What is fractionation in dating
Ice is lost at the edges of the glacier to icebergs, or to summer melting, and the overall shape of the glacier does not change much with time.Impurities in the ice provide information on the environment from when they were deposited.The bubbles disappear and the ice becomes more transparent.The weight above makes deeper layers of ice thin and flow outwards.At Summit Camp in Greenland, the depth is 77 m and the ice is 230 years old; at Dome C in Antarctica the depth is 95 m and the age 2500 years.
The fluid must have a low kinematic viscosity to reduce tripping time (the time taken to pull the drilling equipment out of the hole and return it to the bottom of the hole).It can make some snow sublimate, leaving the top inch or so less dense.When the sun approaches its lowest point in the sky, the temperature drops and hoar frost forms on the top layer.Cores are drilled with hand augers (for shallow holes) or powered drills; they can reach depths of over two miles (3.2 km), and contain ice up to 800,000 years old.The physical properties of the ice and of material trapped in it can be used to reconstruct the climate over the age range of the core.
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It can be up to about 20 m thick, and though it has scientific value (for example, it may contain subglacial microbial populations), Cores are often drilled in areas such as Antarctica and central Greenland where the temperature is almost never warm enough to cause melting, but the summer sun can still alter the snow.