stable isotope analysis
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Stable Isotope Analysis. The Significance of Stable Isotopes. Isotopes are atoms of an element that vary by mass, meaning greater or fewer neutrons. - PowerPoint PPT PresentationTRANSCRIPT
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Stable Isotope Analysis
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The Significance of Stable Isotopes
• Isotopes are atoms of an element that vary by mass, meaning greater or fewer neutrons.
• The isotopes of interest to archaeologists are those that are lighter and which figure in organic compounds, principally those of carbon, nitrogen, and sulphur.
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• Scientists look at the isotopic chemistry of bone collagen, apatite, and hair. The assumption is that an animal’s diet will leave a specific isotopic signature.
• Plants vary in their isotopic ratios of carbon and nitrogen depending on the way they obtain (“fix”) these elements through photosynthesis.
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Plant Isotopic Categories
• C3 Plants: Photosynthesis results in 3-carbon molecule products. These are plants of temperate climates and regions with plentiful groundwater. Examples: wheat, rice, barley, oats, & legumes.
• C4 Plants: Photosynthesis results in 4-carbon molecule products. These are plants of the tropics. Examples: corn and sugarcane.
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• There are also CAM (Crassulacean acid metabolism) plants. These are plants in arid environments that shut their stomata (pores) during the day to avoid water loss. Examples: prickly pear, agave, mesquite and pineapples.
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Dietary Signatures
• A diet high in C3 plants leaves behind low levels of 13C.
• A diet high in C4 plants leaves high levels of 13C in bone collagen.
• A diet high in marine foods products results in high levels of 13C, 15N, and 34S.
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Example from the Tehuacan Valley
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The St. Brice’s Day Massacre
• King Æthlred “Unræd” (Ill-advised) of Wessex ordered that all Danes in England be killed by the Anglo-Saxon population. This mass killing was timed to happen on Nov. 13th 1002 AD.
• The Danish men of Oxford were said to have been killed after they had taken refuge in St. Frideswides’ Church.
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In 2008 the remains of 38 males were found to have been dumped in the ditch of a Neolithic henge by archaeologists excavating on the campus of St. John’s College, Oxford University.
A subsequent bone pit was discovered in 2009 in Weymouth, Dorset.
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• The remains at the two sites were carbon dated, yielding spans 960-1020 AD & 980-1030 AD.
Stable Isotope Analysis
There two areas of a skeleton that yield distinct sets of information
Bone collagen: Isotope mix reflects diet and isotopes in soil, but these will change if an individual moves so collagen isotopes will reflect the last place a person lived before death.
Teeth: Isotope mix is fixed during childhood, and does not change subsequently. Dental isotopes will therefore reflect the place of origin.
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Analysis
• Carbon and nitrogen isotopes were examined in the collagen, and strontium and oxygen isotopes in the enamel.
• The isotopes revealed that not only did the men have diets high in seafood, but that they had diets higher in protein than the norm for the Anglo-Saxon population, and had lived in colder climates when young.