Editing Ice core (section)

== Core processing ==
[[File:Gripsaw.jpg|thumb|Sawing the [[Greenland ice core project|GRIP]] core|alt=Scientist standing at a bench, sawing an ice core]]

With some variation between projects, the following steps must occur between drilling and final storage of the ice core.<ref name="UNH">{{Cite web|url=http://icecores.org/icecores/drilling.shtml|title=About Ice Cores :: Drilling Ice Cores|last=UNH|first=Joe Souney|publisher=National Ice Core Laboratory|language=en|access-date=21 May 2017|url-status=dead|archive-url=https://web.archive.org/web/20170504192232/http://icecores.org/icecores/drilling.shtml|archive-date=4 May 2017}}</ref>

The drill removes an annulus of ice around the core but does not cut under it. A spring-loaded lever arm called a core dog can break off the core and hold it in place while it is brought to the surface.  The core is then extracted from the drill barrel, usually by laying it out flat so that the core can slide out onto a prepared surface.<ref name="UNH" /> The core must be cleaned of drilling fluid as it is slid out; for the [[WAIS Divide]] coring project, a vacuuming system was set up to facilitate this.  The surface that receives the core should be aligned as accurately as possible with the drill barrel to minimise mechanical stress on the core, which can easily break.  The ambient temperature is kept well below freezing to avoid thermal shock.<ref name="Souney-2014-1">{{harvnb|Souney et al.|2014}}, pp. 16–19.</ref>

A log is kept with information about the core, including its length and the depth it was retrieved from, and the core may be marked to show its orientation.  It is usually cut into shorter sections, the standard length in the US being one metre.   The cores are then stored on site, usually in a space below snow level to simplify temperature maintenance, though additional refrigeration can be used.  If more drilling fluid must be removed, air may be blown over the cores.  Any samples needed for preliminary analysis are taken.  The core is then bagged, often in [[polythene]], and stored for shipment.  Additional packing, including padding material, is added.  When the cores are flown from the drilling site, the aircraft's flight deck is unheated to help maintain a low temperature; when they are transported by ship they must be kept in a refrigeration unit.<ref name="Souney-2014-1" />

There are several locations around the world that store ice cores, such as the [[National Ice Core Laboratory]] in the US. These locations make samples available for testing.  A substantial fraction of each core is archived for future analyses.<ref name="Souney-2014-1" /><ref>{{Cite journal|last=Hinkley|first=Todd|date=9 December 2003|title=International ice core community meets to discuss best practices for ice core curation|journal=Eos Trans AGU|volume=84|issue=49|page=549|doi=10.1029/2003EO490006|bibcode=2003EOSTr..84..549H|doi-access=free}}.</ref>

=== Brittle ice ===
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| image1            = CSIRO ScienceImage 518 Air Bubbles Trapped in Ice.jpg
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| caption1          = Bubbles in an Antarctic ice sample. Illuminated with polarised light
| image2            = CSIRO ScienceImage 521 Bubbles in Ice.jpg
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| caption2          = Sliver of Antarctic ice showing trapped bubbles. Images from [[CSIRO]].
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Over a depth range known as the [[brittle ice]] zone, bubbles of air are trapped in the ice under great pressure.  When the core is brought to the surface, the bubbles can exert a stress that exceeds the tensile strength of the ice, resulting in cracks and [[spall]].<ref name="Souney-2014-2" /> At greater depths, the air disappears into clathrates and the ice becomes stable again.<ref name="Souney-2014-2" /><ref>{{Cite journal|last1=Uchida|first1=Tsutomu|last2=Duval|first2=P.|last3=Lipenkov|first3=V.Ya.|last4=Hondoh|first4=T.|last5=Mae|first5=S.|last6=Shoji|first6=H.|year=1994|title=Brittle zone and air-hydrate formation in polar ice sheets|url=http://id.nii.ac.jp/1291/00002234/|journal=Memoirs of National Institute of Polar Research|volume=49 |issue=49|page=302}}.</ref> At the WAIS Divide site, the brittle ice zone was from 520&nbsp;m to 1340&nbsp;m depth.<ref name="Souney-2014-2">{{harvnb|Souney et al.|2014}}, pp. 20–21.</ref>

The brittle ice zone typically returns poorer quality samples than for the rest of the core.  Some steps can be taken to alleviate the problem.  Liners can be placed inside the drill barrel to enclose the core before it is brought to the surface, but this makes it difficult to clean off the drilling fluid.  In mineral drilling, special machinery can bring core samples to the surface at bottom-hole pressure, but this is too expensive for the inaccessible locations of most drilling sites.  Keeping the processing facilities at very low temperatures limits thermal shocks.  Cores are most brittle at the surface, so another approach is to break them into 1&nbsp;m lengths in the hole.  Extruding the core from the drill barrel into a net helps keep it together if it shatters. Brittle cores are also often allowed to rest in storage at the drill site for some time, up to a full year between drilling seasons, to let the ice gradually relax.<ref name="Souney-2014-2" /><ref>{{harvnb|Talalay|2016}}, pp. 265–266.</ref>