Post on 25-Jun-2015
description
Stable Isotope Analysis
Stable Isotope Analysis
a brief introductionby Maggie Z
a brief introductionby Maggie Z
The BasicsThe BasicsAtoms
Protons
no. in the nucleus defines the chemical element
Electrons
the no. of electrons determines the chemical properties
Neutrons
no. can vary
these variations are called isotopes
isotopes of the same element will have different masses
the balance of neutrons and electrons determines if the element is stable
in Archaeologyin Archaeology
Dietary reconstruction
spread of maize in the Americas
terrestrial vs. marine diets
Determining mechanisms of evolution
Establishing migration patternsEstablishing migration patterns
Carbon and NitrogenCarbon and Nitrogen
Both have two stable isotopes
Both are used to reconstruct diet
C & N in bone tissue is derived from food consumed
differing foods have differing ratios of these isotopes
¹²C:¹³C = δ¹³C
¹⁴N:¹⁵N = δ¹⁵N
based on the ratio of δ¹³C to δ¹⁵N it is possible to reconstruct the diet of an individual
CarbonCarbon
plants fall into three groups based on the pathway through which atmospheric carbon is converted into energy
C₃, C₄, and CAM
Average δ¹³C of temperate region terrestrial plants -26.5‰
Average δ¹³C of marine plants -13.0‰
The human range of δ¹³C is between -21‰ and -12‰
distinguishes diets based predominately on terrestrial staples from those based on marine foodstuffs
NitrogenNitrogen
used to add resolution to δ¹³C analyses
δ¹⁵N signals increase at each step of the food chain
around 3.0-4.0‰ per trophic level
Eg carnivores will have a significantly heavier δ¹⁵N than plants
aquatic food chains are much longer
δ¹⁵N of aquatic foods are heavier than terrestrial resources
except when terrestrial animals consume marine resources
except when terrestrial animals consume marine resources
OxygenOxygenThe use of oxygen isotopes to determine prehistoric migration is dependent on the ability to identify variation in the precipitation within the study region.
The oxygen composition of water is dependent on
geography
climate
decreases with
relatively lower temperature
increasing distance from the sea
increasing elevation (estimated -0.28‰/ 100m) Examples
δ¹⁸O of the pacific islands is around ±2‰ (main contributing factors included distance from the ocean and altitude)
StrontiumStrontiumNaturally occurring element
Product of decaying Rubidium
Found in plants, animals and water
ratios are based on the bedrock
ratios are known in most areas
Necropolis 6Necropolis 6
To the East of the city
Stone lined tombs
Oriented East-West
Christian
Multiple burials per tomb
Evidence of VisigothsEvidence of Visigoths
in material remains
raises the question of migration vs. trade
The PlanThe Plan
test strontium and oxygen levels in the enamel of individuals
test floral and faunal remains
test soil and water
Use isotope analysis to determine the origins of the individuals interred
at necropolis 6
Some GravesSome Graves
MaterialsMaterialsI have...
77 samples (teeth)
from 41 stratigraphic units
and 27 tombs
excavated over 3 years
I also have
bone fragments associated with 23 of the samples
I hope to have
faunal samples
soil samples
water samples
TestingTesting
Isotopic analysis is a destructive process
there are many steps, the specifics of which vary based on the laboratory the tests are being performed at
Basically...Basically...
cleaning
drilling
dissolving
filtering
heating
filtering
cooling
analyzing using a mass spectrometer
ResultsResults
Strontium levels compared to samples from site and pre-existing samples taken from known sources
Oxygen levels compared to water samples and to hydrological maps
carbon and nitrogen ratios taken from humans analyzed to reconstruct diet
then compared to faunal samples
possible future studies
possible future studies
compared to the other necropoli
compared to earlier sites from the island
compare to sites from Ibiza or Majorca
compare to sites from the mainland
Questions?Questions?
The End