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For decades, scientists have been probing the Greenland Ice Sheet from the ground, air

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and space. Now a new study uses those observations

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to see within the ice sheet…laying bare a tale more than

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one hundred thousand years in the making.

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When we look inside an ice sheet, we can see distinct layers formed by thousands of years of snowfall.

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As snow accumulates, these layers get

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progressively compacted into ice, which then flows under its own weight.

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To get a precise history of a particular spot on

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an ice sheet, scientists drill into it and recover ice cores,

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which provide a record of the ice’s age and what the past

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climate was like. Seasonal variations, along with ash

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from volcanic eruptions show up in the cores allowing us

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to date the ice and correlate samples from different sites.

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To extend this age information across the ice sheet,

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the best tool that we have is ice-penetrating radar, mounted on aircraft

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flying low over the surface. Radar transmits

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electromagnetic pulses into the ice and records the reflected signals,

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allowing us to track the depth of the layers detected in the ice.

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Since 2009, NASA’s Operation IceBridge has

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flown over Greenland more than one hundred times with a wide variety of instruments,

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including radar, and generated vast quantities of data,

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adding to the work from many other missions. This has allowed researchers

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to generate a three dimensional map depicting the age of the ice throughout

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the Greenland Ice sheet. This 3D age map

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shows that three distinct periods of climate are evident within the ice sheet:

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The Holocene, shown here in green. The last ice age,

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shown in blue. And the Eemian, shown here in red.

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The top layers from the Holocene Period, formed during the last

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11.7 thousand years and are fairly flat and uniform.

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though the thickness varies depending on how much snowfall occurred.

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Below this, deeper within the ice sheet, we see layers that formed

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during the last ice age. Layers from this period are darker

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and more complex, having been further squeezed and sometimes folded

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as they flowed over the rugged bedrock below.

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Deeper still are layers of ice leftover from the warm period before the last ice age,

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more than one hundred fifteen thousand years ago.

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Eemian ice can reveal how the ice sheet responded to a period of warmth

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similar to the one we are experiencing today.

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Several ice cores have recovered Eemian ice, but it is difficult to interpret.

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This new map of the age of the ice sheet shows that there

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is more Eemian ice than expected in northern Greenland, where it may be easier

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for scientists to collect and analyze.

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This new analysis reveals a 3D map of the age

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of the Greenland ice sheet , from the oldest Eemian ice,

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to the layers deposited during the last ice age, to the ice that formed during the Holocene.

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The response of the ice sheet to past climate change

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led to its current age structure. Further study will help us

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to better understand how the Greenland Ice Sheet will respond to today’s changing climate.

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