Clumped isotopes: potentials and challenges
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)
11/1/12
The Idea
Consider the isotope exchange rxn:
we would expect an equilibrium
constant of 0.25, given random
distribution of isotopes
BUT… there is a slight preference
for D2, b/c of heavy isotope
“clumping”
AND… this preference is greater
at low temperatures and less
at 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
Relevant Reaction
and Isotopologues
Elements
Ghosh et al, 2006
CO32-
Definition of Δ47
(where 47=16+18+13)
Eiler and Schauble, 2004
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 temperature
sensitivity of Δ47 in
inorganic and
biogenic
carbonates
-
observe a
fractionation of
of Δ47 from statistical
model. Assuming it’s
also T-dependent,
must control
for it when doing
measurement
Ghosh et al, 2006
2) test the temperature
sensitivity of Δ47 in
inorganic and
biogenic
carbonates
-
aragonite samples
fall on calcite curve
-
some “vital” effects,
as observed for
these samples δ18O
and δ13C
Ghosh et al, 2006
3) go after real signals
in real geologic
records
-
eg: Red Sea coral
Ghosh et al, 2006
3) go after real signals
in 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 signal
Ghosh et al, 2006
2) test the temperature
sensitivity of Δ47 in
inorganic and
biogenic
carbonates
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
Data look pretty good,
especially considering how the
temperature is unknown for some
forams’ habitats
planktonic
thermocline
benthic
Tripati et al, 2010
Δ47 of forams does not
contain obvious “vital
effects”
Tripati et al, 2010
47 in Soreq cave speleothems
Modern speleothem: 47=0.642±0.006‰, 26±1ºC.
Modern bedrock temperature: 18 ºC.
Kinetic isotope effect?
47 (‰)
18O from Matthews et al., 2000
18O reflects equilibrium within the range of observed cave water.
Assumption: kinetic effect must be small.
Affek et al, 2008
Combining kinetic and equilibrium effects
- if you know the fluid composition, and you know the
temperature, then you can predict a certain relationship
between Δ47 and δ18O
drip water 18O = -5.32±0.76‰
Affek et al, 2008
Combining kinetic and equilibrium effects
drip water 18O = -5.32±0.76‰
Affek et al, 2008
• Both 18O and 47 are consistent with KIE offset at ~19°C.
• The offset in 18O is lost in the natural variability of cave water 18O.
Million dollar question: Is the offset constant through time?
Affek et al, 2008
Temperature
(°C)
Yes?
Clumped isotope T estimates
agree with paleo-T estimates
from other techniques
Affek et al, 2008
Question: How fast did the
Bolivian Altiplano uplift?
Approach: Measure Δ47
and δ18Owater in carbonate
nodules 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?
Ghosh et al, 2008
Question: How fast did the
Colorado Plateau uplift?
Approach: Measure Δ47
and δ18Owater in modern and
ancient carbonates along
an elevation gradient
modern = calibration
ancient = reconstruction
Modern carbonates show
that δ18Owater is not a good
proxy for elevation,
but Δ47 is
Huntington et al, 2010
-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
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, 2010
Large dinosaurs: warm- or cold-blooded?
Eagle et al, 2011