Thursday, April 19th, 2012
There can be problems encountered when dating cores (organic sediment fraction) that have been stored for long periods of time depending on the storage conditions.
When cores are stored damp, contaminants like mold, mildew and other fungus can thrive and grow in the cores thereby introducing new carbon. Sometimes these mold, mildew and fungus get there carbon solely from:
(1) the organic substances in the cores
(2) from the atmosphere only, and
(3) from both the organic substances in the core and the CO2 in the atmosphere.
In situations 2 & 3, the radiocarbon ages can be biased in the more recent direction by some unknown amount.
If radiocarbon dating is being performed on shell, forams or other carbonate found in the core, then core drying or freezing is not a requirement as any mold, mildew or fungus won’t affect the age of the shells (since it is the carbonate fraction being dated). This also sometimes applies to larger chunks of wood, plant or charcoal that are preserved well enough for the lab to remove the outer surfaces and date the inner, unaffected organic materials (usually with acid/alkali/acid + cellulose extraction pretreatments).
The best way to store cores is to immediately dry them out so that mold, mildew and fungus will not grow. If this is not possible then the cores should be covered in plastic wrap with all of the air removed. The wrapped core should then be kept solidly frozen in a sub-zero freezer.
Please note however that such storage conditions do not 100% inhibit the growth of these contaminants. The best situation is to always collect the core and perform radiocarbon dating immediately.
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