Stable Isotope Analysis Flashcards
(17 cards)
1
Q
What are isotopes
A
- Different versions of the same element
- Different numbers of neutrons in the nucleus of an atom
- Different physical properties
- Same chemical properties
2
Q
Stable isotopes
A
- Do not undergo decay
- Coexist in nature, but not in equal amounts
3
Q
Carbon and Nitrogen isotopes ratio
A
- Isotopes are measured as ratios of two isotopes
- 3 naturally occuring Carbon isotopes:
- 13C, 13C:12C
- 2 naturally occuring Nitrogen isotopes:
- 15N, 15:14N
3
Q
Mass Spectrometry
A
- Measurements expressed as per mill
- Compared to a standard for interlab consistency/comparison of datasets
- 13C of all photosynthesised carbon is less than 13C (environmental? naturally occuring??) so all values are NEGATIVE compared to the standard
4
Q
What tissues can be sampled?
A
- Any well preserved tissue
- Bone: inorganic and organic
- Tooth enamel and dentine
- Soft tissues and organs
- Hair and nails
5
Q
Bone Apatite
A
- Bone remodels throughout life
- Carbon composition of bone apatite reflects the lifetime average primarily of energy sources in diet
- Bone apatite is very susceptible to diagenetic alteration and environmental exchange so not often used as a dietary proxy
6
Q
Tooth enamel
A
- Fixed during childhood, one of the hardest and strongest in the body
- A proxy for dietary energy sources during the period of enamel development
- Teeth that develop in utero record diet
- Choose tooth sample accordingly
7
Q
Bone collagen
A
- Carbon and nitrogen in bone collagen are derived largely from dietary protein
- Bone collagen remodels throughout life
8
Q
Bone collagen in adults
A
- Cortical bone has slow turnover
- Average of lifetime diet
- Femur sample = 10+ years
- Mid-shaft femur = adolesence
- Cancellous bone has quick turnover
- Short term diet
- Rib sample = diet over <5 years prior to death
9
Q
Bone collagen in sub-adults
A
- During periods of bone growth, apatite/collagen turnover rates are very quick
- Collagen is completely replaced in as little as weeks to months: short term dietary intake
10
Q
Tooth dentine
A
- Tooth dentine does not remodel it is fixed during childhood
- Records diet during the period of dentine development
- Incramental growth layers
- Short-term dietary variation (weeks - months)
- 2 dietary proxies: carbon and nitrogen stable analysis
11
Q
Keratinaceous Tissues
A
- Hair and nails
- Not remodelled
- Incramental growth patterns reflect short-term diet/dietary changes
- Non-invasive
- 6-12 days
12
Q
3 main groups of plants
A
- Terrestrial C3: Most temperate plants including wheat and rice
- Terrestrial C4: tropical grasses including maize, millet, sorghum
- Marine plants
13
Q
Carbon Fractionation
A
- Carbon isotopes are fractioned by plants during photosynthesis
- Preferential uptake of 12C
- But, C4 plants incorporate more 13C than C3 plants
- C3 plants have lower 13 ratios than C4 plants
- Differences are passed on through the food chain
14
Q
Carbon in marine food webs
A
- Marine plants are C3
- Obtain CO2 from dissolved bicarbonate which is relatively 13C enriched
- Marine resources generally have higher 13C values than terrestrial C3 plants
- 13C values can be similar to C4 terrestrial values
15
Q
Nitrogen and food webs
A
- Stable isotope nitrogen increase with each step along the food chain, expecting to increase 3-6 parts per mill
- Humans consuming more terrestrial herbivores or dairy produce will have nitrogen stable isotope of 9-10 parts per mill
- Vegans 6-7 parts per mill
- Cannot identify vegetarians
16
Q
Nitrogen and aquatic food webs
A
- Aquatic food webs are generally more complex than terrestrial food webs
- Humans subsisting on aquatic diets have higher nitrogen SI levels than those consuming terrestrial diets
- Typical nitrogen SI of humans subsiding on mainly aquatic diet is 15-20 parts per mill
