By looking at past concentrations of greenhouse gasses in layers in ice cores, scientists can calculate how modern amounts of carbon dioxide and methane compare to those of the past, and, essentially, compare past concentrations of greenhouse gasses to temperature. Ice cores have been drilled in ice sheets worldwide, but notably in Greenland and Antarctica[4, 5]. * Solar variation at 65°N due to en: Milankovitch cycles (connected to 18O). Ice core records allow us to generate continuous reconstructions of past climate, going back at least 800,000 years. Norsemen settled the uninhabited southern part of Greenland beginning in the 10th century, and Inuit peoples arrived in the 13th century.The Norse colonies disappeared in the late 15th century.The Arctic Umiaq Line ferry acts as a lifeline for western Greenland, connecting the various cities and settlements.Greenland has been inhabited off and on for at least the last 4,500 years by Arctic peoples whose forebears migrated there from what is now Canada.Drilling a vertical hole through this ice involves a serious effort involving many scientists and technicians, and usually involves a static field camp for a prolonged period of time. Shallow ice cores (100-200 m long) are easier to collect and can cover up to a few hundred years of accumulation, depending on accumulation rates.
Nearby, a specially built drill bored into the thick ice sheet twenty-four hours a day under the perpetual Arctic sun.
"The length of the drill barrel determines the maximum length of a core sample [...].
Collection of a long core record [...] requires many cycles of lowering a drill assembly, cutting a core 4–6 m in length, raising the assembly to the surface, emptying the core barrel, and preparing another assembly for drilling." "Boring ice to depths in excess of about 300 meters requires a fluid with a density closely matched to that of ice to prevent lithostatic pressure from causing plastic collapse of the borehole; the latter frequently results in loss of the drilling equipment.
They allow us to go back in time and to sample accumulation, air temperature and air chemistry from another time.
Slow ice flow at the centre of these ice sheets (near the ice divide) means that the stratigraphy of the snow and ice is preserved.