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2.12. Food and Diet Analysis. Important aspect in archaeology is migration and trade; isotope analysis of human remains such as bone and teeth delivers important information on diet & origin. . Isotope distribution in teeth

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2 12 food and diet analysis l.jpg
2.12. Food and Diet Analysis

Important aspect in archaeology is migration and trade;

isotope analysis of human remains such as bone and

teeth delivers important

information on diet & origin.

Isotope distribution in teeth

and bone reflects characteristic isotope ratios (C, N, O, Sr) in food and water from local habitat. Teeth mineralize at early age, maintaining the isotopic signature from early age in teeth enamel. Dentin and bones adopt every twenty years. Comparison of teeth and bone isotope ratios indicates changes if a person has drastically changed its habitat.


Depth analysis in teeth l.jpg
Depth analysis in teeth

tooth enamel is formed in

early childhood  origin

dentin & bone changes

with time  death

Drilling and sequential isotope

ratio analysis reveals fine structure,

possibly due to migration habits.


World wide 18 o 16 o distribution l.jpg
World wide 18O/16O distribution


Fractionation l.jpg
Fractionation

Natural chemical or physical processes can fractionate the carbon, nitrogen, or oxygen isotopes during the up-take and alter the 13C/12C, 15N/14N, and 18O/16O isotopic ratios. This requires correction.

e.g. photosynthesis enriches lighter isotopes → carbon in plant has relatively higher 12C/13C ratio than atmosphere.

18O/16O ratio fractionates by weight, the ratio decreases with altitude and with distance to coast due to weight difference in isotopes

Fractionation is expressed in terms of δ13C which is a measure (in parts of a thousand ppm) of the deviation of the isotopic ratio 13C/12C from a standard material (PDB belemnitella americana). Typical δ13C vary between +2ppm to -27ppm and need to be determined for the material to be dated. Additional fractionation may occur during the chemical preparation of the sample.


Fractionation effects l.jpg
Fractionation effects

fractionation term δ13C is defined from 13C/12C isotopic

ratios for the sample (sm) and the standard (st) as:

A negative value δ13C means that the sample is isotopically lighter than the standard probe. The standard is the fossil belemnite from the Pee Dee formation in South Carolina, PDB, (13C/12C)PDB = 0.0112372. A positive value means that the sample is enriched in the heavier isotope components.


The 13 c map l.jpg
The δ13C Map

Global mean value =-23.23


Excursion fractionation and eating habits and its impact on human isotope ratios l.jpg

C4-photosynthesis

C3-photosynthesis

sample number

Excursion: fractionation and eating habits and its impact on human isotope ratios

There are two different processes of photochemical assimilation of CO2 in plants (photosynthesis cycles).This leads to different carbon fractionation values δ13C in plants an the associated food chains ranging from δ13C =-26.5‰ (C3) to δ13C= -12.5 ‰ (C4).

C3 plants dominate the northern cooler regions of Europe and North America. The habitat of C4 plants are the warmer regions in South- and Central America, Africa, and Australia.


Fractionation in food chain processes l.jpg

bicarbonate in ocean

water and in ground

pure C4 eaters

CO2 in air

bones

of

plant-

eaters

bones

of

meat-

eaters

human

bones

plants

plants

pure C3 eaters

plant eater

or

animals

Fractionation in food chain processes

enrichment

in δ13C in

bone collage

N. Van der Merve, American Scientist 70 (1982) 596


North american values l.jpg
North American Values

North American plants are predominantly C3 plants

 fractionation values of δ13C = -21.4 are observed

in bone collages of plant and meat eating animals.

If additional C4 plants - like corn – are consumed

than will the δ13C value increase accordingly.

e.g. ≈10% corn  δ13C ≈ -20 ‰. Pure maize diet

will result in δ13C ≈ -10 ‰.

Is sea food consumed, drastic changes occur since

the ocean food chain is characterized by different

fractionation processes leading to δ13C ≈ -18 ‰.


Ancient eating habits l.jpg

fraction of C4 plant consumption in %

BC time [y] AD

Ancient eating habits

The fractionation analysis of bone material with parallel

14C dating can help to identify changing eating habits.

Example: increase of corn

consumption (C4 plant) by

population due to the corn

migration into North America.

The values result from bone

analysis of human skeletons.

At 1500 AD: ~75% corn

consumption.

N. Van den Merve, J. Vogel, Nature, 276 (1978) 815


Sea food chains l.jpg

bicarbonate in ocean

water and in ground

CO2 in air

plankton

similar C3

(-17.8)

nutrition

bone material

of coastal

residents

ocean proteins

100%

from sea

mammals

fish, crabs,

and coastal

fauna

bone material

of inland

residents

C3 consumer

100%

from land

(C3)

land fauna

animal meat

birds, fresh

water fish

Sea food chains


Observations l.jpg

Analysis of skeletons of early population of

coastal British Columbia:

δ13C=-13.4±0.9‰  ≈100% seafood based nutrition

Analysis of skeletons of early population of

Ottawa region:

δ13C=-19.6±0.9‰  ≈ 100% C3 originated nutrition.

Analysis of skeletons of early population of

central British Columbia:

δ13C=-15.4±0.3‰  ≈65% seafood (salmon)

& ≈35% C3 originated nutrition.

Observations


Development of mayan diet l.jpg

vegetable

maize

Development of Mayan diet

From fish and vegetable towards maize dominated food

Demonstrated on a nitrogen/ carbon isotope ratio study

Tykot et al. Arch. Chemistry 625 (1996) 355-365


Meso american food characteristics during the classical period l.jpg
Meso-American food characteristicsduring the classical period

Local differences can be detected for

isotope ratios in human bone collages.

Drastic differences due to corn or fish diet!


Checking on yax k uk mo l.jpg
Checking on Yax K’uk Mo

5th century AD the City of Copan in southern Yucatan converted from a small village to a center of Mayan culture within only decades through installation of Yax K’uk Mo as local ruler (coronation 9. 5. 426 AD).

Origin of Yax K’uk Mo is unknown! Speculation is that he was installed by Teotihuacán (Central Mexico) to extend its political influence south.

Main indicator “Goggles”


Strontium sr isotope ratio in upper incisor l.jpg
Strontium Sr isotope ratio in upper incisor

Ratio 87Sr/86Sr is an

important indicator

for tooth analysis

Strontium Sr behaves

chemically similar to

Calcium Ca in tooth

enamel (formed during

the early childhood).

Sr can replace Ca by

food intake. Isotopic

ratio reflects origin.

87Sr/86Sr = 0.7084

C. Day, Physics Today 57

(2004) 20-21


Origin of 87 sr 86 sr l.jpg
Origin of 87Sr/86Sr

Stable Strontium Sr isotopes:

84Sr (0.56%) 86Sr (9.86%), 87Sr (6.94%), 88Sr (82.58%)

-decay

87Ru

87Sr

T1/2=4.71010 y

86,87Sr are stable isotopes, 87Sr/86Sr=0.704

Stable 87Sr is enriched by decay of 87Rb.

An environment with high Rb content

therefore causes high 87Sr/86Sr ratio!


Development of sr isotope ratios in yucatan l.jpg
Development of Sr isotope ratios in Yucatan

Abundance of non-radioactive 86Sr in mineral is constant. 87Sr is stable but continuously produced by decay of the radioactive 87Rb (T1/2=48.8 Gy). Continental rock is rich in 87Rb, limestone contains little 87Rb.

D. A. Hodell et al., J. Arch. Sci 31 (2004) 585-601


87 sr 86 sr distribution in mexico l.jpg

Central Mexico is volcanic

origin low Ca/Rb content

47

Yucatan peninsula formed by Ca/Rb containing

Marine sediments  87Sr enrichment declining south.

87Sr/86Sr distribution in Mexico


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