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To: Brumar89 who wrote (754588)	11/25/2013 2:26:59 PM
From: TideGlider	1 Recommendation Recommended By Brumar89 Read Replies (1) \| Respond to of 1583493

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 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. Like Us on Facebook [iframe align="absmiddle" src="http://www.facebook.com/plugins/like.php?href=http%3A%2F%2Fwww.facebook.com%2Fpages%2FIScience-Times%2F452831571409727&send=false&layout=button_count&width=100&show_faces=false&action=like&colorscheme=light&font&height=21" frameborder="0" scrolling="no" style="border: currentColor; width: 100px; height: 21px; overflow: hidden;" allowtransparency="true"][/iframe] 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.

To: Brumar89 who wrote (754588)	11/25/2013 2:27:51 PM
From: TideGlider	1 Recommendation Recommended By Brumar89 Respond to of 1583493

Clam shells date when Greenland’s ice sheet was smaller University at Buffalo ?Original Study Posted by Charlotte Hsu-Buffalo on November 25, 2013 Clues from a new dating technique that utilizes ancient clam shells suggest that 3,000 to 5,000 years ago Greenland’s ice sheet was the smallest it has been in the past 10,000 years. “What’s really interesting about this is that on land, the atmosphere was warmest between 9,000 and 5,000 years ago, maybe as late as 4,000 years ago. The oceans, on the other hand, were warmest between 5,000 to 3,000 years ago,” says Jason Briner, University at Buffalo associate professor of geology, who led the study. “What it tells us is that the ice sheets might really respond to ocean temperatures,” he says. “It’s a clue to what might happen in the future as the Earth continues to warm.” The findings appeared online in the journal Geology. The study is important not only for illuminating the history of Greenland’s ice sheet, but for providing geologists with an important new tool—a method of using Arctic fossils to deduce when glaciers were smaller than they are today. Scientists have many techniques for figuring out when ice sheets were larger, but few for the opposite scenario. “Traditional approaches have a difficult time identifying when ice sheets were smaller,” Briner says. “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.” Ice sheets are like bulldozersThe technique the scientists developed involves dating fossils in piles of debris found at the edge of glaciers. Growing ice sheets are like bulldozers, pushing rocks, boulders, and other detritus into heaps of rubble called moraines. Because glaciers only do this plowing when they’re getting bigger, logic dictates that rocks or fossils found in a moraine must have been scooped up at a time when the associated glacier was older and smaller. So if a moraine contains fossils from 3,000 years ago, that means the glacier was growing—and smaller than it is today—3,000 years ago. This is exactly what the scientists saw in Greenland. They looked at 250 ancient clams from moraines in three western regions, and discovered that most of the fossils were between 3,000 to 5,000 years old. The finding suggests that this was the period when the ice sheet’s western extent was at its smallest in recent history, Briner says. Dating ancient clams“Because we see the most shells dating to the 5,000- to 3000-year period, we think that this is when the most land was ice-free, when large layers of mud and fossils were allowed to accumulate before the glacier came and bulldozed them up,” he says. Because radiocarbon dating is expensive, Briner and his colleagues found another way to trace the age of their fossils. Their solution was to look at the structure of amino acids—the building blocks of proteins—in the fossils of ancient clams. Amino acids come in two orientations that are mirror images of each other, known as D and L, and living organisms generally keep their amino acids in an L configuration. When organisms die, however, the amino acids begin to flip. In dead clams, for example, D forms of aspartic acid start turning to L’s. Because this shift takes place slowly over time, the ratio of D’s to L’s in a fossil is a giveaway of its age. Knowing this, Briner’s research team matched D and L ratios in 20 Arctic clamshells to their radiocarbon-dated ages to generate a scale showing which ratios corresponded with which ages. The researchers then looked at the D and L ratios of aspartic acid in the 250 Greenland clamshells to come up with the fossils’ ages. Amino acid dating is not new, but applying it to the study of glaciers could help scientists better understand the history of ice—and climate change—on Earth. The National Geographic Society and US National Science Foundation funded the project.