Greenland Ice Sheet at its Smallest Point Between 3,000-5,000 Years Ago: Study

Ice sheets in Greenland are unequivocally losing its mass at an incredible rate due to the rise in the global temperature. Researchers looked at the hidden clues embedded in the Arctic fossil record to understand the history of ice sheets in Greenland

After analyzing ancient fossils like the shells from Greenland, scientists have devised a new technique to determine the when the glaciers were smaller than today. As they expand, ice- sheets push rocks, fossil and other debris into piles called as moraines. If a 3,000 year old fossil is present in a moraine, it reveals that the glacier was at a growing stage and was smaller than it is today.

The new technique stated that the Greenland ice sheet was at its smallest point between 3,000-5,000 years ago. This conclusion was based on analysis of nearly 250 ancient clams from moraines in three western regions.

"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 5-3,000 years ago," Jason Briner, PhD, University at Buffalo associate professor of geology, who led the study, said in a press statement.

He continues to state that the ice sheets start responding to the ocean temperature and this is an indication of the events that might occur in future as the climate continues to warm. This study apart from presenting the history of the Greenland's ice sheet, gives the geologists a new technique for using Arctic fossils to retrieve details on when the glaciers were smaller than they are today.

Till date, scientists have come up with techniques to trace details on when the ice sheets were larger but this is the first study to trace when the ice sheets at Greenland were at its smallest point. Focusing on the traditional technique to retrieve data, they are challenged with time identification on when the ice sheets were smaller. With this study, we now know that a novel tool exists that allows to check how the ice sheets in the past responded, to the warm climatic conditions.

"Because we see the most shells dating to the 5-3000-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," Briner said.

Not going by the expensive radiodating technique, the team instead looked at the structure of amino acids present in the fossils of the ancient clams. There are two orientations within amino acids-D&L. The living organisms maintain their amino acids in an L configuration.  The amino acid flips once the organism dies. In a dead clam the D forms of aspartic acid forms into L. This transition takes places slowly and the age of the fossil is determined by the ration of D and L.

After matching D and L ratios in 20 Arctic clamshell, the researchers radiocarbon-dated the age and generated a scale that reveals which ratio corresponds to which age.  Then they analyzed the D&L ration of aspartic acid in 250 Greenland clamshells to determine the age of the fossil.

The findings have been reported in the journal Geology.