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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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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)
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
Elements
CO32-
Relevant Reaction and Isotopologues
Ghosh et al, 2006
Eiler and Schauble, 2004
Definition of Δ47
(where 47=16+18+13)
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
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
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
3) go after real signalsin real geologic records
- eg: Red Sea coral
Ghosh et al, 2006
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
2) test the temperaturesensitivity of Δ47 in inorganic and biogeniccarbonates
WOW: this really seems to work!
Tripati et al, 2010
Vital effects and Δ47
Tripati et al, 2010
δ18O and δ13C of forams contain obvious “vital effects”
Tripati et al, 2010
planktonic
thermocline
benthic
Data look pretty good,especially considering how the temperature is unknown for some forams’ habitats
Tripati et al, 2010
Tripati et al, 2010
Δ47 of forams does not contain obvious “vital effects”
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
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
Combining kinetic and equilibrium effects
drip water δ18O = -5.32±0.76‰
Affek et al, 2008
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
Tem
pera
ture
(°
C)
Yes?
Clumped isotope T estimatesagree with paleo-T estimatesfrom other techniques
Affek et al, 2008
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!
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?
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
-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
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…
Eagle et al, 2011
Large dinosaurs: warm- or cold-blooded?
