Stable isotopes
Colin MacLeod
Using Stable Isotopes (SI) To
Investigate Ecological Aspects
Background (the boring bit)
• Nucleus of elements made up
E.g. Carbon Nucleus
of protons and neutrons
P
N
P
N
N
P
P
N N
P N P
6 Protons, 6 Neutrons
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 12
P
N
P
N
N
P
P
N N
P N P
6 Protons, 6 Neutrons
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
P
N
N
P
P
N N N
P N P
6 Protons, 7 Neutrons
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
N
P
N
N
P
N
P
P
N N N
P N P
6 Protons, 8 Neutrons
Using Stable Isotopes (SI) To
Investigate Ecological Aspects
Background (the boring bit)
• Nucleus of elements made up
E.g. Carbon 14
of protons and neutrons
• Some elements have different
P N
N
forms with different numbers
of neutrons (but same number
P
P
N
N
of protons)
N N
P
N
• Number of neutrons does
NOT affect chemical
P N P
reactions but affects weight
• Some are radio-active: C14
6 Protons, 8 Neutrons
• Others are stable: C12, C13
Using Stable Isotopes (SI) To
Investigate Ecological Aspects
Background (the boring bit)
• Radioactive isotopes used for
E.g. Carbon 14
measuring time e.g.
radiocarbon dating (C14)
P N
N
• Stable isotopes used for
measuring rates of biological
P
P
N
N
reactions, patterns of energy
N N
P
N
flow etc.
• Usually measured as ratio of
P N P
two stable isotopes of same
element (e.g. C12:C13 or
delta C13 or ΔC13 or C13) 6 Protons, 8 Neutrons
Using Stable Isotopes (SI) To
Investigate Ecological Aspects
Why Does This Work ?
• One neutron = 1·675 × 10-27 kg
• Therefore, atoms with more neutrons will be slightly
heavier
• This affects how they ‘behave’: e.g. CO2 in Solution
Air
Water
(cold)
C12
C12
C13
C12 C12
C12
C12 C12
C12 C13
Ratio of C12:C13
1000:12
Using Stable Isotopes (SI) To
Investigate Ecological Aspects
Why Does This Work ?
• One neutron = 1·675 × 10-27 kg
• Therefore, atoms with more neutrons will be slightly
heavier
• This affects how they ‘behave’: e.g. CO2 in Solution
Air
C12
Water
(less cold)
C12
C13
C12 C12
C12
C12 C12
C12 C13
Using Stable Isotopes (SI) To
Investigate Ecological Aspects
Why Does This Work ?
• One neutron = 1·675 × 10-27 kg
• Therefore, atoms with more neutrons will be slightly
heavier
• This affects how they ‘behave’: e.g. CO2 in Solution
Air
C12
Water
(luke warm)
C12
C12
C13
C12 C12
C12
C12
C12 C13
Using Stable Isotopes (SI) To
Investigate Ecological Aspects
Why Does This Work ?
• One neutron = 1·675 × 10-27 kg
• Therefore, atoms with more neutrons will be slightly
heavier
• This affects how they ‘behave’: e.g. CO2 in Solution
Air
Water
(warm)
C12
C12
C13
C12
C12 C12
C12
C12
C12 C13
Using Stable Isotopes (SI) To
Investigate Ecological Aspects
Why Does This Work ?
• One neutron = 1·675 × 10-27 kg
• Therefore, atoms with more neutrons will be slightly
heavier
• This affects how they ‘behave’: e.g. CO2 in Solution
Air
C12 C13
Water
(quite warm)
C12
C12
C12
C12
C12 C12
C12 C13
Using Stable Isotopes (SI) To
Investigate Ecological Aspects
Why Does This Work ?
• One neutron = 1·675 × 10-27 kg
• Therefore, atoms with more neutrons will be slightly
heavier
• This affects how they ‘behave’: e.g. CO2 in Solution
Air
C12 C13
Water
(very warm)
C12
C12
C12 C12
C12
C12
C12 C13
Using Stable Isotopes (SI) To
Investigate Ecological Aspects
Why Does This Work ?
• One neutron = 1·675 × 10-27 kg
• Therefore, atoms with more neutrons will be slightly
heavier
• This affects how they ‘behave’: e.g. CO2 in Solution
Air C12
Water
(hot)
C12 C13
C12
C12 C12
C12
C12
C12 C13
Ratio of C12:C13
1000:20
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
Using Stable Isotopes (SI) To
Investigate Ecological Aspects
What Happens in Nature ?
(N14:N15)
1000:3
NH3
NH3
+
+
NH3
NH3
+
1000:6
1000:9
Plankton
Primary
Carnivore
+3‰
+
Seawater
+3‰
Top Carnivore
+3‰
1000:12
Secondary Carnivore
+3‰
Tertiary Carnivore
+3‰
1000:18
1000:15
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??
Using Stable Isotopes (SI) To
Investigate Ecological Aspects
How Can Scientists Use This To Study
Ecology ?
Blender
Ratio of different isotopes e.g.
1000:14
N14:N15
(reflects trophic level of animal)
PREPARATION
Decalcification
Delipification
Dehydration
ON
OFF
Mass Spectrometer
(measures weights all atoms
of specific elements in
sample)
Using Stable Isotopes (SI) To
Investigate Ecological Aspects
How Can Scientists Use This To Study
Ecology ?
(N14:N15)
1000:3
NH3
NH3
+
+
NH3
NH3
+
1000:6
1000:9
1000:12
+
Seawater
Plankton
Top Carnivore
1000:18
Primary
Carnivore
Secondary Carnivore
Tertiary
Carnivore
1000:14
1000:15
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!
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