Expression of Stable Isotope Values – Delta Notation:
Delta Units (δ): are expressed in molecules per
thousand (‰), or “per mil”.
For example, δ15NAir = 12 per mil means that the sample was analyzed
against a reference material and found to be 12 molecules per thousand
more abundant than in air – the accepted zero point for expression of
nitrogen-15 in per mil notation.
For the calculation:
where
δ = [ (Rs / Rr) - 1 ] * 1000
Rs is the ratio of the heavy isotope to the light isotope of the sample
and
Rr is the ratio of the heavy isotope to the light isotope of the reference.
Isotope Ratio Mass Spectrometer – “IRMS”
bending
magnet
A mass spectrometer is an
instrument which separates
charged molecules by
mass.
An isotope ratio mass
spectrometer (IRMS) works
on this principle, but unlike
other conventional mass
spectrometers it has been
specifically designed to
measure the proportions
of particular isotopes. An
IRMS will be much more
precise, but much less
sensitive than other mass
spectrometers.
Ionisation
Principle of a Quadrupole Mass Spectrometer
For mass separation, quadrupole systems use a high-frequency alternating electrical field.
A Faraday cup and a secondary electron multiplier serve as detectors. Commonly used in
conjunction with either gas-chromatography or liquid-chromatography, and more recently
with ICP, as a simple high throughput screening system.
A quadrupole has four parallel rods
that have fixed DC and alternating RF
potentials applied to them. Ions
produced in the source of the
instrument are then focused and
passed along the middle of the
quadrupoles.
Stable Isotopes – Mass Dependant Fractionation
Rayleigh Effects two species (or phases as in water) that are in equilibrium with
one another, or where the reactants and products become separated from one
another
Kinetic Effects kinetic effects are most commonly seen in processes that are
influenced by biologic processes, during unidirectional processes
Diffusion the light isotope of an element will diffuse more rapidly than the heavy isotope
The most widely studied stable isotopes are:
Element
Isotopes
Hydrogen 1H, 2H
10B, 11B
Boron
12C, 13C
Carbon
Nitrogen 14N, 15N
16O, 17O, 18O
Oxygen
32S, 33S, 34S, 36S
Sulfur
α is the isotope fractionation factor, (e.g. α for water liquid and vapor is 10‰
i.e., the δ18O of the liquid is 10‰ heavier).
α is typically calculated in K (degrees Kelvin) which is equal to oC + 273.
α is the isotope fractionation factor,
(e.g. α for water liquid and vapor is 10 ‰, i.e., the δ18O of the liquid is 10‰ heavier).
The size of this isotopic fractionation can be expressed in several ways:
Natural log notation, 1000ln(α):
1000ln(α) – 1000 ln (1- ε) = ε
ε
The epsilon notation, :
εA-B = (αA-B – 1) * 1000
The epsilon notation has the advantage over the 1000ln(α) notation in
that it is an exact expression of the per mil fractionation.
The capital delta notation, Δ:
Δ A-B = δA - δB
Some General “Rules”
• Isotope fractionation factors are greater at lower temperatures.
• Light isotopes are enriched in biogenic compounds.
• Light isotopes are enriched in reduced species and heavy isotopes are enriched
in oxidized species (e.g., the δ13C of CO2 is higher than that of CH4).
• It follows from this that reactions which involve a change in oxidation state
result in a greater degree of stable isotope fractionation than those that do not.
• Where two minerals of the same oxidation state are in equilibrium with one
another, the mineral with the heaviest cation will have the lightest stable isotope
composition (e.g., the δ 34S of ZnS (sphalerite) is higher than that of PbS (galena)).
• The extent of stable isotope fractionation is inversely proportion to the square
of the relative mass difference between two isotopes. This means that the extent
of stable isotope fractionation between 100Ru and 101Ru is less than 1% of that
between 10B and 11B. In practice this has meant that stable isotope fractionation is
effectively below detection limits for elements with masses greater than 40 (i.e., for
elements with masses greater than that of Ca). Recent advances in mass spectrometry are
increasing the range of elements for which stable isotope variations can be detected.
Ranges of O Isotopic Values in Geologic Systems
meteoric waters
ocean water – VSMOW = 0 ‰
sedimentary rocks
metamorphic rocks
granitic rocks
basaltic rocks
extraterrestrial materials
(meteorites and lunar rocks)
-70
-60
-50
-40
-30
-20
-10
0
10
20
30
40
δ18O (‰ VSMOW)
Oxygen isotopes of meteoric water are generally lighter than those of seawater (Hoefs, 1980, fig. 10).
Rainout effect on δ2H
and δ18O values;
(based on Hoefs 1997 and
Coplen et al. 2000).
Change in the 18O content of rainfall
according to a Rayleigh distillation, starting
with δ18Ovapor = -11‰, temp. = 25°C, and final
temp. of -30°C. Note that at 0°C, fractionation
between snow and water vapor replaces rainvapor fractionation. The fraction remaining
has been calculated from the decrease in
moisture carrying capacity of air at lower
temperatures, starting at 25°C. Dashed lines
link δ18O of precipitation with temperature of
condensation. (Reproduced from Clark and
Fritz 1997, p.48)
W
Ocean
Water
(Clark and Fritz 1997, p. 37, as compiled in Rozanski et al. 1993,
modified by permission of American Geophysical Union).
http://www.sahra.arizona.edu/programs/isotopes/images/diagram7.gif
Vienna Standard Mean Ocean Water
(VSMOW) is a water standard defining the
isotopic composition of water. It was
promulgated by the International Atomic Energy
Agency in 1968.
Despite the misleading designation ocean water,
VSMOW does not include any salt or other
substances usually found in seawater and refers
to pure water with a particular composition of
isotopes. VSMOW serves as a reference standard
for comparing hydrogen and oxygen isotope
ratios, mostly in water samples.
Very pure, distilled VSMOW water is also used for making high
accuracy measurement of water's physical properties and for
defining laboratory standards since it is considered to be
representative of average ocean water, in effect representing all
water on Earth.
0‰
0‰
http://www.sahra.arizona.edu/programs/isotopes/images/diagram7.gif
The isotopic composition of VSMOW water is specified
as ratios of the molar abundance of the rare isotope in
question divided by that of its most common isotope
and is expressed as parts per million (ppm). For instance
16O (the most common isotope of oxygen with eight
protons and eight neutrons) is roughly 2,632 times more
prevalent in sea water than is 17O (with an additional
neutron). The isotopic ratios of VSMOW water are
defined as follows:
2H/1H = 155.76 ±0.1 ppm
(a ratio of 1 part per approximately 6420 parts)
3H/1H = 1.85 ±0.36 × 10−11 ppm
(a ratio of 1 part per approximately 5.41 × 1016 parts,
ignored for physical properties-related work)
18O/16O = 2,005.20 ±0.43 ppm
(a ratio of 1 part per approximately 498.7 parts)
17O/16O = 379.9 ±1.6 ppm
(a ratio of 1 part per approximately 2,632 parts)
Annual Climate
Records:
Variation in the closely spaced rings of a bristlecone pine correspond to annual
changes in rainfall and temperature. (Photograph copyright Henri D. Grissino-Mayer)
sclectarian corals
An ice core with a layer of
algae.
Water vapor gradually loses 18O as it travels from the equator to the poles. Because water
molecules with heavy 18O isotopes in them condense more easily than normal water
molecules, air becomes progressively depleted in 18O as it travels to high latitudes and
becomes colder and drier. In turn, the snow that forms most glacial ice is also depleted in
18O. As glacial ice melts, it returns 16O-rich fresh water to the ocean. Therefore, oxygen
isotopes preserved in ocean sediments provide evidence for past ice ages and records of
salinity. (Illustration by Robert Simmon, NASA GSFC based on data provided by Cole et. al. 2000, archived
at the World Data Center for Paleoclimatology).
http://earthobservatory.nasa.gov/Features/Paleoclimatology_Evidence/
A Greenland ice core with a layer of algae.
global-warming.accuweather.com/ice_core_algae
From Gercke, in preparation
Cyprideis sp.
Perissocytheridea sp.
Age
y.b.p.
From Gercke, in preparation
δ18O
Large scale Climate Records:
Diagram showing the nature of the loess
stratigraphic record. In most regions, including
much of North America, Europe, and China,
loess was deposited during glacial periods and
soils were formed during interglacial periods.
Soils that become buried by younger loess are
called "paleosols."
http://esp.cr.usgs.gov/info/eolian/task2.html
Global Records:
http://earthobservatory.nasa.gov/Features/Paleoclimatology_Evidence/
Shriner, C.M., Elswick, E.R., Ripley, E.M., Shimmelmann, A., and Murray, H.H., (in press) Natural Environment as a Determinative Factor in
Greek Early Helladic Cultural Change on the Argive Plain: in Katsonopoulou, D. Ed., The Early Helladic Peloponnesos, Helike IV; The Heike
Society; Athens, Greece.
Shriner, C.M., Elswick, E.R., Ripley, E.M., Shimmelmann, A., and Murray, H.H., (in press) Natural Environment as a Determinative Factor in
Greek Early Helladic Cultural Change on the Argive Plain: in Katsonopoulou, D. Ed., The Early Helladic Peloponnesos, Helike IV; The Heike
Society; Athens, Greece.
Ranges of C Isotopic Values in Geologic Systems
freshwater ΣCO2
shallow ocean ΣCO2
deep ocean ΣCO2
marine organic C
land plants
soil organic C
volcanic CO2
biogenic methane
soil CO2
sedimentary organic matter, petroleum, coal
marine and non-marine organisms
freshwater carbonates
marine carbonates
atmospheric CO2
carbonatites, diamonds
extraterrestrial materials
(meteorites and lunar rocks)
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
δ13C (‰ VPDB)
Carbon isotopes in geologic systems. Carbonate carbon derived from seawater is
much heavier than organic carbon, and hence than carbonate formed by oxidation
of organic matter (Hoefs, 1980, fig. 9; Trumbore and Druffel, 1995).
Diagrammatic Representation of the
Exogenic Cycles of Carbon and Sulfur
Carbonate Carbon
6460 x Car
1018 moles
δ13C = -0.4
Gypsum
166 x 1018 moles
δ34S= +8.4
SW sulfate
40 x 1018 moles
δ34S= +20
Ocean
Carbonate, DIC
3.3 x 1018 moles
δ13C = +0.46
Pyrite
Organic
Carbon
180 x 1018 moles
δ34S= -7.9
1180 x 1018 moles
δ13C = -27
S - Cycle
C - Cycle
Gregor et al.. 1988
The denominations are because in the plants of group C3, the first photosynthesized
organic compound has 3 atoms of carbon while in group C4, there are 4. (There is
also a third, very minor, group called CAM, a combination of C3 and C4 where some
cactus and succulents belong to.)
http://homepage.mac.com/uriarte/carbon13.html
Most plants (85%) (e.g. trees and crops) follow the C3 photosynthesis
pathway and have lower values of δ13C, between -22‰ and -30‰.
The remaining 15% of the plants are of type C4. The majority are tropical
herbs and have high values of δ13C, between –10 ‰ and –14 ‰.
Carbon-13 ---------------------C3 and C4 plants
Almost 99% of atmospheric CO2, contains the less heavy
carbon, 12C. A small part, 1.1% of CO2, is somewhat heavier,
since it contains 13C.
Terrestrial vegetation and marine phytoplankton, in the
process of photosynthetic absorption of CO2, discriminate
against heavy molecules preferring 12C to 13C. In this way,
the carbon trapped in continental flora contains a smaller
proportion of 13C than the carbon in atmospheric CO2.
CAM
C3
C4
frequency
The isotopes of a chemical element are the various
configurations of its atoms. There are three carbon isotopes
in nature: 12C, 13C and 14C. These are three varieties of the
same chemical element, carbon, whose nuclei contain the
same number of protons (six), but a different number of
neutrons (six, seven and eight, respectively). Thus, besides
having the same chemical properties, the isotopes have
different atomic masses: twelve, thirteen and fourteen,
respectively.
-30
-20
-10
δ13C (‰ VPDB)
C3 – plants
The isotopic signature of C3 plants shows
higher degree of 13C depletion than the C4
plants. Examples of C3 plants include wheat,
rice, soybeans, maples.
An illustration of the stomatal CO2 proxy.
(Left) Photomicrograph of fossil leaf cuticle of the fern aff.
Stenochlaena from just after the Cretaceous/Tertiary (K/T)
boundary.
(Right) The fern's nearest living relative, Stenochlaena palustris.
The stomatal index of the fossil cuticle is considerably lower than
the extant cuticle, indicating that CO2 was higher directly after the
K/T boundary than today (21).
Photos courtesy of Barry Lomax (University of Sheffield, Sheffield, U.K.). (Scale
bars, 10 μm.) www.pnas.org/content/105/2/407/F2.large.jpg
C4 – plants
Over 8000 species of angiosperms have
developed adaptations which minimize the
losses to photorespiration developed in the
Oligocene (25-32 mya) and became ecologically
important in the Miocene (5-12 mya).
The formula for calculating δ13C (in ‰) is as follows:
(13C/12C)sampled – (13C/12C)standard
——————————––––––––––––––– x 1.000
(13C/12C)standard
These C4 plants are well adapted to (and likely to be found in) habitats with high
daytime temperatures and intense sunlight, as well as potential nitrogen or CO2
limitations. Some examples: crabgrass, corn (maize), sugarcane , sorghum
Although only ~3% of the angiosperms, C4 plants are responsible for ~25% of all
the photosynthesis on land.
Increase in δ13C from palaeosols and tooth enamel
showing apparent synchronicity in the transition to C4dominated terrestrial ecosystems across continents. Data
for (a) from Cerling et al. (1997), (b) from Quade & Cerling
(1995) and (c) from Passey et al. (2002).
wetter  dryer
www.enviroone.com/images/crops/corn.jpg
Present-day C4 plants are concentrated
in the tropics (below latitudes of 45°)
where the high air temperature
contributes to higher possible levels of
oxygenase activity by rubisco.
www.illinoistimes.com
Monocot examples:
Forty-six percent of grasses are C4 and together
account for 61% of C4 species.
Dicot examples:
Members of the sedge family Cyperaceae, and
numerous families of Eudicots, including the
daisies Asteraceae, cabbages Brassicaceae, and
spurges Euphorbiaceae also use C4.
Vienna- PeeDee Belemnite standard -- V-PDB
The common reference for delta 13C Marine Carbonate
Standard was obtained from a Cretaceous marine fossil,
Belemnitella americana, from the PeeDee Formation in
South Carolina. This material has a higher 13C/12C ratio than
nearly all other natural carbon-based substances. For
convenience it is assigned a delta 13C value of zero, giving
almost all other naturally-occurring samples a positive delta
value.
The original sample was used up long ago, but the IAEA
calibrated a new reference sample to the original fossil,
giving rise to the widespread use of the term ViennaPeeDee Belemnite standard, abbreviated to V-PDB.
www.ucmp.berkeley.edu/.../belemnite_anatomy.gif
ucmp.berkeley.edu
www.nhm.ac.uk/.../fossil_types/belemnites.htm
Bullet-shaped fossils called belemnites
occur commonly in rocks of Jurassic and
Cretaceous age (65-205 million years
old). They can be found weathered out
of clays and chalks in great abundance at
some localities. These examples are from
the Pee Dee Formation, Florence County,
South Carolina.
Pee Dee Formation, Florence County, SC
www.blackriverfossils.org
Ranges of S Isotopic Values in Geologic Systems
evaporate sulfate
ocean water
sedimentary rocks
metamorphic rocks
granitic rocks
basaltic rocks
extraterrestrial materials
(meteorites and lunar rocks)
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
δ34S (‰ VCDT)
Range of sulfur isotopes in geologic systems. Note the
difference between mantle-derived S and Sedimentary
sulfides (Hoefs, 1980, fig. 12).
Diagrammatic Representation of the
Exogenic Cycles of Carbon and Sulfur
Carbonate Carbon
6460 x Car
1018 moles
δ13C = -0.4
Gypsum
166 x 1018 moles
δ34S= +8.4
SW sulfate
40 x 1018 moles
δ34S= +20
Ocean
Carbonate, DIC
3.3 x 1018 moles
δ13C = +0.46
Pyrite
Organic
Carbon
180 x 1018 moles
δ34S= -7.9
1180 x 1018 moles
δ13C = -27
S - Cycle
C - Cycle
Gregor et al.. 1988
weathering
72
104
MOR volcanic
emissions 10
sea-salt
sulfur 144
deposition over
oceans 207
some as OCS
to stratosphere
volatile biological
emissions 22
volatile biological
emissions 43
some from explosive
volcanism to stratosphere
deposition over
continents 32
volcanic
emissions 10
eolian erosion
10
Natural Sulfur Cycle
precipitation of
evaporites
BSR to pyrite
http://www.libraryindex.com/article_images/www.libraryindex.com/sulfur.01.jpg&imgrefurl=http://www.libraryindex.com/pages/3406/Sulfur-
Depth (m)
GENERALIZED STRATIGRAPHY (YAX-1)
AND SAMPLE DISTRIBUTION (n=46)
rst.gsfc.nasa.gov/Sect18/Chicxulub
d34S sulfates (‰)
-30
-20
-10
0
10
20
30
40
700
Paleocene
800
900
Cretaceous
1100
W.S.S.
A.S.S.
1200
1300
R.S.
Cretaceous Seawater Sulfate
(Kampschulte and Strauss, 2004)
Depth (m)
1000
1400
(Keller et al., 2004)
1500
Evolution of the sulfide and sulfate reservoirs.
BSR – bacterial sulfate reduction
www.lifesci.dundee.ac.uk
Evolution of the sulfide and sulfate reservoirs
Biomineral formation by fungi and sulphate-reducing bacteria. (A) a cord-forming fungus
growing on copper phosphate (B) light micrograph of moolooite crystals (copper oxalate,
CuC2O4.xH2O) around the hyphal cords (C) scanning electron micrograph of moolooite
crystals associated with hyphal cord and mucilaginous sheath (Fomina, M. et al. (2005)
Applied and Environmental Microbiology 71, 371-381) (D) a crust of calcium oxalate
(weddelite and whewellite) crystals and tubular crystalline sheath around fungal hyphae
(ESEM dry mode) (Gadd, G.M. et al. (2006) In: Fungi in the Environment, Cambridge
University Press.
(E) hydrated sulphate-reducing bacterial biofilm (Desulphomicrobium sp.) transforming
selenite to abundant Se/S granules. Inset shows granules associated with the surface of
an individual bacterium and precipitation in the extracellular matrix (Hockin, S.L. &
Gadd, G.M. (2003) Applied and Environmental Microbiology 69, 7063-7072).
Vienna- Canyon Diablo Triolite -- V-CDT
The Canyon Diablo meteorite comprises many fragments
of the asteroid that impacted at Barringer Crater (Meteor
Crater), Arizona, about 50,000 years ago. Meteorites have
been found around the crater rim, and are named for
nearby Canyon Diablo, which lies about three to four
miles west of the crater.
Pyrrhotite var.Triolite: An unusual iron sulfide mineral
in which the ratio of iron to sulfur atoms is somewhat
variable Fe(1-x)S (x = 0 to 0.2) but is always slightly less
than 1. It commonly is found in association with other
sulfides. The variety troilite, with a composition near
that of iron sulfide (FeS), is an important constituent of
some iron-nickel meteorites.
Canyon Diablo Troilite (CDT) is used as a zero standard of
relative concentration of different isotopes of sulfur. A
meteoritic standard was chosen because of the constancy
of the sulfur isotopic ratio in meteorites, while the sulfur
isotopic composition in Earth materials varies owing to
bacterial activity. VCDT is the synthetic standard -0.3‰
more depleted than the original CDT.