Editing Ice core (section)

{{Short description|Cylindrical sample drilled from an ice sheet}}
{{Featured article}}
{{Use British English|date=October 2017}}
{{Use dmy dates|date=August 2022}}
[[File:Icecore 4.jpg|thumb|Ice core sample taken from drill|alt=An ice core being slid out of a drill barrel sideways]]
An '''ice core''' is a [[core sample]] that is typically removed from an [[ice sheet]] or a high mountain [[glacier]].  Since the ice forms from the incremental buildup of annual layers of snow, lower layers are older than upper ones, and an ice core contains ice formed over a range of years.  Cores are [[Ice drilling|drilled]] with hand [[Auger (drill)|augers]] (for shallow holes) or powered drills; they can reach depths of over two miles (3.2&nbsp;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.  The proportions of different oxygen and hydrogen [[isotope]]s provide information about [[Paleothermometer|ancient temperatures]], and the [[Atmosphere of Earth|air]] trapped in tiny bubbles can be analysed to determine the level of atmospheric gases such as [[carbon dioxide]].  Since [[Heat transfer|heat flow]] in a large ice sheet is very slow, the borehole temperature is another indicator of temperature in the past.  This data can be combined to find the [[climate model]] that best fits all the available data.

Impurities in ice cores may depend on location.  Coastal areas are more likely to include material of marine origin, such as sea salt [[ion]]s.  [[Greenland]] ice cores contain layers of [[Loess|wind-blown dust]] that correlate with cold, dry periods in the past, when cold deserts were scoured by wind.  [[Radioactivity|Radioactive]] elements, either of natural origin or created by [[Nuclear weapons testing|nuclear testing]], can be used to date the layers of ice.  Some volcanic events that were sufficiently powerful to send material around the globe have left a signature in many different cores that can be used to synchronise their time scales.

Ice cores have been studied since the early 20th century, and several cores were drilled as a result of the [[International Geophysical Year]] (1957–1958).  Depths of over 400 m were reached, a record which was extended in the 1960s to 2164 m at [[Byrd Station]] in Antarctica.  [[Soviet Union|Soviet]] ice drilling projects in Antarctica include decades of work at [[Vostok Station]], with the deepest core reaching 3769 m.  Numerous other deep cores in the Antarctic have been completed over the years, including the [[West Antarctic Ice Sheet]] project, and cores managed by the [[British Antarctic Survey]] and the [[ITASE|International Trans-Antarctic Scientific Expedition]].  In Greenland, a sequence of collaborative projects began in the 1970s with the [[Greenland Ice Sheet Project]]; there have been multiple follow-up projects, with the most recent, the [[East Greenland Ice-Core Project]], originally expected to complete a deep core in east Greenland in 2020 but since postponed.<ref name="corona">{{Cite web|url=https://insideclimatenews.org/news/26032020/coronavirus-climate-science-research-impact|title=Coronavirus Already Hindering Climate Science, But the Worst Disruptions Are Likely Yet to Come|date=27 March 2020|first=Bob|last=Berwyn|access-date=5 April 2020}}</ref>