Transcript Stable Isotope Analysis

Stable Isotope Analysis
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.
• 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.
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.
• 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.
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.
Example from the Tehuacan Valley
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.
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.
• 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.
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.