Strontium 87Sr/86Sr(radiogenic Sr)

84Sr = 0.56%86Sr = 9.86%87Sr = 7.00%88Sr = 82.58%

Stable Isotopes of Sr

These abundances are somewhat variable because 87Sr is a radiogenic isotope generated by emission of a negative -particle from 87Rb.

Strontium Isotope Systematics

~2 x 106 yrOceanic Residence Time

87Sr/86Sr = .70916887Sr/86Sr = .710220

Seawater StandardNBS 987, SrCO3

4.99 x 1010 yrHalf Life

87Rb87SrDecay

87Sr/86SrRatio

normalized to86Sr/88Sr =.1194

Analysis by TIMS86Sr, 87Sr ,88Sr

87Sr = { (87Sr/86Sr)sample -1} x 104

(87Sr/86Sr)seawater

0.709168

Typical 2 long term analytical error is 0.000020; (0.05 permil)

87Sr/86Sr = 0.7XXXX

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• 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 (paleo-

salinity). • 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 Waterfall Locality

• Dominated by Precambrian metamorphic rocks and till derived from those rocks.

•87Sr/86Sr > 0.711

• Dominated by Eocene volcanics and sediment derived from those volcanics

• 87Sr/86Sr < 0.707

5 km 5 km

Sr Ratios of Small Mammal Bones From Waterfall Locality and Lamar Cave

0.70500

0.70600

0.70700

0.70800

0.70900

0.71000

0.71100

0.71200

0.71300

0 3 6 9 12 15 18

Unit

Sr ra

tio

Age

Lamar

Waterfall

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

English et al., 2001

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 Ketlembedded with wooden beams.

Specific logging sites can be identified by comparing 87Sr/68Sr ratios in construction beams to ratios in living trees from surrounding mountains.

87Sr/68Sr ratios show that the beams came from both Chuska and San Mateo mountains but not from San Pedro mountains which are equally close.

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

0.7143

0.7078

0.7095

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 wereanalyzed for Sr isotopes to address these questions.

Ezzo et al., (1997)

Large dark balls – immigrantsSmall white balls - local

Immigrants came from two distinct areas; From thewest and south and from nearby areas to the north.

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.

Locals ?

Immigrants?

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.

UK Sr

Scandinavia Sr

Budd et al., 2003

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 African-born 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.

Montgomery et al., (2000)

~ 80 km

Burial Site

(childhood)

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.

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 homeAfter spending the winter in Vinschgau.

Hoogewerff et al., (2001)

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)

SEAWATER Sr ISOTOPES

Oceanic RecordFrom 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

• “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

VARIATION IN Sr ISOTOPIC COMPOSITION OF SEAWATER DURING THE PHANEROZOIC

Oceanic Crust.703

Continental Crust .716

Limestone.707-.709

Seawater.7092

Rivers

.711

Weathering Hydrothermal Circulation

N is the total number of moles of Sr in the ocean,Rsw is the 87Sr/86Sr of seawater, Jn is the flux ofSr into the oceans from source 'n', which has anaverage 87Sr/86Sr of R n, and Jout is the total fluxof 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 ClimateIncrease 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 authigeniccomponents (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

Stevenson et al., 2014

3 species cultured at 10-25° Cδ88/86Sr, Sr/Ca, and δ18O measured as function of temperature

As temperature is increased all species show a negative stable Srisotopic 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 clavusfrom Galapagos. This was not confirmed with other corals….