Dakota State University in Fargo said. "I said 'No,'" but further examination proved that's exactly what they were -- Ostracod eyes.

Some 60,000 species of Ostracods thrive today around the planet in both fresh and salt water. The tiny invertebrates are found in places where summer temperatures are as low as 5 degrees Centigrade (41 degrees Fahrenheit). But there are none alive in the Antarctic Dry Valleys, where the austral summer averages between -15 and -20 degrees C (5 to -4 degrees F).

Scientists know that Antarctica used to be much warmer -- fossil leaves from ancient plants have been found to exist up until around 40 million years ago, and pollen has been dated to as early as 20 million years ago.

But how the continent came to be so cold is something of a mystery.

Around 14 million years ago, scientists are fairly certain the climate resembled modern-day Alaska. Within a million years a deep freeze had settled in, and the ice sheets grew to mammoth proportions, where they mostly remain today.

The newly discovered Ostracod fossils confirm that the changes -- which until now had only been observed in ocean floor sediments -- were also playing out on land in Antarctica.

"We've shown that this change in climate had a profound impact on Antarctica," Ashworth said. "The evidence tends to suggest the threshold of temperature was never reached again in that part of Antarctica. We'd argue that it's been locked down and frozen for the past 14 million years."

Timothy Naish of Victoria University of Wellington in New Zealand agreed that the team's study was "important to our understanding of Antarctic climate." But he added that there's still a lot of uncertainty about what happened after the 14-million-year mark.

"We see a lot of variability in climate, and there is evidence that a significant amount of the Antarctic ice sheets melted recently, around three million years ago," before freezing again, Naish told Discovery News.