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