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?