7_stable_isotopes - Stable Isotopes 18 O- oxygen isotopes...

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Unformatted text preview: Stable Isotopes 18 O- oxygen isotopes temperature ice volume 13 C- carbon isotopes Carbon cycle Oxygen Isotopes Oxygen has 3 isotopes #protons #neutrons isotope 8 8 8 8 9 10 16 O 17 O 18 O Oxygen isotopes 16 O = 99.8% 17 O = 0.08% 18 O = 0.2% 18 O [ 18 O/ 16 O sample - 18 O/ 16 O standard ] 18 O () = 18 O/ 16 O standard * 1000 Standard = PeeDee Belemnite (PDB) SMOW (Std Mean Ocean Water) Measure the 2 most abundant isotopes Analyze ratios on stable isotope mass spectrometer Calcite shells (foraminifera) = CaCO 3 Oxygen Isotopes 18 O Seawater: HC 16 O 16 O 16 O HC 18 O 16 O 16 O HC 17 O 16 O 16 O CaC 16 O 16 O 16 O CaC 16 O 16 O 18 O Ratio in the foram CaCO 3 reflects the ratio in the seawater Oxygen Isotopes Ruddiman (App. 1) Differences in mass are great enough to make the atoms behave differently during physical and chemical processes 1. Evaporation 16 O is lighter- evaporates more readily 2. Incorporation into a solid 16 O greater vibrational energy- more difficult to incorporate into solid Oxygen Isotopes Evaporation Effect (Ice volume, salinity) 16 O preferentially evaporated incorporated into rain and snow Stored on land as ice During glacials- more 16 O removed from the ocean and stored on land 18 O/ 16 O of remaining ocean becomes heavier (or higher O) Oxygen Isotopes Temperature Effect Differences in vibrational energies are more pronounced at lower temperatures More discrimination against 16 O when it is colder Shells incorporate a greater % of 18 O when it is cold (= heavier 18 O/ 16 O or 18 O) Oxygen Isotopes...
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7_stable_isotopes - Stable Isotopes 18 O- oxygen isotopes...

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