1. Stable isotopes Colin MacLeod

2. Using Stable Isotopes (SI) To Investigate Ecological Aspects
Background (the boring bit)
Nucleus of elements made up of protons and neutrons
E.g. Carbon Nucleus P N
6 Protons,
6 Neutrons

3. Using Stable Isotopes (SI) To Investigate Ecological Aspects
Background (the boring bit)
Nucleus of elements made up of protons and neutrons P
E.g. Carbon 12 N
6 Protons, 6 Neutrons
Some elements have different forms with different numbers of neutrons (but same number of protons)

4. Using Stable Isotopes (SI) To Investigate Ecological Aspects
Background (the boring bit)
Nucleus of elements made up of protons and neutrons
Some elements have different forms with different numbers of neutrons (but same number of protons)
E.g. Carbon 13 P N N P P N N N P N P P N
6 Protons, 7 Neutrons

5. Using Stable Isotopes (SI) To Investigate Ecological Aspects
Background (the boring bit)
Nucleus of elements made up of protons and neutrons
Some elements have different forms with different numbers of neutrons (but same number of protons)
E.g. Carbon 14 P N N N P P N N N P N P P N
6 Protons, 8 Neutrons

6. Using Stable Isotopes (SI) To Investigate Ecological Aspects
Background (the boring bit)
Nucleus of elements made up of protons and neutrons
Some elements have different forms with different numbers of neutrons (but same number of protons)
E.g. Carbon 14 P N N N P P N N N P N
Number of neutrons does NOT affect chemical reactions but affects weight
Some are radio-active: C14
Others are stable: C12, C13 P P N
6 Protons, 8 Neutrons

7. Using Stable Isotopes (SI) To Investigate Ecological Aspects
Background (the boring bit)
Radioactive isotopes used for measuring time e.g. radiocarbon dating (C14)
Stable isotopes used for measuring rates of biological reactions, patterns of energy flow etc.
Usually measured as ratio of two stable isotopes of same element (e.g. C12:C13 or delta C13 or ΔC13 or C13)
E.g. Carbon 14 P N N N P P N N N P N P P N
6 Protons, 8 Neutrons

8. Using Stable Isotopes (SI) To Investigate Ecological Aspects
Why Does This Work ?
One neutron = 1·675 × kg
Therefore, atoms with more neutrons will be slightly heavier
This affects how they ‘behave’: e.g. CO2 in Solution
Air
C12
C13
Water
(cold)
Ratio of C12:C13
1000:12

9. Using Stable Isotopes (SI) To Investigate Ecological Aspects
Why Does This Work ?
One neutron = 1·675 × kg
Therefore, atoms with more neutrons will be slightly heavier
This affects how they ‘behave’: e.g. CO2 in Solution
C12
Air
C13
C12
C12
Water
(less cold)
C12
C12
C12
C13
C12
C12

10. Using Stable Isotopes (SI) To Investigate Ecological Aspects
Why Does This Work ?
One neutron = 1·675 × kg
Therefore, atoms with more neutrons will be slightly heavier
This affects how they ‘behave’: e.g. CO2 in Solution
C12
C12
Air
C13
C12
Water
(luke warm)
C12
C12
C12
C13
C12
C12

11. Using Stable Isotopes (SI) To Investigate Ecological Aspects
Why Does This Work ?
One neutron = 1·675 × kg
Therefore, atoms with more neutrons will be slightly heavier
This affects how they ‘behave’: e.g. CO2 in Solution
C12
C12
C12
Air
C13
Water
(warm)
C12
C12
C12
C13
C12
C12

12. Using Stable Isotopes (SI) To Investigate Ecological Aspects
Why Does This Work ?
One neutron = 1·675 × kg
Therefore, atoms with more neutrons will be slightly heavier
This affects how they ‘behave’: e.g. CO2 in Solution
C12
C13
C12
C12
Air
Water
(quite warm)
C12
C12
C12
C13
C12
C12

13. Using Stable Isotopes (SI) To Investigate Ecological Aspects
Why Does This Work ?
One neutron = 1·675 × kg
Therefore, atoms with more neutrons will be slightly heavier
This affects how they ‘behave’: e.g. CO2 in Solution
C12
C13
C12
C12
C12
Air
Water
(very warm)
C12
C12
C13
C12
C12

14. Using Stable Isotopes (SI) To Investigate Ecological Aspects
Why Does This Work ?
One neutron = 1·675 × kg
Therefore, atoms with more neutrons will be slightly heavier
This affects how they ‘behave’: e.g. CO2 in Solution
C12
C12
C13
C12
C12
C12
Air
Water
(hot)
C12
C12
C12
C13
Ratio of C12:C13
1000:20

15. Using Stable Isotopes (SI) To Investigate Ecological Aspects
Why Does This Work ?
The same happens in animals as they metabolise food they have eaten
C12 gets preferentially exhaled in C02 and animal becomes relatively enriched with the heavier C13
Similarly, with isotopes of nitrogen, N14 gets preferentially excreted in urea etc. and animal becomes relatively enriched with the heavier N15
This happens with each trophic level
Therefore, the higher up a food-web the greater the enrichment in heavier isotopes of C and N
In addition, in marine environment, warmer waters = greater C13 enrichment at base of food-web

16. Using Stable Isotopes (SI) To Investigate Ecological Aspects
What Happens in Nature ?
(N14:N15)
1000:6
1000:3
1000:9
1000:12
+3‰
+3‰
+3‰
NH3+
Seawater
Secondary Carnivore
Plankton
Primary Carnivore
+3‰
Top Carnivore
Tertiary Carnivore
+3‰
1000:15
1000:18

17. Using Stable Isotopes (SI) To Investigate Ecological Aspects
How Can Scientists Use This To Study Ecology ?
What Trophic Level Does a Species Feed At ?
Rephrase Question In Terms of Isotopes
What is the Ratio of Nitrogen Isotopes in its Tissues ?
???????
N14:N15??

18. Using Stable Isotopes (SI) To Investigate Ecological Aspects
How Can Scientists Use This To Study Ecology ?
N14:N15?
Ratio of different isotopes e.g. 1000:14
N14:N15
(reflects trophic level of animal)
Blender ON
OFF
Blender ON
OFF
PREPARATION
Decalcification
Delipification
Dehydration
Mass Spectrometer
(measures weights all atoms of specific elements in sample)

19. Using Stable Isotopes (SI) To Investigate Ecological Aspects
How Can Scientists Use This To Study Ecology ?
NH3+
Seawater
Plankton
Primary Carnivore
Secondary Carnivore
Tertiary Carnivore
Top Carnivore
(N14:N15)
1000:3
1000:6
1000:9
1000:12
1000:15
1000:18
1000:14

20. Using Stable Isotopes To Investigate Beaked Whale Ecology
(the interesting bit!!)
Used data from stranded animals to develop hypotheses on beaked whale ecology in the North Atlantic
But Strandings data subject to an number of unquantifiable biases - therefore need independent testing of hypotheses
Used stable isotope analysis of bones from stranded animals for testing hypotheses
Why bones ? Easy to obtain, reflects long-term diet...
...And hard to get a whole whale into a blender!

21. Using Stable Isotopes To Investigate Beaked Whale Ecology
(the interesting bit!!)
In total, samples from 150 different individuals collected between 1800 to 2002 obtained from:
Museums e.g. National Museums of Scotland
Strandings networks e.g. SAC
Researchers and naturalists
Represent six different species - all found in North Atlantic
Primarily sampled inner posterior mandible - least damage to valuable museum specimens
Samples taken weighed around 0.25g
Decalcified to remove inorganic carbon (Soak in 0.5N HCl)
De-lipified to remove fats and lipids (Using Chloroform)
Actual tissue analysed: Bone collagen (Protein component of bones - makes them flexible)
Size of samples analysed in mass spec: 0.7mg