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GEOG5426 Stable isotopes
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 O T O P E S I N P A L E O C L I M AT O L O G Y
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.
O16 O18
Stable isotopes of oxygen
O1699.76%
O180.2%
O170.04%
Photograph: David SifrySMOW standard mean ocean water
Evaporation Condensation
Fractionation
H2O18
H2O18H2O18
H2O18
H2O18
H2O16H2O16
H2O16
H2O16
H2O16
H2O18
H2O18H2O18
H2O18
H2O18
H2O16H2O16
H2O16
H2O16
H2O16
H2O16
H2O16
H2O16
more O18“enriched”
more O18“enriched”
less O18“depleted”
more O18“enriched”
more O18
“enriched”
more O18
“enriched”
less O18“depleted”
“heavy”
“heavy”
“light”
O18
O16
O18
O16
small
O18
O16
small
BIG
O18
O16SMOW
O18
O16sample
“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”
paleothermometer
Source: Bowen and Revenaugh, Water Resources Research, 2003δO18 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
O16O16
O16O16
O18
O18 O18
O18O16
O16O16
O16O16
O16
O16
“more negative” δO18 = “light” = “depleted”
O18
O18 O18
O18O16 O16
O16
O16
O16
O18
O18 O18O18O16
O16
O16
O16
“more positive” δO18 = “heavy” = “enriched”
Source: Shanahan et al., Science, 2009
less O18
more negative“depleted”
more O18
more positive“enriched”