Strontium 87Sr/86Sr
(radiogenic Sr)
Stable Isotopes of Sr
84Sr
= 0.56%
86Sr
= 9.86%
87Sr
= 7.00%
88Sr
= 82.58%
These abundances are somewhat
variable because 87Sr is a radiogenic
isotope generated by emission of a
negative -particle from 87Rb.
Strontium Isotope Systematics
Ratio
87Sr/86Sr
Decay
87Rb87Sr
Half Life
4.99 x 1010 yr
Oceanic Residence Time
~2 x 106 yr
Seawater Standard
NBS 987, SrCO3
Analysis by TIMS
86Sr, 87Sr ,88Sr
87Sr/86Sr
= .709168
87Sr/86Sr = .710220
normalized to
86Sr/88Sr =.1194
87Sr/86Sr
= 0.7XXXX
87Sr = { (87Sr/86Sr)sample -1} x 104
(87Sr/86Sr)seawater
0.709168
Typical 2 long term analytical error is 0.000020; (0.05 permil)
Evolution of Sr Isotope Ratios
• During early separation of crust and mantle there was
significant elemental fractionation (fractional crystallization).
• Incompatible elements like Rb were excluded from basaltic
melts and incorporated into silicic residues (continental
crust).
• Continental crust developed with a larger Rb/Sr ratio than
the upper mantle
The present-day quantity of 87Sr depends on its initial
stock (87Sr at time zero) and the amount of radiogenic
Sr generated from 87Rb over time.
The 87Sr enrichment is high in old continental rocks
(granites) and low 87/86 ratios are found in the mantle
and rocks derived from it (basalts).
Therefore the Sr isotope ratio is characteristic of
different rock types.
Marine sedimentary rocks will reflect the seawater
composition which in turn depends on the relative
inputs from different weathering and hydrothermal
sources (e.g. between continental rocks and basalts).
FUNDAMENTALS
Differences in Sr isotope composition reflect
differences in the radiogenic 87Sr component
that has grown into the various Sr source pools.
The Sr isotopic signature of a bedrock is
transferred to the soil, vegetation, and up the
food web with minimal isotopic fractionation.
Applications
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Stratigraphy and correlation of marine sediments.
Global weathering and hydrothermal activity cycles.
Provenance identification (dust, suspended load, etc.).
Habitat range, migration patterns and food source
identification (ecology, archeology).
Mixing of seawater and freshwater sources (paleosalinity).
Tracing the source and constraining the timing of
formation of diagenetic cements, dolomitization, ore
deposits, groundwater pathways and processes.
Proxy for Ca cycling in soil and plant material.
Forensics (ceramics, ivory, wood, weed etc.)
Determining Raptor Foraging
Ranges by Analyzing Strontium
Isotopes in Bones
Stephen Porder, Elizabeth Hadly, Adina Paytan
Work Site
• Two fossil collections in caves from the
northeastern part of Yellowstone
National Park.
• Over 10,000 specimens have been
collected and identified.
• The sites represent 3,000 years of
accumulation in wood rat middens.
Sites are 20 kilometers apart
Lamar Cave
Waterfall Locality
Relative abundance changes with climate
Questions
• Do the climate related changes
represent changes in local population or
in collection sites?
• What is the geographic area represented
in the deposits (foraging range)?
• Do the sites contain distinct or
overlapping populations?
• Can we determine if foraging range has
changed through time?
How can strontium help?
• Yellowstone is geologically heterogenous.
• Different rock types have different 87Sr/86Sr
signatures.
• Sr is not fractionated by biological processes.
• Bones of herbivores reflect the 87Sr/86Sr ratio
of the plants they eat, which reflects the ratio
of the soil, and the bedrock from which the
soil was derived.
Lamar Cave
5 km
Waterfall Locality
5 km
• Dominated by Precambrian
metamorphic rocks and till
derived from those rocks.
• Dominated by Eocene
volcanics and sediment
derived from those volcanics
•87Sr/86Sr > 0.711
• 87Sr/86Sr < 0.707
Sr Ratios of Small Mammal Bones From
Waterfall Locality and Lamar Cave
0.71300
0.71200
0.71100
Lamar
Sr ratio
0.71000
0.70900
0.70800
0.70700
0.70600
Waterfall
0.70500
0
3
6
9
Unit
12
Age 
15
18
Conclusions
• The fossils at Lamar Cave and Waterfall
Locality represent local and separate
populations.
• Despite climate change, the predators at
Waterfall Locality, and possibly Lamar Cave,
have consistently foraged over the same rock
type.
• Sr isotopes are a powerful tool for
determining the provenience of fossil
remains.
Strontium Isotopes Reveal Sources of Architectural
Timber in Chaco Canyon, New Mexico
Between A.D. 900 and 1150, more than
200,000 conifer trees were used to build
the prehistoric great houses of Chaco
Canyon.
The lumber came from trees that had to
be hauled from distant (~75 km) and
widely separated mountains.
Location of logging sites can reveal
information about the organization ability
of the Chaco Anasazi as well as details
with respect to the economic, political
and social relationships across the San
Juan Basin.
The walls of Chetro Ketl
embedded with wooden beams.
English et al., 2001
Specific logging sites can be identified
by comparing 87Sr/68Sr ratios in
construction beams to ratios in living
trees from surrounding mountains.
ratios show that the beams
came from both Chuska and San Mateo
mountains but not from San Pedro
mountains which are equally close.
0.7095
0.7143
87Sr/68Sr
0.7078
Incorporation of logs from two sources
in the same room and year suggest
stocking and intercommunity
collaboration at Chaco Canyon.
Timber sources may have been
determined by pre-existing sociopolitical
ties between Chaco Canyon and
outlying communities.
English et al., 2001
Prehistoric Migration: A Case Study from Grasshopper Pueblo
Patterns of residential mobility and settlement were studied using Sr isotopes at
Grasshopper Pueblo (14th century, AZ).
The pueblo began as several small units which by AD 1350 expanded to 10 sites
with over 1800 rooms.
Distinctive social groups possibly of different ethnic origins,have been identified
based on architecture, distribution of ceramics, and diet.
Where did the immigrants come form?
When did they come?
Where in the complex did they live?
Did they mix with the local population?
Teeth and bones from 69 adults from several clusters were
analyzed for Sr isotopes to address these questions.
Ezzo et al., (1997)
Immigrants came from two distinct areas; From the
west and south and from nearby areas to the north.
Locals ?
Immigrants?
Large dark balls – immigrants
Small white balls - local
Proportion of immigrants to locals is ~ 50:50.
This distribution holds for Early and Late periods.
No difference between males and females.
Block 2 majority local and blocks 1 majority
immigrants, but both populations present in each.
Outlying blocks all immigrants.
Individuals with diagnostic artefacts include
members from both groups, suggesting that
artefacts represent sodality membership which
cross-cut the various social groups.
yes
yes
no
Anglo-Saxon or Viking?
Tooth enamel (formed in early childhood) from several people from burial
sites in Britain was analyzed for O and Sr isotopes to determine if the people
were the first generation Vikings, buried in Britain but born is Scandinavia.
All of the Riccall people and two dating from the Viking period (late 9th
century) at Repton must have come from Scandinavia.
Budd et al., 2003
UK Sr
Scandinavia Sr
Female Import
Studies of Sr isotope of human skeletons from some of the earliest agriculture
settlements in central Europe (Germany, 5200 BC) show high incidence of
“non-local” females in Neolithic farming cemeteries.
These females came form nearby uplands and possibly give evidence to
intermarriage between foraging and farming communities.
The “non-locals” were buried differently from locals (based on body orientation
and artifacts) and may have been mobile pastoralists associated with the
framing community.
Bentley et al., (2002)
Birthplaces and Migration of Enslaved Africans
In 1991, 408 burials of 18th century enslaved Africans were discovered in
lower Manhattan.
87Sr/86Sr
in tooth enamel was used to distinguish New York-born from Africanborn individuals.
It was found that at least 3 distinct groups exist. The younger individuals (< 25
years old at death) displayed a tightly clustered 87Sr/86Sr (0.71159) and were
identified as native New Yorkers. A second group with 87Sr/86Sr higher than
0.715 and as high as 0.7257 most likely came from west Africa. The third
group with 87Sr/86Sr around 0.709 may reflect either a seafood Sr source
and/or origins from the Caribbean islands.
Angel et al., (2001)
A Neolithic Travelogue in Teeth
An adult female and 3 juveniles recovered from a henge-type monument, dated to the early
Neolithic in southern England (one burial).
Did the early Neolithic adopt a sedentary life style or were they like the Mesolithic in terms
of mobility?
Deciduous and permanent tooth enamel used.
(childhood)
~ 80 km
Burial Site
Considerable level of mobility for all individuals. Adult must have moved at least 80 km
between early childhood and birth. Early Neolithic lifestyle was largely mobile and at most only
short-term sedentism observed.
Montgomery et al., (2000)
The last domicile of the Iceman from Hauslabjoch
Mummy discovered in the ice in 1991 on a mountain pass in Tyrol.
Where did “Otzi” come from and where was he going to?
Sr isotopes indicate he spent the last 10 years of his life in the Central Alps.
18O are low suggesting Otzi spent most of his time in the high pastures.
Trace elements imply there is a 99% chance his last domicile was the Otztal.
Otzi died on the Hauslabjoch pass at the end of Spring on his way back home
After spending the winter in Vinschgau.
Hoogewerff et al., (2001)
SEAWATER Sr ISOTOPES
The 87Sr/86Sr ratio of seawater has changed
significantly with time in response to the
input of varying proportions of Sr derived
from two main sources:
• Continental crust
(river input of chemical weathering products)
• Upper mantle
(hydrothermal activity & submarine
“weathering”/exchange of basalts)
Oceanic Record
From high precision measurements of marine carbonates.
Elderfield et al.,1982
• Isotope record can be used for stratigraphic correlation and absolute dating
Variations of 87Sr/86Sr of seawater
through The Phanerozoic
VARIATION IN Sr ISOTOPIC
COMPOSITION OF SEAWATER
DURING THE PHANEROZOIC
Weathering
Continental Crust
.716
Limestone
.707-.709
rs
ve
i
R 11
.7
Seawater
.7092
Hydrothermal
Circulation
Oceanic Crust
.703
• “Burke Curve”
• 87Sr/86Sr ratio has ranged
between .7092 (now and
late Cambrian) and .7068
(Jurassic and later
Permian).
• Range between
continental crust (~0.716
and submarine basalts
(~0.703)
• Oceanic Sr must be added
from both sources but the
relative contribution of
these sources varied
Burk et al.,1982
N is the total number of moles
of Sr in the ocean,
Rsw is the 87Sr/86Sr of
seawater, Jn is the flux of
Sr into the oceans from
source 'n', which has an
average 87Sr/86Sr of R n, and
Jout is the total flux
of Sr out of the oceans.
There are three major fluxes of Sr into the oceans, that carried by rivers (Jr),
that due to the hydrothermal alteration of seafloor basalt (Jh), and that due to
diagenesis or dissolution of carbonates already on the ocean floor.
Richter et al., 1992
Sr isotopes, Weathering and Climate
Increase in the 87/86 in the
past 40Ma related to the uplift
of the Himalayas.
Increased weathering (and Sr
input) consumes CO2 thus
cooling the Earth and
glaciations (e.g higher 18O
ratios).
Problem: no negative
feedback proposed.
Raymo et al., 1988
Sr isotopes used for deciphering change in the global biogeochemical record.
Sr and Glaciations
• The increase in global erosional fluxes has also
been attributed to the growth of continental ice
sheets and their effect on erosion, both directly
through the exposure and grinding of rock
(Armstrong, 1971) and indirectly through lowering of
sea-level and increased land area (DePaolo, 1986).
• The rate of change in the 87/86 ratio seems to
coincide with periods of increased glacial activity.
• Note, in this scenario the cooling and glacial activity
causes the increased weathering and is not a
consequence of it.
Other Applications
Trading Routes and Relations – Sources of ivory, gems,
shell, metal, building material, garments, paint, and food.
Where did Herod get the marble and granite to build Caesarea from?
Diet – Food sources – marine or terrestrial, grassland or
forests, local or imported, fruit or meat.
Did coastal populations in California relay predominantly on land or marine food
sources (fishing or farming)?
Did the early hominids from the Swartkrans Cave, South Africa, prefer the
grassland or greenbelt habitat?
Forensics – Originality of artifacts.
Is this statue that I just got for $25,000 authentic or was it made in Mexico City?
Problems:
Diagenenetic alteration and recystallization may change the original
Sr isotopic composition of a mineral.
Analytical problems due to contamination from non authigenic
components (e.g. terrigenous clays in carbonates).
Different skeleton parts may have different turnover rates for Sr,
resulting in scatter in cases of migration.
Biologically available Sr may not always be similar to bedrock.
Mass Depended Sr Isotopes
• New application
• Species, temperature, weathering, seawater
changes, carbonate deposition…….
• MC-ICPMS or TIMS using double spike
• Standards IAPSO, JCp1, SRM987
(88Sr/86Sr=8.37861)
(DE SOUZA et al., 2010)
Controls on stable strontium isotope fractionation in
coccolithophores with implications for the marine Sr cycle
3 species cultured at 10-25° C
δ88/86Sr, Sr/Ca, and δ18O measured as function of temperature
Stevenson et al., 2014
As temperature is increased all species show a negative stable Sr
isotopic fractionation, related to a temperature controlled growth rate
Strontium concentration dependent fractionation of
∆88/86Sr(cocco-sw) vs KDSr; as the concentration of Sr increases
δ88/86Sr isotopes become more fractionated from seawater as a
larger proportion of the lighter isotope is incorporated.
Stable strontium isotope ratios (δ88/86Sr) of cold-water coral
Lophelia pertusa samples of investigated locations vs.
temperature.
Ruggeberg et al., 2008
The δ88/86Sr-temperature relationship of cold-water coral
Lophelia pertusa (diamonds) and tropical coral Pavona clavus
from Galapagos. This was not confirmed with other corals….