Greenland’s Shrunken Ice Sheet Was Even Smaller 3,000-5,000 Years Ago

Scientists use amino acid dating method on fossil record to understand history of the ice sheet.

By Ajit Jha on November 23, 2013 5:10 PM EST

NASA / Michael Studinger
NASA / Michael Studinger

Scientists studying the history of Greenland's ice sheet through analyzing the Artic fossil record have stumbled upon an important finding: Greenland's ice sheet was much smaller between 3,000 to 5,000 years ago than it is today.

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According to Jason Briner, associate professor of geology at the University at Buffalo, who led the study, one of the most interesting findings is that the atmosphere was warmest on land between 9,000 and 4,000 years ago, while oceans were warmest between 5,000 and 3,000 years ago.

Other members of Briner's team included Darrel Kaufman, an organic geochemist from Northern Arizona University; Ole Bennike, a clam taxonomist from the Geological Survey of Denmark and Greenland; and Matthew Kosnik, a statistician from Australia's Macquarie University.

The findings have been published online in the journal Geology.

"What it tells us is that the ice sheets might really respond to ocean temperatures," Briner said. "It's a clue to what might happen in the future as the Earth continues to warm."

The study is also significant because geologists were able to apply the Artic fossils method to determine the period when glaciers were smaller than they are today. Scientists have techniques to find out when ice sheets were larger, but lacked methods to determine when the ice sheets were smaller, until now.

"Traditional approaches have a difficult time identifying when ice sheets were smaller," Briner said. "The outcome of our work is that we now have a tool that allows us to see how the ice sheet responded to past times that were as warm or warmer than present — times analogous to today and the near future."

The newly developed technique is based on dating fossils found within debris at the edge of glaciers. Growing ice sheets push rocks, boulders, and debris into rubble called moraines. Logically, it is presumed rocks and fossils found in moraines originate from a time when the glacier was smaller and older.

So, finding 3,000-year-old fossils found in a moraine implies that the glacier was much smaller 3000 years ago than it is today. The scientists in Greenland studied 250 ancient clams from moraines in three western regions and found most of them to be between 3,000 to 5,000 years old.

The finding indicates that the western extent of the ice sheet was at its smallest between 3,000 to 5,000 years ago, according to Briner. In light of the expense of radiocarbon dating, Briner and colleagues used the structure of amino acids to determine the age of the fossils.

Amino acids have two orientations, D & L. These two orientations are mirror images of each other. Living organisms generally keep their amino acids in an L configuration, but the amino acids flip to a D formation once the organism dies. Measuring the ratio of D to L amino acids can approximate how long an organism has been dead.

Briner and his team used this method to come determine the fossil's age. While amino acid dating is not new, its application could help scientists understand the history of ice on Earth.

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