Calcium and Magnesium Isotopes

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Ca =5th Mg=8th alkaline earth metals +2 oxidation Rocks Water Life

Essentials of Calcium Isotopes 40Ca

0.96941

44Ca

0.02086

42Ca

0.00647

46Ca

0.00004

43Ca

0.00135

48Ca

0.00187

from Coplen et al., 2002; Russell et al., 1978

44/40Ca = 1000 (44Ca/40Ca)sample - (44Ca/40Ca)standard (44Ca/40Ca)standard

Standard = modern seawater or NIST SRM 915a Thermal Ionization Mass Spectrometry (TIMS) using double spike or MC-ICPMS

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Essentials of Calcium Isotopes 44Ca/40Ca is easiest ratio to measure based on abundances Lots of possibilities of combinations of minor isotopes for “double spike” amendments to provide internal normalization during analysis in thermal instruments Using TIMS, we measure 40Ca, 42Ca, 44Ca and 48Ca, and then determine the 44Ca/40Ca ratio, using well characterized “enriched” 48Ca-42Ca (or 43Ca-42Ca) double spike amendments to correct for analytical fractionation (for a useful description of the double spike data reduction algorithm, see Skulan and DePaolo (1997, GCA, 61/12, 2505-2510)

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Calcium Stable Isotope Fractionation Mechanisms:  “Kinetic Isotope Effects” (disequilibrium): Biological preference for lighter isotopes (foraminifera and corals have isotopically light Ca relative to seawater) Diffusion (preferential transport of isotopically light Ca to site of reaction)  Equilibrium Fractionation between coexisting aqueous and solidphase complexes: “Hexaquo-Ca” (Ca++ ion surrounded by hydration sphere) vs. Ca-O ionic bonds in solids (by analogy, spectroscopic theory predicts that hexaquo-Fe is isotopically heavier than Fe in siderite (FeCO3), which is isostructural with calcite)

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Calcium Isotope Factoids:  Seawater contains the heaviest Ca of analyzed natural materials; bone contains the lightest Ca of analyzed natural materials; industrially purified Ca can be very light  44Ca is per mil deviation of 44Ca/40Ca from value for seawater  Igneous rocks and minerals have essentially uniform Ca stable isotope composition (although there is some interesting variability that may be real, may be artifact)  Ca in carbonate is isotopically light compared to coexisting aqueous Ca; the fractionation is dependent on temperature and precipitation rate

Important Limitations! Ca in ocean ~10 mM (~400mg/kg) 15x1018 moles of Ca in ocean (6x1017 kg) Residence time in ocean ~ 1 m.y. Analytical limits ±0.2‰ Difference between ocean and in/out put < 2‰

Change of >20% in Ca cycle must occur to be detected in 44Ca of seawater

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Modern Calcium Isotopes in the Ocean: Sources & Sinks

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River Flux

Source: River Water

44Ca = -0.87 to -1.3‰ Seawater 44Ca = 0.00‰

 Volcanic-Seawater Reactions

Carbonate Sedimentation Sink: Marine Carbonates

44Ca

= ~ -1.6‰

Source: Hydrothermal Fluid

44Ca = -0.96‰

Sink: Alteration of oceanic crust

44Ca = -0.98 to -1.60‰

How does 44Ca change in the ocean? Fin > Fsed 44Cain = 44Cased

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Fin < Fsed 44Cain = 44Cased

Delivery > Burial : NEGATIVE EXCURSION – [Ca] increase Burial > Delivery : POSITIVE EXCURSION – [Ca] decrease

-

d44Casw/dt

+

+ -

dNCa /dt

N Ca d  44/40Casw  Fin  44/ 40Cain   44/ 40Casw   Fsed   44/ 40Cased  dt

d44Casw/dt



N Ca Fsed

dNCa /dt

dN Ca  Fin  Fsed dt

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Global biogeochemical cycling of CaCO3 Ridgwell and Zeebe, 2005

Dominant processes, sources and sinks:

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2

1 2

3 4

Calcium isotopes record the ratio of calcium fluxes into and out of seawater, linked to carbonate chemistry (Alk, DIC, pH) and pCO2 Changes in 44Ca indicate changes9in [Ca] - may be related to [CO3]

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Ca isotopes and ocean acidification • High weathering flux (Fin > Fsed) = increase in ocean Alk., higher Ca concentrations and lower 44Ca • Increased CaCO3 burial (Fin < Fsed) = decrease in ocean Alk., lower Ca concentrations and higher 44Ca • High pCO2 – weathering = lower 44Ca • High pCO2 - OA pH – dissolution = lower 44Ca

Examples in the Geological Record Kasemann et al., 2005, EPSL

Boron and calcium isotope composition in Neoproterozoic carbonate rocks from Namibia: evidence for extreme environmental change In the snowball Earth hypothesis, rapid melt back of the ice cover resulted in the transfer of atmospheric carbon dioxide to the oceans and hence deposition of postglacial cap carbonates. Such CO2 transfer to the oceans should have caused a rapid decrease in seawater pH.

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A negative 11B excursion – decrease in ocean pH (1-2 pH units) A negative 44Ca excursion – increased weathering rates High pCO2 (7,000-90,000ppm) during the melt back of Neoproterozoic glaciations and precipitation of cap carbonates. Ca and C isotopes were coupled through silicate weathering with CO2 drawdown.

Calcium isotope constraints on the end-Permian mass extinction

Payne et al., 2011

History of Biodiversity

Raup and Sepkoski Science 1982

How Bad Was the End-Permian Extinction? •80-95% of marine animal species were lost •Similarly large proportions of animal species were lost on land •Coal-forming forests with large trees were lost, replaced by smaller, shrubbier plants •Little recovery occurred during the first few million years following the event COMPARISON •Mammal extinctions since the Late Pleistocene total 10-13% of species in the Americas. Less in Africa and Eurasia.

Examples in the Geological Record P/T Extinction

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Payne et al., 2010, PNAS

Stratified Ocean / Ocean Overturn Upwelling from a highly alkaline deep ocean would cause carbonate precipitation and a drawdown in [Ca2+] and thus Ca Burial > Ca input - positive Ca isotope excursion

Siberian Traps Volcanism Release of carbon dioxide from volcanic and sedimentary rocks could cause ocean acidification and carbonate dissolution (reduced ppt.) an increase in dissolved Ca concentration, Ca input > Ca output - negative Ca isotope excursion

Permian-Triassic Overturn

CO2 release

44/40Ca

44/40Ca

Payne et al., 2012

44  Ca

Record

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Explanations 1. Change in fractionation during carbonate precipitation •

Temperature increased, which would result in reduced fractionation (more positive values)

•

Precipitation rate Sr/Ca is a proxy for precipitation rate and shows no correlation with Ca isotope data

•

Mineralogy – a shift from calcite-dominated to aragonite-dominated sediment would result in a negative isotope excursion. Consistent with global shift in the most abundant animals

2. Decreased carbonate burial flux •

Loss of skeletal carbonate sinks – higher omega, and thus higher [Ca2+] needed to balance weathering flux

•

Ocean acidification (e.g., via addition of CO2 or H2SO4) – decreased carbonate

ion concentration, possible dissolution of seafloor carbonate sediments

Ocean acidification scenario • Is the only scenario for the Ca isotope excursion that also explains associated paleontological, geochemical, and sedimentary observations – – – –

Selective extinction of heavily calcified marine invertebrates Negative carbon isotope excursion Dissolution of uppermost Permian limestone Deposition of microbialites and oolites during subsequent weathering pulse

• Is the only extinction scenario that accounts for the Ca isotope record

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Hinojosa et al., 2012

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Marine Pelagic Barite

5 m

BaSO4 •

Precipitates authigenically in the upper water column in association with decaying organic matter

(Mearon et al., 2002)

•

Incorporates Ca2+ into crystal structure as a ‘trace metal’, substituting for Ba2+

•

Advantages: • • •

Nonbiogenic phase Well preserved, high resolution potential Constant fractionation from seawater (-2.01‰) Griffith, Schauble, Paytan & Bullen, Geochim. Cosmochim. Acta 2008

Neogene seawater 44Ca: marine barite

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1.What variations do we see from marine barite over this time in seawater 44Ca? 2. Are variations coincident with changes in the CCD? 3. Can we quantify/model = 49 changes inn seawater Ca2+?

Neogene seawater 44Ca: marine barite

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Griffith, Paytan, Caldeira, Bullen & Thomas, Science 2008

n = 49

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Model: Ca concentrations (NCa) Model Inputs  = 1.3 Myr

Model Results

= fluid inclusion data (Horita 25 et al., 2002)

Results: Eocene-Oligocene Transition

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Griffith, et al., 2011

Largest permanent change in n=25 CCD in Cenozoic (deepening) Associated with start of Antarctic glaciation and lowering of pCO*2 and SST Dissolution compromises carbonate record?

Model: Determining d44Casw/dt, dNCa/dt

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1. 200kyr doubling of Fin (Rea and Lyle, 2005) with linear increase of Fsed to equal Fin at end of 200kyr 2. Initial 44Casw = -0.2‰; NCa = 1.5 x modern

 = 1.0 My  = 0.5 My  = 1.0 My  = 0.5 My  = 1.0 My  = 0.5 My

44Cain

44Cased

44Casw

NCa

-1.2‰

-1.2‰

-0.02‰

110%

-1.2‰

-1.2‰

-0.16‰

120%

-1.3‰

-0.7‰

-0.18‰

110%

-1.3‰

-0.7‰

-0.28‰

120%

-0.9‰

-1.6‰

+0.17‰

110%

-0.9‰

-1.6‰

+0.29‰

120%

Implications from EOT seawater Ca-isotope record:

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Largest permanent deepening of CCD in Cenozoic: – Scenario must include near balance of Ca2+ sources and sinks to the ocean ( 44Ca of Oi Majority of fine feeder roots are observed to be in forest floor

Soil total

Weathering Studies Along a Chronosequence: Ca and Sr Isotope Variations Along Hawaiian Chain 0.710 0.709

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S r/86 S r

0.708

Foliage from Metrosideros Polymorpha

0.707

Seawater 1400 Ka

4100 Ka 150 Ka

“vital” effect?

0.706 20 Ka

0.705 0.704 0.703 -1.5

2 Ka

0.3 Ka

Basalt weathering -1.0

-0.5

0.0

0.5

44

 Ca (per mil, relative to seawater)

(Sr isotope values from Kennedy et al., Geology, 1998)

Food Web Studies:  44Ca of “structural” material should decrease with increasing trophic level Water source

44Ca

Plants

Herbivores

Carnivores

Trophic Level

Biomedical Applications:  The most obvious application is for the study of osteoporosis  Bone in general has the lightest Ca of natural materials yet measured (lighter than soft tissue by 1+ ‰ in terms of 44Ca/40Ca)  Adding bone should make Ca in body fluids heavier; resorption of bone should make Ca in body fluids lighter  Urine is a convenient monitor of body function with respect to trace metal cycles  We are currently studying urine from astronauts subjected to a “bed resting experiment”: one group bed-rested, one bed rested with exercise, one bed rested with drug “Fosamax”

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Heuser & Eisenhauer 2009

Urine samples of an old women and a 4 year old boy

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Change in bone mineral balance following bed rest. Ca isotopes in urine more indicative than bone densitometry or X-ray.

Morgan et al., 2011

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Magnesium Isotopes

DSM-3 Seawater SRM980 Multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) after extensive purification due to isobaric interferences and matrix effects

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44

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Carbonate Fractionation

Li et al., 2012

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Teng et al., 2010

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Teng et al., 2013

Handler et al., 2009

Li et al., 2013

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Riechelmann et al., 2012

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