Clumped isotopes: potentials and challenges 11/1/12
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Clumped isotopes: potentials and challenges 11/1/12
Artist’s rendition of Mammuthus primigenius,whose body temp was measured at 38.4 +/- 1.8°C
by clumped isotopes (Eagle et al., PNAS, 2010)
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The Idea
Consider the isotope exchange rxn:
we would expect an equilibriumconstant of 0.25, given randomdistribution of isotopes
BUT… there is a slight preferencefor D2, b/c of heavy isotope“clumping”
AND… this preference is greaterat low temperatures and lessat high temperatures
THEREFORE, we have established the basis for a paleo-thermometer that is based on the ordering of heavy isotopes in carbonate only (single phase equilbrium)NO dependence on fluid composition
Eiler, 2007
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Elements
CO32-
Relevant Reaction and Isotopologues
Ghosh et al, 2006
Eiler and Schauble, 2004
Definition of Δ47
(where 47=16+18+13)
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How do you establish a new paleo-thermometer?
1) develop a way to reliably and repeatably measure the quantity of interest- choose to dissolve carbonate in H3PO4, measure evolved CO2
Ghosh et al, 2006
nominal precision = +/- 0.03‰
reducible to +/- 0.01-0.02‰ for repeat measurements
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2) test the temperaturesensitivity of Δ47 in inorganic and biogeniccarbonates
Ghosh et al, 2006
- observe afractionation ofof Δ47 from statistical model. Assuming it’s also T-dependent, must controlfor it when doingmeasurement
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2) test the temperaturesensitivity of Δ47 in inorganic and biogeniccarbonates
Ghosh et al, 2006
- aragonite samplesfall on calcite curve
- some “vital” effects, as observed for these samples δ18O and δ13C
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3) go after real signalsin real geologic records
- eg: Red Sea coral
Ghosh et al, 2006
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3) go after real signalsin real geologic records
- sense of Δ47 signal matches that of Sr/Ca-based temperatures, but amplitude far exceeds that predicted from observed SST variations and calibrations of Δ47 (cause unknown “vital effect”?)
expected Δ47 signalGhosh et al, 2006
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2) test the temperaturesensitivity of Δ47 in inorganic and biogeniccarbonates
WOW: this really seems to work!
Tripati et al, 2010
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Vital effects and Δ47
Tripati et al, 2010
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δ18O and δ13C of forams contain obvious “vital effects”
Tripati et al, 2010
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planktonic
thermocline
benthic
Data look pretty good,especially considering how the temperature is unknown for some forams’ habitats
Tripati et al, 2010
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Tripati et al, 2010
Δ47 of forams does not contain obvious “vital effects”
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Δ 47 (
‰)
Δ47 in Soreq cave speleothemsModern speleothem: Δ47=0.642±0.006‰, 26±1ºC.
Modern bedrock temperature: 18 ºC.Kinetic isotope effect?
δ18O reflects equilibrium within the range of observed cave water.Assumption: kinetic effect must be small.
δ18O from Matthews et al., 2000
Affek et al, 2008
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Combining kinetic and equilibrium effects
drip water δ18O = -5.32±0.76‰
- if you know the fluid composition, and you know the temperature, then you can predict a certain relationship between Δ47 and δ18O
Affek et al, 2008
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Combining kinetic and equilibrium effects
drip water δ18O = -5.32±0.76‰
Affek et al, 2008
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Million dollar question: Is the offset constant through time?
• Both δ18O and Δ47 are consistent with KIE offset at ~19°C.
• The offset in δ18O is lost in the natural variability of cave water δ18O.
Affek et al, 2008
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Tem
pera
ture
(°
C)
Yes?
Clumped isotope T estimatesagree with paleo-T estimatesfrom other techniques
Affek et al, 2008
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Ghosh et al, 2008
Question: How fast did the Bolivian Altiplano uplift?
Approach: Measure Δ47
and δ18Owater in carbonatenodules in paleosol
Answer: it uplifted FAST!
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Ghosh et al, 2008
Implications of fast uplift:- removal of dense lower crust and/or mantle lithosphere, replacement by less dense, hot aesthenosphere caused isostatic rise in Altiplano?
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Huntington et al, 2010
Question: How fast did the Colorado Plateau uplift?
Approach: Measure Δ47
and δ18Owater in modern and ancient carbonates alongan elevation gradientmodern = calibrationancient = reconstruction
Modern carbonates showthat δ18Owater is not a goodproxy for elevation,but Δ47 is
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-little change in lapse rate inferred, so no change in elevation post-20Ma
-large 8°C temperature change inferred (consistent with paleo-T from sediments off California?)
Huntington et al, 2010
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Eagle et al, 2010
Modern Δ47 calibration of teeth bio-apatite
Lesson: use enamel!
So you can see the difference in old teeth from warm- and cold-blooded animals…
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Eagle et al, 2011
Large dinosaurs: warm- or cold-blooded?