Relative age dating and radiometric age dating
The relationship is consistent and linear over Antarctica.
Snow falls over Antarctica and is slowly converted to ice.
U from dust in the ice matrix can be used to provide an additional core chronology.
The thickness of the annual layers in ice cores can be used to derive a precipitation rate (after correcting for thinning by glacier flow).
Melt layers are formed when the surface snow melts, releasing water to percolate down through the snow pack.
They form bubble-free ice layers, visible in the ice core.
Deeper cores require more equipment, and the borehole must be filled with drill fluid to keep it open.
The drill fluid used is normally a petroleum-derived liquid like kerosene.
Ice cores provide us with lots of information beyond bubbles of gas in the ice. Other ways of dating ice cores include geochemisty, layers of ash (tephra), electrical conductivity, and using numerical flow models to understand age-depth relationships. This 19 cm long of GISP2 ice core from 1855 m depth shows annual layers in the ice. If we want to reconstruct past air temperatures, one of the most critical parameters is the age of the ice being analysed. Fortunately, ice cores preserve annual layers, making it simple to date the ice.
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This section contains 11 annual layers with summer layers (arrowed) sandwiched between darker winter layers.