A far different place
Plant fossils from ANDRILL sediment cores shed new light on warmer Antarctica
Posted June 22, 2012
Ancient Antarctica was warmer and wetter than previously suspected, enough to support vegetation along its edges, according to a new study.
Researchers came to that conclusion by examining the remnants of plant leaf wax found in sediment cores taken from below the seafloor in McMurdo Sound in the Ross Sea region of Antarctica in 2007 during the two-year ANtarctic Geological DRILLing Program (ANDRILL) .
The $30 million ANDRILL program was one of the premiere projects of the International Polar Year , a two-year scientific campaign that ran from March 2007 to March 2009. The National Science Foundation (NSF) funded about two-thirds of the ANDRILL project, with international partners New Zealand, Italy and Germany funding the remainder.
Scientists from the University of Southern California (USC) , Louisiana State University and NASA’s Jet Propulsion Laboratory (JPL) determined that summer temperatures along the Antarctic coast 15 to 20 million years ago were about 11 degrees Celsius warmer than they are today, reaching up to about 7 degrees Celsius, with more precipitation.
This occurred during a period of global warming in the middle Miocene epoch that coincided with increased levels of atmospheric carbon dioxide.
“This is some of the first evidence of just how much warmer it was,” said Sarah J. Feakins , an assistant professor of earth sciences at the USC and lead author of a paper on the research published in journal Nature Geoscience on June 17, in a press release.
Photo Credit: Peter West/Antarctic Photo Library
Scientists examine a section of sediment core from the ANDRILL project.
Scientists began to suspect that high-latitude temperatures during the middle Miocene were warmer than previously believed when Sophie Warny , co-author of the Nature Geoscience paper, discovered large quantities of pollen and algae in sediment cores taken around Antarctica. Those initial results were published in 2009 in an issue of Geology, the journal of the Geological Society of America. [See previous article — Rich layer: New ANDRILL fossil find denotes significant warm period 15.7 million years ago.]
Fossils of plant life in Antarctica are difficult to come by because the movement of the massive ice sheets covering the landmass grinds and scrapes away the evidence.
“Deep sea cores are ideal to look for clues of past vegetation, as the fossils deposited are protected from ice-sheet advances, but these are technically very difficult to acquire in the Antarctic and require international collaboration,” said Warny, assistant professor of palynology at LSU, in the USC press release .
Tipped off by the tiny pollen samples from the 2009 study, the researchers opted to look at the remnants of leaf wax taken from the ANDRILL sediment cores for clues. Leaf wax acts as a record of climate change by documenting details about the hydrogen isotope ratios of the water the plant drank while it was alive.
Jung-Eun Lee , a scientist at JPL and a co-author on the paper, created model experiments to find out just how much warmer and wetter climate may have been. “When the planet heats up, the biggest changes are seen toward the poles. The southward movement of rain bands made the margins of Antarctica less like a polar desert, and more like present-day Iceland,” she explained.
The peak of Antarctic greening during this time period, known as the middle Miocene, occurred between 16.4 and 15.7 million years ago when mostly modern-looking animals such as three-toed horses, deer and camel roamed Earth. Various species of apes also existed, though modern humans did not appear until 200,000 years ago.
Warm conditions during the middle Miocene are thought to be associated with carbon dioxide levels, probably around 400 to 600 parts per million (ppm). In 2012, carbon dioxide levels have climbed to 393 ppm, the highest they’ve been in the past several million years. At the current rate of increase, atmospheric carbon dioxide levels are on track to reach middle Miocene levels by the end of this century.
The ultimate goal of the study was to better understand what the future of climate change may look like, Feakins said. “Just as history has a lot to teach us about the future, so does past climate: what this record shows us is how much warmer and wetter it can get around the Antarctic ice sheet as the climate system heats up.”