These include soot, ash, and other types of particle from forest fires and volcanoes; isotopes such as beryllium-10 created by cosmic rays; micrometeorites; and pollen.The lowest layer of a glacier, called basal ice, is frequently formed of subglacial meltwater that has refrozen.
In polar areas, the sun is visible day and night during the local summer and invisible all winter.The proportions of different oxygen and hydrogen isotopes provide information about ancient temperatures, and the air trapped in tiny bubbles can be analysed to determine the level of atmospheric gases such as carbon dioxide.Since heat flow in a large ice sheet is very slow, the borehole temperature is another indicator of temperature in the past.These data can be combined to find the climate model that best fits all the available data. Coastal areas are more likely to include material of marine origin, such as sea salt ions.
Greenland ice cores contain layers of wind-blown dust that correlate with cold, dry periods in the past, when cold deserts were scoured by wind.
It can make some snow sublimate, leaving the top inch or so less dense.