Photo Credit: Tim Cully/ANDRILL

An aerial view of the ANDRILL drilling camp on the ice over McMurdo Sound in 2007. The drill rig, located under the tall white shroud, recovered a sediment core more than 1,000 meters long from below the seafloor.

Antarctica once enjoyed summer-time temperatures that averaged 10 degrees Celsius — a climate more suited for a warm fleece than a thick parka — about 15.7 million years ago.

That’s the conclusion scientists drew from the discovery of a thick layer of fossils from marine algae and the pollen of woody plants in a sediment core drilled into the seafloor of McMurdo Sound in 2007.

Researchers with the ANtarctic Geological DRILLing Program (ANDRILL) published their research this month in the issue of Geology, the journal of the Geological Society of America.

Sophie Warny , an assistant professor of geology and geophysics at Louisiana State University , found the first indication of the warm period while studying samples from the project last year. One sample, she said in a press release, stood out as a complete anomaly.

“First I thought it was a mistake, that it was a sample from another location, not Antarctica, because of the unusual abundance in microscopic fossil cysts of marine algae called dinoflagellates. But it turned out not to be a mistake, it was just an amazingly rich layer,” Warny said.

ANDRILL took two sediment cores near the U.S. Antarctic Program’s McMurdo Station over two successive field seasons beginning in 2006. The $30 million ANDRILL program was one of the premiere projects of the International Polar Year , a two-year scientific campaign that officially ended in March 2009. The National Science Foundation (NSF) funded about two-third of the program, with international partners New Zealand, Italy and Germany funding the remainder.

The microscopic fossils were found in unusual abundance in a two-meter-thick layer from the 2007 core of seafloor sediments that measured more than 1,100 meters long.

“We all analyzed the new samples and saw a 2,000-fold increase in two species of fossil dinoflagellate cysts, a five-fold increase in freshwater algae and up to an 80-fold increase in terrestrial pollen,” Warny said. “Together, these shifts in the microfossil assemblages represent a relatively short period of time during which Antarctica became abruptly much warmer.”

This apparent bloom of life in Antarctica occurred during a generally warm time referred to as the Mid-Miocene Climatic Optimum, according to the scientists. This was a time when global temperatures were warmer than at present. It could serve as an analogue to how the ice sheets of today may respond to warming temperatures in the coming century.  

“This event will lead to a better understanding of global connections and climate forcing,” said David Harwood , professor of geosciences at the University of Nebraska-Lincoln and research director for ANDRILL’s Science Management Office. “In other words, it will provide a better understanding of how external factors imposed fluctuations in Earth’s climate system.”

ANDRILL scientists say these findings corroborate and expand evidence for lakes and vegetation farther inland in the nearby McMurdo Dry Valleys . In that separate study, also funded by the NSF, scientists discovered the last traces of tundra in the form of fossilized plants and insects. [See previous article: Warmer continent.]

That research team — headed by David Marchant , an earth scientist at Boston University , and Allan Ashworth and Adam Lewis , geoscientists at North Dakota State University — concluded from fossilized evidence that the climate cooled abruptly about 14 million years ago. Their findings appeared in the Aug. 4, 2008 edition of the Proceedings of the National Academy of Sciences.

Earlier this year, ANDRILL scientists published two papers in the journal Nature, including one that suggested even a slight rise in atmospheric concentrations of carbon dioxide, one of the gases that drives global warming, affects the stability of the West Antarctic Ice Sheet (WAIS). The ice sheet contains enough ice to raise sea level by about six meters.

The evidence from the 2006 core, nearly 1,300 meters long, traveled back in time to the Pliocene era, roughly 2 million to 5 million years ago. During that era, Antarctica was also warmer than today, and atmospheric carbon dioxide levels were higher. Data from the core indicate the ice sheet advanced and retreated numerous times in response to climate changes.

“Geological archives, such as the ANDRILL core, highlight the risk that a significant body of permanent Antarctic ice could be lost within the next century as Earth’s climate continues to warm,” said Tim Naish , director of Victoria University of Wellington's Antarctic Research Centre and co-chief scientist during the first ANDRILL field season.

“Based on ANDRILL data combined with computer models of ice sheet behavior, collapse of the entire WAIS is likely to occur on the order of 1,000 years, but recent studies show that melting has already begun,” said Naish when Nature published the papers in March 2009.

NSF-funded research in this story: David Harwood and Richard Levy, University of Nebraska-Lincoln, Award No. 0342484 ; David Marchant, Boston University, Award No. 0440711 ; and Allan Ashworth, North Dakota State University, Award No. 0440761 .