Since heat flow in a large ice sheet is very slow, the borehole temperature is another indicator of temperature in the past, and these sources of information can be combined to find the climate model that best fits all the available data.Impurities in ice cores may depend on location; for example, coastal areas are more likely to include material of marine origin, such as sea salt ions.
Radioactive elements, either of natural origin or created by nuclear testing, can be used to date the layers of ice in the cores.
Both the physical properties of the ice itself and material trapped in the ice can be used to reconstruct information about climate over the age range of the core.
The ratio of oxygen and hydrogen isotopes in the ice provides information about ancient temperatures; and the air trapped in tiny bubbles in the ice can be analyzed to determine the level of atmospheric gases such as carbon dioxide.
Long ago, Ask a Mathematician / Ask a Physicist was two guys sitting around in the desert talking to strangers about whatever came to mind.
It’s been a while, but we’re heading back to Burning Man for more of the same!