Class 10, Stable isotopes

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Scott St. George

Educación Tecnología

November 24
Brief (15-minute) summaries of project topics.
(1) What are the most important features of the modern
climate in your region?
(2) What proxies are available in your region, over the time
interval speciﬁed? How are they related to climate? and
(3) How diﬀerent were past climates from modern
conditions? Why is that important?

S TA B L E I S OTO P E S I N PA L E O C L I M ATO LO GY

Isotopes are elements with the same number of protons
but varying numbers of neutrons.

Stable isotopes are either not radioactive or decay so
slowly that their half-lives cannot be measured.

Stable isotopes have the same chemical properties
but don’t have the same atomic mass.

Stable isotopes of oxygen
O16
99.76%
O18
0.2%
O17
0.04%

Photograph: David Sifry
SMOW standard mean ocean water

H2O18
H2O18
H2O18
H
H
H2O16
H2O16
H2O16
H2O16
H2O16

H2O18
H2O18
H2O18
H
H
H2O16
H2O16
H2O16
H2O16
H2O16
H2O16
H2O16
H2O16

“more positive” δO18 = “heavy” = “enriched”
for example, ocean water

“more negative” δO18 = “light” = “depleted”
for example, glacial ice

Source: Jouzel et al., Journal of Geophysical Research, 1994

Source: Jouzel et al., Journal of Geophysical Research, 1994
“light”
“heavy”

Source: Bowen and Revenaugh, Water Resources Research, 2003
δO18 in precipitation

Source: Bowen and Wilkinson, Geology, 2002
δO18 in precipitation

The “amount eﬀect”: The greater the amount of
rainfall, the lower the δO18 of the rainfall.
(i.e., more negative)

O18
O18
O18
O18O16
O16
O16
O16O16
O16
O16
“more negative” δO18 = “light” = “depleted”

O18
O18 O18
O18O16
O16
O16
O16
“more positive” δO18 = “heavy” = “enriched”

Source: Shanahan et al., Science, 2009
less O18
more negative
“depleted”
more O18
more positive
“enriched”

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Class 10, Stable isotopes

1. GEOG5426 Stable isotopes

2. November 24 Brief (15-minute) summaries of project topics. (1) What are the most important features of the modern climate in your region? (2) What proxies are available in your region, over the time interval speciﬁed? How are they related to climate? and (3) How diﬀerent were past climates from modern conditions? Why is that important?

3. S TA B L E I S OTO P E S I N PA L E O C L I M ATO LO GY

4. Isotopes are elements with the same number of protons but varying numbers of neutrons.

5. Stable isotopes are either not radioactive or decay so slowly that their half-lives cannot be measured.

6. Stable isotopes have the same chemical properties but don’t have the same atomic mass.

7. O16 O18

8. Stable isotopes of oxygen O16 99.76% O18 0.2% O17 0.04%

9. Photograph: David Sifry SMOW standard mean ocean water

10. Evaporation Condensation

11. Fractionation

12. H2O18 H2O18 H2O18 H H H2O16 H2O16 H2O16 H2O16 H2O16

13. H2O18 H2O18 H2O18 H H H2O16 H2O16 H2O16 H2O16 H2O16 H2O16 H2O16 H2O16

14.